جستجوی مقالات مرتبط با کلیدواژه « بارش شدید » در نشریات گروه « هواشناسی »

the events of extremum rainfall in northeastern Iran during the last 20 years (2021-2000) have been studied using rainfall indexes. For this purpose, data from synoptic meteorological stations of Mashhad, Sabzevar, Quchan, Neishabour, Bojnourd and Gonbad Kavous were used and Atmospheric patterns leading to these extremum events and the trend of extreme indexes were investigated using linear regression. The results showed that in all stations studied, highest standard deviation for all extreme indices was related to Gonbad Kavous station, which indicates the higher probability of unconventional rainfall for this station. The highest frequency distribution index of number of very heavy precipitation days (R20mm) in the statistical period and in the seasonal period with 37.4% frequency belongs to winter and in the monthly period with 19.3% frequency belongs to March. Synoptic analysis of heavy rainfall in the northeastern region of the country, mean sea level pressure maps, geopotential elevation and wind field maps at 850 hPa, omega pattern at 700 hPa and specific moisture distribution pattern at 850 and 700 hPa were used. The results showed that the most important feature of large-scale patterns leading to extreme rainfall is their high persistence in the eastern part of the Mediterranean. These blocking patterns are accompanied by the deployment of a low pressure system on the ground and the middle and upper levels of troposphere, which includes rising speeds in the lower levels of troposphere and adequate moisture supply from sources from the Sea of Oman, the Red Sea and the Persian Gulf.

The application of the RegCM4 dynamic model has enabled the study of mesoscale and regional scale atmospheric phenomena in different regions. Heavy precipitation is one of the essential atmospheric phenomena critical for agriculture in arid regions. Optimal use of rainwater increases water resources in the arid region. One of the solutions for optimal use of water in arid climate is to utilize crop pattern. The crop pattern means the share of cropping and selection of crops in an area, employing the optimal cropping pattern as one of the important solutions to water efficiency in agriculture. In this research, various data including rainfall data, NCEP/NCAR, TRMM satellite model, RegCM4 regional climate model, Aphrodite, and finally, agricultural data were used to change the cropping pattern for optimum use of water. Then, 5% precipitation threshold method was used to investigate heavy rainfall and selected as a representative of heavy rainfall in the study area on March 14th. The seasonal rainfall percentile chart, heavy rainfall maps and rainfall zones and performance of crops were then prepared and analyzed. The results indicate that the percentage of seasonal precipitation is in ascending and descending order in spring and winter, respectively. According to the regression model, Birjand, Nehbandan, and Ghayen stations are suitable in spring, and Ferdows and Boshrouyeh stations in winter. Moreover, the intensity of atmospheric streams in NCEP/NCAR and TRMM model maps gradually in northeast and east areas especially south Khorasan has led to heavy rainfall that RegCM4 model has been able to significantly simulate it and this rainfall has considerable values. Humidity values have increased on CAPE and thermodynamic graphs. Furthermore, in the zoning maps in the output of the observation map on Birjand station, Birjand, Ghayen, and Nehabandan, with the highest rainfall show better agricultural performance, while Boshrouyeh and Ferdows stations have the lowest performance. Therefore, since crop performance is directly related to rainfall, heavy rainfall can improve in agricultural in South Khorasan as a dry climate province. One way to deal with low-water resources in arid climates is to use crops such as Jujube, Barberry, and Saffron that are less water-intensive in agriculture and more adaptable to climate and regional conditions than other crops. Therefore, with proper use of rainwater during heavy rainfall in low-lying areas, the performance of agricultural products will greatly improve in South Khorasan province.