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TRITA-EPP-84-05

ROCKET AND SATELLITE OBSERVATIONS OF

ELECTRIC FIELDS AND ION CONVECTION

IN THE DAYSIDE AURORAL IONOSPHERE

G. Marklund and R.A. Heelis*

June 1984

Department of Plasma Physics

Royal Institute of Technology

S-100 4 4 Stockholm, Sweden

*Centre for Space Sciences, The University of Texas at Dallas,P.O. Box 688, Richardson, TX 75080, USA

ROCKET AND SATELLITE OBSERVATIONS OF ELECTRIC FIELDS

CONVECTION IN THE DAYSIDE AURORAL IONOSPHERE

G. Marklund(1) and R.A. Heelis(2)

Abstract

AND ION

Electric field observations fro» two high-altitude rocket,

flights in the polar cusp have been combined with satellite

observations of ion drifts to infer details of the electric.

field and convection pattern of the dayaide auroral

ionosphere. A region of shear flow reversal can be inferred

from the electric field observations on one flight near 15,30

MLT 20 minutes after the Dynamics Explorer 2 satellite crossed

trough the same region. The drift patterns observed by the

eo spacecrafts wsre very similar although shifted by 0.5

Agrees, a shift which i 3 expected from the observed ch&nge in

m e interplanetary magnetic field (IMF) B component during

.his time. A regica of rotational flow reversal was covered by

the other flight shortly after Ut&qaetic noon, at the same time

the DE-2 satellite travelled along roughly the dawn-dusk

meridian. Ey joining points of equal potential, integrated

from the two datasets and assuming the reversal boundary to be

an equipotential, the instantaneous convection pattern could

be drawn showing cre3cent~shaped convection contours in the

dusk cell and more circular shaped contours in the dawn cell.

In order to reproduce this pattern using the convection model

recently proposed by Heelis e,fc _ a,j. (1982) it was found

necessary to introduce a local-time dependence of the decay of

the electric field with distance from the reversal boundary.

Moreover this pattern is 3hown to be qualitatively in

agreement with the predictions of a geometrical model by

Crooker (1979) when the IMF is oriented towards dawn. The same

characteristic patterns but with the du»? and dawn cells

reversed, as presented in a recent radar-satellite study for

the IMF oriented towards dusk may serve as additional evidence

in favour of this model.

(1 ) Dept of Plasma P h y s i c s . . The Jfoynj. TnsV.it.U.K of T<;chro l o g y , S-'.OO <-,4S t o c k h o l m j J,W(jiieri

( 2 ) C c n t r ' . : f o r : S p a c e - a c j ^ n c - , . , 'jh.t.- 'iv '<•« , - ; - ; ' . t .y >f ' " . • ; •«? . a'. Di-.j J .- ir- , I ' . ' . ' , '^y

1.

The daysxde auroral ionosphere and the polar cusp have

attracted specific interest due to the fact that fundamental

processes taking place in the; outer magnetoaphere, its

boundary regions and the magnef-.osheath are reflected here and

focused to a relatively small area easily accessible for

observations by spacecraft and trow tb» ground.

Electric fields have been measured in this region either

directly by double probes on satellites (Cauffaann and

Gurnett, 1972), rockets (Maynard £$L~H- . 1974; Ungafcrup eJL_&l,

1975; Primdahl £i__al. 1979, 1984; Joxgenaen ä£_ftl, 1980;

Kintner et aj. • , 1978; Daly and a.uå Vhalen, 1978) and balloons

(Mozer et; al • 1974} or indirectly fro» the motxon of Barium

clouds (Weacott ££_Ä1- *'V/6) or the acfcient ion drift as

observed toy back? c-s.t ter radars (Foster iLfc_/li.> 1981). Many of

these studies *uVfei from en inisufficient data coverage to

enable an instancaneou.-- pic-cur*; of the large jjcale electric

field oj. convection ^Ht'-.erii to b« constructed. In the vicinity

of auroral arcs, axc-ÄBsocxa';ed electric f.i.elda associated

with Bi eke land currents -^m" poi.sri.3ati on eiectexe fields may

drastically change anc- complicate 'r.he pic cure (Marklund

1383, 1984). Direct iaeapureBient,3 of the plasma motion as

observed by earth orbxeing sa.teili.tew (Han»on and Keelia,

1975) formed the starting point for more systematic studies of

the large scale convection pattern. Not until recently was an

attempt made to reconstruct the instantaneous convection

pattern using simultaneous satellite (DE-2 5 and radar

observations (Chatanika, Millstone Hill) for a number of

events with the interplanetary magnetic field pointing toward»

duak (Heelis et al, 1983). By joining point» of equal

potential integrated from the various datasets, instantaneous

equipotential contours could be constructed showing -i

crescent-shaped and narrow dawn cell and a wider and

circular-shaped duak ceil The only local ti ne sector for

which the data coverage was poor or missing was between 11.00

MLT and 16.00 MLT i.e. un important part of the dayside

auroral cval.

