Nocturnal circulations under weak pressure gradients in the island of Mallorca

To study the local nocturnal circulations under weak pressure gradient conditions a winter clear sky night over Mallorca Island is simulated. The run, made with the Meso-Nh model, goes from noon on January 5th, 1999 to the dawn of the next day, including a 15 hour-long night. Two nested domains are used: the larger one, with a resolution of 5 km, includes the Balearic Islands, whereas the inner domain, at 1 km, covers only the Island of Mallorca.

A study of the orographically generated circulations is made through the extensive analyses of vertical and horizontal cross-sections. The katabatic flows at each bassin of the Island are identified and their vertical structure and time evolution are described. To evaluate the performance of the model for this case study, the surface temperature field is compared to the field provided by a NOAA satellite image and to the available automatic surface weather stations. Finally, to inspect the sensitivity to the model formulation, the same case is studied at similar temporal and spatial discretisations with the MM5 model. Both models are able to find the more relevant structures generated by the topography of the Island.