From approximately late April to early October the coastal seabreezes, their return flows aloft and their compensatory subsidences over the Western Mediterranean Basin become Satellite retrieved water vapour column as an indicator of vertical recirculations in the Mediterranean Basin self-organized in vertical recirculations that extend to the whole basin for periods of 3 to 10 days. Thus, in contrast with regions dominated by advection, pollutants and water vapor accumulate over the sea in layers piled up to approximately 5000 m. And, without requiring the high evaporation rates of more tropical latitudes, this mechanism can generate a very large, polluted, moist, and potentially unstable airmass after a few days.

Although the available experimental and modelling evidence on these processes has been accumulating over the years, several questions remain to be answered: (1) are the experimental measurements from one, or several, places in the Mediterranean basin really representative of regional-scale processes? and (2) are the observed high ozone values the result of accumulating recirculations?, or (3) are they the result of long-range transport from North America?

In this presentation we will review the stages involved in developing our understanding of Western Mediterranean atmospheric processes over the years. We will also see how the proposed recirculation mechanisms can be used to re-interpret satellite-based water vapour column measurements and explain their observed day-night cycle over this region.