Observations of Wind in Nares Strait

There is incidental evidence that winds are strong … but how strong?

And why?

3 November 2006

01:06 UTC

Observations of surface wind are very sparse

Numerical simulation demonstrates that wind along the strait increases with end-to-end sea-level pressure drop

3 November 2006

00:00 UTC

High terrain in northern Canada & Greenland can facilitate a close juxtaposition of disparate SLP anomalies – here 41 mb

1974-1990

Primarily during late spring & summer

Only 2x per day

76W

72W

68W

64W

60W

56W

78N

79N

80N

81N

82N

83N

Lafayette BayC am p April 2005

Beaufort Lakes

C ape H erschel

D obbin Bay

Fort C onger

C arl R itter Bay

Lincoln Bay

P im Island

Scoresby Bay

PC S P C am ps, N ares S tra itLincoln Bay: 1974Beaufort Lakes: 1981Fort C onger: 1977-1979, 1981-1982Carl R itter Bay: 1978Scoresby Bay: 1983Dobbin Bay: 1985Pim Is land: 1990Cape H erschel: 1974-1989

Atkinson, D .E ., B . A lt and K . G a jew ski. 2000.A new da tabase o f H igh A rctic c lim ate da ta fromPolar C ontinenta l She lf P ro ject arch ives.Bu ll. A m er. M eteor. Soc. 81(11), 2621-2629.Surface weather has been

routinely observed by field teams operating from PCSP camps along Nares Strait

0 5 10 15 20 25 30 35 40W ind Speed (kt)

0.0

00

.05

0.1

00

.15

0.2

0

Rel

ativ

e fr

eque

ncy

of o

ccur

renc

e

1974 1976 1978 1980 1982 1984 1986 1988 1990

01

00

20

03

00

400

Nu

mb

er

of d

ata

1-Apr 1-M ay 1-Jun 1-Jul 1-Aug 31-Aug

04

08

01

20

160

20

0N

um

ber

of d

ata

PC SP C am ps, N ares S tra itLincoln Bay: 1974Beaufort Lakes: 1981Fort C onger: 1977-1979, 1981-1982Carl R itter Bay: 1978Scoresby Bay: 1983Dobbin Bay: 1985P im Is land: 1990Cape H erschel: 1974-1989

Atkinson, D .E ., B . A lt and K . G a jew ski. 2000.A new database of H igh A rctic c lim ate da ta fromPolar C ontinenta l She lf P ro ject arch ives.Bull. A m er. M eteor. Soc. 81(11), 2621-2629.

But no extreme winds were reported

Maximum 19 m/s

Rare above 15 m/s

Perhaps lack of strong winds reflects indolence?

Hall Expedition, Polaris Bay November 1871 – August 1871

Hall Expedition, Life Boat Cove

November 1872 – May 1873

Lady Franklin Bay Expedition

Fort Conger (Greely during IPY)

August 1881 – July 1883

24x per day 76W

72W

68W

64W

60W

56W

78N

79N

80N

81N

82N

83N

Lafayette BayC am p April 2005

Fort C ongerH all Land

Polaris Bay

Polaris H ouse

A lert

The only other observations were made by 19th century explorers at several over-wintering sites

1-M ay-72 1-Jun-72 1-Jul-72 1-A ug-72 1-S ep-72

010

20

30

40S

peed

(m

/s)

090

180

270

360

1-N ov-71 1-D ec-71 1-Jan-72 1-Feb-72 1-M ar-72 1-A pr-72 1-M ay-72

010

2030

40S

peed

(m

/s)

090

180

270

360

W ind at Po laris Bay1871 - 1872H ourly average

90 th percentile

D irection

0 10 20 30 40 50H ourly m ean speed (m /s)

010

2030

4050

Spe

ed o

n th

e ho

ur (

m/s

)

7 7 6 8 5 3

3 2 2 0

Wind topped 20 m/s once or twice per week, especially during the winter months

6 November 1871 to 31 August 1872

The maximum hourly speed was about 35 m/s (68 kt)… but stronger winds were missed for operational reasons

Polaris Bay

6 November 1871

to 31 August 1872

Strongest & most common winds blew along the strait

Speed histogram was strongly skewed < 5 m/s for 65% of the time> 20 m/s for 5%

0 10 20 30 40Speed on the hour (m /s)

0.0

00

.04

0.0

80

.12

0.1

6F

ract

ion

of d

ata

0 10 20 30 40H ourly average speed (m /s)

0.0

00

.04

0.0

80

.12

0.1

6F

ract

ion

of d

ata

0

45

90

135

180

225

270

315

10% 20% 30%

<=5

>5 - 15

>15 - 25

>25

0

45

90

135

180

225

270

315

0 10 20 30 40

Speed (m /s)M edian

M axim um

Most of the net atmospheric displacement occurred during winter

-50,000 -40,000 -30,000 -20,000 -10,000 0East (km )

-40,

000

-30,

000

-20,

000

-10,

000

0

Nor

th (

km)

15-N ov

30-N ov

15-D ec

30-D ec

14-Jan

29-Jan

13-Feb

28-Feb

14-M ar

29-M ar13-A pr

28-A pr

13-M ay28-M ay

12-Jun

27-Jun

12-Ju l

27-Ju l

11-Aug

26-A ug

6 November 1881 to

31 August 1882

Wind speed at Fort Conger, Discovery Harbour

Wind topped 20 m/s only twice in 2 years

15 August 1881

to 31 July 1883

1-Feb-83 1-M ar-83 1-Apr-83 1-M ay-83 1-Jun-83 1-Jul-83 1-Aug-83

05

10

15

20

Spe

ed

(m

/s)

