The climate change of tropical cyclone frequency and its relationship with environment factors in the western North Pacific

Based on the tropical cyclone(TC)data from Joint Typhoon Warning Center and the monthly reanalysis data provided by the European Center for Medium-range Weather Forecasts,the TC genesis frequency and climatology of GPI in the western North Pacific(WNP) during the period of 1970-2001 were compared and the influence of TC frequency of the spatial distribution interannual changes by the environment factors included in the GPI was analyzed with a calculation of genesis potential index(GPI)developed by Emanuel and Nolan.The results show that GPI could describe approximately the seasonal changes and spatial distribution of the TC frequency in the WNP.Impact environmental factors have on the TC,and weaker and stronger the TC frequency has significant difference.The stronger the TC intensity is,the weaker relative humidity is,while the vertical wind shear is opposite.The positive anomaly of the spatial distribution of interannual changes of the TC frequentcy in the WNP appears primarily in the area of east 130 °E.The largest of the positive anomaly of TC frequencies center near(15 °N,140 °E) is affected by the positive anomaly of the absolute vorticity and relative humidity.The abnomal variation of the negative vertical wind shear and positive relative humidity leads to TC frequencies positive anomaly near(10-15 °N,160 °E).