Synopsis

I. In the first part the characteristic observational facts are given. Average comfortable winter temperatures, hot summers, and a dry period in summer are the significant features. Cloudiness is little, even in winter, in the rainy period.

II. The physical explanation is based on the pressure distribution and the main streamlines of the air. In winter, a “lake of low pressure” above the Mediterranean Sea caused by the warm surface water is embedded in the huge region of high pressure from the center of action at the Azores reaching to the continental high pressure. The warm sea intensifies cyclones invading from the Atlantic and gives rise to cyclones in the three parts of the Mediterranean Sea: the Gulf of Lyon, the Adriatic Sea, and the Cyprus region. The first and the last and Northwest Africa as well, are regions of convergence, as is seen from the streamlines of January.

In summer the well developed west-to-east pressure gradient causes three main currents directed toward the Persian Gulf. The northern and southern currents, over the high pressure areas of the cool Black Sea and the Mediterranean, respectively, are lines of divergence; the middle current over the heated south European lands is one of convergence. The important wind systems are indicated by this representation. The rainlessness during summer in the southern and eastern portions of the basin finds its explanation in the wind systems, on the one hand, and in the stability of the atmosphere caused by thermal conditions, on the other hand.

III. In the last part important local climatic features are presented: excessive rains in the desert; the bora and other cold winds; winter easterlies of Palestine; peaks of temperature; great daily ranges of temperature in the deserts; and the airmass analysis of the sirocco.

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