Seasonal Variation of Precipitating Clouds near Syowa Station, Antarctica Derived from Liquid Water Content Data

摘要

Snow clouds were observed by vertically-pointing radar and microwave radiometer at Syowa Station in Antarctica in 1989 to measure vertically integrated ice water content (IWC) and liquid water content (LWC) in the clouds. Most of the water-rich clouds, which are defined here as those of more than 40 mg/cm2 in LWC, appeared in autumn, when the area of sea ice was at its annual minimum. On the other hand, the water-poor clouds, which are defined as those less than 10 mg/cm2 in LWC, appeared in almost all seasons, especially frequently in winter and early spring when the sea ice area was at its annual maximum. The occurrence frequency of these clouds seems to correlate with the area of sea ice rather than with air temperature. The convective activity to produce supercooled water droplets becomes suppressed during their passage above the sea ice with less supply of water vapor from the sea. There was a difference in the amount and area of snowfall among the clouds. The water-rich clouds brought much more snowfall within 50 km of the coastline than the water-poor clouds. This localization of snowfall would stem from the orographic effect caused by production of water condensate in clouds due to lifting of air along the slope of the continent. The water-poor clouds brought less condensed water after lifting.