Climatological Bulletin Vol. 25, No.1, April/avril 1991

Bulletin climatologique

Canadian Mete<)(ologoeal and OceanographIC Society

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Climatological Bulletin Bulletin climatologique Vol. 25, No. I, April/avril 1991

2 FOREWORD / AVANT-PROPOS

ARTICLES

3 The Frequency and Surface Characteristics of Sea Breezes at St. John 's , Newfoundland Colin E. Banfield

21 Break-up in Hudson Bay: Its Sensitivity to Air Temperatures and Implications for Climate Warming D.A . Etkin

NOTES

35 Estimation des flux de chaleurs l.atente et sensible a partir de I 'energie radiante pour certaines surfaces: Nouveau-Quebec Gerald Renaud et Bhawan Singh

47 Climatology of Tomado Days 1960- 1989 for Manitoba and Saskatchewan R.L. Raddatz and J.M. Hanesiak

NEWS AND COMMENTS / NOuvELLES ET COMMENTAIRES

60 Climate/Agriculture Symposium - Announcement 60 Canada/China International Mesoscale Workshop - Announcement 61 The Mackenzie Basin Climate Impact Study

ISSN 0541-6256

Editor / Redacteur en chef: A.H. Paul Associate Editors T.A. Allsopp K. Drinkwater

I Redacteurs assoch~s: J.Hall B.L. Magill A.Hufty G.A.McKay

S.Tabata E.E. Wheaton

Foreword / Avant-Propos

T he three issues of Volume 24, 1990 contained J I artjcle.~ and nOles, 1 climalc­review piece. and 9 news ilCms . The 100ai of 183 pages rcpreseOis a healthy 35 per cent increa!>e over Volume 23. 1989. The number of manuscripts submitted is also continuing to risc, with 17 arriving in 1990 compared with IJ in 1989.

CMOS's ad hoc committee to consider the options forconljnuing \0

publish climate-related material afterthcend of 1991 is uctive at the prescnt time. lis report wi ll be available for discussion bcrore thc Winn ipeg Congres~ in June.

Les trois numeros du volume 24 (1990)comcnaienl II aniclcsct noles, 1 rcvucdu climat. el 9 faits divers. Le lolal de 183 pages reprcsenle une augmcnl<llion significative de 35 pour cent par rapport au volume 23 de 1989. Lc nombre de manuscrilS soum is a egalcment passe de 13 en 1989 a 17 en 1990.

Le comilc ad hoc de Ja SCMO charge d'elUdicr la question de Ja publication du materiel climatologique apres la fi n de 1991 eSI prcsentemcnl au travail. Son rapport sera disponible avanlle Congrell de Winnipeg cn juin.

Alec Palll EdjlOr/Redacteur en chef

2 Climatological Bulletin I Bullelin climalOiogique 25( I), 1991

The Frequency and Surface Characteristics of Sea Breezes at St. John 's, Newfoundland Coli" £. Bmifield Department o f GCllgraphy Memorial University of Newfoundland St . John's, Newfoundland A J B 3X9 !OriginaJ malluscript received J 8 M:.ty 1990; in revised ronn 10 January 199 1J

The frequency and surface char3Clcmtics ofsca breezes il l SI. John '5. Newfoundland over a len year period were investigated. The primary sea breeze idenrificr was the occurrence of reversals of surface wind direction withm spe<.:ifietl ponion$ of a 24-houfpcnod, dctcmlined

from the hourly record al SL John's AirpUl1 . Surf:lccsynuplic charts wereellaminetl in ortler to screen oul wind shifts duc to sYnopIk-scslc control. l bc overal! frequency is rclativdy low, averaging two or three events per mooth from May thmugh August. Sea breeze

duration varies from a mcdian of two hours fIJr Junl'! 10 six hours for July. A bi-modal distribution of directional frcqueOl:ks and speeds is observed, Almost half of the sea breezes produced cooling of 1.0 w 3.0°C; appro~imatciy 10% resulted in a temrcl1lture drop of at leaS15.0QC, The Biggs-G raves Lake Breeze lndex (HCI) was determined as a check on the validity ofthesclcction method; 7~% of lhe d .. ys satisfying the Ofhersea breeze tests met the criterion of BGI < 3.0. The majority of cases with 801 > 3 ,0 wcre associated with a spccil1c synoptic gnldicnt wind paucm which may, in some cases, lead to meso-scale fe;mrre.~ affccting coa~ta l wind conditions_

Celie etude porte sur J3 frequenee dies caraelcristiques ilia surface des brises de mer a Saint-Jean, Terre-Nel.lve dl.lran t Ullt:: periode de dix annees, Lc critere principal employe pour idcntilier les briscsde merest un changemcnt en .<;ens oppose de la direc tion uu vellt a la surface iP. I' inlerieurde ccnaim:s panies d'unc periodc de 24 heures, a panir des donnees horaircs it J'aeropon de SainI-Jean. On a clUdie des canes sYlloptiques de surface afill d'eliminer les changemenl~ dus it des phe!lQmenes u'cchelle synopliquc , La frequcnce gcncrale cllI relativcmenl f3ible; 011 a nOle un moyen de 2 a J hrisesdc Iller paf1ll0iS pendant la periodedu mois de rnai au mois d'aoul . La duree mooiane deccae brise varieue 2 heurcs en juin u 6 heures en juillet. On a observe une dislributioll bi_modale des frequellC.:es de

direction et de vitessc. Presque la moitiedcs briscsde meronl produit un rcfroidisscment de J ,0 it 3,OOC et it peu pre.~ 10 pour cent 0111 res l.l ite en oue haissc de temperature d'an moills 5.0°C_ L 'jndieede Biggs-Graves Lake Brceze(BGI) II etc utilise afin de verifier 13 precisiun

Climatological Bulletin I Bullctin ciimafOlogiquc 25( I) 1991 © Canadilln Meteorological lind Oceanographic Society

des cru~ r()s sek ctlcmncs; 78 pourccnl desjouf!i repondllot au,~ aUlres critercs d' identi lication de la brise lle mcronl cgaJemenl une valeur du BOI 3,0. Pour la plupan dc.'ic.:lS ou Ie BOI '> 3,0 la si tuation $e canlctCrise par un p:1tron parliculier du VC llt ill'cchel1e synoptil{uc . Ce patron. en cenains CIIS, pcut produire dc~ phenomenes a I'ccbcl!e moycnnc qui pcuvcnt affeclcr Ics ventS d'une regIon i::oticrc LiOnncc,

I , lNJ'1I.0DUCTI ON ANDOR JE C nVES

The study of the sea brccze has largely been prompted by recognition ofils implicatio ns for IQw-level dispersion o f natural and man-made atmospheric particulates and gases, impacts on outdoor human activi ty and/or the need tC) incorporate knowledge of it<J chaI3eleriSlics into local weather forecast preparation. Interest in the subject has gencrated much research on seveml methodological fronts in contrasting climatic regions; Atkinson ( 1981) provides a thorough revicw of major contributions up to the 1970's,

Empirically-based studies have expanded over the years to encompass not onl y the surface manifestation~ of [he sea (or lake) brcc:l'.c but [he spatial and temporal evolutioll o f lhe entire vcrtical c irculation system involved. Such work i~ exempli fied by the contribu tions of Staley ( 1957), Frizzola and Fishcr (1963), G i,1I (1 968), Lyons (1972), Barbato ( 1979), Sturman and Tyson (l98 1) and Prezerakos ( 1986) at mid-latitude locations, and by Moritz ( 1977) and Kozo ( 1978) in a Low Arclicenvironment. During the pastlhrec decades the e arlier theoretical foundations of the sea brcc7,e mechanism have becn subjected to increasing scrutiny using analytical and numerical modelling approaches, occasionally supported by observational tcst ing (for example Fisher. 196 1; E.\;tuquc , 196 1; Pielke, 1974). While some o f thcse analyses have modelled the effects of differing topographic and/or synoptic metcorological settings on thc evolutio n and fonn of the sea brecze (Estoque, 1962 ; Mahre and Piclke, 1977; McKendry et aJ .. 1988), this aspect clearly requires further research. Moreover, in order to improve the design and utili ty of the models fu rther empirical study oftbe sea breeze is required under vary ing synoptic conditiuns. as noted by Sturmall and Tyson ( 1981) and Mc Kendry ( 1989). Hence the present paper will provide information on the climato logy of thc sea breeze, and liS accompanying synopt ic weather situations , within an area ufthe Canadian east CO<lst from which the phenomenon has not yet been reported in the literature .

Recognition of a sea breeze normally requi res a local to meso-scale onshore component of the surface-wind to override or ampl ify the synoptic-scale gradient now, <IS' a result of horizonlal pTCssure gradient forces produced by unequal heating of land and sea surfaces. In the Ne wfoundland context the cold waters of sub-Arctic origin that surround the island portion of the pmvince can lead to considerable horiwntal temperalUre gradients across the coastline during the season of Slrongest solar irradiance. However. the synoptic-scale pressure patterns often produce fairly slrong gradienl winds , which may aci to reduce lhefrcquency

4 Cl imatological Bulletin I Bulletin climatologique 25( I), 199 1

with which small-sca le thennally-driven circulall()ns are allowed 10 develop. T hus, there are two objectives of th is panicular analysis. namely:

I . to document the frequency, duration , speed, direction anti accompanying cooling e ffects of the sea breeze (as defined hclow) al St. John's , Newfoundland , based upon adal:! set of len yearsdurmion,

2. to eharactelise the synoptic-scale mctcorological conditions that were associated with the development of these sea brce~..c occurrences , includ ing an exam ination of the applicability o f the Biggs-Graves Lake Brecz.e Index (Riggs and GraveS, 1962) for identifying sea breeze onset at 51. John's,

2, DA T A SOURCES AND SEA BRf.f.Z I:.DE FtNITIOI'I

In the vicinity of SI. lohn's the Atlantic coastl ine is characterised by a series of hills and headlands dissected by the short valleys o f streams draining from the higher terr.!i n which separates the city area from the Conception Bay coastal zone 10 the west (Figure I). Local rel ief is generally in the range 150- 250 m.

The idemification and characterisation orsca breezes was bascu upun examination of meteorological records from SI, Juhn's Airpon, located 6- 7km from the c ast coast at 140m asl , lind Memorial University of Newfoundland (M. U.N .), 4krn west orSt. lohn's harbour at nn elcvalionof60m. The hourly wind record at the airpon meteorological stat io n served as the ini lial data source for the identification of sea breezes, Subsequent anal ysis of accompanying temperature and humidity changes focused upon the thermohygrograph record at the Memorial Universi ty station , in o rder to take advantage of its greater time resolution.

Figure I also indicates the wi nd d irectional sectors that.are regarded as " onshore " and ·' offshore'· for the de ii nition or lhe diurnal wimJ reversals . With refere nce to SI. John 's Airpon the o nshore sector was chosen to lie between the true azimuths 01"20 and 150 degrees , i.e. blowing directly offlhe AtlanticOcean The defi nition adopted for offshore (200- 320") re lates to the location of the ci ty with reference to the island as a whole and includes winds whose fetch ex tends across the interior of the Avalo n Pe,ninsula 10 the southwest or via central Newfoundland funher to the west. Strictly, however, aictlow from Conception Bay to the west o f the city can also be regarded as onshore and Ihe possibi lity exists fo r sea breezes from this di rection to reach SI. John's Airpon. Also, sea breezes arc k.nown to develop contemporaneously on opposite sides o f a peninsu la under suitable synopt ic situalions (La!as i!1 at., 1983; Noonan and Smi lh , 1986; Mc Kendry , 1989), The progression of a sea breeze fro m Conception Bay as far as St. John's Airport cou ldconceivubly oc"Cur, fo r example, during westerly grJdicnt now, if the latter were strong enough to prevent an ea.~terly sea bree-lc reaching the airport. identification of th is panicula.rcondi tion would have to rely upon detection of a sea-breeze induccd diurnal variation in the speed of the general westerly fl ow al the airport , since meteorological information was lacking for the. Conception Bay coastal area. Given the uncertainties involved in confinlJing any

C.E, Banfield I Sell Breezes a/ Sf. John's 5

Concepfion &ly

D

• • •. ,"""w.

FIGURE I. Study area, sllowing wpogrllplly, InclCllrlllngical slalions and onshore/ofrshore: airllow sectors.

westerly sea breezes at the aipon, the onshore flow scclOr has been limited in this study to the open ocean area east o [ SI. John 's, as defined above .

Accordingly, the principal criterion used to recognize a sea breeze at the airpon was the occurrence of a distinct reversal of surface wind direction within a panicular 24-hour period which cou ld not be attributed to synoptic scale circulation fealures. Specifically, thediumal wi nd reversal was defined by the follo wing sequence:

6 Climatological Bulletin I Bulletin c1imatologique 25( 1), 199 1

co wind:; are predominantly from the offshore sector between 2200 and 0600 Newfoundland Standard Time (N ST);

(ii ) a windshift o f at least 40 degrees from Ihc o ffshore to the onshQre sector occurs for a minimum of one hourly observation from 0800 to 20Cl0 NST. This windshifl llJust be abrupt , i.ft. occur withi n a one-hour period.

(iii) a Jirectional shifl back 10 the offshore SeClor occurs by 2200 NST o n Ihe same day. All days meeting this initial screcning criterion during the study

decade 1979- 1988 were identified as Ihe inili:tl sel of"potcntial sea breeze days " . Fo reac h oftllesc days the surface synoptic analysis chans from the Newfoundland We3lher Centre (Gander) were inspected to detennine whether the observed c hanges in wind direelion could have resulted from synoptic-scale cOllfrol over local wind behaviour, such as pas.~age ofa fro nt , trough line . centre ofa closed isobaric system or strongly curved isobars. The surfacc analyses for 1200Z (0830 NST), 1800Z (1 430 NST) and OOOOZ (2030 NST) on each of the potential sea breeze days were examined fo r any possibility of the o nshore now resulting from such synoptic situatio ns. If the surface analyses reve31ed (a) no evidence o f syno ptic control over the windshift to onshore and (b) an offshore :lurfacc gmdient airnow overthe St. John 's are3, then the wi nd reversal was attributed to local-sc3 le thermal control and c lassed as a sca brce1.e occurrencc. A total of 90 sea breeze days were identificd fo llowing thcsecriteria, ovcrlhcten-yearpcriod . This may be a conservative total since Ille screening process may have resu lted in lhe omission of some cases of sea breezes thm were superimposed upon synoptically aided o nshore flow; also, by de finition, any westerly sea breezes from Conception Bay that may have reached the airport arc excl uded. The 90 sea breeze days all occurred within the period April through September: during these months 3n additional 27 days that satisfied the wind reversal cri tcria were rejccted because of sy noptic e ffects. All subsC<.juenl climatological and meteorological attributes were determined using this 90-day data sel.

In addition , iorcach sea breeze day, the Biggs-Graves Lakc Breeze Index (B iggs and Graves, 1962) was detennined in order to exami ne its potential as a sea breeze predictoratlhis location. Initially developed to aid prediction of the lake breeze at tne wcstern end o f Lake Erie. this index has also been found to be reasonably suece!>sful in predicting sea breeze occurrence across the Lower Mainland of British Columbia (Stcyn and Faulkner, 1986) and the east and south coasts of Ne w Brunswick (Neumann and Mukammal, 1979). The authors determined daily values of this index from:

8GI =-!L cp t:.T

where u = a representative local surface wind speed preceding Ihe onset (11' onshore flow (ms-l)

c.£. Banfield I Sea Breeze.f at St. John's 7

t:.T = difference between local offshore water .~urface tt'"01peruturc and ~l

representat ive daytime maximum temperature reached inland (K);

cp = specific heal of air (J .003 Jg- I K _I) (Qrigi nal authors' units) .

