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Climatology of Cyclogenesis Mechanisms in the Mediterranean

Isabel F. TrigoClimatic Research Unit, University of East Anglia, Norwich, United Kingdom

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Grant R. BiggSchool of Environmental Sciences, University of East Anglia, Norwich, United Kingdom

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Trevor D. DaviesClimatic Research Unit, University of East Anglia, Norwich, United Kingdom

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Abstract

A general climatology of the main mechanisms involved in Mediterranean cyclogenesis is presented. A diagnostic study of both composite means and case studies is performed to analyze processes occurring in different seasons, and in different cyclogenetic regions within the same season. It is shown that cyclones that developed over the three most active areas in winter—the Gulf of Genoa, the Aegean Sea, and the Black Sea—are essentially subsynoptic lows, triggered by the major North Atlantic synoptic systems being affected by local orography and/or low-level baroclinicity over the northern Mediterranean coast. It is also suggested that cyclones in two, or all three, of these regions often occur consecutively, linked to the same synoptic system. In spring and summer, thermally induced lows become progressively more important, despite the existence of other factors, such as the Atlas Mountains contributing to lee cyclogenesis in northern Africa, or the extension of the Asian monsoon into the eastern part of the Mediterranean. As a consequence, the behavior of Mediterranean cyclones becomes modulated by the diurnal forcing; the triggering and mature stages are mostly reached by late afternoon or early nighttime, while cyclolysis tends to occur in early morning.

 Current affiliation: Departamento de Física, Faculdade de Ciências de Lisboa, Lisboa, Portugal.

Corresponding author address: Isabel Franco Trigo, Departamento de Física, Faculdade de Ciências de Lisboa, Campo Grande, Ed. C8, Piso 6, 1749-016 Lisboa, Portugal. Email: iftrigo@fc.ul.pt

Abstract

A general climatology of the main mechanisms involved in Mediterranean cyclogenesis is presented. A diagnostic study of both composite means and case studies is performed to analyze processes occurring in different seasons, and in different cyclogenetic regions within the same season. It is shown that cyclones that developed over the three most active areas in winter—the Gulf of Genoa, the Aegean Sea, and the Black Sea—are essentially subsynoptic lows, triggered by the major North Atlantic synoptic systems being affected by local orography and/or low-level baroclinicity over the northern Mediterranean coast. It is also suggested that cyclones in two, or all three, of these regions often occur consecutively, linked to the same synoptic system. In spring and summer, thermally induced lows become progressively more important, despite the existence of other factors, such as the Atlas Mountains contributing to lee cyclogenesis in northern Africa, or the extension of the Asian monsoon into the eastern part of the Mediterranean. As a consequence, the behavior of Mediterranean cyclones becomes modulated by the diurnal forcing; the triggering and mature stages are mostly reached by late afternoon or early nighttime, while cyclolysis tends to occur in early morning.

 Current affiliation: Departamento de Física, Faculdade de Ciências de Lisboa, Lisboa, Portugal.

Corresponding author address: Isabel Franco Trigo, Departamento de Física, Faculdade de Ciências de Lisboa, Campo Grande, Ed. C8, Piso 6, 1749-016 Lisboa, Portugal. Email: iftrigo@fc.ul.pt

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