In this study we have concentrated upor» this region to enable

a detailed picture of the Wayside convection pattern clone to

the convection reversal boundary. Thus, a region of rotational

flow reversal is covered by cr,e. rocket flight shortly afc&x

magnetic noon while tihe L'E-2 satellite travelled in

essentially the dawn iusk serijional plane. For this event

detailed equipotentiel contours could be dtawrt base! on the

two datasets described in Section 4

The other rocket parsed through a xsqior» of shiar flow

reversal a3 inferred frow electric field observations close to

15.30 MLT. 3ince tiie ssue xayi.oti w.x passed within >'C sinutas

by the DE-2 satellite; the two datasets together provide verv

detailed information on the convection reversal itself but

cannot be used tc draw the .inst&nt&ij«i.>u,* convection pattern at;

in the other case.

Addition-ni plasxadxiit. observations are provided by th^ Sachs

Harbour radar trom a regiotx close to the r*:v«u"3al boun«Iaiy

nore towards noon than the rockets.

An important point is chat he two events uifscusaed here

geomagnetically quiet, with a relatively stable orientation of

the IMF, as will be described in more detail in Section 3.

This implies chat eny large temporal variations are not likely

to have occureU during the short tiae intervals between the

different datasets.

2.

As part of the Project CENTAUR twe Black Srant 10 rockets were

launched fro» Cape Parry (invariant: latitude 75°), Canada in

December 1981, to study tht; electrodynamics of the polar cusp.

The payloads carried detectors to measure the energetic

particle composition, DC and AC electric and magnetic fjelda,

plasma density and temperatu/e and finally the ion drift. We

shall here concentrate on the observations made by The Royal.

Institute of Technology iRIT) double probe electric field

experiments on the two rockets observations of tht other

parameters mentioned abov* will be described in companion

papers. The RIT experiment C&A be operated in two mode». the

high impedance mode providing vector electric field

measurements with a tame resolution of 3 »» and the Langmuir

node providing information on plasma density and temperature

every 5 a. A detailed description cl the operational »odes for

a similar experiment, is qiwtn in Marklund #.£_AA (1531). A£t.er

subtraction of the v*rB contribution the electric £2 eld has

oeert transformed to ?. local geomagnetic coords »»ate system with

the north axis oriented &pt>r<. ximataly 3fc clockviae froie

geographic north.

At the time of the two CENTAOB flights the DE--2 satellite

crossed the high -latitude northern Aeaisphsre along

approximately the dawn-dusk meridian. During these passes,

taking about 20 minutes between the 50 invariant latitude on

the dawn and dusk side, the ion drift velocity is measured

every second alrmg the satellite track. Oiily the component

perpendicular to the trajectory is dvailaole for these two

events. Detail3 of this experiment and the DE 2 satellite have

been given by Hoffmann (1981).

A number of ground-based experiments delivered important

information on the geophysial condition» during the two

events. These will be discussed in Section 3. The Sachs

Harbour radar provided plasma irregularity drift observations

as deduced from the received scattered. 3igua,l3 originating

from a satellite transmitter. Due to the gftonetry of the

irregularities and the viewing direction of the radar only the

drift component in roughly the geomagnetic north-south

direction is available.

3. Gc.ophyg;ictt,L

fr 1; December 1 • 13,8 \

The CENTAUR 35.001 rocket was launched fAonj Cape Parry at

01.38 vjy ( 15.00 MLT) during « geomagnetical] y v«ry quiet

period ao demonstrated by viq. 1a, showir-ij the magnetometer

H - component, fro» the. Alaska meridian chain for a 24 hour

period including the flight. The 3-hour K - index waa 0+. In

Fig. 2a the interplanetary magnetic field data are plotted as

vectors in the x--y and y-z planes respectively. The vectors

have been averaged over the time intervals indicated by the

attached numbers, during which the IMF-orientation was

relatively stable ft. toward 3ector of the IMF with a strong

sunward component (B >O), a somewhat weaker component towards

dawn (B <C) and an even smaller z~component that changed from

negative to positive about one and a half hour before launch,

characterised this e

2J

The CENTAUR 35.002 rocicet WÖS launched at 27.54 Wl* { 12.30

MLT) on December 13, a day characterized by moderate

geoaagnetic activity as can be seen in Fxg. 1b.

Several hours before launch, however, the activity dropped

away aLaost completely. The 3 hour K -index during this flight

was 1. The IMF data are plotted in Fig. 2b as vectors averaged

over 15 minute» intervals starting at the indicated time»

before launch.

