Characteristics And Possible Mechanism Of The Ocean-atmosphere Relationship In The Western Indian Ocean In Summer

Based on the high resolution satellite data from 1982 to 2015,this study reveals the characteristics and possible mechanisms of the ocean-atmosphere relationship in the equatorial Indian Ocean on the inter-annual timescale and synoptic timescale in terms of the correlation between the sea surface temperature(SST)and sea surface wind speed.The results show that the ocean-atmosphere relationship in Indian Ocean manifests significant regional and seasonal characteristics.The correlation between the SST and surface wind speed anomalies appears positive only in the western equatorial Indian Ocean and southeast equatorial Indian Ocean during summer(July-September),indicative of an ocean-to-atmosphere forcing,while the correlations in other regions and months are all negative,corresponding to an atmosphere-to-ocean forcing.The regression analysis shows that the SST anomalies in the western equatorial Indian Ocean during the summer maybe influence the sea surface wind mainly via the pressure adjustment mechanism.The overlying air temperature in the boundary layer is increased due to the positive SST anomalies,leads to the convergence of sea surface wind,and vice versa.The AM2.1 model simulations further confirm the positive correlation between the SST and the sea surface wind speed in the western equatorial Indian Ocean during summer.In addition,based on the heat budget equation,it is found that the SST anomalies in the western equatorial Indian Ocean in summer are caused by the ocean zonal advection term and vertical convection term.On the synoptic timescale,the ocean-atmosphere relationship in the western equatorial Indian Ocean is also dominated by ocean forcing atmosphere in summer,and other regions and months are dominated by atmospheric forcing ocean.WRF model can successfully reproduce the co-phase relationship between the SST and the sea surface wind speed on the synoptic timescale in the western equatorial Indian Ocean during summer.Through the analysis of the vertical structure of the boundary layer,it is verified that the change of sea temperature can change the stability in the vertical direction of the boundary layer to force the atmosphere to respond.Through the analysis of the momentum budget,it is found that the pressure gradient term and turbulent viscous force term have a great contribution to the atmospheric change over the western equatorial Indian Ocean,and the pressure gradient term accelerates the surface wind speed over the western equatorial Indian Ocean.The integrated observation and numerical simulation show that the vertical mixing mechanism and the pressure adjustment mechanism play a role in the process of the ocean-to-atmosphere forcing in the western equatorial Indian Ocean in summer on the synoptic timescale.