Analyses And Numerical Modeling Of An Explosive Extratropical Cyclone Over The Northwestern Pacific

The structure, evolutionary process and physical mechanism of an explosive extratropical cyclonewhich occurred over the Northwestern Pacific from3to6March2007were investigated by usingobservational data, including the NCEP (National Centers for Environmental Prediction) ADPGlobal Upper Air/Surface Observational Weather Data, JMA (Japan Meteorological Agency)MTSAT-1R (Multi-functional Transport Satellites-1R) infrared channel albedo data, NCEP FNL(Final Analyses) data and CFSR (Climate Forecast System Reanalysis) data. The cyclone initiatedover the central China through the combination of an inverted trough and a cold front which wasformed due to a cold-air outbreak, and then underwent an explosive cyclogenesis over the offshoreEast Asia. Warm core and wet core showed up in the developing stage and the central part of thecyclone defined with isobar was structurally corresponding to the cold front. On the eastern andwestern sides of the cold front, two low-level jet streams which presented warm/wet conveyer beltand cold/dry conveyer belt existed. The60-hour simulation, which was initiated from00UTC3March2007with45-km resolution by using WRF-3.4(Weather Research Forecasting Model),reproduced the cyclone reasonably well. The vorticity budget analysis based upon the simulationresult indicated that the stretching term played an important role in the cyclone development.Low-level jet streams induced the enhancement of the baroclinicity which then increased therelative vorticity of the cyclone indirectly by convergent motion in the low-level atmosphere. Theanalyses of PV (Potential Vorticity) showed that the positive PV anomaly above600hPa made asubstantial contribution to the development of the cyclone.