ANGEO Annales Geophysicae ANGEO 1432-0576 Copernicus GmbH Göttingen, Germany 10.1007/s00585-999-0566-7 Intercomparison of oceanic and atmospheric forced and coupled mesoscale simulations <br>Part I: Surface fluxes Josse P. 1 2 Caniaux G. 1 Giordani H. 1 Planton S. 1 Météo France, Centre National de Recherche Météorologique, 42 Av. G. Coriolis, 31057 Toulouse Cedex, France, Fax: 335.61.07.8209, e-mail: patrick.josse@meteo.frs.gif 30 11 1999 17 4 566 576 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.ann-geophys.net/17/566/1999/angeo-17-566-1999.html The full text article is available as a PDF file from http://www.ann-geophys.net/17/566/1999/angeo-17-566-1999.pdf

A mesoscale non-hydrostatic atmospheric model has been coupled with a mesoscale oceanic model. The case study is a four-day simulation of a strong storm event observed during the SEMAPHORE experiment over a 500 × 500 km<sup>2</sup> domain. This domain encompasses a thermohaline front associated with the Azores current. In order to analyze the effect of mesoscale coupling, three simulations are compared: the first one with the atmospheric model forced by realistic sea surface temperature analyses; the second one with the ocean model forced by atmospheric fields, derived from weather forecast re-analyses; the third one with the models being coupled. For these three simulations the surface fluxes were computed with the same bulk parametrization. All three simulations succeed well in representing the main oceanic or atmospheric features observed during the storm. Comparison of surface fields with in situ observations reveals that the winds of the fine mesh atmospheric model are more realistic than those of the weather forecast re-analyses. The low-level winds simulated with the atmospheric model in the forced and coupled simulations are appreciably stronger than the re-analyzed winds. They also generate stronger fluxes. The coupled simulation has the strongest surface heat fluxes: the difference in the net heat budget with the oceanic forced simulation reaches on average 50 Wm<sup>-2</sup> over the simulation period. Sea surface-temperature cooling is too weak in both simulations, but is improved in the coupled run and matches better the cooling observed with drifters. The spatial distributions of sea surface-temperature cooling and surface fluxes are strongly inhomogeneous over the simulation domain. The amplitude of the flux variation is maximum in the coupled run. Moreover the weak correlation between the cooling and heat flux patterns indicates that the surface fluxes are not responsible for the whole cooling and suggests that the response of the ocean mixed layer to the atmosphere is highly non-local and enhanced in the coupled simulation.<br><br><b>Key words. </b>Oceanography: physical (air · sea interac- tion; eddies and mesoscale processes). Meteorology and atmospheric dynamics (ocean · atmosphere interactions)