Characteristics of atmosphere-ocean interactions along North Atlantic extratropical storm tracks

Abstract

This study explores the characteristics of the air-sea interactions and extratropical autumn storms in the northwest Atlantic. Simulations are performed with a relatively fine resolution coupled atmosphere-ocean model system. The model system consists of the Canadian Mesoscale Compressible Community atmospheric model coupled to a recent version of the Princeton Ocean model. Atmospheric boundary conditions for storm simulations are given by the Canadian Climate Centre model, Second Generation Coupled Global Climate Model (CGCM2), following the Intergovernmental Panel on Climate Change IS92a scenario conditions. The CGCM2 control conditions are obtained from simulated years 1975-1994. Our results show that interactions between extratropical storms and the upper ocean are affected by the upper ocean, latent and sensible heat fluxes across the air-sea interface, and the atmospheric structure, which propagates relative to the ocean surface as storms move along their storm tracks. Three types of numerical storm experiments are conducted, for storms that (1) make landfall, (2) move along the coastline without landfall, and (3) remain over the open ocean. Our results suggest that the locations of the maximum storm-induced sea surface temperature (SST) cooling are mainly dominated by the upper ocean thermostructure. The storm's intensity, as represented by its maximum wind speed, can cause further SST cooling. In turn, the upper ocean can reduce storm intensity by as much as 4-5 hPa in minimum sea level pressure, or 2-4 m s -1 in surface winds. Although the impacts of these effects are most notable in the lower atmospheric boundary layer, they extend to the top of the troposphere.