In this study u is defi ned as the mean hourly surface wind speed at SI. John 's Airport for the three hours immediately preceding the shift to onshore now on a sea breeze day. In the detemlinalion o rlhe t:. T values, rather than use Ihe dai ly maxjmum air temperature repurted at an inland station (which cou ld conceivably occur fo llowing, instead of before, a brief sea breeze) the highest temperature ob~rved from the Memorial University thermohygrograph record prior to thc o nset of the sea bree:re was used . This was considered more representative of the degree of solar- heating requ ired for local sea breeze development. Estimates of local sea surface lempcrdturc (SST) on sea breeze days were obtained from examination of weekly SST maps issued for Allanlic Canada waters by Canadian Forces METOC Centre, Halifax. These maps arc recompiled twice weekly using data collected via satel li te and bathymetric soundings from ai rcmi't and ships-of­o pportunity. Given the limitations imposed by the spatial and temporal coverage­of these data , thc maps (and hence the SST values detcmlined in this work) probably have a margin of error in the range of I.O- 2.0aC (personal communication, Canadian Forces METOC Centre, Halifax).

3. SE A HREEZE CI.tM ATOt.OG V

3.1 Relevamfeatures of the St. Joh ll's climate Figure 2 ill ustrates Ihe annual cyc les of two factors important ror sea breeze development, namely the local intensity of solar- irradiance at the surface and the maximum land-sea tempcmlure contrast; the latter was obtained by subtraction of the long-term mo nthly mean values ofthc sea surface tempcratureat " 5Ialion27" (an oceanographic buoy loc:ucd approximately 7km east of SI. John 's) from the dai ly maximum airlcmpcraturc at St. John 's West. Monthly frequencies and speeds of winds from Ihe o ffshore directions are given by Table I .

3.2 Sea breeze frequency a"d duratioll 11le tota] numbcr of sea breeze days identified over the len-year period, by month (Table 2), shows a clear " season" of most frequent occurrences from May until August; from one to four sea breezes were recognized for each o f these months in each year. No sea breezes were detected for the period October through Marc h. These frequencies arcsignifieantl y less Ihan reported for eastern New Brunswick (Neumann , 1979). Halifax. Nova Scotia (Dexter, 1958) and for (he Vancouver area (Stcyn and Faulkner, 1986). A major ractor preventing a greater sea breeze frequency at St . Jo hn 's is considered to be the relatively high mean strength o ftbe preva iling offshore wind compared with other mid-lat itude sites in Canada (Environment Canada, Canadia/l Clil1UJte Normals, Vol ume 5 - Wind; 1951- 1980).

8 Cl imatological Bulletin / Bu lletin c1hnatologiquc 25( I) , 199 /

T~Bt.£ I , Mean pen:entagefrequency lind speed (ms-' I of offshore wind direction~ . Sl John's Airpon.

SSW SW WSW W WNW NW All offshore % ij % ij % ij % ij 'k ij % ij " ij

April 4.1 6.1 1.3 1.0 '" 1.5 12 .0 68 H I' 1 U 6.' 1.5 SO.3 1. 1

M,y 48 6.J 1.3 6.' 17. 3 1.5 12.9 1.1 '-' 6.' 4 .2 6.' SO.O •. , June H 6,0 ' .1 6.75 23.4 1.6 13 . 1 6.' 3.1 6.1 J . I 6.2 58_6 6.6

July 6.' 6.0 12.7 6.6 26.2 1. 1 15. 1 6.1 2.4 ' .3 2.1 5.6 65' ' .2 AuguSI 1.0 ,., IV' '.25 23.S 6.1 14.4 6A 3.3 , .• J . I 5.8 640 6.1

Se~mber •• ' .2 10.7 6.3 19.0 •. , lb . I 6.' 5.5 ' .3 4.3 6.0 62.0 6.4

SoUI\.1:: Environmem Camilla. CollOdion Climau.> Normals. Volume 5 - Wind; 1951- 1980.

" 20 I \

I \ GLOBAL SOlAR I \ / RADIATION 18 ,.

I \ / \

,. I \

• / \ 14 I \

Q: / \ ~

I \ 12 • • " "' / \ ... w I w \ 10 E

'" / '" LAND-SEA \ , W 4 I ,. 0

I Y TEMPERA TURE \ • I DIFFERENCE \

I \ , , I

\ - I " 4

• , -, •

~ > it' " ~$" ." '" "

;:,'> , i>v ~ <3 ~ ,f ~ IE' "

FIG URE 2. Annual cycles of mean daily global solarradialion on a horiwotal surfa..-e al St. Jotm 's West and mean excess of daily maxim um air [em~ratUre (SI. John"" Wc.~t ) oyer local offshore lea surf3L'C t.:mperature.

T"BLE 2 . Fre<juency of st:;! brct:7.cs al St. John's I\'rpon , 1979_ 19RlI .

Jan. Feb. MM. ApL M.y June July Aug. Sop' "",, . Nov , Doc.

Overall Total 0 0 0 , 21 " 24 20 4 0 0 " Least P" yOM 0 0 0 0 0 0 0 () 0 " MOSt

P" YO M 0 0 0 3 4 3 4 ] 0 0 0

10 Climatological Bulletin I Bullcli nclimatologique25( 1), 199 1

(a) 23

21

" " ~ 15

~ 13

L . M .

~ 11

• ~

(b)

1

5

3

1 APR

23

21

" . ~" ~15 ~

213

11

• 1

5 '

3

1 APR

MAY

L

E

MAY

ONSET

---JUN Jue AUG SEP

END

JUN Jue AUG SEP

FIGURE 3. TirnCSQf onsct {al and ending (b) oflhescn bn:c7.(! at St . John·s Airport. 1979- 1988. M "" median; E - carrics!; L = lacest .

C.E, Ballfield I Sea Breezes at 51 . John's II

A fairly wide rangcof limcsofonsel andcnding of the sea breeze, and result ing durat ions, is apparent from Figure 3 and Table 3. The median time of onset occurs short ly before noon (NST) during \he months of greatest land-sea temperature contrast (May through Jul y) bur is delayed by two hours (ali:r in thc summer, when Ihe later sunrise and thc diminished land-se:.. temperat ure difference would act to de lllY sea breeze onset. Sea bree.zes are capable of selling in as early as 0730 NSTbut may be ext inguis hed before noon . Themed ian dtlration is ge nerally between two and four hours, but inere:..sing 10 six hours for J uly_

H.II I..F. ). OUTBIJOn (houls) o r.he ,o;;:a breez.: JI 5 1. John·5 Ai rpon. 1919 l !Jlt!t

April M., June July A .. g""t S..,p! ~mD<:r

MedIan \luntliOl1 2.5 4 , 6 ) )

Shortest

Longest , , 9 12 0 •

3.3 Sea brea.e strength, cooling effect and directional frequellcies G iven that theoretical considerdtions imply that the speed and cooling effect of a sea breeze are a function of the land-sea temperature gradient and the strength of the preceding offshore airflow , the mean monthly values of these pardmeters arc compared in f.·ig urcs 4a and 4b for the Apri l-September period of sea brcelc occurrence . The cooling e ffel~t was defi ned as the fa Jl in temperature (dctemlined from the M, U. N. themlohygrograph) over a period of approximately two hours fo llowing the estimated time of o nset of the sea breeze . This duralion was ch<Jscn in order to reduce the likelihood o f cooling fro m the sea breeze bei ng con fused with mdiational cooling in the lale afternoon and evening.

The average sea breeze strength ranges from 3.1 ms~ 1 for July 10 4. 7 illS I for May, with an overall average of 3.7 m s-I. This is similar to speeds reponed from comparable lati tudes e lsewhere (Dexter. 1958; Brittain. 1978; Bums et aI., 1980; Steyn and Faulkner, 1986). Howeve r Ihc antecedent speeds (prev ious three hours) are somewhat greater, reflecting the stronger prevailing offshore winds encountered in this area . It foll ows that in order to overcome a stronger offshore wind the thenna l driving force, represented by the land-sea temperature contrast, must be sufficiently pronounced . In this respect the characteristic low o ffshoresca temperatures would serve to magnify this force and improve the chances of local sea breeze development . In this regard the magnituue o f (MAX T - SST) shown by Figure 4b refers to the cslimated local land-sea temperature di fference immediately prior to sea breeze onset , averaged for all sea breeze cases by month .

The Olean sea breeze cooling effect was greater during the months of stro ngest land-sea temperature differcrtce (May. June, July), as may be eXpl-'Cted. However, the relatively strong cooling e ffect for the month of May (which was

12 Cl imatological Bulletin I Buileti n ciimatologique 25( I) . 199 1

(a) 5.----,,--- - ------, .. ' .... 4.5

~ .. - 3.5 ," c .

~ 3 -

~ 2.5

2

1.5

1 •

0.5

....•...

,. Sea breeze speed

Preceding speed / . ........... . .... .......

' " ' .

. .... , ....... ,.

o L-----~------~----~~----~----~ APR MAY JUN JUL AUG SEP

(b) " r------------,

12 ryAXT-SST)

10

Cooling effect ....."- I -- ---------------2 " ..... ---

•

oL-----~----~ ____ ~ ______ ~ ____ ~ APR MAY JUN JUL. AUG $EP

FIGURE 4 , (al ~kan speed of sea breeze and prettdlllS wmd, SI. J()bo's Ai rpon, 1979~198S .

(b) M~n cool ing erfe.::t Qf sea breeu ro l3teil {O (jll,),lime land-sea lempcnllurc difference .

C. E. Banfield I Sell Breezes at St . John's 13

PRECEDING o·

270·-.... 90·

180·

MIS

PERCENTAGE FREQUENCY

FIG URE 5. Oin::cr;onsl frequencies (10 deg n:c ullervals) ar><lnlcao spo..><:ds d~fi ng sea "rec~.cs, and for the rhroe hoo~ prcc~..:li ng s~ a bt«« onser, at 51. John's Airport. 1979-1981L

significantly grcatcrlhan for April,June, Augustand September) is probably also panly due to Ihe significantly stronger sea brcc ... .es during Ihis month . The reduced cooling effect for June , despite its relatively large value of (MAX T - SST), is likely re lated to the fact that sea breeze duration was noticeably shorter for Ihal month (less than two houfs for 40% orlhe cases). Ortne 90 sea breeze cases examined, 45% produced a cooling effect of I.O- 3.0°C: cases of strong cooling (5.0-1O.0QC) were limited to I I % of the study sample.

A closer examination of the relative strength and frequency of the sea breeze according to specific onshore directions is afforded by the right-hand side of Figure 5, which was compiled from all hourly winds observed at the airpon

14 Climatolo!lical Bulletin I Bulletin climatologique 25(1), 1991

during tbe 90cases examined. Di rections from the southeast sector (120- 150°) arc clearly do minant , with speeds averaging 3.0- 4.2 ms I. A secondary peak in frequency ex ists from the northea'l t (40- 60"), having marginally grcuter mean vcloci ties in the range of3.3- 4. 7 m:.- I. Sea brec"l.es from the intcrvcningsectm arc relat ively wcak (2.2- 3.3 IllS-I) and less freq uelll, especially from 70_800

• The possibili ty of synoptic-scale cuntrol over sea breeze direction is addressed in section 4 below .

4. Mt;TEOKOLOGICA L CQN O/1' If)NS ASSOC I ATEO WITII

SEA BREEZE DEVELOt'MENT

With respect to the second pJincipal study objC(.·tivc. certain aspects of the syno ptic-scale meteorological s ituation at the time of sea bree1"..e development were investigated in order {o estublish some aids to local forecasting of the phenomenon.

4.1 Amecedelll wind conditions The distribution of surface wind conditions obServed during the three hours prior to onset of the sea breeze is summaris .. -d by the left-hand side o f Figure 5. The majority of these antecedent offshore winds were from 230- 3100

• with a peak frequency from 270Q and a broadcr sccondary maximum fro m 240- 250". It shou ld be no ted that winds from 270_3200 wi ll have a previous fetch over the eastern sections of the island's imenor and Ihc northern Avalon Pcninsula. BClwccn SSW and WSW (200_ 250°) the upwind fe tch Ijes across the smal ler interior of the Avalon Peninsula. Antecedcnt winds from the· northwest (290- 320°) were stronger 00 average (4.75 ms-I) than Ihose from wesl or southwest (average 3.6 ms- I) d ue 10 the fact that a significant pan ion of the former group occurred in association wi th fairly strong northwesterly gradient wi nds at the 850 mb and surface levels (as illustraled in subsection 4.3 below).

4 .2 Applicaliotl of tile Biggs-Gralles Lake Breez.e Index II is also instructive to examine the distributio n of the calcuhlted val ues o f the Biggs-Graves Index and its relation to the surface w ind preceding the sea breeze. The original study by Biggs and G raves determined Ihat approximalely 90% o f the lake breezes at the western end of Lake Erie occurred when the calcu lated Index for the day was less than 3.0 (given the unils employed). This criterio n has also been fo und to predict successfully the majority of the sea breezes occurring in the Vancouver. British Columbia area (Steyn and Faulkner , 1986) and over theeastern New Brunswick coast (Neumann and Mukammai, 1979). In this study the Index was calculated for each orthe 90 days on which a sea breeze is considered to have developed, using the values defined above for the Index components. Figure 6 re lates each of the daily 6.T values used in the calculat ions of Ih.e Index (i.e. M AX T - SST) to the corresponding mean ~ulface wind speed for the threc hours preced ing the sea breeze; it also distinguishes those cases having calculated

C.E. Ballfield I Sea Breez.es al SI. John's 15

24 .: 22

., . BGI = 3.0, .

20 0

1B 0 • .',

" .' BGI =3.2

u g 16 " " · · iii " • • '" "' • q, , • •

~ 12 u i ~, oJ.,

• • • ~ ". 0 . , •

>- 10 • 0

0 I\, • •

" • 8 " • • , • , • 6 • • ,,'

0

4 ' . ' . • • 2 • I .. NW synoptic flowl

0 0 2 3 4 5 6 7 6 9 10

PRECEDING u (m/s)

fiGURE 6. Local land-5Cl1lemperalUrcdiffercn"", (T MAX _ SST) and mean surface wind s~d (il) l'rC<.:cding theunsci of ~a bl\:C7.eli II! St. John 's, 197':)- 1988. PlI.f1lbolic lines dcr.nc HOI .. JJI and RGI = 3.2

BGI < 3.0 and cases with BGI > 3.0. There were 70 cases with BGI 3.0 (78% of the total) and an addit ional 4 cases o f 801 3 ,0- 3 .2 Ihm may be considered " marginal ", fo llowing Biggs and Graves; the remaining 18% were characterised by a wide range of BOI values above 3 .2.

F igure 6 aloo indicates thai of the si)(teen events with DOl > 3. 2. twelve had been identified , frum the synoptic charts . as occumng in association with northwesterly gmdient flow. I,n comparison, this type oftlow occurred with only five of the 70 sea breeze cases with BGI < 3.0. The majori ty ofthcsc twclvc­events were characterised by a relatively strung preceding wind from WNW or NW ( > 4 .0 ms-J), fo llowed by an abrupt shift 10 onshore tlow from thcnortheasl. A pronounced fall in temperature amouming to 5.0- 9.0°C accompanied the windshift in several cases. Two examples arc included with the sea brceze sy noptic situations described below.

4.3 Synoptic patterns Representative examples of the types or synoptic-scale pressure patterns associated with sea breeze development at SI. John 's are illustrated by Figure 7.

16 Climatological Bulletin I Bullet in cl imatologique25(1 ), 199 1

19a1 MO. lO ... -:;;~ 143l'1 NST ,. ... \1 ,

:~----1-"-.-'l '" " ... 1~~Vj;''''F==::j:0» .... -• " 1 , " .

"

a

1982 Jul, 31 "3l'1 NSf

("

b

. ,,~ .. " .

ff:· ....

1979 Ayg. 2. 1430 Nsr

' ... ... _. -.... ---L~ ,

, "

c

,

~~--~'::..' ... •

." '-...... ::..--~ .', ,

., -. , ,-, " (, ',. , ', .

..;-~

\\ ( ,

1982 Mo. 13 1~3O NST

.. n.· . . . .. " . '" ...

'987 Mo" 21 1430 NST

::::: .... .0 -~

e

FIGURE 7. Eumplcs ofslIrfacc synopllc pallcms accomp.,nYlng sea breeze dcvclopl1lcnl al 51. Johlfs; {8) unt1cyclorlC U) sou th , (b) trJnSlcnl ndCt!, (e) s lack pressure gmdi~nt. (d) and \~)

IlOnhweslnly now_ "T FALL" AND " RH RISE" refer totooling Cm:Cltn ·Caoo increase In relatIve humidi lY in percerl!uge points within two hours rollowing sea breeze_onsct.

