Observations of Wind in Nares Strait
There is incidental evidence that winds are strong … but how strong? And why? Observations of surface wind are very sparse 3 November 2006 01: 06 UTC
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 00: 00 UTC
Surface weather has been routinely observed by field teams operating from PCSP camps along Nares Strait 1974 -1990 Primarily during late spring & summer Only 2 x per day
But no extreme winds were reported Maximum 19 m/s Rare above 15 m/s Perhaps lack of strong winds reflects indolence?
The only other observations were made by 19 th century explorers at several overwintering 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 24 x per day
6 November 1871 to 31 August 1872 Wind topped 20 m/s once or twice per week, especially during the winter months
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 < 5 m/s for 65% of the time > 20 m/s for 5% Polaris Bay 6 November 1871 to 31 August 1872
Most of the net atmospheric displacement occurred during winter 6 November 1881 to 31 August 1882
Wind speed at Fort Conger, Discovery Harbour 15 August 1881 to 31 July 1883 Wind topped 20 m/s only twice in 2 years
The strongest winds were aligned with Nares Strait Direction histogram reflects local terrain Speed histogram is strongly skewed < 5 m/s for 95% of the time Discovery Harbour 15 August 1881 to 31 July 1883
Wind speed at Polaris House, Life Boat Cove 1 November 1872 to 31 May 1873 Wind topped 20 m/s infrequently, but low wind speed was uncommon
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
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 Carey Islands Alert minus 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 freestream 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 … 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
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