The Role of Surface Heat and Moisture Fluxes Associated with Large-Scale Ocean Current Meanders in Maritime Cyclogenesis

Abstract

A structurally simple analytic quasi-geostrophic model is used to investigate the role of diabatic process resulting from surface fluxes of heat and moisture associated with ocean current meanders in midlatitude maritime cyclogenesis. The combined effect of sensible heat transfer and convective latent heating resulting both from surface water vapor fluxes and large-scale moisture convergence can contribute both directly and indirectly to cyclogenesis, the extent of the contribution being dependent on a number of cooperative processes interacting within the cyclone. Latent and sensible heating associated with shallow convection in a moist adiabatic environment in which the large scale convergence supplies ample moisture to the cumulus clouds represent the conditions under which the greatest enhancement of adiabatic model cyclogenesis occurs; but cyclogenesis induced by differential vorticity advection is 90° out of phase (with respect to the Large-scale tropospheric thermal wave) with direct diabatic intensification associated with sensible heating. The indirect effects of surface fluxes associated with the moistening and destabilization of the boundary layer and the amplification of the overall atmospheric baroclinity have greater potential to enhance model cyclogenesis than direct diabatic process under conditions of strong adiabatic forcing. Preliminary observational evidence suggests that the occurrence of explosive cyclogenesis over the western Atlantic Ocean is marginally more likely when cyclones propagate across the positions of mean warm sea surface temperature anomalies along the Gulf Stream boundary than in the absence of such features. The existence of such anomalies is neither a necessary nor a sufficient condition for explosive cyclogenesis to occur, but way enhance the development in some cases.