Dynamical coupling between the atmosphere and the ocean is effected through fluxes at the air-sea interface. In numerical models for atmosphere-ocean interactions, boundary layer similarity theory and air-sea flux observations are used to parameterize the heat and momentum fluxes. The former provide positive feed-backs within the system, tending to energize the atmosphere and give intensification of synoptic storms, whereas the later provide negative feed-backs, resulting in atmospheric slowing and de-intensification of synoptic storms. In this study we present the interplay between positive and negative feed-backs. We show the partitioning of energy and momentum into waves and upper ocean currents, as the storm evolves.

This study focuses on simulations of Hurricane Erin from September 9-14 2001 in the NW Atlantic. Our model is a composite model. We use a meso-scale atmospheric model (MC2 http://www.cmc.ec.gc.ca/rpn/modcom/index2.html ) coupled to an ocean wave model (SWAN http://swan.ct.tudelft.nl/) and a mixed layer (Kraus-Niiler) model (Tang and DeTracy, 1998, JGR). The ocean grid resolution is 0.2 degrees for the NW Atlantic. This is nested to a coarse grid of 1-degree resolution, west of 65 degrees W. and north of 10 degrees N. MC2 coupling to SWAN is effected by wave-induced formulations of Janssen (1989, 1991, JPO) which are part of the SWAN code, and empirical roughness parameterizations by Smith et al. (1992, Bound. Layer Meteor.) from the HEXOS experiment. This latter coupling mechanism is documented by Perrie and Zhang (2001, JGR) and Zhang and Perrie (2001, Bound. Layer Meteor.). SWAN is coupled to the mixed layer model to give impacts of waves on surface currents following the wave-induced currents formulation of Jenkins (1986, 1987, JPO). This simulation of impacts of waves on surface currents has also been tested by Perrie and Hu (1997, JPO) and also Perrie et al. (2001, submitted to JPO). MC2 and the mixed layer model are coupled by passing heat, moisture and related fluxes to the mixed layer model, and passing SST back to MC2. Sea spray is parameterized following recent formulations by Andreas (1998, JPO; 2001 submitted to Adv. In Fluid Mech.) and Andreas and Emanuel (2001, submitted to JAS).

We show the impacts of heat and momentum fluxes, showing the tendency of roughness to slow the hurricane, as opposed to thermal flux tendencies to energize it. Results are compared to similar recent studies, for example, Bao et al. (2000, Monthly Wea. Rev.). Coupled model simulations of the eye of Erin are compared to COAMPS wind estimates, as a baseline for the study. Moreover, estimates of winds and waves are also compared to wind and wave fields inferred from direct images captured by RADARSAT SAR. Winds are inverted following the Vachon and Dobson (1996, 2000) wind inversion algorithm for SAR measurements. Waves are inferred by the SAR waves algorithm of Dowd et al. (2001, IEEE Journal), following earlier work by Hasselmann and Krogstad.