Generation and development of a polar mesoscale cyclone over the east coast of Asia as simulated in a AGCM

Abstract

A polar mesoscale cyclone (PMC) developed over the east coast of Asia in an atmospheric general circulation model (AGCM) that used seasonally varying climatological sea surface temperatures (SSTs). The AGCM had 52 layers and triangular spectral truncation at wavenumber 106 (T106L52). This study compares the model PMC, which formed in February, 8 years after model spin-up, with observational studies. The simulated PMC formed over the western Sea of Japan under the influence of a short-wave trough propagating around a cold upper low. PMC genesis occurred as a surface trough over the Sea of Japan. The surface trough extended northward from a major cyclone that developed over the western North Pacific south of Japan. Large sensible heat fluxes from the sea surface facilitated PMC genesis by decreasing the vertical stability and maintaining a thermal gradient in the lower troposphere. Significant weakening of the PMC as it passed over Japan suggests that energy supplied from the surface played an important role in the evolution of the PMC. The PMC subsequently developed rapidly over the western North Pacific east of Japan, under the influence of the upper cold low and a short-wave trough. Precipitation, diabatic heating, and energy from the sea surface all increased as the PMC developed. The evolution of the simulated PMC matched the evolution of observed PMCs. Realistic formation of synoptic-scale circulation systems, such as the upper cold low, short-wave troughs, and a major cyclone in the model, are crucial if PMCs are to be simulated realistically in the AGCM. © 2004, Meteorological Society of Japan.