Included with each is a summary of conditions observed ordctennincd for that case, and the observed winds forlhccloseSI sy noptic houral stations in the eastern Newfoundland region and offshore. Based upon the isobaric curvature in the vicini ty of the study area at the time, 65% of all the 1\ea breezes identified developed under anticyclonic flow situations, which are normally regarded as most suitable for sea breeze development (exemplified by Figure.~ 7a and 7b) . A funher 15% occurrcd with slightcyc!onic curvature and the remaining 20% can be

C E. Banfield I Sea Breezes at SI. lolm's 17

classed as indctemlinatc or transitional patterns such as straight isobaric now or col regions, e.g., Figure 71;.

The nonhweste rly gradicnt now Iype Ihat occasionally precedes II marked northeasterly sea breeze, wilh a BGJ value well in excess of 3.0. is illustrated by Figures 7d and 7e. In the case of May 23 , t9821hc isobaric anal.ysis suggests Ihe possibili ty of a wcak tmugh near thc ea. .. ! coast oflhe island , although at SI. John's Airport lhe only pressure fall amounted 10 0. 1 mh between 1130 and 1230 NST. The windshift, from 280" at 8 rns- I 10 50" al5 In..- I , occurred abruptly at 1410 NSl': sky conditions changed from cloudless at 1230 NST to scattered cumu lus from 1330 I(J 1730 NST. Hence it appears more likely that fairl y strong solar heating inland was a prime faclor in produci ng a sea breeze on this occasion.

A vcry similar type of windshift occurred on May 2 1. 1987 , again preceded by moderate gradient now rrom 280- 310". In this instance the surface analysis. indudiJlg thc light WNW wind observed by Ihe ship 150km to the NNE of SI. John 's, suggests that a meso-scale high pressure area developed off the east coast of the island, contributing to onshore northeast flow over the s tudy area by midday . Such a fealure could have developed as a result of the prcvailing low offshore sea surface temperature. .. ( 1-4"C) conlra.~ling wilh Ihe solar healing inland and produc ing a meso-scale "cold high" circulat ion system over the offshore walers. SuppOrt forlhis hYpOthesisean bedrawn from the workofHurns, Dick ison and Neumann ( 1980), whowerc able to idemify "regional anlit:ycJones '· developing during daytime-over the.cool waters of the Gu lf of Sr. Lawrence during slack: synoptic-scale pressure gradient~ in summer. These systems were held responsible for a particular category of sea-la -land flow observed over eastcm New Brun,<;wick atlhis time of the year. It can be argued Ihal asimi lar type of situation occurred over eas tcm Newfoundland on May 21, 1987; if so, this was not a straightforward sea breeze but an onshore now partly dircelcd by the location of the meso-high offshore. which itself was the result o f the land -sea temperature conlraSt.

5. SUM M A I(Y AN D CONel US IO NS

The reduced frequency wilh which sea breezes occur at St. John 's. compared wilh most other cases reported rrom simitar latilUdes, is attributed largely to the local prevalence of relat ively strong offshore gradient winds and a lower fl\:cluency of large land-to-sca temperd(Ure gradients . It is likely (hat in a minority of cases the daytime wind reversal resu lted from the offshore development of suh·synoptic scale systems such as a meso·scale anticyclone .

Research into olher aspects of thiS question, such as the inland penetralion of sea breezes underdirferent gradient flow conditions and their occurrence along the Conception Bay ooaslto the wcst ofSL John 's (and whether these are linked to or distinct rrom those oflhe Atlantic shoreline), would enhance the understanding or lhe sea breeze process. On the applied side the impact of the sea breeze upon indices of outdoor human comfort may reveal contrasts with other

18 ClimatOlogical Bulletin I Bulletin clim<ltologique 25( I). 1991

regions. Por many mid-latitude and tropical locat ions sea breezes are viewed a s

welcome relief from uncomfortable he at. Along the Newfoundland coast the cooling sensation from sea breezes can be more drastic, cspl.:ciaJly in spring and

early summer, due to low sea te mperatures.

AC KNOW LfDG6 ME NTS

The a~s i stancc of Stuart Porter (Scientific Services, Atmospheric Envimnmelll

Scrvk;e, S I. John 's) and Harold Janes (Officer-in-Charge, SI. John 's Weathe r

Office , Atmospheric Environment Se rvice) ;n providing data in support of this work is appreciated . The figures were prepared by slaffatlhc M e morial University

of Newfoundland Canographic Laboratory .

R~I: E R t N CES

Atk inson, B . W .• 1 9~1 ; MeSQ'lTaleAtmospheric Cirt;u/miolls . Acudcmic Prcss . London,

495 pp. Barbmo . J .P., 1978: Areal paralllcI!':r.; of the sea breeze and ilS verticlI l structure in lhc

Bo.~lOn basin. Bull. Amt'r. Melforul. SO(:,. 59{ I I ): 1420 143 t. Biggs. W. Galc and M.E:. Graves , 1%2: A lake hrec~.c inde", . J . Appl. M eleor. ,

1(4): 474--480.

Brillllin, O . W. , 1978: Forecasting sea breezes at Eskmcals , Mi!!. Mug " I07( 12(8): 88-96.

Hums, L .M.D .• R. B,B . Dickiwllllnd H.l l. Ncuman!], 1980: Eastcrly marine nows in

New Brunswick during July, Paper.! in lJiometl~orology , Faculty of Forestry , Univcn;ity of New Brunswick, Fredericton.

De"'tl!r, R. V., 1958: Thc sell breelc hodogrnph ul HuliflOl . BIIII.Amer. Meleoml. Soc .. 39(5): 2A 1- 247 .

Estoquc, M.A. , 1961: A theoretical inveslig:lIion of the sea brtez!!. QHart . J, Hayal Me/.

Soc., 87: 136- 146.

£~ltXjue , M.A., 1962: The SC;J breeze a.~ a function o f the prevai ling 5 il u~tion . J . Almus.

Sci ., 19: 244-250. Pishet, E. L., 1% 1: A iheorl!lical study arthe sea brcc:.:e . J. M et. , 18: 216- 23] .

Frizzola, J .A. and E.L. Fisher. 1963: A series o f sea brec7.e ohservations in the New York

City area. J . Appl. Meleor _, 2(6): 722-739.

Gill , D .S . , 1968 : The d iurnal variation of the sea breeze at three stations in nOl1hcast

Scotland. Mt!t. Mag. , 97( 11 46): 19- 23 , Kozo, T,L., 1982: An ohservat ional Study of sea brcC'l.cs along the Alaskan Beaufort ~i:a

coast: Part I. J. Appl. Meleor .. 21(7): 891- 924 .

Lalas, D.P., D .N. Asimakopoulos. lind D.G . Deligiurgi, 1983: Sea-brec1.c ci rculation Ilnd photochemical pollution in Athens, Grcet:e, AIllIO.r. Envirtmmenr,

17(9): 162 1- 16]2. Lyol)s, W.A. , 1972: 'The climatology and prediction of Ihe Chicago lake brcCl,c.

J . Appi. Mereor., 11 (8): 1259- 1270.

C.E. Banfield I Sea Breezesa/ Sf . John 's 19

Mahre, Y. lind R.A. Piclkc. 1977: Th~ cffccts oftopogmphy on land and sca hr~i:l.e~ ill &

(Wt}-dimCnsionai numerical modd . Momh/y Weather Rev., 105: 1151 _ 11 62.

McKendry, I.G., 1989: Numerical ~imu l :l!ion of sea brCC1.cs overthe Auckland n.:gion, New

Zealand - lIir quali ty implications . HOIllldllry Layer Meteor%.t;y, 39: 1-22.

McKendry, I.G., A.P. Stumlatl , and I.A. Owcns. 1988: Nurm:rieal simulat ion oflocll l thennal ~ffec(s on tllc wind fie ld of the Canterbury Pl:lins, New ZcalarKI .

New Zealalld Jr}!lrt /i l / ojGe%gyal1dCeol,hysics, 31 : 51 1-524.

Moritz. R. E., 1917: On a possible sea bree'lc circulation near Barrow, Aluska. Arelie lIIld

Alpl,le ReSf!arch. 9(4): 427-431.

Neumann. H .H . . 1979: Sea /JrcI'ze elfet·1S 01110118 disumce driji cail:ulatiOlIS. Presented althe Conlt rcllce on Long OlSllIncc L>rift Ilf ,",orest InSCl,ticiUci: New Brunswick Dept . of NllIural Rcsources. Forest Protection Ud., Univ of

New Urunswiek, 26 pp .

Neumann, H.H. and E. I. Mukammlll , 1979: Inddel!cl!-ojmelo-scu{e tU/lvergt' /l!"e lill e,\· (l.~

WI iI/put /0 spruce bllliwurm COil/wi srfflltgies. Presented at lhe

8th International Cllngrcss in Biom!;lcorology, ShefaYlfIl. Israel; 25 pp.

Noomm , J .A . and R. K. Smith , 1986: Sea bree7.c circulation over the. Clip;! York Peninsulll and generation of the Gul f of Carpcnlaria cloud line dislUm:lnces. J . Afm()$,

Sci , 43(J6): J679~lb9J.

Pidke. R.A. , 1974: A th ree_dimensional numerical mudd <Jf the scn brc~7.c Ilvt:r !>QUIll

Florida. MomMy We(//ill'rRev. , 102: 115-139_

Prc/.erakus, N.G .• 1986: Characlenstics or lhc sea breeze nt An!en, Grecce.

Boundary Luyer Mell!oroiogy, ]6: 245-260.

Staley, 0 .0" 1957: The low-l.:.vel seu brCC1.c or nnnh-west Wuslunglon. J. Mel"

14: 458-470.

Steyn, D.G . and D.A. Faulkner, J 986: TIlt: climatology of sea breezes in the Lower Fraser Valley, B.C. ClimulOlogiL'(11 Hul/nin, 20(3): 21 - ]9.

Stunnan , A.P. and P.O. Tyson, 1981: Sea brcc7CS a!ong theCllntcrbtJry CO~5t In Iht' vlcinJlY

ofChnstehurch, New ZeuJand, J. Climalolo8Y, i: 10]-2 19.

20 Climatological Bulletin I Bulletin dilllallllllgiquc 25( 1). I~ I

Break-up in Hudson Bay: Its Sensi tivity to Air Temperatures and Implications for Climate Warming D.A . e lkin Arctic C limatology Sl!clion Canad ian C limate Centre 4905 Ou fferi n Street Downsview. O ntario M3 H 5T4 [Onginallllanuscript received 21 June 1990; in revised form 30 September 19901

IIUSTRJ\ CT

A grjdded data sclofsea iccconccntratioll for Ilud!WrI Hay ami Jam<!s Bay gener~ 'ed by Ice Branch . Atmospheric Environment Serv ice, Canada was compared 10 Incliing degree day

data in ordcrto ~ssess the sensi tivity Oflllc ice to Climalc.wamling. The cOlllparison showed Ihat the two \lari able~ correlate well oyer SQmc parts of the Ilays while over others they correlate very poorly. A sensi!iv;l), analysis indicatcS lhal a climate w:mning of ! ~C could

advance break-up by over 2 weeks ill eaStern Hudson I1n),. while thc-suuthwestcrn part of the

Ba~ show~ II lower scn~ it jvily of6 to 8 days , ~nl.l1 arne,~ l1ay4 to 7 days. Thcprecise patlem of break-up depends upon such factors liS ice IIdv(:(;IIOI1, fresh water inOulY in the Bays and

modification within the boundary layer as the air OOIYS o~er the icc and wain ,

Poun!valuer la scnsibilitc de I ~ glace au rechauffement ciimutique, on a compare :IUX

donnees des degres-joursde fonlc un cnsembledc dorlnees de In CQllccnlration des,glnccs de mer pour la baie d' H udsou et la b:ue James ctabJi sur quadrillagc par la Direction dC/l glaces

du Service de I'cnvimnnement atmosphcrique dll Canada, La comparaison a revele UIlC bonne correlation des deux variable~ dans certaines I.ones des baies, mais une mau~aisc correlation dans d 'autrt:s , D'apres une analyse de la sen~ibll i te, un rcchauffemcnt de I °Cdu

dim.:.! pourrnit faire avancer la debacle de plu~ de dcux SCI1l11ine~ dans l'est de la baie d' Hudson, alors que , sous l'cffct d'une ~en~ i hilitc Illfcficufe , la d~b:aelt.p()lIrr3it8vanccrik: 6 a 8 joul'li dans Ie sud-oueSI de celie baie ct de 4 a 7 jours dans la baie James. Ll

configumuon pr~e i se de la dcbiide dtpend, d 'cntrc aUlres, de t'adveclion des glaccs, I 'appon d·eau douce dans Jcs baies e! la modi fi ca tIon ~ U fVerlant dans la couchc limite qUllnd ['llif c ircuJc au-dc~sus de la glace et de I'eau.

O,A, Elki/l I Hudson Bay Brcilk-up ami Climate Warming 11

I. lNTkODUC T 10N

Climate models are predicting significant increases in tropospheric temperatures as a rcsu lt ofchanges in grcenhousegas concentrations within the atmosphere. The winter lempemlurc change in polar regions, especially within the marginal snow and ice zones, is expectcd to be several times larger Than that in more temperate latitudes. O utput from general ci rculation models indicates that winter temperature increases over northern Canada result ing from a doubling of glohal atmospheric carbon dioxide could range from 4 to I S~C. with summerlempcralUrc increases ranging from 2 to 6QC (Etkin , 199Oa).

Especially within the marginal sea icezones, the prediCliollsare likely 10 d iffer fro m each other, depending upon how the icc is p<lramclerized and uj>Qn the sensitivity of the model to various feedback loops involving the albedo of snow and ice. For examplc , in the middle o f Hudson Bay, one model shows JllllUaty

te mperature increases exceeding 14"C, wh ile anothe r shows about 4°C (Elkin , 1990a) , Theeffect ofthesc anticipated temperature increases on sea icc is expected lobe very s ignificant. However, it is d ifficult 10 assess. As pomtedout by Mitchell et af. ( 1990), ··on the basis of current simulatio ns , it is nOl possible to make reliable quantitati ve cstimates of the changes in the sea-icc extent and depth ,"

The oceans and lakes in the marginal icc wnes uf pular regions respond to freez ing winler temperatures by foml ing a layer of relative ly thin noaling icc, and 10 summer tempcmtures by melting the ice. The timing of melt and freezing depends upon a number of oceanographic and atmospheric parameters. the most important nfwhich is usually airtempcralure (Rogers, 1978; Mackay , 1952) although other factors such as salinity. winds and ocean currents can be significant (Mysak and Manak, 1989; Walsh and Chapman. 1990). Since air temperatures can be highly variable from year to year. the pattern of sea ice fomlation is subject to variations ali well; as a result rhe historical relationship between sea ke and air temperature is potentially an indicator which can gauge the sensitivi ty o rthe ice-sea.~on to change in climate. Previous studies have~hown that such relat ionships can be valuable (e.g. Palecki el Qt .• 1985;' Barry, 1978; Walsh and Johnson, 1979) and a general rev iew of this subject can be found in Skinner ( 1986) .

The purposc of th is paper is to a.~sess whcther the statis tical relationship betwecn air temperature, or sume deri .... ati .... e thereof, and sea ice concentratio n is sufficient to estimate the scnsitivity of the timing of icc break-up to climate wamling, The geogmphieal area selected for this slUdy is Hudson Ray andJamc5 Bay, wh ich together ronn the world 's Iar-g.est inlandSea. Martini ( 1986) provides a complete review of geology , climate, geography , oceanography and icc conditions,

2. DESClt tPTtON OFS T UDY AKt::A

Hudson Bay and James Bay (Figure I) together foml a large Saline body of water

22 Cli matological Bulletin I Bulletin cJimatologique 2S( J). 1991

".

.' ~,~.'

'0'

Hudson Bay

- 9 "lo

FIGURE. I. LQcauClfl ",liP of li ud.>OlI Bay 1'he numh<.'red dO(s md,t ale gild pOlMS ur.ed ,n !he regression au~Jy~is .