09

01

80

27

03

60

1-Aug-82 1-Sep-82 1-O ct-82 1-N ov-82 1-D ec-82 1-Jan-83 1-Feb-83

05

10

15

20

Spe

ed

(m

/s)

09

01

80

27

03

60

1-Feb-82 1-M ar-82 1-Apr-82 1-M ay-82 1-Jun-82 1-Jul-82 1-Aug-82

05

10

15

20

Spe

ed

(m

/s)

09

01

80

27

03

60

1-Aug-81 1-Sep-81 1-O ct-81 1-N ov-81 1-D ec-81 1-Jan-82 1-Feb-82

05

10

15

20

Spe

ed

(m

/s)

09

01

80

27

03

60

The strongest winds were aligned with Nares Strait

Discovery Harbour15 August 1881to 31 July 1883

0 10 20 30 40H ourly average speed (m /s)

0.0

00

.04

0.0

80

.12

0.1

6F

ract

ion

of d

ata

0

45

90

135

180

225

270

315

10% 20% 30%

<=5

>5 - 10

>10 - 15

>15

0

45

90

135

180

225

270

315

0 10 20 30

S peed (m /s)M edian

M axim um

Direction histogram reflects local terrain

Speed histogram is strongly skewed < 5 m/s for 95% of the time

1-M ay-73 1-Jun-73 1-Ju l-73 1-A ug-73 1-S ep-73

01

02

03

0S

pee

d (

m/s

)

09

01

80

27

03

60

1-N ov-72 1-D ec-72 1-Jan-73 1-Feb-73 1-M ar-73 1-A pr-73 1-M ay-73

01

02

03

0S

pee

d (

m/s

)

09

01

80

27

03

60

0 10 20 30H ourly m ean speed (m /s)

01

02

03

0S

pee

d o

n th

e ho

ur

(m/s

)

Wind speed at Polaris House, Life Boat Cove

Wind topped 20 m/s infrequently, but low wind speed was uncommon

1 November 1872

to 31 May 1873

The wind regime was dominated by north-easterlies from Kane Basin

Polaris House1 November 1872to 31 May 1873

Strongest winds blow along the strait

Average wind speed is high

Speed histogram is bi-modal

0 10 20 30 40Speed on the hour (m /s)

0.0

00

.10

0.2

00

.30

0.4

0F

ract

ion

of d

ata

0 10 20 30 40H ourly average speed (m /s)

0.0

00

.05

0.1

00

.15

0.2

0F

ract

ion

of d

ata

0

45

90

135

180

225

270

315

20% 40% 60% 80%

<=5

>5 - 15

>15 - 25

>25

0

45

90

135

180

225

270

315

0 10 20 30 40

Speed (m /s)M edian

M axim um

Histograms of along-channel airflow suggests two regimes of wind

Atmospheric modeling has revealed strong correlation between along-strait airflow & SLP difference.

Samelson et al. (2006)

25 20 15 10 5 0 -5 -10 -15 -20 -25Pressure d ifference (m b)

0

50

100

150

200

250

-45 -35 -25 -15 -5 5 15 25 35 45Hourly average speed (m /s)

0

200

400

600

800

1000

1200

3.10 m b M ean7.33 m b S tnd dev'n

-0.5 m /s M ean 2.0 m /s S tnd dev'n

-7.0 m /s M ean10.0 m /s S tnd dev'n

W ind A long C hannel1871-1872

Pressure D rop A long C hannel2005-06

Alert minus Carey Islands

1) Light winds dominate to a degree varying with season & site

2) Occasional very strong winds follow the Strait

These observations suggest an important role for boundary-layer stability

The incidence of light wind at Polaris Bay was much higher than the likely incidence of weak along-channel pressure gradient

This suggests a non-linear response of surface wind to pressure forcing

The most likely cause of non-linearity under weak forcing is stable stratification of the atmospheric boundary layer

This prevalent condition is known as the Polar Inversion. Potential temperature may increase by 20°C in the lowest 300 m of the atmosphere

Contributing factors are atmospheric subsidence (adiabatic heating), cloud-free skies, strong long-wave radiative heat loss from the high emissivity snow-surface & weak insolation

The resulting stratification in potential density suppresses turbulence generated by shear in airflow near the ground

In consequence, momentum is not mixed down to the surface and ground-level wind remains light

Strong boundary-layer stratification decouples airflow aloft from surface friction (for a while)

Air flow through Nares Strait is not subject to geostrophic control on a synoptic scale

Suppression of boundary-layer turbulence permits continued acceleration of airflow aloft

Acceleration continues until shear production of TKE via free-stream instability (e.g. KH) overcomes buoyancy suppression

The atmospheric boundary then becomes turbulent, first intermittently and then explosively as eddies bring high-speed air to the surface

The implied sudden onset of extreme wind from calm is consistent with events at Lafayette Bay in April 2005

-9 -6 -3 0 3 6 9 12E lapsed tim e (hours)

010

20

3040

Spe

ed (

m/s

)

… and with a composite of windstorms measured at Polaris Bay during the winter of 1871-1872

Factors influencing the Polar Inversion affect the wind climate of Nares Strait

Snow cover (through surface emissivity)

Cloudiness (through down-welling long wave radiation)

Solar season

Lateral & vertical (viz. subsidence) advection of warm air aloft

Nares Strait may harbour a unique wind regime, by virtue of:

Its great length (550 km)

Its high relief (2000-3000 m)

Its strong boundary-layer stratification (Polar Inversion)

Its lack of a diurnal cycle in B-L stratification in winter