The two rockets were launched Iron: Cape Parry (invariant

latitude 75. ) in a direction roughly towards local

geomagnetic north. They reached an apogee ot about: 670 k» 7.5

»inute» after launch and traversed 7° ot invariant latitude.

The spin axe:? of the rccketa were kept closely paiilL^l to the

direction» of the local magnetic field wi.th «n Almost

negligible coning angle.

k inoxe coapreher.sive xepoil on -Je project CENTAUR and the

geophysical conditions and initiaj result0 will be given ia a

companion paper.

4.1 Rocket and radar observations

The result of the eiecLric .field ct ta anal"s.is for the two

CENTAUR flrght3 on December 1 (afternoon> <*ni êceabur 3

(noon) are plotted in Figs. 3a and 3b respectively. A similar

trend can be recognised tor the two events nameiv a reversal

of the geoisagnetxc earthward component wiiiie the eastward

component, i? positivt* throughout vixe flight a:?.ci shovs Ies'3

variation. Detaaeps are se^n it- Fi^ 3s corresponding *.o

peri.ods for whicn rr.f- •ei-ictric Ei.eJc proi-e« w-tre -53iv-'.;r'ii.tccf and

intense ion ibefisas ve.-e c-p wxv.i.i , rhi.r< wi.i I nor. DH ti^Äted hex-e

bur in a sepa.rat« paf'-u: In FJ..TS. 4;i a rue, 4b '0 t aêxsgâ o£

the 'lata shown at-'>v« a.'t plotted •:;« fleÛio f.:»5ia vectors

every hall; minuet -i;.ong the 100 icrc ?«9;K^ it f ;oc.i;.-o.irii: of the

rocket trajectory By coiapaxing the revs*ssis tor the two

events one notes thf; tox:.o*t±nq >

1) The reversal for the afternoon event (Event 1) occured

almost two degrees more pol^Kard than for the noon event

(Event 2)

2) The eastward component of the electric ilield tends to zero

at the reversal boundary for the afternoon event thus

indiceting an equjpotential boundary. Thi« i» not the case

for the noon event.

3) Poleward of the reversal boundary an abrupt variation is

seen in Fi-j. 3a in the northward "jl«ctric f', eld component.

An almost 1 : 1 correspondence is found between thi.8 and the

magnetic di3turb^rco in the perpendicular direction as

observed by the onboard magru-./torsev.*iö (data not shown

here), r e f k e t m j <? paa.-i.igc '-hrcugn u-ivrjenr fi«ld aliened

current sheets.

(Pri^ndahl

This, is *.n separate paper

4) The electric field was very intense during vise noon event

especially poleward ct tie reversal where it exceeds '»OO

»V/w, while it was weaker for the afternoon event.

2In Fiy. 5 the ExB/B ' drif ts &a inferred frön the <?l«o*vl <:•

field <?c;t.i for ché (,vo »-vent are preseittca in .1»

invariant-lati tude vi a&tjr-.&tic local i viw MI&Siari, 'A

rotational ravexsal with relatively strong north*-n.rd år i i t f

can be recognised for tihe r'oorj evert and a •ilv.:.*?. flow zi*vr ci,a'i

for the ^fLGinoor;

obaerva-Jori 2 above.

fc &u t-?.! t-nt aescrxpr ion of

hvj rö cowpcnerit o£ the

f»> tl».e Sa -ha Harbour radar,

iti,. re^pectj vcly, xn the

.-VÄCS^I i'r'und.':;:v. For the

tlv.i.fL W.AS v«.ry siaiili as

ia and 6b dhew tht ii

i rregulari ty dr i f t s , --.?. Okwyrv

duriiig the aitc-rro.>n ai-d n m e

vicini ty of the ÄT/£ -CJOI-:

afternoon evet:.t, "ch?. r-.octriw .c

expecteU for a &htis.t £1-.;* reversal, »vhiJc fox the noon evert

tha drs.ft v?as coiisid i'ctfci.Y larger- cDrifsÄoterm with »•

rotational flow revtrKi.. A zcl<» civey good ^.gxeeiaent can be

seen betveen the rorkst anc re<if.i observation» i.Vi tii« region

of cLofest approach å»etwf-e» fcht; two th^t i s .: n<ii.f;-ut«Q by the

shaded area.

In Fiq. 7 are shown the »lectton <3exigi';y a:v<J temperature as

deduced from tha f»angauir aweeo^ of the HIT experiment on the

noon flight. The electro^ density variation reflects an11 - 3altitude variation with an F-regxon peak of about 10

seen close to 400 k?n altitude during the upleg. An increase in

T e fro» about 2000°K tc 3000°K can be seen in the latex part

of the flight, within the polar cap. Corresponding data for

flight 1 have not yet b«en evaluated.