D.A. Etkin f HudsOn Bay Rreak-up and Climate Warming 23

extending over 12 degrees of latitude and 19 degrees of longitude in central and northern Canada . It is connected 10 the oceans through a set of rcl<ltively narrow c hannels located along its northem cdgc. As such, it tends U) act more like a closed .~ystem than many other parts of the world 's ocean system, and this is onc of its advantages; oneean expect simpler relationships between atmosphcric and oceanographic variables as a resul t. For conveniencc, Hudson and James Bays together will be referred to as Hudson Bay or the B<lY for the remainder of this paper. Cold Arctic Ocean water enters the B<lY mostly through Roes Welcome Sound at the extreme northwestern part orlhe Bay, and Atlantic water (atieasl

F1GURh 2. Typical break-up ofsCll kc In Hudson Bay (aller Mlltkhwn. 1981:1).

24 Climatological Bulletin I Bullelin clill1atologiquc 25( 1), 199 1

according to a rathcr limited number of mcasurements) cntcrs the Bay east of Southampton Island; wanner water from the Bayexits through Hudson Straileasl of Southampton Island (Prinscnberg, 1986). The Bay is al!K) fed by numerous freshwater rivers around its perimeter (Prinsenberg, 1988). Within Hudson Bay, summer currents revolve cyclonically with an average current strength of 5 cm/s (Pri senberg, 1986).

Complete freeze-over QCcurs each winter as the Uay becomes filled with f1rst-year ice. Only theelltreme nonhwcstem por1ions of Hudson BlIY experience multi-year ice. During break-up open water appear!; first in sl)uthem James Bay as one would cxpect. but also in eastern Hudson Bay due to spri ng run-off (Markham , (986), and just southwest of Soulhampton Island as ice is removed from that region by the currents and wind faster than it can be replaced from the narrow Roes Welcome. Sound. These open areas grow with lime, with open water expanding northward along the eastern shore of the Bay, and icc being ad vecled southward and then .~oulheastward along the western and southern shores. By early August the Bay is essentiaity ice-free (Figure 2). This description of Hudson Bay ice is consistent with the data presented in Mysak and Manak (1989).

Prevailing winds in the Day during July are west to nonhwesterty although James Bay shows a strong southwesterly component (Maxweit , 1986). As the air in the boundary layer paSses over the icc and water, illends to come into equ ilibrium with the surface. Following snowmelt, which begi ns in May to the south bUI can occur in mid-June to dre nonh. relatively wann airbcgins to pass ovcrthe Bay (Elkin , I 99Ob). This airtends to have the most cffeclncarthe shore , with its ability to melt ice diminishing as il mnves progressively over the Bay. The result of both these factors (icc advection and airflow) is that the la.':it areas IQ lIlelt are along the southern coast of the Bay and in Iheextremc Ilonh, just east of Southampton Island.

The spatial pallern o f weekJy mean air temperature, wind , and ice concentration from May 28 h) July 29 , 1980 is shown in Figure 3. The year 1980 was typical for Hudson Bay wealherand ice conditions (Mysakand Manak, 1~1I9) .

In late May and early June most of the Bay was icc-covered although brcak·up had begun along the eastern shore and in James Bay. Temperatures were fairl y zonal with below-freezing values in the northern half of the Bay. As time progresS1.!d , the air temperatures became increasingly meridional (with thcexception of June 25 10 July I) , with colder temperatures in the eastern half of the Bay, the region where break-up occurs first! This tcndency for the isothcnns to lie nonh to south is assunred to exist because orthe continual COOLing of {he air as it progresses across the Bay _ The inclinalion for the contours of constant ice concen/rations to lie at large angles to (he isothenns confinn!; the importance of processes such as ice advection in determining regional icc concenlmtions. By the end of July, ice had disappearedcverywhereexcept for a few tcnths in the extremc nonh and along the southem coast of Hudson Bay and James Bay, where temper:Hures ranged from 9to 15°C .

D.A. Elkin I Hudson Bay Break-up and Climate Warming 25

... " ... AA ","PO"'~'" Wi,,,,, .... "'0 """, >, ,_ .",roco AI, '''''PO'"''''' • Wl ... ' ...... .... Juno 10, 'Mel

...... Ieo C_ .. ".U.~, ...... 10 J .... >. , ....

"

26 Climatological Bulletin I Bulletin chmatologique 2S( I), 1991

........... T ............. _,~_,' "' ...... n ... ... .... ,"" .... T ...... ''' .... ' W_, ....... 1110 ....... 14.''''

....... k. Con,."". """: J""ol1 '~J .... 11, '_

\ ' '-{ , (

FIGURE 1. Mean air lelllperahlTeS ("C). winds .TId iee cOl1£enlfalionsover Hudson lIay and James BHY during break-up of 1980, by week.

D.A. Etkin I Hudson Bay Break-up and Climate Warming 27

Su'(K . .... ' T"" ... .,. ' •• W(M : """ . .. I . .... I ,"" So" ... ~" T. '" ..... ' ..... WInd: . .... I •• '" I, lNO

..... to. CO" .. ,,,'.""., ........ "' •• Or I. ,_ .... " ''''' """,,,.,,,,,_ •• ,, 1 'oJ"", .. lno

28 Climatological Bulletin I Bulletin cJ imalOlogiquc 25( I). 1991

,",~".""r T_.,.r • . W,"", .I.,., '0 .I .... IS. ' .. 0 s ..... ,. A~ T_p., ....... Wl ........ 11 ....... , U. 'NO

.. --.....

M.." "'. c." .... "",...: "'"'I" '" .h" •• ,. ,_

,- ..

FIGURE 3. (cunliou~'d) Mean air tempeflltures (OC). winds und ice concentra tions over Hudslln flay and James Bay during b~ak·up uf 11180, by week .

D.A . Elkill I Hudson Bay Bre'lk-up alld Climate Warming 29

FIGURE] , (concluded) Me~n air tcmpcraturc.~("C). winds and ic~ CtmCenlrulinns over Hudson Bay and l amcs Bay during brc.~l:·up 01 1980, by week. .

3. ANA l.YS t S

A data set o f sea ice concentrat ion for Hudson Bay covering the period 1963 to 1984 was created and digitized by Ice Branch, Atmospheric Environment Service (AES) (Markham, 1988). T his data sel provides one icc concentrat ion value per week at each grid point . Ice concentrations from this data sel were compared to ai r temperatures over the Bay usingdala from the Naval Environmental Data Network Set (NEDN). which extends from 1974 onward (Brown. (988) . The two data sets were regridded on identical grids in the Bay (Figure I) using two programs resident on the AES mainframe computer, ·Climale Research in Ice Statist.ics· (CRISP)and 'Contour Analysis Software Package· (CONAN). The~ twO programs arc described in Agnew and Maxwell ( 1987) ,md Brown ( 1988) .

Due to the lemporalli mitations of the data, only Ihe years fro m 1974 (0

1984 inclusive could be analyzed . For each of the 16 grids, a cumulative nlClting degree day (MDO) value beginning June I was calculated (MOD = mean dai ly temperature above Q0C) , for comparison with ice concentrations. The laller (Ihe dependcnt variable) were linearly regressed against MOD data (the indepenucnI variable) . Each regression included 99 data points . Correlation cocrlicie nls (8) were used to eslimiJle the goodness o r lit between thc two variables. An R value()r + 1 o r - I indicates a perfcci fi t, while a value o f 0 indicates no correlat ion . The results of these regressions arc shown in Table I.

The best fits occurred over James Ray and In a swalh ranging from the northeaste rn part of Hudson Bay west-southwestward. The highest values of R tended to occur in the centre o r the Bay, which makes sense intuiti vely as this is the area where there are no coaslal effects and climate variabil ity would be 1.11 a

30 C limatologica l Bulletin I Bulletin climatologique 25( I), 1991

I A Jj l I'.. I. SUIIllll,uy of Linear Regre.~skm : Jee C(lrweUlralion tYJ and MDI) IX).

Grid Point Equation Com:latlofl Coetficicnl (RJ

1 y= 6,21 ,00939 ~ 0.34-1 y= 6. 12- 0094Jx 0.34 3 y= 6,9S - .0148x 063 4 'r791 .0167 x 0.09 , y= 954 _.0194~ 077

6 Y- 8.19-.0215.\ 0.'" 1 Y'" 6.56 ,0195x 0.74 8 )'=9.07 _.0 14));; 075 9 y = 10.3 - .0144 x 0,76

10 Y'" 9.40 - .0207 ~ 0,81 11 , 6.52 - .0191 ~ o.n

" y= 9.::1 1 ,0129 ~ 0.69 J3 y~ 9 . 63 -.0 1 0Sx U.78 14 y= 7.40 _ .0155 , 0.68 IS y= 8.45 - .O l3h 0.75 16 y= 7.83 .01 10'" 0.81

- wilere ice conccnlnuion (y) is rnea.'ilm:d in tenlhs and rndling degree days (x) is mcasun:.:! In

dllys-·~

1/\ nl!'. 2. N umheru(Ooys aftllr Junl' I Required for Break_up underCurrent Climah! Hnd under a Clmtate Warmed by I"C.

MOD for I)ay~ Umxr Days Under Clin13tc G rid I'oint Break_up Current Clllnat\' with l"CWamung Difference , 234 '" " 8

6 176 49 '8 11 1 '" ... 29 " 8 285 " 19 6 9 371 56 " 7

10 212 56 '" 12 11 80 " J<) 17

" 429 61 53 , is 249 46 39 7 16 2" 35 31 4

uverage _ •. 236 411 .7 39 " minimum . Presumably those areas with the lower value~ are more subject 10 variations in icc conccnlr.ltio n due to ice advection by winds and currents, a more complicmed iceregimc due 10 the presence of such facto rs as polynyas or fast ice, or a more complicated climate regi me such as would exist near coastal areas.

An estimate of tile MOD IOtal required to melt iee to five -telllhs (5/1 0) concentrution (break~up), as detemlined by the regression equation, is shown in Table 2, which uses only grid points with a R value o f O. 7 or higher; lower R values

D.A . Etkin / Hudson Bay Break-up and Climate Warming 31

bring into question the value of any analysis as the variables are not well corre lated. The pattern d early shows that the southwest pari of the Bay requires the most heating in orderio melt the icc to 5/ 10. This is reasQnable as that is the area which experie nces the most iee advection. The smallest MDD totals req uired to mellthe ice 10 5/10 oceur in Ihe northeastern part or tile Bay. Agai n, as the current patlern brings wanner waters and icc-free areas from Jamcs Bay and southern Hudson Bay up the east coaSI, th is is an expected resulL Nole that thc M.DDtotals required in the southwest arcover 5 limes as large as those required in the northeast. The pattern of maximum winter ice th ick ness (Markham. 198 1) appears to be poorly rdatcd 10 thc mdt pattern , as the areas which break up earliest experiencc some of the thickest ice, while the areas of thin iee(James Bay) require MOD totals near the-mean value.

For each grid point , the a vcmge MOD requi red to rcach 5/10 ice can be calculated. With climate wanning, MODs will accumulate more rapidly. and melting wi ll occur earlier. The number of days required to melt the ice under wanner cl imate conditions can be estimated (Table 2) by multiplying the number o f days requ ired to melt the ice under current cli mate conditions by the ra tio at which the MDD accumu late undcr a warmcd cli mate to the mtc undcr the current climate.

Table 2 shows Ihal if the dimate. were. to warnl by I"C. the northeastem part of Hudson Bay would break up about 17 days carl ier, southwestern Hudson Bay 6 to 8 days earlieralld James Bay only about 4 days. These estimates arc consistent with a study by Hamilton ( 1985) who noted thaI strong ENSO events (assuming an associaled wamling o f about 1°C in central Callada) resultcd in brcak~up jn James Bay occurring on average 5.6 days earl ier than nonnal. By comparison, the standard deviation of break· up for an average of a ll points wilh R ~ 0.7 is 7 days; ind ividual grid points Iypically have standard

r A a lE 3 . IccCOnCenlf:llion by Y~ar. C~nrrat Hullson IJuy

_U ••• ~.HP.~nn.,.n."W' RV '.M OS/ZI 9. 9' ~ 9 ' 9' 9 9' 9 9' 9. 0')"/2&9 99' 8' 9'9'9'9'9 ~'9'9.,.9. 9'9.9'9.9.9.9.

06/049. II 9'9.9 9.a 'I.' 9'9 ""9.9'~9.9"'9 9' 9. 06/119' ,_ II 9. 1, 9'8 9999 "9.9'9 9" '9_9_' 9_9_

06"8' a 'I.' 9 9 'I.' 8 9 9911 9 9_9'9.' 9.9 9 9'9 9 9_

O(I/l~' e a 9 6 9'8 9 9'" '!tt' 9'9'9'9 9 9' 9 9 II 9' 0110~ 9 8 II :/:\9. 1 9' a 7 8 1 ~'I ,. 9 II 1 1 9 II 7 ~ 07109 7 II a II 0_ 9 6\;'J~~ l l ~'{;. ~~ 8 .... 4\ 8 l" V 9.

or/ll o. a 6 l 0 sV 0 • 1 0 Q. Q. 0 Q. 0 0 g. I o. 3 l 0' ; 01116 6

Ve 8 0 6..,.l , 7 O. l l O' S 0 9_ j l-:,.r 4 Vz ~ II

07{lOO O'OlO] 0200000400000DO~ 0I!/D6 0 , 0 0 0 0_ 0 0 0 0 2 0 0 0 0 0 0 0 0 0 0 a 0 0 OSf1 3 0QQOOO 00'000000 0 000 081<lIOOOOOO 000000000000 08,1270 00000 0 00 ooooo ~OO OO

1962 1983 .. _ AESdata 1984- 1986 , • . u .s . NOAA/Nav~ d~la

32 Clirnatological Bulletin I Bulletin clirnatologique 25( I), 199 1

dc.viations over the II years of between I and 2 weeks. A time series of icc concentrations. wi th break-up, is shown in Table 3, for an area encompassing grid points 6 and 10 for Ihc.pcriod 1962- 86. Break-up has occurred as early as Junc25 and as late as the firsl week of August.

4. DISCU!iSIOl'J .... ND CONCLUSION

The sensitivity calculations in Table 2 assume thtlt other factors are unchanged; however. this assumption becomes more and more questionable as onc considers increasingly wUJ111erclimales. For example, it is likely Ihaliee thil·kness wou ld be less during a wanner winter, and that break-up would require fewer MOD than arc needed undcrcunent c limate conditiom; . This would leau to an even larger differellce than that calculated above, as the critical MOD would be reached soone r than a.<;sumcd. If wind and ocean cum::nts changed. then the adv(."<."tivc component of the ice regime would be affected. The relative importance of air temperature to otherOleteorological parameters could shift as well, in <tn unknown way. Increased runoff, a likely result of increased precipitation in a 2 x C02 cnvironll1lo!nt , would tend to enhance the formation of sea icc, for instance.

Despite these uncertaimies, this study has shown that the concentration of sea ice in most of Hudson Bay and James Bay is sign ificantly controlled by air temperature, and is sensitive to variations thereof. A wanlling of I ~C (small re lativlt to those predicled by climate models) could impact the datc:.of break-up in northeastem pans of Hudson Bay by 2 weeks or more , while other areas such as James Bay wou ld likely beaffcctetl toa much srnaJlerdegrce. Larger climate changes, which the climate models suggesl are highly likely fur the Hudson Bay region, would impact the ice regime in increasingly significant but also increasingly uncertain ways .

.... C K NQWL IWG(iMIlN'I"$

I wuuld lik.e to acknowledge the assistance of Klaas Slaker for much or the data hand ling during this project.

REFE RENCES

Agnew, T.A. and B. Maxwell, 1987 : An Icc and Snow Climnt.! InfOOlln tion System (CRISP). Proceeding.f, Third /lIIerll(JliolUll COIiferellu {Jll/ntu<l.Clive

Injoml(Jlioll und Prou!.uing Systems Jor Meteorology. OcelUlQgrophy'md

Hydrolugy, NewOr!\!ans: !73- 177 . Burry , R.G . • 1978: Seasonal Controls ofl ce Mel!. (n R.O. Barry . J.D. lllcobs et ul ., £,.ergy

Hl4dgel Studies in Relation /Q Fast·/ce Breflkllp Pmcel·Ses in iluviJ Stmit: CUltwfulugical O~·erview . Institute of AICljC ~ Alpine Research, Uni~ersi ty

of Colorado, Occa5lonal Paper no. 26: 262- 267. Brown. R.O., 19118: Marine ClimO/e Directory DlIfaset.f and Services . Infernal Repon

V.A. Etkin ! HIIlJs(m Bay Break-tIp and Climate Warming 33

nO. 88- 1, Hydrometcorology and Marine Division . Canatlian Clim3te Centre.

