Prediction Of Typhoon Environmental Fields In The Northwest Pacific Region

The relationship between global warming and typhoon activity has been a hot topic in the future climate prediction research.This study projects the change in environmental fields and the typhoon GPI(genesis potential index)in the western North Pacific(0°-40°N and 100°E-180°)in the late 21st century(2080-2099)using outputs from the RCP(Representative Concentration Pathway)4.5 and RCP8.5experiments of CMIP5(Phase 5 of Coupled Model Intercomparison Project),carried out using 19 climate models.These models are capable of reasonably reproducing modern typhoon-related environmental fields and are thus selected for the analysis.Compared to the reference period of 1986-2005,the sea surface temperature(SST)over the western North Pacific at the end of the 21^stcentury is projected to increase,and the vertical wind shear(VWS)and the outgoing longwave radiation(OLR)are projected to decrease over the key regions where they are significantly negative correlated with the typhoon frequency,which are beneficial to the formation and development of typhoon.In contrast,the low pressure system extending from the mainland to the South China Sea is weakened,suppressing the typhoon activities.Taken together,the changes of environmental fields of typhoon under the RCP8.5 scenario are larger than those under the RCP4.5 scenario.Furthermore,the signal to noise ratio is examined to measure the consistency across individual models.It is shown that the ratio is higher than 3.0 in most regions for the change of SST,and it is larger than 1.0 for the change of sea level pressure over the regions dominated by the low pressure system,both of which show a high model consistency.The ratio is less than 0.6 for changes of VWS and OLR,denoting a degree of disagreement across models;nevertheless,models agree well on the sign of the change of OLR in regions highly correlated with typhoon frequencies.The aforementioned changes of typhoon environmental fields are in line with the increased GPI in the future.The contribution of various environmental factors to the change of GPI is also analyzed.The potential intensity of typhoon has the most significant contribution to the change of GPI,followed by the VWS and relative humidity of the middle troposphere,and the absolute vorticity at 850 h Pa has no obvious effect on the GPI change.