Changes And Mechanisms Of The Main Characteristics Of The MJO And Its Teleconnection Effects Under Global Warmin

A dominant intraseasonal mode in the tropics,the Madden-Julian Oscillation（MJO）,has a considerable influence on a wide range of extratropical weather and climate events.Under global warming,the changes in the MJO characteristics,in the presence of the changing mean states,would have great impacts on the current extratropical weather and climate systems.In this study,the CMIP5/6 multi-model outputs,CESM2 large ensemble,reanalysis,and observation data were employed to explore the changes of MJO intensity,period,horizontal and vertical structures,and propagation characteristics and the corresponding mechanisms under global warming from the beginning of the 20^th century to the future.Then,the complexity of the change in the MJO circulation under different warming stages was revealed by constructing a theoretical model.Also,the influences of MJO activities on global precipitation variability and teleconnection patterns were explored under global warming.The main conclusions are summarized as follows:（1）Two sets of 20th-century reanalysis（i.e.,NOAA-20CR and ERA-20C）with only surface variables assimilated reproduce the observed MJO well in terms of propagation and vertical structure.Based on the two reanalysis,it is found that the MJO intensity increased by about 50%in the past century,so the induced intraseasonal precipitation has an overall increase around the globe.The enhanced MJO circulation/precipitation affects the anomalous local circulation and strengthens the moisture convergence,which leads to moistening and anomalous precipitation.In addition,the stronger MJO provides favorable conditions for the enhancement of high-frequency precipitation and extreme events by regulating large-scale moisture.（2）An amplified MJO with higher frequency and faster phase speed is found under future warming.It is because of the strengthened meridional advection of the mean moist static energy（MSE）by the MJO wind,so an increase in the zonal asymmetry of the MSE tendency.However,the reason for the enhancement of meridional MSE advection is stage-dependent which is due to the non-uniform growth of MJO circulation change under global warming.The constructed theoretical framework revealing how MJO heating and mean static stability changes determine MJO circulation change under global warming.When the contribution from the MJO diabatic heating dominates,the MJO circulation will increase,and while the stability increase is dominant,the growth of the MJO circulation will slow down or even decrease.（3）An amplified MJO teleconnection with an eastward extension in the North Pacific-North America（PNA）region is found under future warming.Due to the strengthened MJO circulation,the induced Rossby wave source is strengthened.Guided by the extended subtropical jet,the stronger Rossby waves induce an amplified and extended North Pacific anomaly.The eastward extension of the North American anomaly is caused by the extended MJO activity.Although most CESM2 ensemble members show consistent teleconnection changes,there are still uncertainties in the teleconnection pattern.The member-simulated meridional gradient of absolute vorticity()and the static stability may be key factors for the uncertainty.When the simulated<0 region in the Northwest Pacific extends eastward,the more Rossby wave is refracted so affecting the teleconnection in the PNA region;when the simulated tropical static stability is small,it is favorable for Rossby wave generation and propagation.