Downsview, Ontario. 45 pp.

Elkin, D .A., 19'Xh: Greenhouse Warming: Consequences for An:tie Climate . JormUl/ 0/ Cold Regions Engineering , 4{ I): .54-66.

Elkin. D .A. , 199Gb: Validation 0/(1 Passive Microwave Sea Ice U(II(I SCI/or 1/1 ... 1$011 RllY. Unpublished M.Sc. thesis, York Univers ily, Toronto.

Hamilton, K. 1985: Evidence for Tropieal-Mid lalitudc Teleconnections in thc Eighteeoth

and Nineteenth Centuries. Tropica/ Oceall .Almospherl.' News/ellcr, No. 30.

Mackay. G.A ., 1952: The Effect of Protracted Spring Thaws on Ice Condi tions in ~I udson

Bay. Bulletin a/tire American Mell.lor(J/ogicu/ Sociel),. 33(3): 10 1- 106.

Markha.rn. W.E .• 198 1: IceAllu.~. CmuI/liQII Arc/ic Waterways. Envimnment Canada.

Atmospheric Envin)llmenl Service. Down~view.

Markham, W.E., 1986: Thc Icc Cover. In Cll/I(ldiOllln/Qlld Seas, Elsevier Occ3Jlography

Series,44: 101- 116.

Markham. W.E. , 1988: Ice AI/as; HudsOll BaYMti Approaches. Environmcnt Canada,

Atmospheric Environment Servi~·e. Downsview, 121 pp.

Mart ini, I. P. (Ed.). 198tl: CwUJtiian In/mid Seas. EIscvicr Oceanography S~ries. 44 . 494 pp.

Maxwell , J .B .• 1986: A Ciimate Overview orthe Canadian Inland Seas. In Ctllrn<iion II,lmui Sea.f, Elsevier Oceanography Series, 44: 79-99.

Milchell, J .F. B., S. Manabc. V. M<!Jeshko and T. Tokioka, \990. Equilibrium Climate

Change - and its implica tions for the fut ure. I.n Policymakers Summary of thl' Sdelltiflc Asses$mem ojCliml1le Change. I ntcrgovcmlllcntal Panel o n Climate

Change OPCC) .

Mysak:, L,A. and O. K. Man:i.k. , 1989: Arctic Sea- Ice b:!cll! and Auo'nalics. 1953- 1984.

Atmo.sphere·Ocecm , 27(2): 376-405.

PaJccki, M . R .O . S any and F. Tr:lInoni. 1985: Lake Freeze·up and Break.up Records as a

Tempcmlllre Indie:lIor for Oelect ing Climatic Change. f'reprint voillme, Third

C(m/erellce 0/1 Cllmolic Voritllioll$ , Los Angeles, J3Jluary. 1985 .

Prinscnbcrg, S.J., 1986: The Circulation P311rm and Current StruCtUfC of Hudson Bay . In

CaluuJiall Inlmu/ Seas. EISt:vier Ckcanography Series, 44: 197- 204 .

Prinscntle rg. S.J ., 1988: Icc-Cover and Icc-RidgeCont ribUl ions tothe FreshwmcrContents

of Hudson Bay and Fox!: Ba~in. Amlt' , 4 1(1): 6- 11.

Rogers, J .C., \ 978: Meteorological Factors Allotting Imcraflllua l Variability of

Sununenime Ice EXlem in Ihe Beaufon SCIl.. Monthly Weathtr Review. 106: 890-897.

Skinoer, W.R ., 1986: rhe' Breok-upanJ f ' r ceZC-lIpuj"Lokr uU(1 Sea /cr in Northern Crl/wdIJ.

Canadian Climate Centre Report no, k6-8 , Atmospheric Env\fl.)Omcnt

Service, DQwnsvicw.

Walsh, J.E . and W.L. Chapman, 1990: Shon-Term Climatic VariabililY of Ihe Arctic.

Journal a/Climate, 3: 237-250.

Walsh , J .E . ilnd C.M. Johnson. 1979: An Analys is ofArchc Sea Ice Fiuctuillions.

1953- 1977. J(}lIrIlal o/Physical Oceanography, 9: 580-591 .

34 Cli matological Bulle lin I Bulletin climatologiquc 25(l). 1991

Estimation des flux de chaleurs latente et sensible it partir de I 'energie radiante pour certaines surfaces : Nouveau-Quebec Gerald Reltalld ct Blwwan Singh Dcpartemcnl de geographie Univcrsitc de Montreal C. P. 6 128, succursalc A Montreal, Que, H3C 3J7 lManuscri t rclfu Ie 20 ma i 1988: en fonne reviscc Ie 21 novcmbre 1990J

kliSUME

DUIlI! eel art icle 1l0lJ.~ IlxaminOJl~ la po5~ibjJilC d'c~ t i lllt:r Ic~ tlUlllUrbulcnts d'cnIJrgie

calorifiquc (QE + QH) par It! biais d u rayonnemcnt net (Q*), du flux d 'cnergic cnlori fi lluc

dans Ie milieu (QG) CI du rayonnemt:nl solaire global (K!). Plus precisefficnl, nOllS

ellilminons Ie componcmcnt relmionncl tlu Q4- - QG par rupport au KJ.. cl ee arin d'ctablir un mooele tJ'estirnauon qui. en aumeUanl Q* - QG ~ QE + QII , tIevicn! cclui dc.~ nUl{

[umulents d 'cncrgic calorifiquc de I'lI lr .

Notre etude utilise les donnees mesurecs it trois dirrt:renls Iypes de surfa..:e tie la

r6gion de Ku u.ijuarllpik, ~"il: une lande a lichens el aftleufC!1lents rocheux (LICHEN); unt'

prairie hum ide a I,lmminees (r-EN): el une pcssicre;1 lichens CI mousses (BOISE).

Nos resullats montrent que Ie Q * - QG diurnc est foncmcnt correle au K

Bien que leQ* - Q<. peut eire cslime Ilaf Ie Kl a I'aide d' unc simple equation lincairc, 11 resson de nOlfe etude que ecnl! ~Iinlal ion gagne il ctre ClUblie ill 'aide d ·une fonction

sinllSliidalequi prt!nd en compte j'heure dt JlI.joumce . Ceci eSISllrtoUt ~ ra i au Slle LICHEN

OU Its cehangcs cnergctiques ne sUlvcnl absolumenl pw; Ie schema t:~olulif homire

hubiludlemcnL impose par Ie rayonncmcnt solnire (KJ).

,4.eS TR,., c r

This aniclccxamincs Ihe possibility of eSlimaliRg lhc turbulclII nuxes of energy (QE + QH)

from m..:.asuremcnts of the ntt radial ion (Q*), the soil hc:u nux (QG) and the iocident solar

radiation (Kl). More specifically. we examine the relationship between Q* - QCi and Kl . in order to derive a method of estimating the tlJrbulenl llu.,es of energy, as~ummg thai

Q* - QG " QE + QH. O ur siudy is busedon data collected over thm: types of surface III th!; ~icinily o f

Kuujjuarapik, namely. a lichen mat interspersed wi th N)eky OUlCropS. n wet st!dgc-covered

bog and an assemblage of pine trees with a lichen and moss under!\fOry .

G. Renaud et B. Singh I f'luxde clwleur el type de surface

Our results show that OJ} adally b<lsis, Q* - QG is st rongly correlllled witli K!, Although Q :j< - QG can be adequately estimated from Kl. by means ora simple linear equation, il is shown thut thiSI!..~timlllion can be made ,nOn! precisely by utilising asinusoidal function which takes the hOUfOr day into coosnJcra tion , This is especially truc in the casc:or

the lichen surfQCC, where the energy cxchungcs did not follow the diurnal pan~rn normally

imposed by K!.

IN TkODUC'ltON

Lcs multiples difficultc!> lices 11 I' instrume ntation, inherenlcs au dOlll ll ine de la rechcrchecn microclim3101ogic ct a In logisliquc que presentc louIe recherche duns les ecosyslemcs , notammenl ccux des regions nOrdiques, cl:lllaliscn! SOuYent les chc rchcurs vCrS ulle s implification de la col lected'i nfonna tion . Un bcll'xemrle dc cela est I 'estimation du rayonneOlent net (Q *) diume de ehaquc Iype desurf'ace par une fonc lion algcbrique du premier dcgre definic ainsi :

Q * = b KJ., ~ . .\

au Q* est Ie rayoll llcment net (Wm 2), h et a !'iont des constantes, K! est Ie rayonnemcnt sol aire global (direcl el diffus) de la regioll

cOllsiderCc (Wm-2),

It cst un ~ousCriplcur 'lui rcrerc a la surface considcree.

( I )

Lc Q* d iume et ::tnt fo rlemcnt consequcnI du K! (Gay , 197 1; W il!ion , 1975 ; Polavarapu . 1970; [Jso et al ., 19 69; Fedcrer, 1968; Davies, 1967; Fritschen , 1967), cellc function pennet une bonne est imat ion. En ealibranl les conslcmtcs de I 'equation I pourunc region do nnee il cst done: possibled'cslimer Ie Q* de plusicurs surfaces par une mcsurc simplcdu K! .

A I' ins tar de I'equation I el tcmmt comple que Ie n ux d'cncrgie ca lm ifique caVlc valla surface (QG) csl auss i flJl tClllClil \:I)lIs~'lUe l1l uu Kl CI q u' iI rcpresellte gencralemcnl une faibl e proportion du Q'" (Okc , 1978; tableau I), nous emello nS I'hypothese d'une poss ibilitC' d 'eSlimer Ie Q* - QG diume de certaines surraces a I'aide du K!.

T,.. III fA U I . I'rvportlOrldu l'IIyonllcmcm IICI CII(lIo..".e par la surfac~ lQU I Q*J dl:..~ regiOn!; nOttliquc,

Type de surfac<: oP/Q * Fcn (III tou rbii:rc TourKlra Boj~ de conlri:rc

0,06-0,]] 0,06-0, 15 0,07 0,16

Sources: Ohmura 119S2), Payalll (1976), Rousc (191!4), Singh tl ai, (191)4). Stewan e( Rouse: (11)77) C( Wroght ( 1981 J.

36 Cl imatolog ical Bulletin I Bulletin c limilloJoglquc 25( 1), 1991

Cettc estimation du Q* - QG poun-ait s'nvercr imcrcssarlle puisqu'cn admcHlInt:

Q*. = QE.. + QH~ + QG.,

au QE est Ie flux turbulent d 'cncrgie calorifiquc latcntc (evaporation au evapotranspiration , Wrn 2),

QH est Ie nux turbulent d 'energic ca[lrurique Sl'nsihle (Wnr 'l) ,

QG est Ie fl ux d 'energic calorifiq uc dans Ie milieu (Wm ..2 ),

(2)

I'estimation de (Q* - QG) lraduirait (QE + QH), soil Jc~ flux lurhu lenls d 'cncrgic ca lo rilique. Plus encuI"C, cn cxploil!lnt I'approche tifec de Bowell ( 1926), jJ serait poss iblc.d'cslimcr soil QE au soil QH ainsi :

QE.. "" (Q '* - QG )~ I (l + Br,; QH. = QE .... Br~ Br~ = QH. I QE~ = '5" (6Ta • .Ill.c,)

ou Br, est Ie laux dc Bowe n, ¥ cSlla cunstante psychromclrique ( = 0,066 X 10·\ Pa °C-I),

(3) (4)

(5)

l:J Tn" cSll' ecurt de temperatures de I'air enlre deux points de I1Icsure vcrt1cU[C (oq

l:Je~ est J'ecan de prcssions panielJes de vapeur d'cau emre dcux l.lDints dc mcsurc vcnicale (Pa).

l e tnux dc Bowen (Br; peut etre fixe afin de correspundre 11 des villeurs moycnnes associees 3UX surfaces clUdiees (Oke, 1978). II peut egalement eire cstillle de d iffcrentes fal;o ns; en exploitam , par exemp[c , [e concept de Pricstley el Taylor ( 1972), ou encore J'approche de )'originc des VC ll tS de Renaud et Singh (1 988).

Noire elude examine la possibil itc d 'eslimcr Ie Q* - QG de certai nes su rfaces de la c6tc hudsonienne du Nouveau-Quebec. Les surf;'lces eludiees son! :

I) une lande a lichens ct afneurcments rocheux; 2) une prairie hum ide 11 g ..... uninces; 3) une pcssiere a lichens Ct mousses.

MET HODE

L 'etude II ete realiseedans un scctcur en uval du bassin hydrographiquc dc la Granderiviere de la 8aleine . pres du viHllgede Kuujjuarapik (poslede lu Baleine : 55°1 TN; 77°45'0), Cc ~cclcureSl approximativernCll1 a 2krn a I 'est de [a haie d'Hudson e t a 3k.m au nord-cst de I 'embouchure dc [a Grande riv ierc de la Balei ne . La localisation precise de nos sites cXpCrimentaux cst montree dans Renaud CI Singh ( 1988). Dans la rncsuredu poss ible, leur localis31ion respcctiveaele.failede facon a minimiser l'effet de J'adveclion locale,

Le si te de la lande a lichens et artlcurements rocheux (ci-apres identifi e LICHEN) est couven a 80% par [a vegetation. Celie vegetation d' unc

G. Renalld er 8. Singh I Flux de chaleur et type de swface 37

epaisseur de 7 Clll eSI inslallee sur un champ de blocs (moraine lessivcc) inondc de sable grossier; quelques blocs sonl en sailJ ic .

Lc site de la prairie hum ide 11 grrullinees (ci-apres identific FEN) est uccupe a 15% par des petits etangs d 'eaudc2 it 20(;01 lie profondcur. Lacouchede Sphagllum aneint it eet endroit 1,5 m. Lc nivcl:lu de la nappe phreatique est pratiqucmenl it la surface.

Lc sile de la pcssicre a lichens et mousses (ci-upres ide ntjfie BOISE) se shue dans une zone a densitc moyc nne. Le Picea Mariana dom ine largement. La eime des arbres se silue a environ 8 Ill . La couche de lichens el mousses est de nse , EI!e a une cpaisseur de JO em environ . Le substratum mineral cst un sable grossie r d 'cnviron 50 em d'epai.~seur superpose Ji une moraine de 3 m. Les Betll/a glulldilosum CI A lI/liS rugosa ctaic nt presents aux slrdtes herbacees et arbusti lies pour oceupcr e nviron 20% de la surt·ace.

Le rayonnemenl nel (0*) aete mcsurea I'aided' un radiomclrc il dome de polyethylene (MIC ROMET) mesurJnt les longeurs d'ondes comprises entre 0,3 a 60,0 microns; soitlc lI is iblcet l'infrarougc. Lc flux d'energiecalorit1qucdans Ie m ilieu (QG) a ete etabli it I'aidc d'une plaque Ihcnnopilc (MIDDLETON). Enfi n, Ie rayonnement solaire global (K ) a etc oble nu it I'aide d' un solarimClre it dome de verre (LiNTRONICS) qui opere dans j' intervalle de longueur~ d 'ondes de 0,3 a 3,0 microns; soit Ie visible et Ie proche infrarougc. Ces instruments de mesures ctaient relics a un cnrcgistlCurdcctroniquc a imprimante mecan ique (FL UKE 2240B) qui effectuai t une lecture nux ci nq minules.

La cue ilJctte de donnees a etc cxcculee au cours de juillel et aoli t 1983. Nos o bservatio ns o nt ete real isCeS entre 6 h 45 et 17 hiS .

Compte tenu de In prox im ite de la bale d' Hudson el de son effet sur I'ad vectio n (Pe rrier el ai, 1977); Plamondo n-Rouchard , 11)75; Wilson , 1968) el donc sur lesechangesenergetiques( Brakkeelal, 1978); Singh ct Taillcfer, 1986), nous c laborons notre recherche e n di!\tinguanl l'advcclion marine de I'advection contine ntale. Et, arin de dis tinguer nellemem ces deux types d 'advection, nous excluons les vents qui longent la cOle (Renaud et S ingh, 1988).

