Seasonal Cycle And Projection Of Atmospheric Mass Oscillations Between The Northern And Southern Hemispheres In The CMIP6 Model

The redistribution of atmospheric mass can reflect the change of atmospheric circulation system.Using the output data of 47 CMIP6 models and NCEP/NCAR reanalysis data from1958 to 2014,the seasonal variation characteristics of interhemispheric oscillation(IHO)in the model atmosphere are studied,and the simulation ability of CMIP6 to the seasonal characteristics of IHO is evaluated.The future scenario data of 16 CMIP6 models from 2015to 2100 are used to predict the seasonal changes of IHO and water vapor mass.The results show that:(1)The 47 CMIP6 models can simulate the seasonal evolution characteristics of IHO,but there are still differences between the models.Through comparison,16 models that simulate the best seasonal cycle of IHO are selected.These 16 models successfully simulate the temporal evolution,spatial structure and factors affecting the seasonal variation of atmospheric mass,but the large value area of surface pressure anomalies and polar vortex simulation are still different from the reanalysis data.In addition,the simulation results of evaporation?precipitation and equatorial meridional wind are poor and still need to be improved.(2)Under different future scenarios,the phase of climate average change of global and hemispheric air mass is the same,but the annual variation range is different.With the increase of anthropogenic radiation,the annual variation range of global atmospheric mass climatically average increases.The spatial distribution of IHO under the four future scenarios is consistent with the historical simulation experiment,and the spatial distribution of IHO is opposite in winter and summer.The increase of CO₂concentration has a significant nonlinear impact on IHO,that is,with the increase of CO₂,the seasonal variation of IHO first weakens and then increases.Moreover,the areas with abnormal high value of atmospheric mass are also areas greatly affected by the change of radiation forcing.These areas are mainly concentrated in the middle and high latitudes of the two hemispheres and the two polar regions.In addition,anthropogenic greenhouse gas emissions can not only affect the troposphere,but also have a significant impact on the stratospheric polar vortex.(3)The changes of total water vapor mass in the atmosphere under different scenarios can offset the seasonal changes of IHO,but there are differences in the changes of water vapor mass between hemispheres.For the Northern hemisphere,the annual variation range of water vapor mass in ssp3-7.0 scenario is the largest.The Southern hemisphere is different from the Northern hemisphere.After ssp1-2.6 scenario,the annual variation of water vapor mass in the Southern hemisphere increases with the increase of CO₂.However,with the increase of CO₂,the ratio of water vapor mass to dry air mass and the ratio of water vapor mass IHO to air mass IHO first increase and then decrease in both the Northern and Southern hemispheres.The ratio is the largest in ssp2-4.5 scenario,indicating that the counteraction effect of seasonal variation of water vapor mass on seasonal variation of IHO first increases and then decreases.The counteraction effect is the strongest in ssp2-4.5 scenario,which also leads to the weakest seasonal variation of IHO in this scenario.The change of CO₂concentration has the most obvious impact on the abnormal change of water vapor pressure near the equator,and the closer it is to the south pole,the smaller the abnormal change of water vapor pressure.However,the closer it is to the north pole,the abnormal change of water vapor pressure in summer is greater than that in winter,and with the increase of CO₂,the water vapor mass in summer converges to the mid latitude of the northern hemisphere.