Estimated geostrophic winds from surface isobar spacing and orientation are compared with the winds actually encountered at Bear Creek, Alaska during the months January to March, 1959. The isobaric orientation (or direction) at which the flow through the pass reverses direction is noted. One interesting result was that the wind through the pass reversed direction before the surface isobaric analysis indicated the pressure was higher on the upwind end of the pass. This apparently resulted from a piling up of air on the upwind side of the mountain range resulting in higher pressure than would be estimated from the surface chart and from a dearth of air (and lower than expected surface pressure) on the downwind side of the range. The same effect was later noted at Seward, Alaska. Wind speeds through Bear Creek Pass averaged near or slightly above the geostrophic indication, but maximum daily speeds were always higher than the geostrophic. Extreme daily maximum wind gusts exceeded the geostrophic estimation by 50 knots in a few cases. Examination of winds at stations near the mouths of other coastal mountain passes gave speeds roughly one-half of the geostrophic indication, suggesting (in view of the smaller pass area above the mouth) that the speeds in the passes are roughly comparable to those found at Bear Creek. |
