The Abnormality Of The SST In The Kuroshio Extension And Its Impacts On North Pacific Storm Tracks And Aleutian

High resolution sea surface temperature(SST)data from National Oceanic and Atmospheric Administration(NOAA),marine reanalysis data from Global Ocean Data Assimilation System(GODAS),satellite altimeter data from Archiving Validation and Interpretation of Satellite Oceanographic data(AVISO)are used to discuss the interdecadal variation of Kuroshio Extension(KE)and synthesise the typical SST patterns in the states of contraction and elongation.By using CESM1.2.0 model,the response of North Pacific storm tracks and Aleutian low to the systematic variability of KE were analysed,the main conclusions are as follows:(1)Zonal perturbation sea surface temperatures(ZPSST,i.e.the deviations of actual SST relative to its zonal average)are proposed in this paper to study the thermal variation structures of the KE,two typical states of the KE,contraction and elongation,are revealed.The contraction state corresponds to the weak intensity of the warm ZPSST and the southerly and westerly scopes of influence,while the elongation state corresponds to the enhanced warm ZPSST and its influence extends northwards and eastward significantly.The two typical phases correspond to the first and second modes of the ZPSST's EOF(Empirical Orthogonal Function)decompositions,while the third and fourth modes reflect the influence of the weak and strong Oyashio respectively.(2)The high value areas of the warm ZPSST correspond to the eddy kinetic energy(EKE)significant regions,and the two maintain a coordinated thermal and dynamical relationship through the intensity of ocean temperature fronts and stability of flows: when the KE strengthens,the flow axis extends northwards,and surface transportations strengthen,the ZPSST enhance,hence the meridional gradients of SST increase,the ocean temperature fronts enhance,the flow axis is stable and vortices shedding flow from the shaft are reduced,the EKE decrease,and vice versa.(3)The response of north Pacific storm tracks to two typical modes of contraction and elongation based on ZPSST EOF decompositions is studied by using the CESM(Community Earth System Model).There are two opposite responses of the storm tracks in meridional and zonal directions respectively driven by the two SST modes: under the contraction mode of the KE,the North Pacific storm tracks shows a reverse change in meridional directions,that is,the intensity of the center and its north is enhanced,while its south is weakened;under the elongation mode,the storm tracks are characterized by the reverse variations in zonal directions,that is,the intensity of the center and its west decreases obviously,while the intensity of the east part of the center increases.(4)The possible response mechanism of the storm tracks response is analyzed from the opinion of energy conversions,the interactions between the deformation of the basic flows and vortices are the main mechanisms of the barotropic energy conversions,under the contraction mode,the change of energy conversion in the north and the south of the central axis of the storm tracks is opposite,the conversion of the basic flow energy to the EKE increase in the north of the axis of storm tracks,while it is reduced in its south,while the conversion from basic flow energy to EKE is enhanced by the whole under the elongation mode.The interactions between the temperature shear of the basic flow and the eddy heat transfer are the main mechanism of the baroclinic effective potential energy conversion,in particular,the response of the interactions between the meridional eddy heat transfer and meridional temteratures gradients of basic flows also show an obvious difference in meridional and zonal directions of the storm tracks axis respectively.The vertical motions of cold and warm air mass is the main mechanism for the conversion of the eddy effective potential energy to EKE,the different response of the correlations between the vertical motion and the eddy temperature are also mainly manifested by the variations in the meridional and zonal directions of the axis of the storm tracks.(5)The intensity of Aleutian both decrease driven by the two KE SST modes,under the KE's contraction mode,the center location of the low pressure shifts slightly westward and northward,the response is reflected as a process that an anticyclone occurs,develops,and the gradually declines in eastern Pacific,while under the KE's elongation state,the central location of Aleutian moves northward and eastward significantly,and the response is reflected as a process that a cyclonic circulation in west Pacific weakens and replaces by an anticyclone in east Pacific.The direct thermal adjustment caused by the SST variations is not the main reason for the Aleutian response,the convergence,divergence and vertical motion are the main mechanism of Aleutian's variation.The center locations of mean zonal wind tendency anomaly,geopotential height tendency anomaly and temperature tendency anomaly caused by transient vortices forcing all have a good correspondence with the center of sea level pressures(SLP)anomaly,indicating that the anomalous activities of transient vortices play an important role in maintaining the Aleutian abnormal states.