ABSTRACT
The general patterns of climate in the Mediterranean are controlled by its location in relation to the general circulation patterns of the Earth’s atmosphere. On the largest scale, the climate is controlled by the location of the subtropical high. During the summer months, the Azores anticyclone is typically well established to the west or north-west of the Iberian peninsula, leading to the blocking of frontal systems from the Atlantic. To the south, the low-pressure zone associated with the northward migration of the inter-tropical convergence zone (ITCZ) borders the region from the Sahara to central Asia (Barry and Chorley, 1992; Figure 3.1a). At this time, circulation in the Mediterranean is dominated by two main forms (Dayan and Miller, 1989). In the first (Figure 3.1b), high-pressure zones over central Europe and the west coast of Africa combined with low pressures over northern Europe and northern Africa lead to the development of a high-pressure trough over the Mediterranean, with regional easterly wind patterns dominating. The second type is characterized by a high-pressure cell in the central part of the basin (Figure 3.1c) leading to westerly winds in the north and easterlies in the south of the basin, although northerly winds dominate the Aegean. These patterns can also occur in the winter, when they are responsible for producing foggy conditions (Conte and Colacino, 1995). Depressions that do form in the summer tend to be weak because the regional anticyclonic activity encourages subsidence of air masses. However, weakening of the highs over North Africa can lead to the enhancement of convective activity over the eastern Mediterranean Basin (Kutiel and Kay, 1992). Thermal lows, due to intense daytime heating of land masses can occur in the summer over the Iberian and Anatolian peninsulas, but these produce little rainfall as the relative humidity of the atmosphere is low (Barry and Chorley, 1992; Martyn, 1992).
