Climatology
Mohsen Armesh; Mahmood khosravi; Mohammad Saligheh
Volume 22, Issue 65 , November 2018, , Pages 45-62
Abstract
This study aimed to evaluate the variability of summer precipitation in the South East of Iran was selected stations and the precipitation associated was investigated with IOD index. For this purpose was used weekly precipitation data from June to September stations of Zahedan, Kerman, Bandar Abbas, ...
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This study aimed to evaluate the variability of summer precipitation in the South East of Iran was selected stations and the precipitation associated was investigated with IOD index. For this purpose was used weekly precipitation data from June to September stations of Zahedan, Kerman, Bandar Abbas, Iranshahr and Bam and weekly IOD index data. The method of this study is the correlation coefficient and discrete wavelet analysis. The results showed that in the positive phase of the IOD Index, warm air and humid of West Africa, sucked by low pressure the Persian Gulf and Pakistan and conditions creates convection in southeast of Iran, while IOD negative phase, in addition to shiftting the intertropical Convergence Zone, low pressure Persian Gulf and Pakistan are gone and West Indian Ocean for cooling than normal, stable atmosphere reigns. Summer precipitation correlation analysis between Bandar Abbas and Iranshahr with IOD index showed the strongest association. After the precipitation signal analysis of the stations showed of the Zahedan station on Level 4 and 3, respectively, at 99 and 95% was related to IOD index. The following series Kerman and Bam precipitation did not show any relationship with IOD index. Data analysis by the discrete wavelet transform showed that the most important cycle repeating 11-year occurred in the IOD index. Zahedan and Iranshahr showed periodic cycles relatively similarly. In Kerman was appeared 7-year cycle dominant and in Bandar Abbas and Bam the 11-year cycle. The process of reducing the number of weeks along with summer precipitation in the form of stations is contrary to the IOD index. But the increased intensity of precipitation stations is directly related to this index. Also Bandar Abbas, Iranshahr and Zahedan have more balanced precipitation cycles, but summer precipitation anomalies are intense in Kerman and Bam.
Climatology
Peyman Mahmoudi; Mahmood Khosravi; Seyed Abolfazl Masoodian; Bahlol Alijani
Volume 19, Issue 54 , February 2016, , Pages 303-327
Abstract
To identify and detect the frequency variation trend of Iran’s pervasive and semi-pervasive frost days in the current research, minimal daily temperature data of 663 Iranian climatology and synoptic stations were acquired from Iran Meteorology Organization during the time interval between 1962 ...
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To identify and detect the frequency variation trend of Iran’s pervasive and semi-pervasive frost days in the current research, minimal daily temperature data of 663 Iranian climatology and synoptic stations were acquired from Iran Meteorology Organization during the time interval between 1962 and 2004 for October to April months. Following data acquisition, Iran’s isothermal maps for each day starting from 1.1.1962 until 31.12.2004 (9116 days) were prepared using Kirging interpolation technique in order to construct the database of the county’s minimal temperature. In the next step, frosts were classified in three types based on a spatial principle: pervasive frosts (simultaneous occurrence in more than 65% of Iran’s surface area), semi-pervasive frosts (simultaneous occurrence in 25% - 65% of Iran’s surface area), and local frosts (simultaneous occurrence in less than 25% of Iran’s surface area). Then, frequency of pervasive and semi-pervasive frost days were analyzed in three scales including monthly, seasonal, and yearly using two estimation techniques of slope SENSE and linear regression.
Results indicated that frequency of pervasive frosts in Iran held a statistically significant decreasing trend in December and January months, during winter, and also, in annual basis. But, for semi-pervasive frost days, it was observed that variation was significant only in January having a positive trend. It signifies that number of days with semi-pervasive frost increased during the 43 years under study. Therefore, number of semi-pervasive frost occurrences increased while number of pervasive frost occurrences decreased in January. The same rule holds for other scales i.e. monthly, seasonal, and yearly basis.
