Impact Of Tropical Indian Ocean Warming On Rapid Arctic Warmin

With the increased greenhouse gas emission,the Arctic is undergoing a significant warming trend.The Arctic warming not only exerts great influences on the global climate,but also leads to the extreme weather events which result in serious economic loss.Although many mechanisms responsible for the Arctic warming have been proposed,the impacts of the multidecadal change of tropical sea surface temperature received little attention.The present study utilizes various observational data and CESM to investigate the impacts of the decadal Indian Ocean(IO)warming on the Arctic warming.We obtain the following main conclusions.(1)The North Atlantic Oscillation(NAO)and Atlantic Meridional Overturning Circulation(AMOC)are highly correlated with the Arctic surface air temperature.The positive NAO pattern can lead to increases in surface air temperature over the north Eurasia and Barents-Kara Seas,but decreases over the Greenland.Besides,the stronger AMOC can contribute to the Arctic surface air warming.Hence,through influencing the NAO and AMOC,the IO warming may impact the Arctic climate.(2)The IO warming plays a significant role in the Arctic warming.Although the entire Arctic warms in the context of the IO warming,the warming is not uniform.The warmest region locates in the Atlantic sector,while the warming closed to the North Pacific sector is relatively weak.(3)The tropical IO warming contributes to the Arctic warming mainly from the oceanic pathway.Through enhancing the Atlantic Meridional Overturning Circulation(AMOC),the IO warming induces more ocean heat transport from the Atlantic Ocean to the Arctic.As a result,the Arctic surface gets warmer.Then,due to the strong surface warming,sea ice melts and more relative warm ocean is in direct contact with the relative cold surface air.Thus,surface loses more heat to surface air and the heat loss contributes to the strong surface air temperature increase in the Arctic.(4)Via the atmospheric pathway,the tropical IO warming does not lead to an entire Arctic warming,but contributes to the warming in parts of the Arctic.In response to the IO warming,a strong positive NAO/AO pattern emerges which induces northward wind anomalies over the Kara Seas,north Eurasia and north America.Thus,relatively warm and moist air are transported to these areas and then downward longwave radiation is enhanced locally,which leads to the local warming.However,in response to the IO warming,the net atmospheric heat transport to the entire Arctic is weakened.Hence,the IO warming does not result in the warming in the whole Arctic through the atmospheric pathway.