The atmospheric conditions for extremery low air temperatures at Mizuho Station, Antarctica

At Mizuho Station (70°42′S, 44°20′E, 2230m), there were 17 days with extremely low air temperature of below -50℃ in the winter of 1980. The atmospheric conditions were investigated to clarify the conditions requisite for the occurrence of these cases. The aerological data at Syowa Station (69°00′S, 39°35′E) were used for this analysis. For the occurrence of extremely low air temperature at Mizuho Station, the following conditions are required : The wind direction at the level of 600mb which can be considered to be the geostrophic flow above the inversion layer, should be from south to west (S-W) at Syowa Station. The wind direction at Mizuho Station is from SE-SW, meaning the synoptic scale pressure gradient from SW-NW to NE-SE which is in the opposite direction of the fall line there. The moisture content of the air mass should be low so that there is no cloud formation. Also the air temperature has to be at least lower than the monthly mean. If these conditions are satisfied, quite strong temperature inversion will occur near the surface, resulting in extremely low surface air temperature. Wind speed at the surface level is only a little lower than the average