Vertical structure in convective clouds producing graupels and snowflake aggregates

This paper describes the vertical air motion and evolution of snow particles in snow clouds that bring heavy snowfall to the north-east coast of the Sea of Japan in winter. The vertical winds are investigated in detail by single Doppler radar and by simultaneous measurement of particle diameter and fall velocity at the radar site. Graupels were formed near the cloud top where updraft was prevailing; they fell in the downdraft region below the cloud base. The downdraft was probably produced by drag force of falling graupels. On the other hand, aggregates grew slowly in comparatively weak updrafts between the cloud top and the ground. When the cloud top was high and the number concentration of the particles was large, the ratio of large aggregates increased because particles aggregate themselves while falling a long distance

Characteristics and seasonal variations of precipitation phenomena at Syowa Station

Long-term observations of precipitating clouds were carried out by a vertical pointing radar, PPI radar and a 37 GHz microwave radiometer at Syowa Station (69°00′S, 39°35′E), Antarctica in 1989. It is concluded from the observations that precipitation near Syowa Station, Antarctica is mainly brought by cloud vortices associated with extratropical cyclones which advance to high latitude while developing to a mature stage. The seasonal variations of clouds and precipitation were analyzed corresponding to the seasonal changes of air temperature and sea ice area. The occurrence frequencies of cloud vortices which brought snowfall to Syowa Station increased in the fall and spring seasons corresponding to activity of the circumpolar trough. However, the activities of cloud systems that bring precipitation weaken in spring when the sea ice area expands to low latitudes, because of less supply of heat and vapor. In 1989,the amount of precipitation in spring brought by a few snowfall events was as large as the amount of precipitation in fall brought by frequent snowfall events. Radar observations revealed that there were three abundant snowfall seasons at Syowa Station and the amount of snowfall was uniform in all seasons except summer. The amounts of precipitation in fall, winter and spring were 74,74 and 53mm respectively