Abstract
Meteorological and thermodynamic factors associated with catastrophic flood events affecting the West Mediterranean Area have been studied. First of all, the usually assumed causal connection between cut-off lows aloft and severe storms has been thoroughly investigated. Once identified the general meteorological features, the synoptic- scale pattern and forcing are studied by using objective techniques. The thermodynamic analysis took specific form in the study of stability, precipitable water mass, convective available potential energy, vertical wind shear and bulk Richardson number. The combination of the synoptic and thermodynamic results show a strong quasi-geostrophic forcing for vertical motion at low levels while only a weak forcing at 500 hPa, high values of precipitable water mass produced by a strong convergence of water vapour near surface and convective and latent instability. Composite charts delineating the area covered by each of the indicated factors seem to be an effective tool for delimiting the are where mesoscale focusing mechanisms become effective.
Sommario
Sono stati studiati i fattori meteorologici e termodinamici associati ad eventi catastrofici di piena nell' Area Mediterranea Occidentale. Prima di tutto, la connessione fra depressioni in alta quota e temporali intensi, usualmente assunta come casuale, è stata esaurientemente investigata. Una volta identificati gli aspetti meteorologici generali, le strutture e le forzanti alla scala sinottica sono studiate usando tecniche oggettive. L'analisi termodinamica ha assunto la forma specifica nello studio della stabilità, della massa d'acqua precipitabile, dell' energia potenziale disponibile alla convenzione, del gradiente verticale di vento e del numero di Richardson. La combinazione dei risultati sinottici e termodinamici mostra una forte forzante quasi-geostrofica per lo spostamento verticale ai bassi livelli mentre la forzante a 500 hPa è debole, alti valori di massa d'acqua precipitabile prodotti da una forte convergenza di vapore d'acqua vicino alla superficie e instabilità convettiva e latente. Le carte composite che delineano l'area coperta da ciascuno dei fattori indicati sembrano essere uno strumento efficace per la delimitazione dell'area dove i meccanismi di concentrazione alla meso-scala diventano efficaci.
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LLasat, M.C., Barrantes, J. Catastrophic rainfalls in the West Mediterranean area. Meccanica 31, 397–406 (1996). https://doi.org/10.1007/BF00429928
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DOI: https://doi.org/10.1007/BF00429928