Simulation And Projection Of Westerly Wind Bursts (WWBs) Based On CMIP

Westerly wind bursts(WWBs)refer to westerly wind gusts occurring in the equatorial ocean(In this study,if the average zonal wind anomaly in the 1000 h Pa region is greater than2m/s and lasts for more than three days in the region of 25° longitude and 10° latitude,it is defined as WWBs).Existing studies show that westerly wind bursts in the equatorial Pacific are closely related to ENSO(El Nino-Southern Oscillation).Based on the sixth Coupled Model Intercomparison Project(CMIP6)data,this paper analyzes the reproduction ability of CMIP6 model to westerly bursts in historical experiments,explores the possible sources of simulation deviations,and predicts the westerly bursts and the possible changes in their relationship with ENSO under the warming scenario of SSP5-8.5,and reveals the causes.The results show that:(1)The average CMIP6 multi-model ensemble simulated the frequency and interannual variability of WWBs in the Pacific Ocean during the historical period.The correlation coefficient between the annual mean frequency of WWB at 150°E and ENSO is 0.82 in the observation,while it is only 0.31 in the multi-model results of CMIP6 in historical climate.The simulated measure and interannual variability of WWBs were lower than that observed,and there was a large spread between the models.The variation of local sea temperature,westerly wind intensity and water vapor content in the middle troposphere among different models are the possible reasons for the dispersion of simulated WWBs.(2)The average multi-model set in the historical period of CMIP6 significantly underestimated the linear relationship between WWBs and ENSO.Although the simulated intensity of WWBs and large-scale circulation anomalies in the model are similar to those observed,in the model,the Kelvin wave response caused by westerly wind anomalies is significantly lower than that observed,resulting in a significantly lower WWBs-ENSO relationship,which may be caused by a significantly lower air-sea coupling intensity in the model than observed(In historical climate,the correlation coefficient between air-sea coupling intensity and WWBs-ENSO is as high as 0.91).(3)Under the warming scenario of SSP5-8.5,the frequency,measure and interannual variability of WWBs increase,which may be caused by the increase of local sea temperature variability,the strengthening of climate westerly winds,and the increase of middle atmospheric water vapor content.(4)Under the SSP5-8.5 warming scenario,the linear relationship between WWBs and ENSO was significantly enhanced.The correlation coefficient between the annual average WWB frequency of 150 ° E and ENSO at the end of the year is 0.31 under the CMIP6multi-model model in the historical climate,and 0.67 under the SSP5-8.5 warming scenario.This is because after warming,the sea-air coupling intensity increases,so the Kelvin wave response caused by westerly anomalies is significantly enhanced,thus strengthening the relationship between WWBs-ENSO(Under the warming scenario of SSP5-8.5,the correlation coefficient between the air-sea coupling intensity and WWBs-ENSO was 0.59).