Analysis of Surface Winds in Shelikof Strait, Alaska, UsingMoored Buoy Observations

Abstract

The winds within Shelikof Strait, Alaska, have been examined using hourly observations from a pair of meteorological buoys moored at the ends of the strait for a 6-month period in 1994. The focus is on periods of gap winds, when the prominent terrain bordering Shelikof Strait constrains the low-level winds to accelerate down the local pressure gradient in a direction approximately parallel to the axis of the strait. Statistics have been amassed on the performance of a simple, Bernoulli-type gap wind model during periods of downstrait (northeasterly) gap flow. A series of model experiments have been conducted to elucidate the processes important to gap flow in Shelikof Strait. The model best predicts the observed alongstrait component of the wind at the exit of the strait (explaining 74% of the variance) when it includes not just surface friction, but also parameterizations of the Coriolis effect due to the cross-strait wind and of entrainment. The latter process is studied further using upper-air soundings collected at Kodiak, Alaska, immediately upstream of the strait. These observations suggest that the entrainment is driven largely by the vertical wind shear at the top of the gap flow. Gap winds are favored more during downstrait flow than during upstrait (southwesterly) flow. The lower terrain on the Kodiak Island side of the strait may often represent an insufficient sidewall for upstrait gap flow, as suggested by the detailed observations from a NOAA P-3 research aircraft flight in May 1996 during upstrait flow. Examination of ECMWF operational analyses for the period of buoy observations shows that the alongstrait pressure gradient was represented adequately but the surface winds were handled poorly. The gap wind model presented here could aid operational forecasting of winds in Shelikof Strait, using coarse-resolution analyses or numerical model output for its input, and could be adapted for other regions with similar topography.