The Influence Of Mesoscale SST Over Kuroshio Extension On The North Pacific Storm Track

Storm track is one of the important components in the air-sea interaction system in mid-latitude and plays a key role in the global heat and moisture transportation.Based on the high-resolution observation data and high-resolution model,the impacts of mesoscale oceanic eddies on the storm track are investigated,which contributes to understanding of the development of storm track and improves the theory of mid-latitude air-sea interaction.This will be of great importance for the prediction of regional and global climate.In this study,by comparing the storm track of high-and low-resolution sea surface temperature(SST)period based on the ERA-Interim global atmospheric reanalysis,the influence of increasing SST on the storm track is investigated.Then,an index for the variability of mesoscale SST anomalies over Kuroshio Extension(KE)region is proposed based on the high-resolution SST dataset.Composite analysis is applied to examine the relationship between the variability of mesoscale SST and the North Pacific storm track.Furthermore,a global atmospheric model is used to study the impact of model resolution on the relationship between mesoscale SST and storm track.Next,the response of North Pacific storm track to the mesoscale SST is further illustrated by a high-resolution global atmospheric model.Finally,the air-sea interaction associated with the mesoscale SST is investigated by comparing a high-resolution fully coupled model and a high-resolution atmospheric model.The main conclusions are as follows.(1)The increasing of SST resolution in ERA-Interim reanalysis has great impacts on the intensity of storm track near KE.During the high-resolution-SST period,the oceanic mesoscale eddies are resolved and then imprint on the surface heat fluxes,leading to the change of convergence at surface through pressure adjustment mechanism and vertical momentum mixing mechanism.The vertical motion induced by the anomalies of convergence then transports the heat and moisture to the free atmosphere.In the end,the storm track is strengthened by eddy diabatic heating and baroclinic energy conversion.(2)The variability of mesoscale SST near KE region and the North Pacific storm track are closely correlated.It is found that the storm track strengthens(weakens)near its climatology and the south region when the mesoscale SST is strong(weak).The mechanism behind can be concluded as follows.The baroclinicity of atmosphere significantly strengthens near the position of climatology of storm track when the mesoscale SST is strong.The stronger baroclinicity contributes to the baroclinic energy conversion.More transient eddy kinetic energy over the region strengthens storm track.The situation is opposite when the mesoscale SST is weak.Besides,analyzing the vertical motion to the sides of storm track shows that the vertical eddy heat and momentum fluxes increase to the south when the mesoscale SST is strong,associated with the increase of storm track,while the significant vertical motion leads to intensified vertical eddy flux to the north when the mesoscale SST is weak.(3)The global atmospheric model used in this study demonstrates high fidelity in simulating the storm track and winter climatology over North Pacific.The storm track reproduced by the high-resolution model shows a higher resemblance with the reanalysis than the low-resolution model.Furthermore,this study has confirmed the influence of mesoscale SST on the storm track using the model data.However,the results seem to be affected by the model resolution.The response of storm track to the mesoscale SST is stronger in the high-resolution model.(4)To further investigate the response of storm track to the mesoscale SST,based on the high-resolution atmospheric model,a simulation forced by eddy-resolving SST is compared with a simulation in which the mesoscale SST is filtered out.The results indicate that the storm track decreases by 20% around KE and shifts southward downstream after removing the mesoscale SST.The main process is as follows.Removing the mesoscale SST changes the thermal structures through the surface heat flux,decreasing the vertical motion along KE and stabilize the atmosphere,which prevents the development of synoptic eddies and then suppresses the storm track.(5)The comparison between a high-resolution fully coupled model and a highresolution atmospheric model shows the air-sea interaction associated with the mesoscale SST can influence the storm track significantly,causing an increment to the north and a decrease to the south in the atmospheric model.Although the SST boundary condition in the atmospheric model is obtained from the output of coupled model,the forcing by SST in two models is still different.This leads to mesoscale imprints on the surface heat flux,near-surface convergence and boundary layer height.Furthermore,the vertical motion induced by the anomalies of near-surface convergence impacts on vertical eddy heat and moisture flux,contributing to the changes of storm track though eddy diabatic heating and baroclinic energy conversion.Besides,removing mesoscale SST leads to significant decrease of storm track in our coupled model and the response of storm track to the mesoscale SST is stronger than that in the atmospheric model.