Structures of Planetary Boundary Layers Observed by a Doppler Sodar in a Cold Season at Sapporo, Japan

概要

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Observations of planetary boundary layers in Sapporo city in a winter monsoon season were carried out from December 1987 to February 1988 with a Doppler sodar. Two typical cases in winter, cold air flows from inland and northwesterly winter monsoon with snowfall, were analyzed in detail. The cold air flows of February 16,1988 showed two upward rising (up to the altitude of 700 m) echo patterns. Wind direction shifted from southwest to east during the period of the two echo patterns. The prominent updrafts of 1.2 and 0.7 m/sec were recorded at the first and the second echo patterns respectively. They corresponded to the first shallow (<90 m) and the second thick (>120 m) cold air flows that penetrated into Sapporo. Effects of snowfalls on planetary boundary layers were examined in the case of February 11, 1988. Wind direction shifted from east to northwest with the beginning of snowfalls. At the same time, the height of strong wind region descended gradually to the ground. Heavy snowfalls produced maximum downdraft speed of 1.6 m/sec. Two rapid mixing processes in winter, from the ground upward by cold air flows and from cloud base to the ground by snowfalls, were revealed by the Doppler sodar observation at Sapporo, Japan.