Influences Of Environmental Factors On The Intensity And Size Of The Tropical Cyclones Over The Western North Pacific

The numerical prediction model is always a difficult problem for the prediction of tropical cyclone(TC)intensity and size changes,especially for the super typhoons and TC intensification.In this paper,the strongest storm in the 21 st century,Haiyan,will be analyzed as a case.TCs with similar track and generation time to Typhoon Haiyan are divided into super typhoons and regular typhoons by dynamic synthesis analysis.The results show that,compared with the dynamic factors,the thermodynamic factors play a more significant role in TC intensity.Compared with regular typhoons,the thermodynamic environment field of super typhoons is mainly reflected in more abundant water vapor,greater temperature in the lower troposphere and greater relative humidity in the middle troposphere.These environmental factors provide favorable thermodynamic conditions for super typhoons.According to the box difference index(BDI)ranking,the key environmental factors in two kinds of TC intensity are quantitatively analyzed.Moist static energy(MSE),specific humidity and temperature in the lower troposphere can be used as the prediction factors.Besides,ocean heat content(OHC)of super typhoons is generally larger than that of regular typhoons.OHC can also be used as a prediction factor to estimate whether super typhoons will be generated.Meanwhile,the sensitivity experiments by WRF model show that,temperature has the greatest effect on TC intensity,water vapor comes second.The relative contribution of water vapor and temperature is about 1:4.In order to get more universal results,TC tracks in the western North Pacific from June to November,1979-2017 are selected.TC tracks are divided into seven distinct clusters by using the finite mixture model.There are too few samples of Cluster-1 and Cluster-4 of super typhoons,so the relative importance of environmental factors in the Cluster-2,3 and Cluster-5,6,7 will be studied.The results show that sea surface temperature(SST)is the most critical factor for the west straight-moving Cluster-2 and Cluster-3;SST and upper tropospheric outflow temperature are the most important environmental factors for the recurving Cluster-5 and Cluster-6;for Cluster-7,the high-level divergence field and middle-level vertical ascending motion are the key factors for predicting TC intensity.Besides,OHC has a significant effect on TC intensity in Cluster-2 and Cluster-5.In last,a set of ideal experiments are designed to increase SST by 1-4 °C respectively to study the changes of TC activity under the ocean warming.The results show that with the increasing SST,TC intensity and size increase by the inner and outer surface entropy flux.TC destructive potential not considering and considering TC size are calculated.The PDI increases linearly,and the PDS increases exponentially.TC size has the greatest contribution to PDS.This suggests that the growth effect of TC size cannot be ignored in estimating destructiveness.