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Accueil du site → Doctorat → États-Unis → 1981 → SYNOPTIC ORIGIN OF PRECIPITATION IN IRAN

Michigan State University (1981)





Université de soutenance : Michigan State University

Grade : Doctor of Philosophy (PhD) 1981

This research was undertaken to investigate the spatial and seasonal variations of precipitation mechanisms in Iran. For the period 1965 to 1969, uplift mechanisms associated with precipitation events at 40 different stations across Iran were determined from 12GMT surface and 500mb synoptic maps of the Northern Hemisphere. Importance of the uplift mechanisms was judged on the basis of their contribution to the number of each station’s annual or seasonal precipitation days. Westerly disturbances, including both upper level and surface disturbances, were the most important uplift mechanism over the entire country throughout the year ; their contribution to annual precipitation days was higher in the South and the Northeast but decreased to the north and northwest. Sea-effect was observed only on the southwest coast of the Caspian Sea in fall and early winter. The contribution by surface heating was low. Based on the patterns of contribution by westerly disturbances to annual precipitation days, the country was divided into six different regions. Representative stations of these regions were then used to analyze the seasonal importance of the identified mechanisms as well as the moisture sources of the precipitation. Seasonally, upper level disturbances were the most frequent and important uplift mechanism during the transition seasons but were co-dominant with surface disturbances in winter, whereas summer was the season of greatest contribution by surface heating. Important moisture sources of the country were determined for days with 10mm or more precipitation at the representative stations through the use of both surface and 700mb maps of the period July 1967 through December 1969. Although moisture from the Caspian Sea appeared to contribute the highest percentage to precipitation totals, moisture from the Mediterranean Sea affected a larger portion of the country. Persian Gulf moisture contributed the highest percentage of warm period precipitation days in the relatively dry South ; the southeastern part of the country received most of its summer moisture from the Bay of Bengal

Mots clés : Cartography, Geography, Earth sciences

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Page publiée le 14 février 2015, mise à jour le 11 décembre 2018