DE-2 observations

In Fig. 8a the DE-2 perpendi.cu.lar ion drifts are shown trom a

northern hemisphere crossing between 1.15 UT and 1.35 UT on

December 1 shortly before the launch of the CENTAUR 35.001

rocket at 01.38 UT. A pronounced region of sunward convection

on the duskside accompanied by somewhat more structured

antisunward flow in the polar cap is seen. The division

between plasma circulating around the dawnside and around the

duskside narked by the location of a "zero potential* line

occurs close to the noon midnight meridian and the maximum and

minimum potentials of +3 kV and -15 kV observed by DE-2 occur

at 82° and 79° invariant latitude, respectively. By comparing2

with the ExB/B drift vectors calculated for this flight, as

shown in Fig. 5, one notes that the rocket and satellite

trajectories almost overlap close to the the dusk reversal

boundary, and that its location Agrees well between the two

datasets. This is more clearly seen in Fig. 9, showing the

DE-data together with the sunward component of the CENTAUR

driftvectors, which have been projected to DE trajectory along

circles of constant invariant latitude. Note that the observed

drift patterns are very similar although a poleward shift of

0.5 to 1 degree can be recognized during the twenty minute

interval between the DE and the CENTAUR observations. Such a

shift is consistent with a shrinking polar cap that might be

expected for the observed change in the IMF B -component from

south to north, taking place roughly one hour before the

rocket launch. Relatively small drift velocities prevailed

along the entire dawn-dusk meridian during this flight.

In Fig. 8b the perpendicular ion drifts are shown for a DE-2

crossing between 22.25UT and 22.45 UT on December 13, shortly

before launch of the CENTAUR 35.002 rocket at 22.54 UT. A

two-cell convection pattern of a more common form can be

recognized for this event with antisunward flow in almost the

entire polar cap region between invariant latitude 75° and 76°

on the dawn and dusk side respectively. The flow velocities

were obviously larger for this event, increasing from the dawn

to the dusk side.

Due to the good data coverage b>- the rocket close to magnetic

noon and by the HE 2 sf-tel lite in roughly the dawn-dusk

meridional plane, separated in tin'.e by leas than 30 minutes, a

detailed picture of the dayaide convection pattern can be

inferred. In Fig. 10a the high-latitude region above invariant

latitude 70 from Fig. 8b ha& been enlarged and supplemented

in the following way: Points of equal potential integrated

from the rocket and satellite data along their respective

trajectories have been joined under the assumption that the

convection reversal boundary is almost &n equipotential; and

with the requirement that the drift vectors are tangential to

the equipotential surfaces. The latter requirement can be used

only on the rocket data since the longitudinal component of

the DE-2 drifts is missing. Thus., there is still some

uncertainty about the exact orientation of the equipotential

surfaces along the satellite path although they are accurately

located. It can be a«en that the dayside pattern is

characterized by crescent-shape-d convection contour?; in the

dusk cell compressed towards noon with a reversal boundary

potential of about -37 kV and a potential distribution in the

dawncell indicative of an anticlockwise circuiarshaped flow

pattern with a reversal boundary potential of about 13 kV.

Assuming the convection reversal boundary forms a circle

passing through the dawn and dusk reversals at invariant

latitude 76. 5 and 75° respectively given by the DE-2 data and

the rotational reversal at 77.°2 close to noon given by the

rocket data, the polar cap radius become3 about 14.6° with a

centre shift of 2° towards magnetic midnight. A »ore detailed

picture of the dusk cell is shown in Fig. 10b.

5. Discussion

The high-latitude convection pattern is known to respond

sensitively to variations in the interplanetary magnetic

field. Any fruitful attempt to picture the instantaneous large

scale convection pattern requires geophysically stable

conditions over a period which exceeds both the typical

response times for changes ia the IMF and the data-taking

periods. Since these times aie typically 30 min, her» and

since it was geomaynet.} cally q>jiiet for 3everai hours prior to

launch (ef. Figs. 1a and 1b> ana the IMF was stable for more

than one hour (cf. Figs. 2a and 2b) for both events the above

requirement was reasonably well fulfilled.

For both events the IMc b -component was negative (c£. Figs,

2a and 2b). When the 1KF B -component is negative the above

condition is known t.o prodnce ar asyaaetiy in. r.he convection

pattern such that electric field naxiifla c-cuT. on the 3us.k ai'.'e

of the northern polar <;.sp and the da^n si.<ä« ot thy souths»*

polar cap, as shown by e o Beppi,eT ;i^7^v- .fid Mo-.-.t-i ( '-374).

This asymmetry is clearly fwi.rtert j.'» *ig. flh oi. Fi<3. 'Oa

showing an increase .».n cue drift vvlocitifis f.r >r: the da^n to

the dusk aide. The M&r; cuii pt.-tentr a i on fchw '.1,'.k &.id-.» »as -1b

kV for the Deceaiber "> evtnt and -:n ?cV foi trs r>ecerofc»-..'i- 13

event -and the correspondin«j viiiuea ;a th?; ''-n.'1 s.d« w»-.-«•:•(* +3 kV

and +13 kv\ inferred frca the inte^rai ion of *-t-e niv- 2 data.

