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Accueil du site → Doctorat → Royaume-Uni → 2006 → Low level jets in the Kingdom of Saudi Arabia : climatology, synoptic analyses and meso-scale modelling

University of East Anglia (2006)

Low level jets in the Kingdom of Saudi Arabia : climatology, synoptic analyses and meso-scale modelling

Sarhan, Naser M. J

Titre : Low level jets in the Kingdom of Saudi Arabia : climatology, synoptic analyses and meso-scale modelling

Auteur : Sarhan, Naser M. J

Université de soutenance : University of East Anglia

Grade : Doctor of Philosophy (PhD) 2006

Résumé
Frequency of LLJ occurrence, geographical an seasonal distributions, and related synoptic circulations were constructed for the first time in Saudi Arabia in order to investigate, interpret and examine the physical mechanisms behind LLJs. This thesis utilises a climatological description of LLJ characteristics employing gridded, six-hourly ERA-40 data over a domain cover Saudi Arabia for the period 1958-2001. The seasonal climatological LLJ frequencies and geographical distributions show that LLJs can occur in any season and at any time of day, however, the strongest cases occur after sunset with the maximum wind speeds and percentages of occurrence at 00.00 GMT in summer. LLJs are a common feature at 925 and 850-hPa over eastern Saudi Arabia and the Persian Gulf, and over western Saudi Arabia and the Red Sea. The highest percentages of nocturnal LLJs occur in the summer season at 925-hPa. Higher percentage frequencies of LLJs generally occur when they are accompanied by local winds, particularly the Khamsin in late autumn and winter at 850-hPa, and the Shamal in the summer at 925 and 850-hPa. Although jet climatology suggests some of the causes of LLJs, meso-scale model simulations (with MM5 V3.6) the domain of Saudi Arabia are undertaken for the first time in order to study this phenomenon further. The simulated case study results show that the major synoptic weather patterns accompanying the formation of LLJ events generally have similar synoptic features to those highlighted by ERA-40. The increasingly finer resolutions in the MM5 simulations are shown to be important, in some cases, in resolving meso-scale features and therefore in accurately simulating LLJs, especially over the more complex terrain

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