Influence Of The Northern Pacific SSTA On The Storm Track For The Winter Season

In the middle latitudes,synoptic scale transient eddies play a very important role in the meridional transport of heat and momentum to keep maintenance of the atmospheric circulation,while the storm track is the most intense region of the synoptic scale transient eddy activity.This paper using the NCEP/NCAR reanalysis data and IAP AGCM4.1 model studies the effects of Sea Surface Temperature Anomalies(SSTA)in the North Pacific on the strength and location of the North Pacific storm track(PST).The main conclusions are as follows:There are three main kinds of North Pacific SSTA distribution mode in winter,the first mode for the Pacific Decadal Oscillation(PDO),the second mode for the North Pacific Gyre Oscillation(NPGO),the third mode for the North Pacific dipole Oscillation.In the positive phase of PDO,there is a significant SSTA distribution in both tropical and mid latitudes.Because of the diabatic heating of the tropical Pacific Ocean,the meridional circulation in the atmosphere is enhanced,stimulating the Pacific North American teleconnection(PNA)and the changes of mid latitude zonal wind and geopotential height.The Aleutian low and northern Pacific zonal wind strengthen too.Then,the anomaly of storm track and eddy kinetic energy(EKE)is negative in the north and positive in the south.In the positive phase of NPGO,the SSTA mainly distributes in mid latitudes.500 hPa geopotential height anomaly distribution is the Western Pacific(WP)teleconnection pattern,the Aleutian low is overall weak.There is a westerly anomaly over the Kuroshio/Oyashio extension,which increases the flow velocity at the western boundary and enhances the intensity of the oceanic front.At the same time,affected by the atmospheric baroclinicity,storm track strengthens and becomes the narrow shaft,appearing on the"-""+""-" tripole distribution.300 hPa EKE appears enhancement for the overall strength.The effects are directly affected by the SSTA of mid latitude.In the positive phase of the North Pacific dipole oscillations,negative SSTA in the Northwest Pacific superimposed on the climatological SST enhances surface temperature gradient and ocean front increases.Under this SSTA distribution,the baroclinicity of storm track entrance increases,resulting in the enhancement of western part.Northeast Pacific SSTA strengths the diabatic heating effect and sub strong center appears in the eastern storm track.There are also two abnormal centers of EKE.In the negative phase year,storm track and EKE anomaly,otherwise.IAP AGCM4.1 model can simulate the climate distribution of main atmospheric variables in the northern hemisphere winter,the climate state of North Pacific storm track,EOF mode spatial distribution and interannual changes:when using the 850 hPa heat meridional transport to characterize the storm track,disturbance is weak in the entrance and strong over Alaska.When the 300 hPa EKE is used to characterize the storm track,the climate intensity of the North Pacific storm track is obviously weak,and the error may be due to the strong static stability of the lower troposphere in the model.Numerical model test results show that in the positive phase of PDO years,the tropical Pacific SSTA is conducive to the enhancement of southern part of North Pacific storm track,while negative SSTA in mid latitudes of North Pacific leads to the weaken of northern storm track.In the positive phase of NPGO,SST in the mid latitude meridional gradient and Oceanfront intensity increase which are the direct factors leading to the increasement and narrowness of storm track.The model can well reproduce the meridional direction"-""+""-"tripole anomaly distribution.In the positive phase of the North Pacific dipole oscillations,the baroclinic properties at the entrance of the storm track increase,resulting in the increase of the western storm track,and the East sub strong center is also well reproduced in the model.