A Comparative Study Of Oceanic Eddies On Atmospheric Forcing In Different Latitudes Of The Northwest Pacific

The Kuroshio Extension(KE)and subtropical North Pacific(NPSUB)region are not only well known for their strong eddy activities,but also play important roles in air-sea interactions.A combination of high-resolution reanalysis,therotical analysis and numericial experiments are applied to investigate the regional differences of effects of mesoscale oceanic eddies(OEs)on the overlying atmosphere,the corresponding mechanism and their long-term climatic effects.The main conclusions are follows.(1)OEs in KE and NPSUB both have significant focing effects on the overlying atmosphere.OEs-induced surface wind speed(SWS)and surface heat flux in KE are stronger averagely due to stronger momentum downward transmission,air-sea temperature differences and surface evaporation.However,OEs in NPSUB can cause more evident impacts on atmospheric water vapor contents,conductive to more changes in local precipitation.Under the same intensity of sea surface temperature anomalies(SSTAs),OEs-induced SWS differences is not significant in this two areas,both observations and numerical models all show that OEsinduced latent heat flux(LHF)anomalies are stronger than that in sensible heat flux(SHF)and OEs in KE have more obvious impacts on SHF and weaker effects on LHF.(2)Numerical experiments of idealized OEs further reveal that OEs-induced atmospheric responses are closely related to the overlying background atmospheric circulation,stability,and water vapor contents.Under strong background wind speed,the influence of OEs on local atmosphere is manifested as vertical mixing mechanism and the corresponding sea level pressure(SLP)and boundary layer height(PBLH)changes are offset.Under weak background wind speed,OEs have effects on surface circulations and their impacts are reflected as the SLP adjustment mechanism.With the increase of atmospheric background circulation and instability,OEs-induced SWS and surface heat flux also increase,but the changes in PBLH are gradually decrease;water vapor contents in atmosphere can not only increase surface wind divergence and secondary circulation,corresponding diabatic heating will further promote the vertical extension.(3)On seasonal timescale,mesoscale OEs over the whole North Pacific can have a certain impacts on springtime atmospheric circulations and storm activities.Compared with the effects of whole North Pacific OEs,effects of the northern and southern North Pacific OEs will be more pronounced and that induced by OEs in the southern North Pacific will be stronger.While as part of the mesoscale SSTAs,OEs in North Pacific will play an opposite role in their impacts on the springtime atmospheric circulation.