Abstract: From hourly zonal winds of the boundary layer in Lechang and Guangzhou, a frequency spectra diagram is worked out. According to it, the spacial scale of mesoscale a is estimated to be 200- 600km. The value is applied in statistical studies of Mar. -Jun. weather maps for East Asia (1981-1985), upper air soundings for the south of China and analyzed GMS cloud images of Japan. It is found that there are 2 types of prominent eastward travelling mesoscale a systems in southern China; mesoscale waves in polar fronts and gale cores in low-level SW jets. Conventional data are used to study the climatological and synoptic features of these mesoscale systems and a number of basic findings are obtained.