جستجوی مقالات مرتبط با کلیدواژه « extreme rainfall » در نشریات گروه « جغرافیا »

In recent years, attention has been paid to climate change, which could be the result of economic, social, and financial losses associated with extreme weather events. The purpose of this study is to investigate the variation of extreme temperature and precipitation in Kurdistan province. For this purpose, daily rainfall data, minimum temperature and maximum temperature of 6 stations were used during the statistical period (1990-1990). And their changes during the period (2041-2060) using the universal HadGEM2 model under two scenarios RCP2.6 and RCP8.5 and the LARS-WG6 statistical downscaling were investigated. In order to study the trend of climatic extreme indexes, rainfall and temperature indices were analyzed using RClimdex software. The results showed that during the period (2016-1990), hot extreme indicators have a positive and incremental trend. This trend is significant for the "number of summer days" and "maximum monthly of maximum daily temperature" indicators. This is while the cold extreme indexes had a decreasing and negative trend. This trend was significant only for the "cold days" index. Extreme precipitation in Kurdistan province has a negative trend in most stations. ،this trend is significant at most stations, that indicates a reduction in the severity, duration and frequency of precipitation during the study period. The results of the climate change outlook also indicate that the temperature will increase over the next period and rainfall will decrease.

In all air maps, without exception, belts or wind straps are seen at high speeds that extend over very long distances. According to the World Meteorological Organization, if the velocities of these velocities are more than 30 meters per second, the flow of the Jet stream is created (Alijani & Kaviani, 2000). However, jet stream is referred to the extreme horizontal winds at speeds exceeding 50 knots or about 26 m/s above the planet's winds. Since the geographical distribution of rainfall intensity on a planetary scale, in addition to system pressure patterns, seating tropical convergence belt, ocean currents affect the make-up jet stream, position and expand them as well. In this paper, an attempt has been made to identify a process of effective factors in the occurrence of storms in order to optimize the use of these rainfall in the study area. In other words, the purpose of this article is to determine the position and frequency of the storms and their average velocity during the storm events of Armand basin.

Essentially, in every ongoing study, there is a need for two databases; one for the environmental event database (surface), and another for the atmospheric database that identifies how atmospheric flows are. First, the daily precipitation data of the synoptic stations of Chaharmahal and Bakhtiari province from 1973 to 2004 were selected and prepared as environmental event database. The second group of variables consisted of wind and orbital component data that was used to plot the basins at 250 and 300 hpa. The first and second groups of variables were obtained from the Iranian Meteorological Organization and website www.cdc.noaa.gov.

3.1. The Role of Jet Stream Instability
The core of the jet stream in the context of long and short wave move. the entrance area on the left and the exit area on the right. In fact, based on the circle model, the core of the velocity is drawn into four sections: the right and left inputs of the divergence and the left and right inputs are convergent.
Frequency and average velocity analysis of the Jet Stream at 300 hectares
The large Jet Stream drawings at 300 hectares indicate that in the hours of 00:00 the highest frequency of inflows is observed on Saudi Arabia. There are two abundant small rivers, one on Uzbekistan and another on the north of the Caspian Sea and on Kazakhstan.
Frequency analysis and average velocity flow of 250 hPa
Frequency analysis of jet stream at the level of 250 hpa shows that in the hours of 00:00, the highest frequency of river flows extends from the Red Sea to the Persian Gulf, and south and west of the country. The analysis of average speed of the storms in the synoptic hours in this alignment shows that the average speeds of the storms are more than 40 m/s. The maximum velocity in the territory under question is at 6:00 pm, with its central core at 55 m/s on the Persian Gulf, Saudi Arabia and the southwest of the country, which also includes the study area. The mean velocity map for the above hour, which corresponds to the maximum occurrence of coincidences and coincidence with their maximum velocity occurrences in the study area, indicates that the fourth quarter (which is associated with positive precipitation increase as well as upper surface divergence and convergence of low atmospheric levels) is located on the study area. This can lead to high-level air mass expansion or upward movement. This seems to provide the necessary basis for the occurrence of instability at the time of flood and basin storms in the area under discussion.

The abundance analysis of the riverbeds at the 250-hp level revealed that over the hours of 00:00, 06:00, 12:00 and 18:00, the abundance of the riverbeds has spread over Saudi Arabia to the Persian Gulf, the center and west of the country In other words, in this area more than 50% of the formation and establishment of the jet stream.. During the four hours of the occurrence of synoptic atmospheric jet streams this level only based on the maximum frequency of the jet stream jet stream At 06:00, the range expanded under the influence of jet streams and jet streams while a wide range of western and southern half of Iran are obvious especially in the southwestern and southern parts of Iran. The most frequent occurrence of the river is the same hour, with the western zone of the country which is more than 60% consistent. The study of riverbed frequencies at 300 hPa level also indicated that the inflow of the Jet Stream in the four-hour significantly reduced compared to the higher levels.