Local and Remote Forcing Effects of Oceanic Eddies in the Subtropical Front Zone on the Mid-latitude Atmosphere in Winter

Abstract

Multiple oceanic eddies coexist in the North Pacific subtropical front zone (STFZ) in winter, which can be classified into the isolated single eddies (ISO), the combined double isotropic eddies (DBL) and pairs of anisotropic eddies (PAIR). The forcings of these eddies on the mid-latitude atmosphere are investigated using Climate Forecast System Reanalysis (CFSR) data from year 1979 to 2009, which are divided into the remote and local effects in this research. In the stronger STFZ years,there are more ISO and DBL cyclonic eddies to the north but more ISO and DBL anticyclonic eddies to the south of the STFZ, meanwhile more PAIR eddies with cold to the north and warm to the south concentrated around the main axis of the STFZ. These eddy distributions enhance the strength of STFZ, intensify the propagation of upwards baroclinic waves in the lower atmosphere, and finally enhance the zonal wind at upper atmosphere, which is defined as the remote effects of the eddies. However, distinct from this basin-scale remote forcings, three types of oceanic eddies also have different local forcings on the maritime atmospheric boundary layer (MABL) over these eddies. The local effects of the ISO and DBL eddies on MABL entirely depend on the numbers and polarity of the eddy center, while the MABL response to the PAIR eddies appears at the boundary of the two eddies. Furthermore, the local effects of the three types of eddies can be traced to the middle atmosphere accompanied by local precipitation differences.