The enhanced electron tenpc;rai..urs of 3000v'K observed bv the

rocket within the polar cap <cf. Fig. 7) Stay be ..re'ared to the

intense electric fields reaching 100 v>V;?u a net oorresponcliris/

intense drifts within this egion.

For the December 1 event, goo>1 agreement between the rocket

and satellite measurement? of £ x fi rtr.ift is obtained in the

duskside auroral zone-., The cJiaxacte-Tiifttioo of: a global

convection pattern la made difficult by the northward IHF

conditions prevailing foe this event and by the *act that the

rocket and satellite data were taken in about, the same

location. Several features are worthy of «ote. The. corvectxon

signatures rtxe generally coiisistetit with two convection ceils

with sunward convection in the auroral aones both or, tne

dawnside and the duakside, In the polar cap, identified by the

absence of plastmasheet electrons observed oa DE-2, the

convection is extremely structured bat has a small antisunward

component.

For the December 13 event, a much clearer and more easily

characterized signature of the. convection pattern is seen.

This is possibly due to the fact that the IMF was here almost

entirely directed toward dawn. In this pass the two convection

cells appear to occupy about the aame area on the dayside but:

crescent-shaped flow contours nxiat only for the higher

negative potentials on the dusksiOe. We loote that, at /.east

some of the rotational reversal, region seen by the. rocket

exists on the duskside of Local noo;i.

The general flow patterns may be understood in ter«a of a.

geometrical model by Crooker (1975) Fig. 11 is a -.reproduction

of Fig. 5 in this paper showing predicted poj.av ca.p convection

patterns for various orientations of I'M!' in the y--s plane,

attributabis to merging of ant i para i Z .el field linet.

The predicted pattern for the- December 1 'jvent involves only

one cell circulating ;.'oTr<;c) ev.»»ly within the polar cap. We

cannot of. coura« rule cuh. su:;h ,-». pt r-svoiU.ty 3ir.ee the

convection velocities xnvo.lveä s:*/ bo .•;««!. 1 and extremeJ. y

structured. NevertheJ.ess?, the most ^torain^nt feati/res include

two convection celJ.s that include sunward convection i.r\ the

dawn and dusk auroral ?.cnca. Xne eJ.o«:."i.ro3tat.ic potentials

associated with these cells are quite small and could be

attributable to additional viscous interaction processes

operating at the nagnetopause (Ctooker, 1977),

For the event of December 13 the preoicted and observed

convection patterns axe root.'» consistent. The crescent-shaped.

convection contours on the dusksioe arc consi^teit- with both

dayaide merging and vit-cous interactiori, and we have not

distinguished the relative importance of these mechanisms. On

the dawns ide the transit..) or* fro» sunward to ant i sunward flow

is very structured and some »mail regions of sunward flow may

exist within the polar cap as required by the model. It

appears, however, that most of the fJ.ow is attributable to

day3ide merging even in this rather extreme orientation of the

IMF.

In a similar study Keelia fi±._ai (t(itf3) pxese/it, on basis of

radar and satellite observations, instantaneous pictures of

the convection patterns for &ix events when the IMF

B -component instead ws,a positive. As expected the

characteristic shapes of the dawn and dusk cells were reversed

fitting qualitatively with the predicted patterns shown in

Fig. 11 for various positive IMF 8 -orientations. The multiple

observations covered essentially the entire ni gfctsidi? fro»

local morning to local evening but not the afternoon sector on

which we have concentrated in th« present study.

To summarize, there is strong evidence in favour of the

geometrical model by Crooker (1975), both from the da^side

convection patterns observed in this study for IMF » < 0 and

from the satellite-radar study by Heeiis e_-fc_al. M983} for IMF

B 0.

An attempt was also made to reproduce t,h<* instantaneous

dayside pattern drawn in Fig. 10 by firting ihe model

parameters in th«: convection model by Heel is &t_.ai.- (1982). I*-

was then found necessary to introduce some modifications in

the model. For example, the clusk cell is, according to Fig.

10, more compressed close to magnetic noon than it i.3 at dusk,

especially poleward of the reversal boundary. By introducing a

local time dependence for the electric field decay index

describing how rapidly the fi^ld decays away from the reversal

boundary this could be accounted for. An exponential increase

in the decay index r- from about 2 at dusk to 5 at noon was

found to reasonably well reproduce the observed pattern.

