A 40 year objective climatology of surface cyclones in the Mediterranean region: spatial and temporal distribution

TLDR

The study conducts a 40‑year climatological analysis of synoptic‑scale cyclones in the Mediterranean region (1958–1997). Cyclones were identified using an objective 6‑hourly grid‑point method, and their seasonal and diurnal frequency variations relative to central pressure were examined to reveal differing triggering mechanisms. Results show higher winter cyclone frequency in the western Mediterranean, diurnal differences in the Gulf of Genoa and nighttime preference in southern Italy, cold‑period location shifts around Cyprus linked to weak/moderate cyclones, two high‑frequency zones in northwestern Africa across spring to autumn, a summer surge driven by weak thermal lows, and a northward increase in rapid deepening events near the Alps and Gulf of Venice after 06:00 UTC. © 2001 Royal Meteorological Society.

Abstract

Abstract A climatological analysis of the synoptic scale cyclones that occur in the Mediterranean region is carried out for an extended period of 40 years (1958–1997). The cyclones are identified with the aid of an objective method based on grid point values, available every 6 h. The study of the seasonal and diurnal variations of the frequency of cyclonic occurrences, with respect to the value of the central pressure, revealed that the major cyclonic centres appear to be different in frequency and location, reflecting the different triggering mechanisms. In the western Mediterranean region, the frequency of occurrence is higher in winter, more so for the intense cyclones, with no substantial diurnal difference in the Gulf of Genoa, and with a preference during the night in southern Italy. The Cyprus centre reveals diurnal variability in location, especially in the cold period, in accordance with the triggering mechanism, being associated principally with weak and moderate cyclones. In northwestern Africa, there appears to be two marked regions of high cyclonic frequency, not only in spring, but also in summer and autumn. The extremely high frequency of cyclonic occurrences in summer in the Mediterranean basin is attributed mainly to the generation of weak thermal lows. The number of rapidly deepening cyclones within 12 h and 24 h increases from the south to the north part of Mediterranean, being mostly favoured near the lee of Alps and the Gulf of Venice, occurring mainly after 06:00 co‐ordinated universal time (UTC). Copyright © 2001 Royal Meteorological Society