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(texte français: cliquez ici)   Meteorological explanation


How to explain the characteristic frequency of squalls in Aeolus' kingdom, the Lipari Islands ? Thermal breezes or contrary winds ?
Winds of Lipari islands
Aeolus' kingdom
3 Squall phenomenon
4 Extract from ship's log
5 Signs of squall
6 Meteorological explanation
7 Weather prediction
Stakes of weather prediction
Metsat analysis, 12TH september 1999.
Let us consider, for example, the day of September 12. 1999 mentioned above. First of all, the synoptic situation at 6 hours UTC shows an area of slightly low pressure centered on Sicily, qualified as "shallow depression", propitious to local meteorological phenomena. Moreover, according to our observations, strong ascending currents are forming over the continental coast. One can assume that they will produce a sea breeze whose influence may extend beyond the Lipari archipelago since the wind there blows towards the continental coast (west wind). Insolation is such that clouds develop and form cumulo-nimbus. In the evening, as the breeze effect disappears and the prevailing south-east wind rises again, these thunderclouds are driven to the islands were they cause the famous squall. It is interesting that the satellite analysis of September 12. 1999 confirmed the presence of these local thunderstorms.
From a temporal point of view the observed chronology confirms this hypothesis : ascending currents in the afternoon, clouds progressively extending into cumulo-nimbus, east wind rising again in the late afternoon when the breeze drops, squall breaking at about 8 p.m. for a short time, since clouds are just passing over the archiopelago. From a spatial point of view, on the contrary, the situation observed verifies this hypothesis but reveals a strong phenomenon, as already suggested by the progressive formation of cumulo-nimbus. Moreover, the Lipari Islands are located some 30 or 40 miles off the continental coast and the west wind observed in the islands suggests a thermal breeze extent that is typical of tropical zones. This could be due to the large vertical extent of the ascending currents indicated by the formation of cumulo-nimbus clouds. In addition, according to the direction of the smokes issuing from the volcano that culminates at 1000 meters the width of this breeze is still important at this distance. A so wide limit layer is however quite possible. next
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