Mechanism For The Spatial Pattern Of Amplitude Changes In Tropical Intraseasonal And Interannual Variability Under Global Warming

Since the industrial evolution,more and more greenhouse gases related to the human activities are released into the atmosphere,leading to the strengthen of greenhouse effect and therefore the increase in global land and sea surface temperature(SST),which exert substantial effect on weather and climate systems.This study investigates what forms the spatial pattern of amplitude changes in tropical intraseasonal and interannual variability-represented by the two most important variables,precipitation(?P')and circulation(??')-under global warming,based on 24 models from CMIP5(phase 5 of the Coupled Model Intercomparison Project)Diagnostic analyses reveal that the moisture budget and thermodynamic energy equations related to the ?P' and ??' proposed separately in previous studies are simultaneously tenable and independent from each other.These two equations are further separated into two parts-thermodynamic component associated with the change in vertical gradient of moisture or temperature represented by dry static energy(<(?)>and<(?)>),and dynamic component associated with the change in circulation variability(<(?)>)and<(?)>).The increase in P' over Indo-Pacific warm pool is attributed to the positive contribution of thermodynamic component overwhelming the negative contribution of dynamic component,but the increase in P'over equatorial Pacific is attributed to the positive contribution both of thermodynamic and dynamic componentsFurthermore,we need to investigate the mechanism for the spatial pattern of ??'As a result,based on the moist static energy(MSE)budget analysis,we can deduce that the spatial pattern of the vertical advection of the climatological MSE by the variance change in pressure velocity<(?)>is largely controlled by the spatial pattern of the vertical advection of the change in climatological MSE by the historical variance of pressure velocity<(?)>.Therefore,the spatial pattern of ??' can be projected based on three factors:background circulation variability ?',the mean-state vertical MSE gradient M,and its future change ?M.Under global warming,M increases over the entire equatorial tropics,but the largest increase is mainly over the northern Indian Ocean and equatorial Pacific,where the increase in SST exceeds the tropical mean.It means that the mean-state vertical MSE gradient is modified by the ?SST pattern through a direct moistening and heating of the lower troposphere.In short,the change in the response of the mean-state vertical MSE gradient to the ?SST pattern under global warming can modify the moisture budget and thermodynamic energy balances,resulting in the spatial pattern of ?P' and??' at intraseasonal and interannual timescales consequently.