7. Concluaiona

In this study a combination of electric field observations on

two CENTAUR rocket flights in the polar cusp, ion drift

observations on the DE~2 satellite along the dawn-dusk

meridional plane and irregularity drift observations from the

Sachs Harbour radar have been used to infer details of the

electric field and the convection pattern of the dayside

auroral ionosphere, during two geoa&gnetioiiXy quiet event»

when the IMF

3unnarized as follows

B -component was negative The resulta tan be*

On December 1, the same region, with a shear flow reversal,

was traversed fir3t by the DE-2 satellite and twenty

minutes latex by the 35 001 rocket. The drift patterns

observed by the two spacecrafts were ver1/ similar altheuqh

shifted by 0.5 degrees, a shift which is expected fro» the

previously observed change in tbe IMF B -coBponent.

Additional evidence that the reversal is of the shear type

and not the rotational type is given froa fiaultaneous

radar observations of almost negligible uoxthward drifts at

the reversal boundary.

2. On December 13, a xegioa with a rotational flow reverse!

centered around 77.°5 was traversed by the 35.002 rocket

close to magnetic noon, 0:1 the DE-2 Satellite passed ever

the dawn and dusk reversal boundaries at 05.30 KLT an«5

16.30 MLT respectively. Intense northward drifts as

observed by the Sachs Harbour radar at the reversal

boundary aerve as additi nal evidence that the reversal is

of the rotational type. A detailed picture of the

instantaneous dayside convection pattern could be drawn by

joining points of equal potential integrated from the

rocket and satellite data. The result shows a

crescent-shaped dusk cell convection contours compressed

towards noon and a more circular shaped dawn cell.

This detailed dayside pattern for the December 13 event and

that inferred qualitatively for the December " event are

shown to be generally consistent with those predicted from

a geometrical model by Croaker (1979) for the given-

IMF-orientations with B negative. The addition of

convective flow from a viscous interaction type »echanism

is required when the IMF has a northward component. The

sane characteristic shape» but wjth the 3usk and dawn cells

reversed, as presented in a recant zaiiar- satellite study

for 8 > 0, may pervf as aååii.tonal evidence in favour of

this »oöei

In order to reproduce the layside convection pattern

presented above usircg the convection model by Heelia et a.1.

(1983) it was found necessary to introduce a iocal-tiae

dependent electric field decay index increasing

exponentially towards noon.

Acknowledgements

The authors thank ft. Mehra for part of the 3ata analysis of

the rocket data, L Blockr C.-C-, Falthammar &nå D.W.

Winninghan for helpful cosnBent3, S.-I, äkasofu for providing

ground magnetometer data and J,h. McDougalj for the Sachs

Harbour radar observations, K Foraberg for snaking the

excellent drawings and. E. Flcrman for typing the a-.anuscrj.pt.

This research was supported by the Swedish Board of Space

Activities and by NASA grant HAG 5-?>O6 and Ait Force

Geophysics Laboratory grant F^€28-S3~K-OO2£ to UTC.

Paae 15

ReLereaces

Cauffsan, D.P. anä Gurxiett • I! £ . , Satellxtft ^asureise^ts of

High-Lat-itude ConvaetiGu Elecv.ris: Fields, S-a.c<: Sci. Rev..

Q , 369, 1972.

CxooXex, N.U., The Magnet o spheric Boundary Layers: A

Geometrically Explicit Model, J. Geophys. Res , £.£ 362"i>,

1977.

Crooker, N.U., Daysxde Merging &n<3 Cu3p Geometry s 0

Res., M r 951, 1S79.

Geophys

Daly , P.W. and Wn&ler-, h h . . R o c k e t - B o r n e K'saaure^-^vc

P a r t i c l e s a n a lor- ••.'or.veccioti ii- uHVa-iOi; A-i..->i.i. .".'. Geo

, &3., 2 - « S 5 , 1 S 7 8 .

cf

Foster, J.C., Dojpr.ik. 0 ft.

Convection. c,,ä Current.:;

13?9r 1. Geophya. Uea . , j

Jon<: -phc L I C

+-ht; Miän.i-jjnt :'e:-tov OK HOV

7217 , t?--;i.

Hanson, W.B. an-I H«elif-, R A., Techniqv.öa J' r s*:s-3.v.ri

Gas Motions fro» Satellites; Space Set jLii

1975.

Bulk

Heppner J.F.f Polar-Cap Electric Field Distributions xels.ted

to the Interplanetary Magnetic Field D.i f-action, J. Geo^lys

Res-, 22, 4877, 1S72.

H«elis, R.A., Lowell, J.K. and Sp.iro, H.W., A Kedc-l of

High-Latitude Ionospheric Convection. J ^eoph^sr - RH> . . $ J.,

6339: 1982

Heelis, R.A , Foster, J.C , df: la Baau jaidiére. O and Holt,

J., Mult '.atdtion HCniauxfibifttTts of !-!iqh ••i- tit'-d*.» Ivi

Convection, J. Ceot;hyr. !^;r; . M ; »O'-'ii, '.?£>.*,

Hoffaaann, R A , uynaaii :u HJ

1981 .

