Aircraft Observations of Offshore-directed Flow near Wide Bay, Alaska

Abstract

The effects of the upstream orography of the Alaska peninsula on the low-level flow in the coastal region are studied using observations from two NOAA P-3 research flights. The terrain in this region includes a low sill at Wide Day (approximately 300 m high and 80 km wide), which is flanked by moderate terrain to the southwest (?900 m high) and higher terrain to the northeast (?1500 m high). For the case of 26 February 1987, a large Froude number (Fr ? 1.6) characterized the incident flow. Boundary-layer wind speeds were approximately 30 m s?1 downstream of the gap at Wide Bay and the moderate terrain. The cross-terrain component of the wind above the boundary layer was 24 m s?1 upstream of the barrier and as lame as 45 m s?1 approximately 70 km downstream of the barrier. Wind speeds were significantly less above and downstream of this wind maximum, as with a hydraulic jump. A prominent trough in sea level pressure was observed in the lee of the higher terrain; the largest 100-m wind speeds (?34 m s?1) observed were near this trough. For the case of 3 March 1987, the incident flow over the Alaska peninsula was weak, and the Froude number was small (Fr ? 0.4). In this situation, a low-level outflow (?300 m high) with large wind speeds, cold air temperatures, and high sea level pressure was isolated to the region downstream from the gap at Wide Bay.