The structure and formation mechanism of transversal cloud bands associated with the Japan-sea polar-airmass convergence zone

Abstract

During a cold-air outbreak, a broad cloud band is occasionally observed over the Japan-Sea Polar-Airmass Convergence Zone (JPCZ) that forms over the Sea of Japan from the base of the Korean Peninsula to the Japanese Islands. On 14 January 2001, a broad cloud band associated with the JPCZ (JPCZ cloud band) extended in a southeastward direction from the base of the Korean Peninsula to Wakasa Bay, and it stagnated for half a day. The JPCZ cloud band consisted of two cloud regions: one was a long cloud band extending along its southwestern edge (a developed convective cloud band), and the other was the region consisting of cloud bands normal to a wind direction of winter monsoon (transversal cloud bands). The structure and formation mechanism of the transversal cloud bands were examined on the basis of observations (e.g., satellite images, in situ measurement and cloud-profiling radar data from an instrumented aircraft and upper-air soundings from observation vessels) and simulation results of a cloud-resolving model with a horizontal resolution of 1 km. The transversal cloud bands had the following characteristic structures; they extended along a northeastsouthwest direction, which was parallel to the direction pointed by the vertical shear vector of horizontal wind © 2010, Meteorological Society of Japan.