Impact of the Midlatitude Storm Track on the Upper Pacific Ocean

Abstract

Transient eddies in the atmosphere induce a poleward transport of heat and moisture. A moist static energy budget of the surface layer is determined from the NCEP reanalysis data to evaluate the impact of the storm track. It is found that the transient eddies induce a cooling and drying of the surface layer with a monthly mean maximum of 60 W m?2. The cooling in the midlatitudes extends zonally over the entire basin. The impact of this cooling and drying on surface heat fluxes, sea surface temperature (SST), water mass transformation, and vertical structure of the Pacific is investigated using an ocean model coupled to an atmospheric mixed layer model. The cooling by atmospheric storms is represented by adding an eddy-induced transfer velocity to the mean velocity in an atmospheric mixed layer model. This is based on a parameterization of tracer transport by eddies in the ocean. When the atmospheric mixed layer model is coupled to an ocean model, realistic SSTs are simulated. The SST is up to 3 K lower due to the cooling by storms. The additional cooling leads to enhanced transformation rates of water masses in the midlatitudes. The enhanced shallow overturning cells affect even tropical regions. Together with realistic SST and deep winter mixed layer depths, this leads to formation of homogeneous water masses in the upper North Pacific, in accordance to observations.