Aircraft observations of offshore-directed flow near Wide Bay, Alaska

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 Bay (approximately 300 m high and 80 km wide), which is flanked by moderate terrain to the southwest ( similar to 900 m high) and higher terrain to the northeast ( similar to 1500 m high). For the case of 26 February 1987, a large Froude number (Fr similar to 1.6) characterized the incident flow. Boundary-layer wind speeds were approximately 30 m s super(-) super(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 super(-) super(1) upstream of the barrier and as large as 45 m s super(-) super(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 ( similar to 34 m s super(-) super(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 similar to 0.4). In this situation, a low-level outflow ( similar to 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.