Mechanisms For The Distinct Responses Of The Afro-Asian Summer Monsoon Precipitation To Global Stabilized And Transient Warming

There are significantly different responses between global stabilized warming and transient warming climates.Examing the distinct responses of the Afro-Asian monsoon,one of the most typical climate systems,to the two warming scenario can provide a scientific basis for climate change decision-making.Based on the Scenario Model Intercomparison Project(Scenario MIP)for CMIP6 climate simulations,we selected datasets for the stabilized and transient warming scenarios according to the global mean surface temperature warming rate.We further studied the changes in summer monsoon precipitation over northern Africa and Asia under global stabilized warming of 1.5?.More importantly,the differences in summer monsoon precipitation between the stabilized and transient climates are compared,and the associated physical mechanisms are discussed.The multi-model mean results show that:(1)Compared with the historical reference period(1985-2014),the global average temperature increased by 0.77?,and the northern African and Asian summer monsoon precipitation increased by 0.17 mm day^-1and 0.32 mm day^-1under the global stabilized warming of 1.5?respectively.Based on the diagnosis of the moisture budget,it is found that the thermodynamic term makes a significant contribution to the increase of total precipitation in the monsoon region,while the dynamic term determines the spatial distribution of precipitation change and the summer precipitation in eastern China is also affected by the evaporation term.For the thermodynamic term,the further increases of the surface temperature and sea-land thermal contrast under the global stabilized warming of 1.5?will be conducive to increasing and maintaining atmospheric precipitable water in the monsoon region.For the dynamic term,the enhancement of the low-level southwest monsoon circulation and the northward movement of the African easterly jet(AEJ)make the cyclonic circulation control the northern part of the monsoon region,and the rain belt also moves northward.The weakening of the upper tropical easterly jet(TEJ)will weaken the vertical upward movement of the whole monsoon region.As for the Asian monsoon region,the strengthening of the subtropical westerly jet in the entrance area will increase the upward movement on the north side of the Indian peninsula.However,the cyclonic circulation anomaly will weaken the upward movement on the north side of the Indochina Peninsula.At the same time,the significant warming of near surface temperature in the east of the monsoon region will be conducive to local evaporation,thus increasing the precipitation in eastern China.(2)For the same global warming level,the northern African summer monsoon precipitation in the stabilized pathway is weaker than the transient one.The moisture budget analysis shows that the thermodynamic and dynamic term are the main reasons.Relative to the transient warming climate:for the thermodynamic term,the transport of water vapor from the Atlantic Ocean and the Gulf of Guinea to the monsoon region in the stabilized climate is weakend,which leads to the weakening of the atmospheric precipitable water in the monsoon region.For dynamics process,the cold temperature anomaly over the Sahara Desert in the stabilized climate causes the anticyclonic circulation anomaly in the north of the monsoon region,which weaken the westerly flow in the lower layer of the monsoon region.And the convergence of the lower layer of the flow is decreased.The change of tropospheric temperature structure makes AEJ move southward and TEJ weaken,which is not conducive to low-level convergence and high-level divergence in the monsoon region,thus weakening the vertical upward movement and reducing the increase of summer monsoon precipitation in northern Africa.(3)Different from the northern African monsoon,the Asian summer monsoon precipitation in the stabilized climate is more than in the transient one.The analysis of moisture budget shows that evaporation and dynamic term are the main reasons.Compared with the transient climate,the larger warming over the Asian monsoon region causes the stronger evaporation in the stabilized climate.Meanwhile,the larger warming also leads to the enhancement of near surface low pressure and promotes the convergence of low-level air flow.And the subtropical high circulation in the Northwest Pacific strengthens in the stabilized climate.The stronger subtropical westerly jet increases the high-level divergence,which will be conducive to the enhancement of the vertical upward movement,so as to increase the summer precipitation over the Asian monsoon region in the stabilized climate.