Nocturnal Cooling of the Moshiri Basin, Hokkaido in Midwinter

[摘要] Observations on three dimensional distribution of air temperature were carried out at the Moshri Basin, Hokkaido in midwinter. It was found that the cooling of air on the slope of the basin started a few hours earlier than on the bottom in the small land basin. Analyzing the observational result by the use of potential temperature of air, it was considered that a down-slope wind occurred directly toward the bottom only for several hours, and after this cooling stage the wind was replaced by small eddy currents along the slope except the foot of the basin. A cold air lake of about 40m depth was formed at the bottom mainly by the cooling of surface air due to the heat exchange with the extremely cooled surface of snow cover.The extremely low temperature of surface air in the basin was attributed to the lack of the down-valley wind which would play a role in prevention of extreme cooling of air near the surface.

[学科分类] 大气科学