Analyses And Numerical Modeling Of A Polar Low Over The Japan Sea On 19 December 2003

The structure and evolutionary process of a meso-α -scale polar low occurred over the Japan Sea on 19 December 2003 were investigated by using almost all available observational data, including the GOES (Geostationary Operational Environmental Satellite)-9, NOAA (National Oceanic and Atmospheric Administration)-17 satellite imagery, the FNL (Final Analyses) data issued by NCEP (National Centers for Environmental Prediction), the surface observational data and the sounding data of Japan Islands, also the QuickSCAT (Quick Scatterometer) data issued by NASA (National Aeronautics and Space Administration) was used. The polar low initiated over the northwestern part of Japan Sea within a synoptic-scale parent low, and disappeared over the east of Japan Islands with a lifetime about 20-h. It is of interest that two concentric "eye" walls associated with this polar low were found in satellite images at its most mature stage. Also, a "warm core" structure of this polar low was found. The intertwinement of the cold air from the Asian continent and the warm air over the ocean with each other provided a strong horizontal wind shear, which is a favorable condition for the development of the polar low. The 24-h simulation with 8-km resolution by using RAMS-4.4 (Regional Atmospheric Modeling System) model with initiated from 12 UTC December 19 2003 reproduced the polar low reasonably well. The vorticity budget analysis based upon the simulation result indicates that the stretching term plays an important role in the polar low development. The analyses of MPV (Moist Potential Vorticity) and disturbed kinetic energy budget show that the barotropic mechanism seems to be the most important factor in maintaining and developing the polar low, which corresponding well with the strong horizontal wind shear found in observational analyses.