Investigations of Strong Valley Winds in Alaska Using Satellite Infrared Imagery

Abstract

During the Alaskan cold season, the extreme low temperatures that prevail in the interior valleys are significantly modified by valley wind episodes. The infrared sensor on the NOAA polar orbiting satellite clearly detects this warming and delineates the exact area covered by valley winds. Satellite IR images were used in conjunction with surface and upper air maps, radiosonde data, and pilot reports to analyze two valley wind episodes during early 1975. Clear weather allowed excellent satellite viewing and strong temperature contrasts, because of strong radiational cooling in non-windy valley locations. In both cases a high-amplitude 500 mb ridge was moving into the interior from the west with a strong surface high centered cast of the windy area. The strength of the surface wind correlated well with the strength of the surface pressure gradient parallel to the valleys. The wind originated in the narrow sections of the valleys and consistently gusted to 45 kt in the Tanana Valley. The ability of the satellite to view these areas of warming and associated turbulence will alert forecasters to valley wind episodes where there are no conventional surface observations or pilot reports.