A Numerical Simulation Of The Effect Of SSTA On The North Pacific Eastern-Pattern Storm Track During The Winter

Over the North Pacific Ocean, storm track often has its strongest center located east of160°W at winter, which is named as the eastern-pattern storm track (EPST). By using NCEP-NCAR reanalysis data, Hadley Center global SST data, and NCAR Community Atmospheric Model (CAM)3.0, this abnormal phenomenon and the possible external forcing mechanism are investigated in detail through observation analysis and numerical simulations.Firstly, the spatial-temporal evolution of storm track in different areas of North Pacific Ocean is studied, while its relationship with sea surface temperature of the Pacific Ocean is also computed through a few statistical methods. Based on these results, positive (P) and negative (N) sea surface temperature anomaly (SSTA) of both the middle-east equatorial Pacific (EP) and Kuroshio Current area (KC) are compounded and multigroup of sensitivity tests were designed to diagnose the variability of storm track under different SST forcings. We focus on the mechanism of the SST As’influence on the EPST and the individual contributions of these two crucial SST areas to storm track. The major conclusions are summarized as follows:Results show that compared with EP, atmospheric response caused by KC’s SSTA is more local in cold season, especially for the KC negative SSTA, whose force mainly influences storm track’s entrance area. Numerical simulations results indicate that winter EP-P (N) SST anomaly can cause subtropical westerly jet (STJ) shifting south (north) and decrease (increase) its width. Moreover, the EP-P (N) SST anomaly is also crucial for the north Pacific storm track shifting south and west (north and east). Moreover, the KC-P (N) SST anomaly plays an important role in enhancing (weakening) the intensity of jet at the entrance area, as well as the intensity of storm track in the climate average position and its shifting north (south) at the east area of north Pacific.Further analysis shows that the EP-N SSTA is significant meaningful for the emergence of eastern-pattern storm track during the winter:the EP-N(P) and KC-P (N) SSTA can lead to the storm track presenting the eastern (western) pattern. When there is the eastern pattern, jet grows wider and weaker. However, Westerly wind speed in the Alaska bay area increases apparently, meanwhile, the baroclinicity at the surface increases. As a result, the transportation of the synoptic-scale’s heat and momentum strengthen. When there is a western pattern, situation is just the opposite.In a word, it seems that storm track’s intensity has a very good relation with the jet and baroclinicity. The activity of storm track in the northeastern Pacific may be caused by the enhancement of low level baroclinicity. SST anomaly in the cold season may affect the STJ through low-frequency teleconnection, and then exert an influence on the storm track. In the mean time, the feedback effect of synoptic-scale eddy turbulence towards STJ enhance significantly, which plays a key role in the maintaining of both jet and storm track.