Study Of Large-Scale Criteria With Tropical Cyclogenesis

Tropical cyclones, which form on the tropical oceans, are kinds of strong synoptic system. For lack reliable data on the vast ocean, the tropical cyclone formation forecasting is on the initial stage. There are hundreds of tropical disturbances happen on the tropical ocean surface every summer, but 10% of them could develop to typhoon. The research of tropical cyclogenesis objective forecasting have great significance.Using new large-scale backgrounds classification, the paper divided the large-scale backgrounds of tropical cyclones into the Intertropical Convergence Zone (ITCZ), monsoon trough, easterly wave, Tropical Upper Tropospheric Trough (TUTT) and baroclinic disturbance. The paper analyses the characters of the cyclones under different large-scale circulation backgrounds, like life cycle,source,intensity,scale and landfall. ITCZ could form TC every month. The situation of monsoon trough to landfall is more than any other backgrounds, easterly wave is the second. Tropical cyclones of baroclinic disturbance have the shortest life cycle.The paper analyses the lager-scale circulation backgrounds accompanying tropical cyclone formation in the Western North Pacific between 1995 and 2004. Some large-scale parameters are obtained and computed from NCEP reanalyses with 2.5°latitude resolution. The paper calculated the difference parameters under different large-scale backgrounds during the period of tropical cyclogenesis, and developed viable large-scale criteria for TC forecast in the Western North Pacific. At the situation that the weighting factors of each parameter are equal, TC would happen when lager-scale parameters meet specific range. The difference sea areas use difference criteria.To examine the effect of lager-scale criteria to forecast TC formation, the paper compare the result with reality at first. We also designed a climate method to forecast TC formation, and compared climate method with large-scale criteria. Using Brier Score, which is a skill of measure probabilistic system, the paper found that large-scale criteria is reasonable.