3c i 'nstr isi. , .5.,

, T.S., MikKeisers, I.S., La^bsti, K., haeier*aei, G. r

Rieger, E., Vaien?,uela, A., Moxer, F.. S. , Teraeriri, M..,

Holback, B. and B^orn, L., Electric Fielis. ifi the Dsysiie

Auroral Oval, J. Geophys. Res., $£. 2B91, 1SSC.

Kintner, P.M.. Ackerson, K L-, Gurnett, D A . ^nd Frank, L.A.,

Correlated Electric Field and Low-Eneigy STffctxoa

Measureaents in the Low-Altitude Pola.r Cusp .>. Geoyhys.

Res., &1, 163, 1978.

Marklund, G., Block. L. and t.xndqvist, ?.-&., Eocicet

Measure»ents of Electric Fields, Electron Density and

Temperature During Different V'hasin of Auroral Suhstoras,

Planet. Space Sci-, 21, -?-4S, 1: 81.

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Gxound-Based St.ady of an Auroral Breakup Event, l;lanet.

Space Sci.f X\, 207, 1

Marklund, G. , Auroral Arc: ux^sai f ication Scneajp Brssed on the

Observed Arc-Associated Electric Field Pattern, Flanet

Space Sci., H , 193, ;984.

Maynarrl, N.C. and Johnstona, A.D., High Latitude Dayside

Electric Field and Pat tide Measurements, ,3, Geophy». Res.,

IS, 3111, 1974.

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Schutz, S. , High-I.i3ti.!;u<*.e rilectri... Fie.-cis :*.nd. the

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and Tetrastrial Magnetic Fields, J cecphys. Re»., 2S-

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Bes., 8A, 6458, 1979.

Primdahl, F.r Bahnsen, A... £jiri, M., H^eg, P., Marklund.; C,

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L.J., Rocket-Borne atsc CAOund-BasevJ Ohsei vat.iojis *-.f

Coincident Fluid-Aligned durents, Election Be.jj&3, and

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Space Sci., j£, 561, 1984.

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Page f t

Figure captions

Fig.1 H-co»ponent of the ground magnetic disturbar»ce a?

measured by the Alaska laexiiian cliain of

during a) the Dec. 1 event and b) the Oecr 13

The shaded area? rei-xeasnt the flight period:?.

Fig. 2 Projections to the y-~ &n-3 x~i- plx-r*

interplanetary »<t iit;t.ic field A- J ! ^ i ^

during a) the Dec, 1 event t>r;d fc> ths Dec.

? ot the

;3 evert.

Fig. 3 Horizontal electric fielö componentp '/s fJi.ght.

(s), altitude (X.*) and universal tj.s*e in a coordinat.e

system with local geccsagnetic north 36 clockwise of

geographic north. Derived from the RIT experiaent, on a)

CENTAUR 35.CO1 on Dec. 1 and b) CENTAUR i5.002 on Dae.

13.

Fig. 4 Vector representation of the results presented in Fig.

3 along ths i00 Ka «agr»etic footpoxn'c of the rocket a)

15.001 on Dec. 1 and b) 35.002 on Dae:. 13.

2Fig.5 E x B/B drifts corresponding to the electric

observations presented in Figs. 3 and 4 plotted in an

invariant latitude vs magnetic local tiiee diagram.

Fig.6 Geomagnetic northward component of the irregularity

drift as seasuxed by the Sachs Harbour radar during a)

the Dec. 1 event and b) the Dec. 13 event. For

comparison the corresponding drift component calculated

fzon the rocket electric field data has been included,

Fig.7 Electron temperature and electron density vs flight

time, altitude and universal time ns deduced from the

RIT Lanyemir sweeps on ilight 35.002, Dec. 13.

Fig.8 The perpendicular ion drift velocity measured by the

DE-2 satellite ai between 01.15 and 01-35 UT on Dec. 1

and b) between 22.25 and 22 45 ÖT on Dec. 13. Also

indicated are the potential distributions along the

respective trajectories, as integrated from the DE-2

data

Fig.9 Comparison of the 3unv»ard drift component observed on

DE-2 and CENTAUR 35.001 in the dusk hemisphere around

01.40 UT on Dec. 1, 1981. For explanation, see text.

Fig.10a An instantaneous picture of the dayside convection

pattern as inferred froa the integrated CENTAUR

electric field and DE-2 ion drift observations around

23.00 UT on Dec. 13, 1984. The estimated polar cap

location is also indicated in the figure.

Fig.10b A detailed picture of the convection contours in the

dusk ceil, presented in Fig. 10a.

