اقليم‌شناسي رخدادهاي توفان گردوخاك در فصل تابستان در استان سيستان و بلوچستان در دوره 30 ساله (2016-1987)

Dust Storm Climatology in Sistan and Baluchestan Province over a 30-year period (1987-2016)

شدت و فراواني رخدادهاي توفان گردوخاك در استان سيستان و بلوچستان در فصل تابستان (ژوئن، ژوئيه و اوت) با تغيير در گردش‌هاي بزرگ‌مقياس جوي تغيير مي‌كند. به‌منظور بررسي گردش‌هاي بزرگ‌مقياس جوي با استفاده از داده‌هاي باز تحليل‌شده NCEP/NCAR شاخص موسمي هند و شاخص اقليمي كاسپين-هندوكش براي بازه زماني 30 ساله (2016-1987) در فصل تابستان محاسبه شده است. نتايج نشان داد كه شدت شاخص موسمي هند در طي اين دوره كاهش پيدا كرده و بر شدت شاخص كاسپين-هندوكش افزوده شده كه سبب تقويت جريان‌هاي شمالي در مرزهاي شرقي ايران و غرب افغانستان شده‌اند؛ از طرفي شاخص‌ توفان گردوخاك كه با استفاده از داده‌هاي ديدباني ايستگاه‌هاي هواشناسي اين استان محاسبه شد، روند معني‌داري در اين بازه زماني نشان نداد. همچنين با بررسي مقادير بيشينه يا كمينه شاخص‌هاي يادشده در سال‌هاي بحراني مشاهده شد كه مقادير بيشينه/كمينه شاخص توفان گردوخاك با بيشينه /كمينه شاخص كاسپين-هندوكش و كمينه/ بيشينه شاخص موسمي هند منطبق است.

This paper investigates the climatological changes of summer dust storm events over 30 years (1987 -2016) in Sistan and Baluchestan province in the southeast of Iran and their relation to large scale atmospheric circulation. The Dust Storm Index (DSI) was calculated for the five selected meteorological stations in Sistan and Baluchestan province. Moreover, the Indian Monsoon Index, as a large-scale atmospheric circulation in the summer and the Caspian-Hindu Kush index were calculated using the re-analyzed data from the National Center for Environmental Prediction and Atmospheric Research (NCEP / NCAR) with a horizontal resolution of 2.5 degrees. The results showed that during the mentioned period, the Indian monsoon experienced a significant decrease, while the Caspian-Hindu Kush index showed a significant upward trend indicating an increase of the sea level pressure difference between the Caspian Sea and the Hindu Kush Mountains, resulting in strengthening the north-south pressure gradient and wind speeds on the eastern borders of Iran and western Afghanistan. However, the dust storm index over the past15 years has declined significantly. In the next step, the correlation coefficients of the Indian Monsoon Index and the Caspian-Hindu Kush index were calculated by the Pearson method. Regarding the increase in the Caspian-Hindu Kush index, temperature has increased, while relative humidity has decreased in the most stations of the province. Surveys showed that in the summer of 1988 when the lowest amount of the Caspian-Hindu Kush index was calculated, the frequency of dust events at the Zabol station was lower than the long-term average, but the Indian monsoon occurred at intensity greater than the 30-year average., While in 2001, the highest incidence of dust storms was recorded in Sistan and Baluchistan province, especially in Zabol station. This year, both the Indian Monsoon Index and the Caspian-Hindu Kush index were higher than the long-term average, leading to dust genesis by strengthening northern currents and reducing relative humidity in this year.