Les donnees pour dcfinir Ie type d 'adveclion prollicnnenl des observations de In station meteorologique du Gouvernemcnt du Canada a Kuu.ijuat"JpiJc , Notre app:rn:il pour mcsurcf la lIi lcSSC e\ la direct.ion du vent etail dCfectueult. Dc plus Ja station mCIL-orologiqueetai t tres pres (11 I km)de nOire site, cc qui rendrai t Ie calcul de I'advection vaJablc. Ccs observations sont nux heutes. Afin d 'etabJir une corrcspondancc, nous avom; calcul6 les moycnncs de nos observations (mcsurecs aux c inq mi nutes) de sone qu 'elJes correspondent a I' heure.

It ljSULTATS

Nous presentons a la figure I Ie Q* - QG mis en relat ion avec Ie K!. Nous constatons qu Oil exiSle une tone relation entre ces vari ables, notammcnt aux si tes FEN , BOISE. Eltception faite du site LICHEN, ni les phenomenes

38 Cl imatological Bu lletin I Bulletin cJimalologique 25( 1), 1991

...

... 8 ,.

• o "

•

N nomb . .. d'ichanl iJion

(ot/fic;"nt d .. co"fLltlon

o aucUn phf"om~nt .tmo.ph,;.lquf' de .u.lac~

( . POUI ad¥ ...... <1 .... / 0 pour .dv. contin .. nl.I .. )

FEN "

•

· . " .". .. - ,,",.11. ''' .... , · - -.... " ""'" • - ...... 01>

• , . ... , . ,. ...

.. '" LICHEN

BOISE

• ..

'" ." '" ." '"

,

,

" . '" • M ' M ... •• 10 { W/ml. )

... '" ."

.:

, ... . ". .. _ 11.'" ,.,.,) • -.0),>1> ,., .. )

• • .", -.¢"

; - 11 • • _1>1 .. - ".U' ,., .. ) • - .." .• " 1"' ''' • _ .150 •. ~,

, . ...

".

'. '"

". ."

."

,N

,w

" . ."

-

aUllospheriqucs de surface ni I 'origine des vents (advection marine ou continentale) ne semble nt introdui re d 'cffct panicuJier sur Ja relation.

Au site LICHEN, J'origine des vents semble affccter la distribution J es points de teUe sane que lcs valeurs corrcspondant ill'ndvce! ion contint:ntale se groupcnt au-dessus de la dmite d'estimation (figure I) et ccl lcs correspondant a I'advection marine se groupent au-dcssous, L'explication vient du double fait que ['advection continentale etili t presente gcncralcmenL ravanl-midi et I'adveetion marine I'apres-midi , et que Ie comportement Q* versus K! de I 'avant-midi dim!railde celui de ['apres-miui (ljgure 2), Naus rcmarquons lit un comportement qui s'apparcnte a un cycle joumaJier; de cc fa it, la nOlion temps (hcure) deviem significative,

"'-~~~~~~ '.---~--~~ , 1 DO"I 1983 I 3 Doill 1983 4 '001 1 983

• • , -, • • - , • 0,

• eJ

'" ,..

'"

• ,

•

6 _ LlC~H'

//):; /' •

... w'

".~, -', -'-, ~. -'-, ---Co -'-, -'-. --j~ 0 , , -I . !o •• II tJ · 661,

II, ( 10" W I "'~) t(lt'O'w/m~l 1\1 {IIl~ w /mt)

A partir de cela, nous avons repone it la figure 3 Ics valeurs (Q* - QG) I Kl versus I'heurc_ L'examen de la distribution rCvCle un comportement qui s'apparcnte a une fonction sinuso'idaledcfinic comme suil :

FrMx = (Tv - A cos (0; O,2617.5H + TIl» ~ (6)

ou FTM" est un taux representant!e comportement hOnlirc moyen du rappon (Q*-QGJ/Kj,

H estl'heure locale, A est une constante indiquam I'amplitude de la fonction, C cst une conSlante indiquant Ie nombre de cycles Th est uneconst,ll1le de translation horizontale. Tv est uneconslante de lranslatio n verticale.

La faclcur O,26 175H transfomlc les heurcs en radians; pour Imllsfomlcr en degfl!s, il suffitde rcmplaccrO,26175 par IS . 11 faulegalcme nt qucTh soil transfonnc en degres de la f~on suivante: 57.29578 Th ,

Lcs coumes dans celie fi gure ont ete etablics selon In methode de Marquardt - Statistical Package for the Social Sciences (SPSS); SOlls-programme

40 Climatological BuBetin / BuUetin cJimatologique 25( 1). 1991

c;)

'" • " • E Fig. , . Comportement hOla 're du "u lo

" LICHEN

"- {Q" _ QGl I ~ t 11 chacun des . ites I!l " • ~ po ~ " '" • • iii

I!l S· _I" n u~ flM

! ill t " ';. • • • j • • r - • aueun phenomene atmospherique dO! surfilce • .. ~

( 0 pour adv. ma ,ine , pou, adv. continentale )

" .. • brouillard au pluie (,a. adv. mar ine ,.:.adv. conti"p"tal .. ). , . 0 I!l '",..... '" ~I """ ....., ~ • .. " , ~

BOi SE:

" FE" ,

" " • .. • ;. i ;. • • • " - " i C " ~ , .. of j f t -4- ----. ~ : -~.

~ ::: 06 • " ~ • • ~ • ~ 04 .. •

" " .. " • ,

" " " ,

" ,

" • , • " " ,

" " " ~£UR~ -~

Tt.. III F.t.. IJ 2. Valcul'5 des paraml,uesde I'':quallon "1M - Tv - A cos (C\O.26 175 H) + Til, 'lUI dcf'"il (Q* - QG)/Kj. i chacun des Sil~ .

Si te

LICHEN FEN BOISE

0,52875 0.46705 0.50349

A

0.13393 0,27262 0,27323

c 1.0 1,0 1,0

Th

0.87 15 1 - 0,20542. -0.22.552

NONLIN EAR (non- linear regression) - et les constanles A, C, Th el Tv corre.~pondantes soni donnees ilU tableau 2. La conSlanlC C (nombrc de cycles) a etc fi xee a 1.0 pour emboitcr la logique du 9t' lc jouma]ier donne par Ie Kl . NOlonsquc nous avonseonsidere seu]cmcnt les valeurs du rapport {Q* - QG)/K! sUpCrieures ou egalcs a O. En effcl, comple Icnu des conditions cl imatiques contcmpor'dines, nous avonsjugc improbablcs, donc crronecs, les valcurs negatives cnregistrees Ie 16 aout a 8 ct 9 heures etle 22 aout it 12 hcurcs.

Nou:-; ]Xluvons remarquer encore une fo is que ni les phenomenes almospheriques de surface ni I' origine des vents (advection mari nc ou contincntale) ne semblent introduire d'effet paniculier sur la relation (fi gure 3) .

Lc taux FTM illlroduitdeuxelcmcnts intcressants. D·abord. it appone une ccrtaine cOnnaiSS'll1ce de I 'effet general des surfaces en ce qui conccrne Ie comportemcnt de." cchangcs energetiqucs se rappurtant au myonncmcnt oct d iminue du flux d 'encrgie calorifi que dans Ie mi.lieu (Q* - QO). Pl us encore. en admcuanl l'equation 2 .. Ie taux fTM devient un indicalcur du componement des echanges cncrgct iques turbulents (QE + QH). Ainsi, en comparant Ics courbcs obtenues pour chacun des sites observes (ligures 3 et 4), nOlls pouvons constatcr

I.O,-L-- ---'---L---'-__ -'--_---' __ -'-_--' __ --'T

_ o.8

" 8°·6 o , 0.4

• o 0.2

---- -----==-===-- - ---- 1- - -- --=-..::::-------------:.... --- -- --.:: ~-- ------------

~ ------------------ Boi se --- Feo

----- Li c he n

O.o-'--,----,--+----,--,----1r---,---.,---.'­• 9 " " " " "

., " H , " , e

I'R . 4 C""II~C ,j''' ' '''''"];''n uu ( Q:t- _ Q~l I ~ , d,HI ,"~ p~, 1'~ (j"'UO " I, lIul" c j,.~"" th'< " I h >." S l~nlt rD'''PIC du 1 11J~ rl ' 4dY~CITon . (YDII l.b lr ;l U II

42 Cl imalOlogical Bulletin I Bulletin c1 imalologique 25(1 ),1991

que Ie site LICHEN dcbute la journccavec un rendem(>nt supe.rieur a ceux des si tes FEN et BOISE. Ccpcndant, aprCs 10 hcures et par1 iculieremcnt au cours de I 'apres-midi , Ie rcndement du LIC HEN devient ncHernent inferieur. Ll'S si tes FEN et BOISE onl un rendemenl respcetift res apparente, mais ce lui du BOISE cSt superieur tout au long de la periode diumc. Le max imum du rcndement des echangesenergetiques turbulents scmble sc produirc un peu aVilnt 9 heurcs au site LICHEN alors qu 'aux autres sites il semble se produire un pcu avant 13 heures.

Selon nos observations slIr Ie terrain, Ie comporteme nt dis tinctif du taux FJ'M au site LICHEN semble Imimement li6 aux eonJitions hyJrillues generales de 13 surfacc. Nous avolls rcmarqHc en effet qu 'au eours des journ6es cnsoleillees la surface p<lssait gradueUement de l'eta! hum Ide it I'ctat sec. Celte variabilite d 'etat a etc eonslatc par Kershaw ct Rouse (1971), Rouse et Kershaw ( 197 1) et Rouse (1984). Scion CUX, eeci cst dll a la enpaci te Cju 'ont Jcs lichens it capter I' humiditcdc I'ai rau cours de la nui t - Ia surface eSl trCS hum ide Ie malin - ct a In nontranspiration des lichens parce qu\~tant nonvasculairc - cc qui praduit I'asscchcmcnt de In surface .

Le deuxicme element interessanl qu' introdui l lc tault "- I'M est qu ' il contribuc it 3meliorer scnsiblement I·eslimation de Q* - QG , et ce en lIlu ltiplianl Ics valeurs mesurec,<; du rayonnemcnt solaire global (K!) par Ie taux FTM (figure 5). L'amclio r3 tion est particul ieremcnt nOlablc au sitc LICHEN. ou Ie coeffident decolTelnlioll (r) a :mgmentedeO,859 (fig. J) 1l0,90R - etoll Ic coefticicnl passe a O,944 - quand la valeur marginale du 31 juillel est excluse (valeurcncadree :lUX .ligures 3 et 5).

CONCI, USl ON

Selo n notre erude , I'estimation du Q* - QGdiume. ct rJonc du QE + QH, si flOUS admetlOIlS l'e.qualioll 2, de certaines surfaces (x) du Nouveau-Quebec pcut eire rcalisee it J'aide du rayonnemcnt solaire (Kl) . Dalls Ie eadre speci/ique de nOtre projet , SOil la p6riode eslivalc dejuillet et :lOUI 1983.11 Kuuijuarapi k, Ie (Q* -QG)~ peut etre estime ~ I'aide des equations lint!aires suivallles :

(Q*- QG) LICHEN = O.703Kl - 43 .573 (Q* - QG) FEN = O. 829Kj - 39.623 (Q* - QG) BOISE ~ O.858K 1- 52,967

Touterois, Ie (Q* - QG)" gagne 11 ctre eSlime par une fonc tion si nuso'idalc qui prend ell compte la notion du lemps (heore de la journee). Cec i cst surtout vrai au site LIC HEN ou les echanges energeliques ne suivent pas Ie schema habituellcmenl impose par Ie rayonncment solai re global (K i) (figures 2, 3 Ct 4). Ainsi, dans I'objeelif d 'uneestimation proche de Is rcalhe el (Qujours dans Ie cadre spCcifique de notre pmjct , nous concluons que Ie (Q* - QG)x doit ctre estimc uinsi:

G. Renaud et B. Sit/gh I Flux de chaleur er type de surface 43

" , , > • • • •

t LICHEN , ' •

fig . 5 , Rehl!iol'l entre {Q' - Qel • "

(FTM x Ktli. chacun de~ si tes • a" ~ •

r: 906

Q "" , N' 45

3 coefficient de corr l! l .. t ioo ,r, ,

" ,

, • 0- N nombre d'echanl illon " n-"- , '" 0

8 -.oIeur ~ 31 juillO! 1'I6~

if • • 3-FEN BOIse: - • " •

'" :. [ • • ,

"

"- , . , r ~.96J ,. 960 3- , N ~ 87

, N' 35 • • • 2- • 0 , > ' . > " -,-

/' E -o 0 ~ ~ ~ .-:-' , , :8 " "

" , • • • • • -, , • • • • • • n .. . ~. (.0'"" .. ' 1 .... .. . ~. PO' "" ~ I

(Q* ~ QG) LICHEN = (O.529 ~ O. 1 34 cos (O.262 H + 0,872») K! {Q *~QG)FEN = (O,467 - 0.273cos(0 ,262H - O,205» Kl (Q* - QG) HOISE = (0.503 - 0,273 cos (O,262H - 0 ,226)) K!

ou H cstl ' he ure localcdc )'observa tion du K!.

Bien enlcndu. nos resultats son.l provisoi res et ils doivent faire I'objet

d'une validation dans Ie cadre d'autres e tudes que nous cncourageons fUltcmenl.

Commc nous I 'avons mentionnc dans I' introduction. I ' interet d 'elUdes de ce genre tiCll1 du fait lJu 'eIles pcm lCtlt:/JI d' ill lmuuirc dcs IIlvyellij d 'clablidc CUltl l.KJrtCII1Cl ll

des parametres etudies en si mpl ifiant la cueilleltc d' information; une simplification qui sc traduit bien sur par unc economic de tcmps et d'argcnt . Ainsi. de tclles estimations ouvrent 13 poss ibilile de real iser des elUdes sur de gr.tnds lerriloi rcs. commc par exemplc : ctude d ' irn pact regionaic suile it la creation d 'un

reservoir hydro..electrique (projet Baic James I)U aulres); ou encore, cartographic du QE moyen d'une mosa'ique de surfaces; etc.

R HM B II. C1EMEN T S

Cctlc. rccbcrchc a ete effcctu6e grace it ( 1(0.$ fond" provcnant dll rnnSl~ i I d(,. Recherches en Sciences Naturelles at en Genic ct du Minislcrcdcs Affaires Indicnnes et du Nord .

BIBllOGR Al' HIE

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Planxmdoll-Bouchard, M. (1975) . Carac(cristiqucs el frequenccs dcs nuagcs bas a

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Rouse, W. R. el K.A. Kershaw (I <)71) . LichclI-domimltcd surfaces , soil water and Ihc cireet

01 burning in the SUbatCI1c environment. ArC//(; (llltl A/pille Rcse(Jrch,

](4): 291- 304. Singh , B .• R . Tailleferel J . Boivill (1984). Les cehangt:s ractialifsct energct iques el ]e bilun

thenll ique du sol en Jamesic . Can. (jI'Olec:h. J., 2 1 (2): 2.23-240 .

Singh, B. d R_ Taillcfcr (1986). The efrul o f synoptic-sell]c :luveelion on the ~rfnnnanec

of\hc PricstJey-TayJorcvapoflition fOOllula. Roulldlll)' Layer Meteorology, 36: 267 - 2112.

Siewan, R .B . <":1 W.R. Rouse (1971). SubSl llmiill ion or lhe Pricstlt'y and Taylor pararlll:ter

a = 1.26 forpolcmial eVllporal ion in high latitudes. J . Applied M eteorology.

16 ; 649-650. Wilson, C. ( 1968). NOIe.r olllht: climate of Posle de la n'l/ei lle, Quebec. Centre des Eludes

Nordiques, Univ. Laval . 24 (HUD-6),

Wilson. C . ( 1975). Net radiulion durin£ clear weather in the Snow-ff<!C season for ~llriou~

types of surface, E'ost.c-dc-Ia Bltleine (Greal Whai!:), Quebec t eli/liaS de Gi(J~raJ!hie dtl Qucbef , 19(48): 505-5].2.

W right. R.K . ( 198 1,. The water balance of a lichelllundrl.lundcrlain by pcnnafrosl , Md;iII SubarClic /t /'J'earch PtI(Jers. Climatc Research Serles, No. 33, II pp.

