| چکیده انگلیسی مقاله |
The occurrence of persistent rainfall, resulting from the integration of multi-scale cyclonic systems, is prone to producing heavy to severe precipitation. Therefore, it is highly significant due to its potential to cause disasters such as floods and landslides, as well as its importance in water resource management for agricultural purposes. In this study, persistent rainfall refers to rainfall events lasting at least three consecutive days with a total precipitation of more than 1 millimeter. The aim of this research is to identify and classify these types of rainfall for the western region of Iran over a 30-year statistical period (1993 to 2022) for the first time using the Lamb-Jenkinson method. In this method, the central coordinates of the study area are used as the reference point in the calculations. Sixteen additional points are also determined around the reference point. With the availability of instantaneous standard sea-level pressure data for these points, it becomes possible to calculate the values of geostrophic wind and vorticity. By comparing these two quantities, the types of weather patterns in the L-J method—which include four types: directional, cyclonic, hybrid, and undefined—are identified and categorized. Disregarding the undefined category, it was ultimately determined that the provinces of Kermanshah, Kurdistan, Hamedan, Lorestan, and Ilam each had 50, 50, 50, 40, and 39 occurrences of the directional state, respectively. Moreover, the frequencies of the cyclonic state for these provinces were 69, 94, 65, 66, and 38, respectively, with cyclonic rotation percentages of 100%, 98%, 97%, 95%, and 97%, respectively. As for the hybrid state, the frequencies obtained for each province were 49, 53, 43, 41, and 38, respectively.
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