The topography surrounding the Adriatic Sea often has a profound influence on the local winds. NRL's nonhydrostatic mesoscale modeling system, the Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS), is used with high horizontal resolution (grid increment of 4 km) to investigate the near-surface thermal and wind structures over the Adriatic Sea. A series of 15 h forecasts were performed twice daily in a data assimilation mode over an extended period from September 1999 through April 2000. These high-resolution re-analysis fields of winds, temperature, moisture and surface fluxes were exploited to identify the spatial and frequency distribution of high-wind events over the Adriatic, which were often linked to local topographic forcing. The surface atmospheric flux and stress fields also were used to force an ocean circulation model to investigate the response of the Adriatic Sea to topographically-forced severe wind events, the results of which will be presented in a companion paper (Pullen et. al).

One of the most famous wind flows in this region is the bora, which refers to the severe northeasterly winds that occur along the western Adriatic coast in the lee of the Dinaric Alps. The structure of the bora has been documented on several occasions using research aircrafts including the 7 November 1999 severe bora event during the recent Mesoscale Alpine Programme (MAP) special observing period. Although the bora has been investigated in a number of observational and numerical studies, there have been relatively few investigations of the air-sea interaction aspects as the bora. Here, we focus on the 7 November 1999 bora event and verify the high-resolution re-analysis fields using research aircraft observations from the NCAR Electra. The air-sea interaction processes operating during the bora are investigated using COAMPS coupled with the Wave Model (WAM) with a horizontal grid increment of 5 km. A comparison of the coupled and uncoupled simulations indicate that wind speeds differ by less than 4.0 m/s, which is small relative to the maximum bora speed of 22 m/s near the surface. However, the feedback due to enhanced roughness associated with young ocean wave results in a significant modulation of the surface flux and stress fields.