Mesoscale energetics and flows induced by sea-land and mountain-valley contrasts

We study the relative importance of sea-land and mountain-valley thermal co ntrasts in determining the development of thermally forced mesoscale circul ations (TFMCs) over a mountainous peninsula. We first analyse the energetic s of the problem, and using this theory, we interprete the numerical simula tions over Calabria, a mountainous peninsula in southern Italy. The CSU 3-D nonlinear numerical model is utilised to simulate the dynamics and the the rmodynamics of the atmospheric fields over Calabria. Results show the impor tance of orography in determining the pattern of the flow and the local cli mate in a region as complex as Calabria. Analysis of the results shows that the energetics due to the sea-land interactions are more efficient when th e peninsula is flat. The importance of the energy due to the sea-land decre ases as the mountain height of the peninsula increases. The energy stored o ver the mountain gains in importance, untill it is released by the readjust ment of the warm mountain air as it prevails over the energy released by th e inland penetration of the sea breeze front. For instance, our results sho w that over a peninsula 100 km wide the energy over the mountain and the en ergy in the sea-land contrast are of the same order when the height of the mountain is about 700 m, for a 1500 m convective boundary layer (CBL) depth . Over the Calabrian peninsula, the energy released by the hot air in the C BL of the mountain prevails over the energy released by the inland penetrat ion of the sea air. Calabria is about 1500 m high and about 50 km wide, and the CBL is of the order of 1500 m. The energy over the mountain is about f our time larger than the energy contained in the sea-land contrast. Further more, the energetics increase with the patch width of the peninsula, and wh en its half width is much less than the Rossby radius, the MAPE of the sea breeze is negligible. When its half width is much larger than the Rossby ra dius, the breezes from the two opposing coastlines do not interact. Over Ca labria peninsula, numerical simulations show that the flow is highly ageost rophic, and that the flow intensity increases from sunrise to reach its max imum in the afternoon but before sunset, which suggests that, in the late p art of the day, the conversion of potential energy into kinetic energy is b alanced by the dissipation.