Observations of Wind in Nares Strait

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Observations of Wind in Nares Strait
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There is incidental evidence that winds are
strong but how strong?And why?
Observations of surface wind are very sparse
3 November 2006 0106 UTC
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Numerical simulation demonstrates that wind along
the strait increases with end-to-end sea-level
pressure drop
High terrain in northern Canada Greenland can
facilitate a close juxtaposition of disparate SLP
anomalies here 41 mb
3 November 2006 0000 UTC
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Surface weather has been routinely observed by
field teams operating from PCSP camps along Nares
Strait
1974-1990 Primarily during late spring
summer Only 2x per day
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But no extreme winds were reported
Maximum 19 m/s Rare above 15 m/s
Perhaps lack of strong winds reflects indolence?
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The only other observations were made by 19th
century explorers at several over-wintering sites
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
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Wind topped 20 m/s once or twice per week,
especially during the winter months
6 November 1871 to 31 August 1872
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The maximum hourly speed was about 35 m/s (68
kt) but stronger winds were missed for
operational reasons
Strongest most common winds blew along the
strait Speed histogram was strongly skewed lt 5
m/s for 65 of the time gt 20 m/s for 5
Polaris Bay 6 November 1871 to 31 August 1872
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Most of the net atmospheric displacement occurred
during winter
6 November 1881 to 31 August 1882
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Wind topped 20 m/s only twice in 2 years
Wind speed at Fort Conger, Discovery Harbour
15 August 1881 to 31 July 1883
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The strongest winds were aligned with Nares Strait
Direction histogram reflects local terrain Speed
histogram is strongly skewed lt 5 m/s for 95 of
the time
Discovery Harbour 15 August 1881 to 31 July 1883
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Wind topped 20 m/s infrequently, but low wind
speed was uncommon
Wind speed at Polaris House, Life Boat Cove
1 November 1872 to 31 May 1873
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The wind regime was dominated by north-easterlies
from Kane Basin
Strongest winds blow along the strait Average
wind speed is high Speed histogram is bi-modal
Polaris House 1 November 1872 to 31 May 1873
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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)
1) Light winds dominate to a degree varying with
season site 2) Occasional very strong winds
follow the Strait
Alert minus Carey Islands
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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
  20C 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

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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

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The implied sudden onset of extreme wind from
calm is consistent with events at Lafayette Bay
in April 2005
and with a composite of windstorms measured at
Polaris Bay during the winter of 1871-1872
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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