Aspect ratios of longitudinal rolls and convection cells observed during cold air outbreaks.

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 from 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. Asai's theory is modified so as to incorporate effects of eddy anisotropic diffusivities proposed by Priestley. We consider increases of the aspect ratio of longitudinal rolls in both cases - those which depend on the stability ratio and those which are independent of it. It is found that his theory explains observational results reasonably well if the ratio of eddy anisotropies is assumed to be 10-20 for the range of the present analysis. - from Author