Roll Clouds Associated with an East Asian Cold Front

On 11 January 1998, a cold front formed in southeast China as a result of a cold-air outbreak in northeast Asia. During this synoptic development, a series of roll clouds (along the SW-NE direction) was observed in East Asia; some of the clouds stretched for over a thousand kilometers. This roll cloud formation moved southeastward across Taiwan, the Ryukyu Islands, and Japan, and eventually into the open ocean. In order to explore the possible cause of these roll clouds the following preliminary analyses were made in this study: 1) the location of roll clouds relative to the cold front was determined in terms of the contrast between the infrared images of the Geostationary Meteorological Satellite of Japan and surface charts issued by the Japan Meteorological Agency, 2) the intrusion of the density current was identified using upper-air soundings at Taipei, and 3) the migrations of roll clouds and the cold front were judged by comparing the arrival time of the first roll cloud and the front with time series of surface meteorological variables measured at a surface station in northwest Taiwan. These observations imply that the series of roll clouds formed in association with solitary wave disturbances generated on the density current (i.e., the outflow from the cold-air break) but behind its leading edge.