چکیده:
Weather circulation patterns play a main role in the occurrence of environmental phenomena especially in middle latitude. Occurrence of dry and wet spells is in relation to synoptical system repetitions and types of weather. In this research first by using of Standard Precipitation Index (SPI)، extensive droughts in the province were identified. Then by using Principal Component Analysis (PCA) and Clustering Analysis (CA)، daily circulation patterns in synoptically scale were realized. In order to classify weather types، daily mean temperature data in 500 hPa and in mean sea level pressure were selected from the NCEP/NCAR reanalysis data with a 2.5 spatial resolution during the period of 1950-2006. For identifying type of weather، array S and Varimax Circulation، and for classifying daily weather types K-Mean Clustering method were used. All the days were divided into 18 groups، which present the most predominant weather circulation patterns in the study region. Composite maps of mean sea level pressure and 500 hPa were drawn for every weather types. At the end، dry and wet spells were compared with frequency occurrence of circulation patterns، then rainy weather and dry weather types were identified.
خلاصه ماشینی:
E Consecutive Page Numbers: 17071-17093 Investigation of Synoptic Patterns of Widespread Droughts in Chaharmahal and Bakhtiari Province Abstract {IBAtmospheric circulation patterns play a major role in the occurrence of environmental phenomena; especially in temperate regions, and the occurrence of dry and wet periods is related to the repetition of synoptic systems and weather types.
(2005) also used the ACP method and multi-core clustering to determine the sea level and 500 hPa atmospheric circulation patterns for southwestern Europe and investigated their relationship with heavy snowfalls in the country of Andorra.
Based on the above method, all days during the statistical period 1950-2006 were divided into eighteen groups, which represent the most alternating atmospheric circulation patterns in the study area, and finally, combined maps of sea level pressure and the 500 hPa level were drawn for each of the weather types.
-Circulation Pattern 9PC According to Figure (1), the combined sea level pressure map (Case A) shows a high pressure with a center of 1028 hPa located over Siberia, whose tongue extends to the Black Sea. In the middle atmosphere, two weak troughs are seen, one in the eastern Mediterranean and another in eastern Pakistan and Afghanistan; in this arrangement, the study area and a vast part of Iran are under the influence of the ridge of this pattern, and the establishment of such a situation causes dry and drought conditions for the study area.
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