Impact Of The Stratospheric Quasi-Biennial Oscillation On The Summer Circulation In The East Asia-Pacific Region And The Arctic Regio

Previous studies have shown that the stratospheric quasi-biennial oscillation(QBO)has a significant impact on the tropospheric atmosphere,but few studies have focused on the exploration of the relationship between the QBO and the tropospheric atmosphere in summer,especially the extratropics.Based on this situation,this paper analyzes the impacts of the QBO on the summer atmospheric circulation,weather and climate in the East Asia–Pacific and Arctic regions by using ERA5 and NCEP-NCAR reanalysis data.Meanwhile,the performance in simulating the response of the extratropics to the QBO in summer is also evaluated based on the historical experimental data provided by the Coupled Model Intercomparison Project Phases6(CMIP6),which provides a basis for future research on the impact of the QBO on troposphere in summer.The main conclusions are as follows:(1)The stratospheric QBO affects the modes of the zonal wind anomalies in the Northern Hemisphere through the QBO-induced mean meridional circulation(MMC)in summer,which has significant influence on the circulation activities,weather and climate in the East Asia–Pacific region.Specifically,in EQBO years,QBO-related easterly anomalies in the stratosphere can extend to the lower troposphere and cause easterly anomalies in the middle and low latitudes and westerly anomalies in the middle and upper latitudes from the lower stratosphere to troposphere in the Northern Hemisphere.This meridional pattern of zonal wind anomalies can excite negative vorticity and thus lead to anomalous high pressure and anticyclonic circulation from Northeast Asia to the North Pacific in summer.Conversely,in WQBO years,the QBO-related circulation are generally in an opposite polarity to those in EQBO years,which lead to cyclonic circulation and low pressure anomalies in the North Pacific to Northeast Asia.(2)Through the above method,the QBO at 50 hPa in June has an important influence on August precipitation in the regions around the Bohai Sea,which is shown as a significant negative correlation between the QBO and precipitation in the key regions during 1979-2018.In EQBO(WQBO),the positive(negative)geopotential height anomalies in the North Pacific to Northeast Asia leads to an obvious convergence(divergence)of water vapor over the regions around the Bohai Sea,and thus more(less)precipitation in these areas in August.In addition,there is a significant negative correlation between 2m temperature in Northeast Asia in June and the QBO in June during 1979-2018.In EQBO(WQBO),positive(negative)geopotential height anomalies in the troposphere in Northeast Asia in June cause the in situ southerly(northerly)anomalies,and thereby relatively high(low)surface air temperature.(3)In addition to its relationship with atmospheric activity in the East Asia-Pacific regions,the QBO also plays an important role in the Arctic circulation.It is found that the influence of the QBO at 30 h Pa on the tropospheric Arctic circulation in July shows obvious interdecadal variation characteristics.During 1987-2018,the JJ-QBO is significantly negatively correlated with tropospheric geopotential height field in the Arctic region in July,while there is no obvious correlation between the QBO and tropospheric geopotential height field during 1951-1986.It is found that the enhancement of the QBO signal in summer is a primary cause for the interdecadal variation characteristics of the Arctic response in July.The intensity of the QBO signal at 30 h Pa from June to July increases abruptly around 1987,which results in the obvious enhancement of the QBO-induced MMC.The anomalous modes of the zonal winds in the Northern Hemisphere enhance and exhibit a poleward shift,which finally causes the more significant response of the Arctic circulation in July to the QBO.(4)After analyzing the relationship between the QBO and the extratropics in summer in the observations,the related results in CMIP6 models has also been evaluated.The CMIP6 models have a good capability in simulating the periodic characteristics of QBO.However,the performance in simulating the response of the extratropics to the QBO in summer needs to be improved in CMIP6 models.Overall,few models in the CMIP6 model can simulate the influence of the QBO on the northern mid-latitude atmospheric circulation in summer and the interdecadal variation characteristics of the QBO’s effect on the Arctic circulation in summer.Only BCC-ESM2-MR can simulate the results that are close to the observations.