Analysis And Application Of Tropical Cyclone Genesis Potential Index With Multiple Reanalyses

The genesis potential index (GPI) is a spatial distribution function that represents the possibility of tropical cyclone (TC) genesis, and the index contains850hPa absolute vorticity,600hPa relative humidity, vertical shear and maximum potential intensity. The GPI in the western North Pacific basin is calculated from seven reanalysis datasets during TC peak season (July-September). Compared with the corresponding observed TC genesis frequency, the results show that spatial distribution of GPI derived from seven analysis datasets is consistent with characteristic of observed TC genesis. However, the time series of GPI is quite different in seven reanalysis datasets. It’s noted that the correlation coefficient of observed tropical cyclone genesis with GPI derived from MERRA and ERA-40is higher, respectively.We analysis the time series of four variables composed GPI from seven reanalysis datasets, the result show that the600hPa relative humidity is more different than another three variables among seven reanalysis datasets. Further research reveals that the differences in time series of GPI are mainly due to relative humidity among seven reanalysis datasets. Time series of GPI from ERA-40reanalysis dataset is more consistent with observation mainly due to the contribution of600hPa relative humidity, while GPI in MERRA is affected by the combination of600hPa relative humidity,850hPa absolute vorticity, vertical shear and maximum potential intensity.GPI derived from MERRA reanalysis dataset is used to analysis the characteristic of the observed July-September mean tropical cyclone genesis during1979-2010through. Base on the characteristic of linear tend of the observed tropical cyclone genesis frequency, we divide the research period into1979-1994and1994-2011. We calculate the linear trend of spatial distribution of GPI during the two research periods, find two key regions (15°-30°N,110°-140°E;5°-23°N,143°-180°E) that the trend of GPI is ascend during1979-1994, and two key regions (5°-21°N,111°-130°E;5°-30°N,140°-180°E) that the trend of GPI is descend during1994-2011. Through analysis the variable affect the change of GPI in key regions during two research periods, we find that the trend of GPI during1979-1994is mainly due to the combination of600hPa relative humidity, maximum potential intensity, and850hPa absolute vorticity, while the trend of GPI during1994-2011is affected by the combination of maximum potential intensity and vertical shear.