46 Climatological Bullet in I Bulleti n c1imato Jogi4uc 25( I), 199 1

Climatology of Tomado Days 1960-1989 for Man itoba and Saskatchewan R.L. Raddatz ilnd j,M. HOl/esiak Wi nnipeg Climate Centre Environment Canada 266 Graham Avenue, Room 1000 Winnipeg. Manitoba R3C 3V4 tOrig il131 manuscript received 9 October 1990: in rev ised form 3 January 199 1 j

A iI!I'fR .... C T

Tom adooccurrcnccs in Manitoba and Saskatchewan from 1960- 89 have been labulalro by a

number of ri:St:il1chers These enofllcnlt ions have been grouped by Statistics Canada census

divisions and by OCCUrTi:nce dales to foml iI 30-ycar lomildo day dimaIOh)gy. The tornado

risk ha~ been detemlined for two bnse areas ( I) 10,000 km 2 , and (2) the median area

damaged per tornado day . O. J 0 kml , This analySis indicmcs that the frequencies of tornado days arc rt:lativdy Illgh, runJling. 10 general, from about 0, I to 1.5 days pcrSdlMm per

10,000 k.m1 • A recurrence can b<! eX!J'Cctcd in most areas within a few years or possibly even

that same season. However, a relatively small area is damaged on a t)'pical lomauo day, Therefore, the annual risk ora given location being hil by a tornado is very low: the odds

gencr:lily range from one in a million up to ont in sevent), lh("~usand. Manitoba and

Saskut!.:hewuo residents should be ilwarc {lfthe fisk but Ihe)' should nOI be unduly alarmed.

lc lIombrc de tomades ayaol touche Ie. Manitoba ella Saskatchewan de 1960 11 1\)119 a etc calcule par un tenain nombrc de. chcrchcurs. Ccs chlffrcs ont ~tc rcgrou!X"s selon la d3U:. de I'cvenement ct !es divisions de reccnsemcnt de St:ui~liqul: Cllnlitlu tlc fll\on it rC.lliscr une

eturlc cJimalologique sur Une p..': riode de lrentC ans basec sur (e jouHornnde, ~ risqLle dc tomadl: u etc elabli pour deux superficies de base : la premiere mesurc 10000 lim} CI III

deuxictnt!, 0, 10 km!, soil III superficic mo)'t!nne endonunllgee par un jour-Iomade ,

L'analyse revele tllle la frequence des jours-Inroadc est rclalivenu:nt c.lc~ee. variant entre

0, I el 1,5 jours parsaison Nur 10 000 k: ml. On peut s'uuendrc accque, dans la pJupufllks regions, une nouvelle loroade se produise dans les anm!es qui ~uivcnl /)u mente pendUIli la

meme saisOn . Toutcfois, une loroadc endomlllage lJabilueJhJmcnll.m sccleur dont la

supcrficie est rclul ivemenl raib le. Ainsi. Ie riS(juc qu 'un liell donne soi llouc:hc par une

tomadcestb3s; il variccnlrc I : 1 000 OOOel l : 70 000. Leshabitamsdu ManilOooeluclu Saskatchewan do; ~enl eIre conscicnts dl:s risques de lomade s~n s pour autant en eire cffruycs

outre mesure.

RL Raddatz alld J.M. Hane.fiak I TOn/ado DLlYs 47

I. LNTRODUCTION

Tornadoes arc violent , local stonns of shon dur.n ion which cannot be readily identified on wcatherchans, conventional radar or satellite imagery. Data gathering, therefore, relics on observations offullllcl clouds on the ground and QII

the post-inspection of damage paths. Some und{~r-repott i ng in Manitoba and Saskatchewan has, undoubtedly. resul ted from thci rrclatively sparse populations .

Tomado occurrences, including waterspouts, in various pans of Manitobaand/orSaskatchewan during the 1960 's and 70's have been tabu latt::d by a nlunber of researchers (Lowe and McKay, 1962; Shannon, 1976; Tortorell i, 1979: Lemieux, 1980; Cote, 1981; Blair. 1983) - each focusing on a specific­region and time period. Their primary data sources were Ihe archives of selecled newspapers from the area of interest. In 1978 for Manitoba and 198 1 for Saskatchewan , the Atmospheric Environment Service (AES) established weather watcher or spotter networks and the Prairie Weather Centre began to issue annual Severe Weather Reports. These summaries ( 1978- 89), which list the tomadocs

I I I

18

Saskatchewan

21

- - -

Manitoba

23

22

FIGURE I , Saskatchewan ami MauilOOa Census Oivisit.ms .

/ /

/

I

I

I

48 Climatological Bulletin / Bulletin cl imatologique 25( 1), 1991

reported directly to AES and those identified via adipping service which monitors a large number of weekly and daily newspapers, have become the main source of infonnation on IOmadic events in the 80 's .

These e numerations have been grouped by Statistics Canada Census Divisions (Figure I ) and by occurrcncedatcs to form il 30-year( 1960- 89) tornado day climatology for Manitoba and Saskatche wan. I.n all cases , the judgement of the original cnumcmtor that an event was, in fact, a tornado has been :1ccepted. A c.hronologicallist containing the date and time of occurrence as well as a reference location for cach to rnadic report is available from thc primary amhor.

This climatology , an update o f Ihe Canadian Climate Cenlre publicatio n (CLI - 6- 83) - Munitoba and Sa.flwrcllewlllI Tomodo Days 1960-<SZ , Raddatz et aI., 1983, ineludes me seasonal and geographical distribution of tornado days as well as an analysis o f their frequencies of OCcUrTCnce, risks and recurrence periods.

2. DATA ANALYSI S

2 .1 Tornado Days Few deta iled post-inspections of Manitoba's and Saskatchewan 's IOmadic events have been undertaken , leaving considerable uncenainty about times, paths <lnd durdlions. Thus, it is d irfieu!t to distinguish multiple sightings from multiple occurrences and thc separation of events on the basis o f approximate times and locations becomes a matter of conjecture . This makes the total tornado count <I

somewhat unreliable figure. The- numbcroftomado days, dctined as calendar days with at least one recorded lomado occurrence , is known with considerably more certainty. Therefore , the statistics del ineating the IOrnado climatology of ManilOba and Sas.katchewan MC based on tornado day counts rather than total occurre nces.

2.2 AnnuaI Coun1.~a/UJT,.end$

A total of 352 tornado days have been labu1ated for the JO-year pcrio<.llo r Manitobaand Saskatchewan from 1960 10 1989 (Table I). Saskatchewan averaged 7. J % 3.4 tornado days per year while Manitoba's yearly counts averaged 5.0 ± 2.2_

The annual numbers of 10m ado days, by province , wen; ploued and trend lines were filled to the data (Figure 2). Saskatt~hewan's trend, given by Y = O.23X + 3.58, where Y is the number oflomado day's and X is Ihc year-number (i .e .• year minus 1959), reveals a notable positive trend while Manitoba's line , Y = O.OSK + 3.7 t , has a somewhat smaller slope , WhiJeSaskalchcwan 's tornado days were trending upward by over 3% of the mean numner per year, the relative increase in Ihunderslonn days, based on ten synoptic stations in the southern hal f oflheprovi nce, was less than 1% per year. Thus the upward swing in tomadodays ev ident in both provinces is likely due to more rigorous tornado reporting coupled with enhanced public aware ness rather Ihan an actual increase in the annual

R. L Radd(lfz and J.M. Hane!>·jak I TOflwdo Day.~ 49

l · ... III. E I . Tomaoo Days. 1960 1989.

Year Manitoba Saskatchewan Mall . and Sask .

1%0 6 J 8 1%1 1 4 5 1%2 1 5 1 1963 5 • II

1964 , , J3 1965 , J 1 1%6 , 3 • 1967 1 1 , 1968 , 6 JO 1%9 , , II

1970 4 , 10 1<)71 3 8 II 1972 1 4 5 1973 , 12 " 1974 , 7 9 1975 8 J1 J8 1976 5 6 II

1977 8 " J6

1\.178 , 9 I, 11J7'J 4 J1 J6

19SO 5 1 J1 1981 4 , , 1982 J 1 , 1983 8 10 " 1984 6 6 J1 1985 3 , 1 1986 1 J3 10 1987 , , J1

1988- 6 II J1

1989 , " "

'fOTAL '" 213 352 MEAN 5.0 7. 1 11.7 STANDI\RD DEVIATION 1.2 3.4 4 .8

number of duys with tornadoes (Prairie Weather Centre. Se ... cre Wealher Rcpons. 1978- 1989).

2.3 Seasonal Distribution anti Length ojSeas()1I The total number of tornado days per month was graphed (Figure 3). The peak number of days was in July with June and August having fewer but still significant numbers. Table 2 contains the stan elate, end date and duration of each tornado season for the entire reg-ion. The mean date orlhe firsl tomado day was May 2 1; however, the season has begun as early as April 6. On average the last tornado day

50 Climatological Bulletin I Bulletin dimatologiquc 25( I), [991

ANNUAL TORNADO DAYS Be TREND: 1960 - 1989 Manitoba

'~O~'~" ad=cO~Day~,c-__________________________________ , lOr

14 ........................ _ ..... , ........................... '

" 10

1965 'Q70 1915 Yam

1980 19 ..

ANNUAL TORNADO DAYS Be TREND: 1960 - 1989 Saskatchewan

~ ,='~"~ad=o~~=cc-__________________________________ , lO r

I ~ •... " ................. __ ............ _ .. _ ..... -.. _ .. __ .••....•...... - ..... -. ............... , ..... ",

1:2 ............... '" - .,,_ ....................... ..... .

10 •. , ... _._ ............ _ ....................... .. . .

• 6

• 2 ••

'96' 'Q70 'Q75 - 1980

FIGURE 2 (a) A!lIlUal Tornado Days and Trend: 1960- 1989. Manitoba. (b) Anllual Tornado Days and Trend: 1960- 1989, Sa~~~tcltcw~n .

RL Radtkltz ana J.M. Hanesiak I Tornado Days

1965

5 1

-0 -Mao

Sa.

TOTAL TORNA DO DAYS / MONTH Saskarcnewan & ManllobQ: 1960 - 198Q

13O TornnclD Days

... 120 110

Man/Sal 100 QO .. 80 " '/0 .. 00 bO

'0 ..

l I" JO

... 1 I '0 10 - -• -II 0-·

AO' Mo! Jun ,lui "0 MOrt!!l

FIGURE 3. TomaOO Days per Month .

•

• •• • •

Sep

was August 26; the season has lasted until September 26 . The. mean duration is 99 :t 25 days.

2.4 Geographical Di~·triburioll

The tornado days were plolted by Slati!itics Canada Census Divi sion (Figure 4) . MO!i1 of Manitoba's and Saskatchewan's census divisions h:t ve rural population densit ies greater than one per!ion pcrsquarc kilometre (Statistics Canada, 1976 and 1986). With denSities of this magnitude all tornadoes, or at least thei r aftemlaths. have a fai rly high probability of bei ng discovered (Newark, 1981). Nevertheless, most div isions have likely experienced more tornado days than the recorded number. Specifically. under-reporting may be signlfk:tnl in Manitoba's divisions 19 and 21 which have very sparse populations . Methods have been suggested. such as those described by Newark (1981) and by Schaefer and Galway (1982), 10 account for population bias. The use of population adjustment factors in the compilation of this climatology was tried but rejected duc to their arbitrary nature and the apparent distortions that they introduced 10 the geogmphical d istribution evident in 'he raw data.

52 Climatological Bulletin I Bulletin cJimutologique 25( I). 1991

U9 U c 2. Stalt , End aud Durnlion flrTUlTU.do Seas.)!!, Mal1.!Ub~ alld Saskatchcwlilt.

Year s~ End Durnlion

1 960~ Jun. , Stp. , 96 1% 1 Juu. " AI,!:. 10 4J 1962 Apr. " Aug. 17 '" 1%3 M" 17 Scpo 16 123 1%4' Mo, " Aug. 10 '" 1%5 May , Auit· • 92 1%6 Jun. • Aug. 16 14 1967 M,y 30 JuL JI 63 19611· Apr. II Aug. " 130 1%9 M,y 26 Sep. 20 118

1970 Jun, 24 Aug. 31 69 197 1 Jul. I Scpo II 73 1972.0- M.y , A •• " 100 1973 Ap<. 20 Aug. 27 130 1974 Jun. I; Aug. 29 72 1975 M.y 24 Scpo (0 "" 1976"' Juu. 3 Aug . 26 " 1977 Apr. 1/ Scpo lO Ito) 197' M.y 10 Aug. " 108 1979 M,y 21 SCI' . , '" IQgO' ApI. , Aug. 10 127 198 1 Jun. • Aug . 30 88 1982 Jun . , Aug. 18 " 1983 M,y " S,' , 11 O 1984"' M,y II Aug. 1 S9 1985 M" " Aug. 30 " 1986 Mr>y 4 St p 2 121 1987 M" 2S Scp" 10 "" 1988"' Apr. 29 Au~. 10 1114 1989 JUIl . , Aug. 17 73

MEDIAN M~y 23 Aug. " 99 days MEAN M.y 21 Aug. 26 99 days

STANDARD DEVIATION 25 days

Earliest d3tC - April 6 , 1980. Ailollll , MB . Lates t date - Scptcmlwr 26, 1977. Vi~ounl, SK. '" Leap yenr.

2.5 Occu.rrence Frequencies, Risks lJnd Return Period~'

The occurrence frequencies oftomado days per 10,000 Ion l, Ij, and the probabilities of risks, Ri, (where the subscript i refers to the illl census division with area Ai and Ni tornado days) thaI a day will contain one or more tomadie events, and tbe periods during which there is a 50% chance of recurrence , T(50:50), and a 95% chance of recurrence, T(95 :05) •. were calculated for each census d ivision as follows (Kendall , 1959; Hendricks, 1983):

RL Raddatz Gild J. M. Hanesiak I Tornado Day.f 53

I

I

1----_ - --

~ I

/ ~ Manitoba

I SaskatchE'wan

16 12

13 15 '- ' - .

14 15

11 12

36 20 1 16 13 24

26 14 ---- _ ._L_. _ _

f, = N\

(30 sc<lsons)(Ai/ IO ,OOO km!)

Rl = f;/99 days per average season

T(SO:50), ~ In(O.5)/lnl l- R,) T(95:05), = In(O.05)/ln( I- R,)

/ I

/

I

I

I

The frequencies, fl, approx imate thc annual probabilities of occurrence of a tornado day for each census division. Since the average tornado season is 99 days long, thc daily risks can be calculated by dh-: iding the annual frequencies by this number. The recurrence periods are then in days. The freque ncies of occurrence (Figure 5) and Ihe rccurren~ periods (Table 3), both per 10,000 kmz. arc g iven. These calculations assume that each day during the tornado

54 Climatolog ical Bulletin I Bu lletin cJimalologiquc 25(1), 1991

1- --_

~ I I

- - - -

Manitoba

I I ~ I

I 10.4

I 0.2

I 0.2

- '-

Saskatchewan

0.2

0.3 0.3

0.2 0,1 0.5

0.3 0.5 '- . '- ' - - '-

0.01

/

I

I

I

I

FIGURE 5. Fr<!(!uc!\C,csot' l ilmado DiY~ po:r IO,Ol)IJ km' by Ccn.,u~ Divisi()(l and Jl nnual Rish (x Jo-J%) ,,(Tornado Damage by C"nsu~ I),v'slon.

season has an equal probability of being a tornado day . Howcvcr, an examination of the seasonal distribution of tomadodays, Figure 4, clearly reveal s that this is an over-simplification, The frequencies of tornado days by month (tirst column for each month in Table 4 , headed " # Days") were , therefore, obtained by proportionaUy allotting each census division's tornado days to the various months in accordance with lite seasonal distribution for the entire region . The seasonal distributions by census d ivision were not used due to the sparseness of lhe data sct at that level. The risks or probabilities o f lomado days per 10,000 km1 by month arc given in the second column for each month in Table 4.

Thc frequenc ies of tornado days were broughllO a common area base of 1O,(X)() km?: to eliminate the apparent higher risks in some census divisions due to their larger areas alonc. This calculation assumes thut there arc no preferred locations for tornadoes, bUI rather that all of u division's sub"ureas have an equal probability of experie ncing a tornado day.

