Aspect Ratios of Longitudinal Rolls and Convection Cells Observed during Cold Air Outbreaks

Abstract

Abstract Atmospheric conditions in which cellular-roll cloud patterns are apparent, and dependence of the aspect ratios of the cells on depths of the convective layer and the stability ratio are investigated by examining satellite pictures and aerological data over eastern Asia during cold air outbreaks in the months January to March for 1975–82. Vertical profiles of temperature and relative humidity in the convective layer along the cloud bands over the ocean show an increase of static stability, relative humidity, and layer depth in the downwind direction. Longitudinal convective rolls are realized when vertical wind shear is between 10−3 and 10−2 sec−1, and three-dimensional open cells are realized below these values. The cloud top height is proportional to l3/5 of the cloud-band spacing for l≲20 km and to l2/5 for l≳20 km. The obtained aspect ratio for longitudinal rolls ranges from 5 to 18, increasing in the downwind direction at a rate of 1/110 km, while open cells are obtained in the range from 8 t...