Subseasonal coupling between subsurface subtropical front and overlying atmosphere in North pacific in winter

At least two main oceanic fronts (the subarctic and subtropical fronts) exist in the North Pacific. Especially in the subtropical frontal zone (STFZ), the sea subsurface temperature gradient is significantly larger than that of the surface layer in winter. Subseasonal interaction between the subsurface subtropical front and overlaying atmosphere is revealed by using empirical orthogonal function (EOF) analysis of oceanic temperature gradient. The first EOF mode mainly corresponds to the atmosphere-to-ocean influences. With the enhanced westerly wind, a cold sea surface temperature anomaly (SSTA) appears and then passes down to affect the subsurface ocean. However, the second EOF mode indicates the ocean-to-atmosphere forcing. For the second mode, cold oceanic temperature anomaly generates in the subsurface layer and passes up, which makes the SST gradient increasing. Due to the increasing atmospheric baroclinicity, the enhanced westerly wind leads to more heat fluxes from the ocean to the atmosphere, which results in a colder SSTA and a larger SST gradient in the STFZ. Therefore, a positive ocean-atmosphere feedback begins to maintain in the mid-latitude in winter.