Analysis of cold air pool formation processes in Tsugaru Plain in winter using a numerical hydrostatic model.

Abstract

In Aomori Prefecture, cold air pool is observed in the southern part of Tsugaru Plain in winter. Previous studies have suggested that distribution of cold air in the plain may affect the snowfall area. In this study, the conditions for the formation of cold air pools in the Tsugaru Plain were investigated by analysis of AMeDAS surface meteorological observation data of the Japan Meteorological Agency, and by using a numerical hydrostatic model. As a result of the model analysis, it was found that cold downward (katabatic) flow was originated in the valleys of Shirakami mountains, and in the saddle between the Shirakami mountains and Hakkoda mountains. This cold flow moved into the Tsugaru Plain. The distribution of cold air pools was classified by the wind speed blowing from the Sea of Japan. When the westerly wind was weak, the whole Tsugaru Plain was covered with cold air. As the wind speed became stronger, the convergence area of the katabatic flow and the westerly wind shifted to inland. When the wind speed became much stronger, the katabatic flow from the Hakkoda side was prevented from moving northward by the westerly wind, then cold air pool was distributed only in the southeast of the plain.