Nocturnal meso-beta basin and katabatic flows on a midlatitude island

A mesoscale simulation for the island of Majorca, Spain, in the western Mediterranean Sea is used to study the nocturnal system of winds under weak synoptic pressure gradients. A very high vertical resolution is used in the first 500 m above ground level to characterize with large detail the thin circulations close to ground, namely, basin and katabatic flows. It is found that the island, the basin, and the slope scales interact strongly, especially when a quasi-steady state is reached in the second part of the night. A high mountain range creates a high pressure area upwind where local winds can develop. Katabatic flows converge to the valleys where they interact with a cold pool, which is advected slowly to sea by the land-sea night-breeze effect combined with a topographic forcing. The katabatic flows experience small entrainment at the top and have well-defined characteristics. The results are partially confirmed by the observations and some satellite images.