Fig.11 Reproduction of Fig 5 in a paper by Cxooker (1979)

showing predicted polar cap convection patterns in the

dayside northern hemisphere, viewed from above, for

various orientations of the interplanetary magnetic

field (IMF) in the y-z plane, attributable to merging

of antiparallfel field lines. The shaded regions are

convection gaps. The IMF-orientation during the two

events discussed here are also inserted in the figure

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Aliitude (km)

Fig. 3b

1800

E x B / B 2 drifts calculated from the RIT DC electric field observations

on CENTAUR flights 35.001 (01.38 UT, dec.1) and 35.002 (22.54 UT, dec. 13),

1500

1200

INVARIANT LATITUDE VS MAGNETIC LOCAL TIME

Fig. 5

2000 m/fc

0600

Drift velocity

(nys)

600

600

400

200

ROCKET-RADAR COMPARISON OF NORTHWARD DRIFTCOMPONENT

35.001d«c.1, 1981

CENTAUR 35.00» Riaht

01.01 UT .15

-200

-400

Drift velocity

(m/s)'

1200

1000

800

600

400

200

launch

Fig. 6aimpact

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35.OO2d«c. 13, 1961

55 23.00 .05

CENTAUR 35.002 Flight

launch

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impact

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Time

(UT>

<—»— N-ward irregular drift a» observed by Sachs Harbour radar.

» « N-ward E I S / B 2 drift as calculated from CCNTAUR electric field.

&M Periods of closest approach and same invariant latitude between the twodatasets.

Fig. 6b

RIT Plasma parameters. CENTAUR 35.002launched 22.54.25 UT. dec., 1981

4000

3000

2000

1000

5x10 11

Ec

101!

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22.56

electron temperature

electron density

•+-200 300

300 400-t-

400I

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4- H h640 600 550 500

22.58 23.00 23.02•+-

23.04

Right time(s)

Altitude

2 3.06 Univ. Time

Fig. 7

DE-B ION DRIFT VELOCITIESMLT V ILAT NORTHERN HEMISPHEREDAY 81335 UT 1=23 ORBIT 1770

1 ? •••

I KM/SEC

DE-B ION DRIFT VELOCITIESMLT V ILAT NORTHERN HEMISPHEREDAY 81347 UT 22 = 31 ORBIT 1962

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!KM/SEC

Fig. 8a Fig. 8b

1200 MLT

1000 mA

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OE p«rp«ndicularion drift

CENTAUR correspondingCENTAUR driftcomponent

INV. LAT

1200 MLT

AWNPOTEMTIALMAXIMUM

POLAR CAP CENTRENiGHTSfOE SHIFT -= 2°

-1/9

/DUSK POTENTIAL MAXIMUM« -36^8 kV

Fig. 10a

en

x-^.

TRITA-EPP-84-05 ISSN 03S8-7539

The Royal Institute of Technology, Department of Plasma Physics,

S-100 44 Stockholm. Sweden

ROCKET AND SATELLITE OBSERVATIONS OF ELECTRIC FIELDS AND ION

CONVECTION IN THE DAYSIDE AURORAL IONOSPHERE

G. Marklund and R.A. Heelis

June 1984, 31 pp. incl. illustr., in English

Electric field observations fro» two high-altitude rocket

flights in the polar cusp have been combined with satellite

observations of ion drifts to infer details of the electric

field and convection pattern of the dayside auroral

ionosphere. A region of shear flow reversal can be inferred

fro» the electric field observations on one flight near 15.30

MLT 20 minutes after the Dynamics Explorer 2 satellite crossed

through the same region. The drift patterns observed by the

two spacecrafts were very similar although shifted by 0.5

degrees, a shift which is expected fxcm the observed change in

the interplanetary magnetic fia!<3 (IMF) B component during

this time. A region of rotational flow reversal was covered by

the oth«sr flight shortly af':er maan^tic noon, at the same time

the DE-2 satellite travelled along roughly the dawn-dusk

meridian. By joining points of equal potential, integrated

from the two datasets and assuming the reversal boundary to be

an equipotential, the instantaneous convection pattern could

be drawn showing crescent-shaped convection contours in the

dusk cell and more circular shaped contours in the dawn cell.

In order to reproduce this pattern using the convection raodel

recently proposed by Heelis efr a,j. {1982} it was found

necessary to introduce a local-time dependence of the decay of

the electric field with distance from the reversal boundary.

Moreover this pattern is shown to be qualitatively in

agreement with the predictions of a geometrical model by

Crooker (1979) when the IMF is oriented towards dawn. The same

characteristic patterns but with the dusk and dawn cells

reversed, as presented in a recent radar-satellite study for

the IMF oriented towards dusk

Keywords; Convection pattern, Electric'fields, Polar

Rotational reversal, Shear reversal.

trita-epp-84-05 rocket and satellite observations of

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