RL. RadcUJtz and 1.M. Ha/lcsiuk I TOrlllldo Dayj' 55

fABLE 3 . Roxurrencc Penoo (Oay,) 1)(:' lU,iXJO k'm' by Census Di~jslon

Recurrence PerIOds Recurrente I'l'ri!/th

CcUSll~ iDays)H CellSus ( f)"y~) ••

Diyi~ion iil T(50,SO), T('i5:05l, [)[y,sion (il [(50:50), T(!J5:05), Manilob.a Sas/.;alchclV"Jn

, 23J '006 , '" ", , 46 '"

, '" 626 J 52 227 3 m 1{)/J4 , 227 '"

, 323 1396 , 118 "" , 149 646

6 131 'M " 9'l '29 7 " 381 7 '" 1407 8 '16 ,OJ 8 '96 1279 , 49 212 9 259 1119

lO/ I I/ 14" 70 J()4 '0 226 979 12/ 13" '" 217 " '" 554

15 \3, m 12 326 1410

\6 323 1395 13 "5 '''' 17 392 1694 " 461 1~1

" IS' '17 15 '"' 1228 J9 4211 1l!205 " "0 22U) 2{J 679 29" 17 '" 1191 2J 9530 41 190

• An.:as COIlltnncd due 10 SI1I311 ~izcs .

•• Retum periods a.e imcrrup!ed by off·~casons

An alternate base-area, inherenllO Ihe data, is Ihc median area damaged on a tornado day. Schaefer el at. ( 191:16), in an analysis of22,840 tornadoes ( 1950-83) over Ihe cOllliguous United States plus 900 IOmadocs (1959-79) in the Canadian Climate Centre·s data base, determined Ihat Ihc median area damaged per tomad() occurrence was 0, 10 k1ll 2. This information is not specilic to ManilOha and Sa~katchewan; however, as tornadoes in Ihis region are likely an extensio n of the U.S . Plains max imum (Newark, 1984), Schaefer 's median tomado damage area wasadoptcd forlh is analysis. In addition, the median o r typical tomadCJ day in Manitoba or Saskatchewan ha.~ one tornado occurrence (Raddatzet ai., 1983). It follows that the median damage area per tornado occurrence also applies ttl a typical tomadu day . Therefore, thc annual risks of damage 3 1 any location within e<lch census division, RDi (%) were calcu lalcd as follows:

RD, (%) = 100.0 (fA./ IO,OOO)/(A,/O. IO)

and plotted (Figure 5). The resulting risk values visually mesh wilh the cross­border val ues in the neighbouring U.S, published by Schaefer el al. ( 1986).

56 Climatological Bulletin I Bulletin cJimatol()gique 2S( I). 199 I

MANI10BA:

'" APRIL MAY JUNE JULY AUGUST SEPTEMBER r- DIVISION I Da)i Ri~k # Days Risk .. Day~ Risk /I Da)'~ Risk " Days Risk #- DI)'~ Risk

il' 0' 0.22 0.02 '29 009 3.52 0.27 4.42 0.32 3.05 0.22 0.50 0.0< .. 02 0.31 0.08 1. 89 0.48 5. 14 1.34 6.46 1.63 4.46 1.12 0.73 0. 19 l} 03 0.33 001 19' 0.42 3" '17 6.1itl 1.43 4.70 0.99 0.77 0. 11

" 0< 0.07 0 .02 0., 0.10 108 0.27 , ,. 0,33 0." 0.23 OIS 0.0< 0 05 0.23 0.03 1.39 0. 19 3.79 0.52 4.76 0." 3.29 OA. 0.54 0.07 ~ 06 0 .10 003 0.60 0. 17 '62 0.47 2.04 0.57 1.41 0.40 0.23 0.01 ,.. 07 0.22 0.0< 12' 0.25 352 0.10 4.42 0.~5 3.05 0.59 050 0.10 ~ " 0.17 0.03 0.99 0. 19 2.7 1 0.53 lAO 0.63 2.35 OA5 0.39 0.08

09 O.W 0.08 I l'i 0.44 325 1.23 4.US 1.S2 2.112 1.05 0.46 0. 18 -~ 10/1 1/ 14 0." 0.05 1.49 0.31 0.06 0.88 5.10 1.07 3.52 0.14 0.58 0. 13

" ]2J1J 0.23 0.07 1.39 ." 3. 79 1.22 4 .76 1..19 3.29 1.03 0.34 011 •• IS 0.23 0.03 1.39 0. ]6 379 046 4.76 0.56 3.29 0.39 0:" 0.01 ~ 16 0.05 0.01 O.JO 007 081 019 I.U2 0.23 070 0.16 0. 12 0.03 - 17 0.12 om 0.70 0.06 1.90 0. 16 2,38 0.19 1.64 0.13 0.27 0.02 ~ " 0.20 0 .02 1.19 O. ]2 W 0.33 4.UI( 0.<0 2.82 0.21 0.46 0.04 o· 19 0.05 0.00 0.30 0.01 0.8] 001 10' 0.Q2 0.70 0.01 0.12 0.00 ~ 20 0.05 0.01 0.30 0.03 0.8! 0.09 lU2 0. 11 0.70 0.08 0.12 0.01 .. 21 0.02 0 .00 0.10 0.00 0 .27 om 0.34 O.UI 0.23 0.01 0.01 0.00 0

'" SASKATCHEWAN. ~ APRIL MAY JUNE JULY Al:GUST SEPTEMBER

DIVISION , Days Risk ., Days OW< If Days Ow. , U .. ys Rllik ,. Da.y~ Risk # Days '"'" 01 0.43 003 2.59 0.19 7.04 0.52 '83 0.63 6.10 044 1.01 0.07 02 0 .40 0.03 239 0.15 ' .50 0.43 8.\5 0.52 3.64 0,36 0.93 0.06 03 0.25 0.02 1.49 009 006 0.24- 5. 10 0.30 3.52 0.21 0.58 O.oJ 04 0.22 O.OJ 1.29 0.07 3.51 0. 19 4.42 o.n 3.OS 0.16 0.50 0.03 OS 033 0,03 1.99 0.15 5.4 1 0.41 MO O.SO 4.70 0.35 0.77 0.06 06 0.", 0 .... 3.58 0.22 9" 0.62 1223 0.76 8.45 0.52 1.39 0.09 07 0.20 0.0\ 1.19 0.07 ] 25 019 0" 0.23 2.82 0. 16 0.46 003 08 0 .21 0.01 ,,, 0.07 4.33 0.21 '" 023 3.16 0. 18 0.62 0.03 1)9 0.20 0.0 \ 1.1'1 0.08 '" 024 ... '" 0.2'1 2.82 0.>3 0.46 0.03

iO 0. 18 0.02 1.09 010 298 0 .27 3.14 0.33 2.58 0.23 04) 0.'"

" 0 .45 0.03 2.69 0.17 7.31 048 9. 17 0.S9 ' .34 0." 1.04 0 .07 ~ 12 0.15 0.0\ 090 am 2.44 019 l .06 0.23 2.11 0.]6 0.35 0.03 ~ 13 0.3 1 0.02 1.89 o.rz .5. 14 0.33 6.46 0 ,41 4.46 0.28 0 .73 0.05

14 0.25 0.0 \ 1.49 O.OS <.06 0. 13 310 0. 1t> 3.52 O. ll 0.58 0.02

" 0.23 0.01 13' 0.08 3.79 0.22 4.70 0.26 3.29 0.18 0.54 0.03 16 0. 15 0.0] 0.90 0." 2.44 0 . 12 l06 0.15 2.11 0. 10 0.35 0.02 17 0. 18 0.01 1.09 0.05 ". 0.15 ) ,74 U. \II 2.58 0. 13 0.43 0.02

3. CONCLUSION

T he-freque ncies of tornado days for Munitob<l's Census Divisions 1 1021 and

SaSk<lIChewan's Divisions I to 17 are relat ively large , running, in general, from about O. t to 1.5 days per season per 10,000 km l. A recurrence can be expected somewhere in the area within a few ycars or possibly thai samc season. However , a relatively small area is damaged t)n a typical turnado day . Therefore, the unnual risk of damage al a given locution is very low , mnginggcnerally from 0 . 1 X 10--'% to 1.5 X 10- 1%. Nevertheless, lomadoes, nature's mosi locally

destructive slonns, pose a d anger to ]ife and property especiaJ Iy in built-up arcas

with a conce ntl'"dted pnpuhui()n. Although the danger is teal and Manitoba and Saskatchewan n::sideniS sho ult.l be aware or tbe risk, they shou ld not be unduly alanncd .

R/!FEREN(;ES

Blair, D. , 198]; nle 1"IIullderSlQrIl Hawn} ifl S(ukmchew(l/I , M.Sc . thesis , University

of Regina.

COte, M. D., 1981: Saslwtchtwun1"Of/rllr/()Cj 1960- 1975. Atmo.lphCfic En ~ironUl<:nt

Service, Regina (unpublished).

Hendrick.~, l .R., 1983: Probllbili t)' Mean Time. AtmospherIC Elwironmen l. ,servi(·c, Celr/ml Regio/l Techllical NOIe.f, 83-1 , Winnipeg .

Kendall , O.R., 1959 : Stmisticul Allalysis of Extreme Vollies. J' ir,;t Canadian Hydrology

Confcrence, Natlullal Research Council Sub·CornmiHec on Hydrology. Ottawa .

Lemieux , P.B., 1980: Tor/lO,/O Ust 1955-1979. Atmosplreric Environmenl Servlct."", Winnipeg (unpublished) .

Lowe, A .B. wld G.A. McK<ly, 1%2: TI>nladoesoj WeJferrl eUllada. Mctc<lrological

Branch . Dcpanmell t ofTmnspon. Canada. Newark, M .J ., 198 1: TnmodfJe.f ill COllada Por lire PeriOl/1950 /() /979. CU - 2- 83,

Canadian Climutc Centre, Atmospheric Environment Service, Envtronmelu

Canada , Toronto.

Newark, M.J . , 1984: Canadian Tomado<:s, 1950 1979, Allllospirere-Oceun ,

22(]): 343-]53. Pl'diric WelitherCe ntro, 1978-89: S('vere WemherRf'porIS. Atmospheric Environmcnt

Service, Winnipeg (unpublished). Raddatz, R.L., R .R. Tortorelli and MJ , Newllrk , 198]; Manitoba (lJuJ Saskflfcirew(ln

Tnmado Days, 1960 to 1982. CLI- 6-83, Canlldian Clifl1U1e Centre,

Atmospheric Environment Service, Tomntl1.

Schaefer , J .T. and J.G. GalwlIY, 1982: Population Biases inTornoooCiimll1Ulogy, Prepri m.

12111 Conference 0 11 Severe Local SumlM, San AntOflio, Te1l.as: American

Meteorological Sociely, Boo\oo.

58 Climatological Bul letin I Bul letin di malOlogiquc 25( I), 1991

Schaefer. J .T .• D.L. Kelly and R.F. Abbey, 1986: II MillinlUm Assumption

Tomado-HalJlJl1 Probability Model, Jmmla/ o/Climate mId Applitd Meleoro/u8)" 25(12): 1934- 1945.

Shannon, '1'.8 ., 1976: ManilObaTorlludoes /960- 1971. Atmospheric b1vironmenl Service ,

Applielltions Branch. Project Rcpon #29. Statistics Canada, 1976: Population , Land Area and PQrulation Density. Census Divisions

and SubdiviSIons, Supplementary Uullelln: GNJgraphic urnlOemographic

Ce'~m.~ a/Cuut/du.

Sialistics Canada, 1986: Popli ialion, Land Arcll and Population Density, Census Divisions

and Subdivisions, Supplementary Bulle!in: GeQgrapllic lind Demograplli('

CCIIJ"J<.I·O/Cwuultr.

Tortorell i. R.R . , 1979; Sas/uJ.tcilew(m Torfwdoes /960 - /975. AlrrrOSphcric Environment Service, Winnipeg (unpublished).

RL Radda/zmIlJJ.M.Hane.~i{lk I TOrrladoDuys 59

News and Comments Nouvelles et commentaires

CLIMATE/AGRICULTURE SYMPOSIUM

A Symposium/Workshop focussing on: "Changing Climate in Relation to Sustainable Agriculture" will be held on 29- 30July 1991 at the University of New Brunswick, Fredericton, N .B. For further infonnation, please contact the Symposium Chainnan , Peter Dzikowski , in Edmonton:

Phone (403)422-4385 Fax (403) 422-0474

CANADA/C HINA INTERNATIONAL MESOSCALE WORKSHOP June 8- 11 , 1991, Winnipeg, Manitoba

This Workshop follows directly the 25th Annual CMOS Congress to be held in Winnipeg June 3-7. It is being sponsored by the State Meteorological Administration of the Peoples ' Republic of China, the Canadian Atmospheric Enironment Service, and the Canadian Meteorological and Oceanographic Society. Its purpose is to continue developing joint Canada-China activities in mesoscale meteorology . Invited speakers from China, the United States and Canada will address the nature and prediction of mesoscale weather in North America and China, with emphasis on current research plans.

There is no charge for registration at the workshop, but a fee will be assessed for those wishing to attend the banquet. Proceedings will be published after the conclusion of the conference. Sunday June 9 will be reserved for sightseeing. with a number of events planned by the local arrangements committee.

60

For further information: contact Mr. Louis Legal Workshop Coordinator Aunosphcric Environment Service 266 Graham Avenue, Room 900 Winnipeg, Manitoba, Canada R3C 3V4 Telephone: (204) 983-2079 Fax: (204) 983-0109

Climatological Bulletin / Bulletin climatologique 25(1),1991

THE MACKENZIE BASIN CLIMATE IMPACT STUDY

As part of the Government of Canada's environmental initiative known as the Green Plan, the Canadian Climate Centre (CCC) of Environment Canada, in cooperation with a number of other government and non-government organizations, is planning a climate impact study on the Mackenzie Basin. This is a high-latitude region where projected greenhouse warming is expected to be greater than the global average temperature change.

The overall purpose of the Mackenzie Study is to describe the impacts of several scenarios of global warming (including General Circulation Model outputs) on the region of Canada bounded by the Mackenzie Basin watershed, including parts of British Columbia (BC), Alberta, Saskatchewan, Yukon and the Northwest Territories (NWT). This is meant to be a broad integrated interdisciplinary study of all regional issues that may be climate-sensitive, such as terrestrial and freshwater resources and ecosystems, resource extraction activities (mining, energy, forestry, etc.) and local/ regional economies (wage , subsistence, mixed). Cenain questions will not easily lend themselves to quantitative investigation , nor are quantitative methods necessarily the most appropriate in all instances. We expect, therefore, to employ a wide range of methodologies in order to provide an objective assessment of regional impacts which could be used by planners and decision makers.

This project has been identified as one of the activities within the ArctiG component of the Canadian Global Change Progranune. It is anticipated that the research will include a combination of existing in-house studies from various agencies, and new studies (government, academic , etc.) to be funded by the Green Plan and other sources.

Because of the issues involved, consultations with government and non-government agencies have been initiated during the early planning phase, and are continuing on an ongoing basis. As a result, an Interagency Working Committee is now in place. It facilitates coordination of research activities, and plays a key role in planning the overall thrust of this S-year project. Committee members include representatives of federal government (Environment, Energy Mines and Resources, Indian and Northern Affairs, Forestry , Agriculture , Tourism, Fisheries and Oceans) and provincia1/1erritorial agencies (Alberta Environment, BC Hydro, NWT-Renewable Resources, NWT-Energy Mines and Petroleum Resources), Native organizations (Dene, Metis, Inuvialuit), and private industry (ESSO) . There is also an Advisory Group, composed of individuals with considerable Northern experience, who will not be participating directly in the Study but have agreed to provide advice on an ad hoc basis . These people come from federal government, academia , a Native organization (Inuit TapirisatofCanada) , a museum (Glenbow Alberta Institute), and the Government of Alaska (advisor to the Governor).

News and Comments / Nouvelles et commentaires 61

Future updates will cover a range of study-related issues, such as global warming scenarios, conununity consultation and integration of research results. For further information, contact

Dr. Stewart Cohen Canadian Climate Centre 4905 Dufferin Street Downsview, Ontario, Canada M3H 5T4

62 Climatological Bulletin / Bulletin c1imatologique 25(1),1991