Simulation Assessment Of Tropical Cyclones By The Global Atmospheric Circulation Model IAP AGCM4.1

As the atmospheric component of the CAS-ESM1(The Chinese Academy of mm Sciences Earth System Model,version 1),IAP-AGCM4.1(The Institute of Atmospheric Physics Atmospheric General Circulation Model,version 4.1)is developed independently by the Institute of Atmospheric Physics.Although the IAP AGCM4.1 has been evaluated by numerous works over different regions at many timescales,its ability to simulate the tropical cyclone(TC)at subseasonal timescale is still unknown.A systematic evaluation of IAP AGCM4.1 on the simulation of tropical cyclone will deepen our knowledge on the model and provide scientific suggestions for its further development.This research uses the IAP AGCM4.1 to perform long term AMIP simulations at0.5° and 1.4° spatial resolutions forced by monthly sea surface temperature from Hadley center.Another 0.5° spatial resolution simulation is also conducted during1982-2012 by using the daily sea surface temperature from NOAA center.Based on the TECA(Toolkit for Extreme Climate Analysis)software,ability of IAP AGCM4.1in simulating the tropical cyclone is evaluated and the impacts from spatial resolution and temporal resolution of sea surface temperature are also investigated.Results show that IAP AGCM4.1 simulation at 0.5° spatial resolution well simulates the generation potential index of the tropical cyclone,as the correlation coefficient between simulation and reanalysis reaches up to 0.66.However,the number of simulated tropical cyclone is only a half of the observation and the underestimation is much obvious over the northwestern pacific ocean.Further analysis based on K-means clustering method shows that the underestimation over northwestern pacific ocean is mostly due to inability to reproduce the northwestward-turning and westward TC.For the TCs with westward-northwestward,westward-turning and eastward-turning tracks,simulated numbers are about 39%,48% and 85% of the observed ones,respectively.Analysis on the large scale circulation reveals that underestimation of the depression over the south China sea and overestimation of the sea surface pressure over the southern region of south China sea to the east of the Philippines will restrict the generation and development of the northwestward-turning and westward TC.Although underestimating the TC numbers,the 0.5° simulation still has improvements in simulating the number,the strength and spatial distribution of TCs compared with the 1.4° one.In addition,higher temporal resolution of the sea surface temperature improves the simulation of TC strength significantly.Compared with the monthly SST,using daily SST reduces the mean bias of TC strength by 24% globally,and the reduction is larger than 30% over northwestern pacific,south Indian ocean and north Atlantic.Thus higher spatial resolution of the model gird and higher temporal resolution of the external SST forcing will improve IAP AGCM4.1's simulation of TC.