Simulated ENSO's Impact On Tropical Cyclone Genesis Over The Western North Pacific In CMIP5 Models And Its Changes Under Global Warming

The tropical cyclones(TC)over the western North Pacific(WNP)has an important influence on the climate disasters in China and the coastal areas of East Asia,and its changes under global warming is of great significance for China to cope with climate change.El Ni?oSouthern Oscillation(ENSO)plays an important role in modulating the location of WNP TC,therefore the changes in the ENSO's impact on WNP TC genesis under global warming are the important aspects to predict the changes of WNP TC genesis under global warming.This study evaluated the simulation of present-climate TC and the changes of TC in future-climate by using a TC detection method to detect model-generated TCs from the 6-hourly output data of 10 CMIP5 models under present-climate(historical runs)and the future climate(representative concentration pathway 8.5(RCP8.5)runs).We first found that CMIP5 models can simulate a reasonable climatological global and WNP TC spatial distribution and match the present-day global annual mean TC frequency well.The result in this paper tended to project a likely decrease in the globally averaged TC genesis frequency which is consistent with the previous studies.Besides,models can also reproduce a reasonable spatial pattern of the large-scale atmospheric environment anomalies(such as the anomalies of 850 hPa relative vorticity,700 hPa relative humidity and vertical wind shear)during El Ni?o and La Ni?a events,although the magnitude is underestimated in the models.The observed southeast–northwest shift role of ENSO in the WNP TC genesis location can be well reproduced in most of the models,although the strength of the ENSO's impact is underestimated as the underestimated climatological TC genesis frequency in these models.The changes in relative vorticity anomalies under global warming tend to a north-south oscillation over the WNP,while the changes in relative humidity anomalies exhibit an east-west fluctuation.However,the changes in vertical wind shear anomalies do not show any regular pattern.Therefore,under the different effect of each variables,the final result of the changes in WNP TC genesis location under global warming remains uncertain.Moreover,we further studied the changes in the ENSO's impact on WNP TC genesis under global warming.we found the WNP TC during EN and LN shows an apparent eastward shift under global warming.However,this eastward shift of WNP TC genesis could be associated with the changes in climatological TC genesis but not the changes in the ENSO's impact.The changes in the ENSO's impact on the location of WNP TC genesis under global warming is obviously uncertain,which is different from the ENSO-induced Pacific rainfall anomalies with certain eastward shift under global warming in previous studies.This may be due to the limited number of models in the current study and the relatively large climate impact factors in the WNP basin.As a result,we suggest that both the TC genesis climatology and ENSO's impact on TC genesis simulated in the models needs improvement in future to project the changes in ENSO's impact under global warming,and more models with 6-hourly outputs used to detect TCs are needed to increase the confidence of multi-model ensemble projections.