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Title

A SURVEY OF CYCLONE ACTIVITY OVER IRAN IN 1996

Author(s)

MASOODIAN S.A. | RASTI M.

Pages

  179-196

Abstract

 The climate variability in the mid altitudes, on the daily basis, is related to the movement of cyclone and anti-cyclone systems. Cyclones on the Earth are mainly resulted from baroclinic waves in middle and lower levels. The first studies identified the major role of cyclones in synoptic variability which have manually determined cyclones, their routs (Lagrangian approach) and their spatial variability (Eulerian approach). The study of structure, behavior, dynamic and synoptic conditions, movement rout and effects of these cyclones are especially important from their reinforcement till their movement towards the Middle East and IRAN. In the recent study, using these two approaches, digital and computerized techniques besides theoretical viewpoints, cyclonic actions of the year 1996 in levels of 1000,925,850, 700, 600,500 HP have been investigated. In this study, NCEP reanalyzed data with temporal resolution of 6 hours and 2.5×2.5 spatial resolution degree arc was used within the studied area of 30 W to 80 E and from 0 to 80 N. The results showed that the highest annual frequency of cyclone occurrences is with level of 500 and the lowest one is with level of 700 hpa Moreover, the study showed that the highest frequency of cyclone occurrences with respect to seasonal distribution respectively belonged to winter, autumn, spring and summer. It is also showed that the origin of most cyclones is out of IRAN and the results indicated that those cyclones reaching IRAN or around it often follow three main routs: 1- west route: Mediterranean region and Atlas Mountains 2- North North-West route: Alp Mountains, Black Sea and Caucasus Mountains, 3-South-West–North-East route. The geopotential gradient shows that in all selected levels the number of strong (weak) cyclones with high (low) gradient is decreased exponentially.

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