The Wintertime Western Developing Synoptic Eddy Activities Linked Air-Sea Interactions In The Northern Pacific

By using NCEP/DOE atmospheric reanalysis 2 data(NCEP R2),HadISST and GODAS oceanic assimilation data,the paper has investigated in detail the activities of the western developing synoptic-scale eddy(WSE)together with the air-sea interactions in the north Pacific during wintertime in the context of dynamic and composite analysis method.The airsea anomalous background that is conducive to the WES development,the interactions between WSE and the large-scale mean atmospheric circulation,and the indirect oceanic response to WES have been documented.The results show the atmospheric circulation and the sea surface temperature(SST)anomalies in the mid-latitude region have an important influence on the intensity of the WSE.When the Aleutian Low is robust,corresponding to the strengthening of subpolar oceanic front,is benefited to enhance the low level atmospheric temperature gradient,namely baroclinicity enhancement,which favors to the development of the WSE.At the same time,the intensification of the subpolar oceanic front can cause the westerly jet to shift northward and its advection is also beneficial to the eastward propagation of the WSE.The interactions between the WSE and the large-scale mean flow have been revealed based on the daily data.The dynamic anomalous forces caused by the strong WSE strengthen the zonal westerly wind on the eddy propagation path,as a result the mid-latitude westerly jet increases and moves northward over the north Pacific.And the thermal anomalous forces weaken the mid-latitude atmospheric baroclinicity.When the WSE is strong,the transformation of the baroclinic disturbance potential energy to the perturbation kinetic energy in the lower troposphere over the northwest Pacific is increased,and the conversion of perturbation kinetic energy to the mean flow increases.But in the mid-latitude upper troposphere,the conversion of the mean flow to the kinetic energy is increased.In addition,the strong WSE plays a certain role on the negative phase of Western Pacific(WP)teleconnection pattern.The indirect response of the ocean to the WSE has also been discusses in terms of the lag composite atmospheric circulation and SST together with the heat budget diagnosis of the oceanic mixed layer.The response time scale of the atmospheric circulation to the WSE is within 1 month,while the oceanic response time scale to the atmospheric circulation is beyond 1 month.After the WSE peak,the conversion of disturbance kinetic energy to the mean flow is weaken,the mean kinetic energy and westerly jet as well as the Aleutian Low are reduced.Such process is completed within 1 month.After 1 month,the subpolar oceanic front still maintains its enhanced status.The variation of SST is mainly determined by the jointly impacts of turbulent heat flux and the Ekman advection transportation,which is cause by the atmospheric circulation related to the WSE abnormal changes over the north Pacific in winter.