Showing 25 results for Alijani
Sahar Afiati, Bohloul Alijani, Sayyed Mohammad Hosseini,
Volume 11, Issue 1 (5-2024)
Abstract
Cold and frost are one of the climatic hazards that cause damage to various activities every year. Climate change, on the other hand, causes spatial and temporal changes in glaciation. The purpose of this study is to analyze the temporal-spatial changes and predict the future of glaciers in Hamadan province. CanESM2 model was used to predict the minimum daily temperature in the province. Data mining of general circulation models was Downscaling using LARS-WG model. The above parameters were simulated for a period of 30 years (2050-2021) under three scenarios RCP2.6, RCP4.5 and RCP8.5 for selected stations. The results of the monthly minimum temperature survey in the study stations of the province showed that the minimum temperature in the period (2050-2021) in all studied stations according to all three scenarios will increase in all months of the year compared to the base period. The average minimum temperature of the province is equal to 2.5 degrees Celsius, which in the coming decades based on the scenarios of RCP2.6, RCP4.5 and RCP8.5 will reach 6, 6.2 and 6.3 degrees Celsius, respectively, which is the highest The changes are related to Nojeh station and the lowest is related to Hamedan. The spatial distribution of the beginning and end of freezing in the future period indicates that freezing in the northeastern and northern parts of the province starts earlier and ends later than in other parts of the province, while in the southern parts of the province it starts later and ends earlier. The results of examining the changes in the onset of frost in the next decade compared to the base period showed that in all stations studied the onset of frost will decrease between 3 to 11 days.
Ms Vahideh Sayad, Doctor Bohloul Alijani, Doctor Zahra Hejazizadeh,
Volume 11, Issue 2 (8-2024)
Abstract
Iran is a country with low rainfall and high-intensity rainfall that is affected by various synoptic systems, the most important of these systems is Sudan low pressure, Therefore, recognizing the low pressures of the Sudan region is of particular importance, The purpose of this study is to gather a complete and comprehensive knowledge of the set of studies conducted about this low pressure, structure and formation and its effects on the surrounding climate. The present study was conducted using the library method and a search for authoritative scientific and research sources in connection with research on low pressure in Sudan and no data processing was performed in it. Thus, it has studied and analyzed the temporal and spatial changes of Sudan's low pressure over several years and its effect on the climate of the surrounding areas, especially Iran. In general, the results of this study can be divided into several categories, including studies on the recognition and study of Sudan low pressure, its structure and formation over time, pressure patterns affecting it at different atmospheric levels, and its effects on the climate of surrounding areas, especially Iran. Has been studied, The effect of this low pressure on seasonal and spring rainfall in Iran, snow and hail, floods, thunderstorms and also the effect of remote connection patterns on this low-pressure system have been studied, and finally, the analysis of these findings has been studied. It can be concluded that the Sudanese low-pressure system is a Low-pressure reverse in the region of Northeast Africa and southwest of the Middle East, which is strengthened and displaced in the upper levels of the Mediterranean and Subtropical jet stream and in the lower surface moisture injection from the Arabian Sea and Oman through high pressure. Saudi Arabia is inwardly the cause of severe instability in Iran and a major cause of heavy rainfall in various parts of the country.
- Mahmoud Roshani, - Mohammad Saligheh, - Bohlol Alijani, - Zahra Begum Hejazizadeh,
Volume 12, Issue 1 (8-2025)
Abstract
In this study, the synoptic patterns of the warm period of the year that lead to the cessation of rainfall and the creation of short to long dry spells were identified and analyzed. For this purpose, the rainfall data of 8 synoptic stations were used to identify the dry spells of the warm season for 30 years (1986 to 2015). The average daily rainfall of each station was used as the threshold value to distinguish between wet and dry spells. Then, according to the effects of dry spells, they were defined subjectively and objectively with different durations. Thus, 5 numerical periods of 12 to 15, 15 to 30, 30 to 45, 45 to 60 and more than 60 days were identified. By factor analysis of Geopotential height data at 500 hPa, 4 components were identified for each period and a total of 20 components for 5 dry spells. Therefore, 5 common patterns control the stable weather conditions of dry spells. Most dry days are caused by subtropical high-pressure nuclei, which have a wide, even, dual-core, triple-core arrangement. The effect of subtropical high pressure on the dryness of the southern coast of the Caspian Sea is quite evident. Other dry days were caused by southerly currents, weakening of northern currents, and the trough Anticyclones’ area. Also, the anomaly map of the components days at the 500 hPa level showed that the anticyclones and cyclones correspond to the positive and negative phases of the anomalies, respectively.
Dr Nabi Mirzaei, Dr Bouhlul Alijani, Dr Mohamad Darand,
Volume 12, Issue 3 (12-2025)
Abstract
subtropical high pressure (STHP) and Mediterranean cyclone are among the most important synoptic systems affecting Iran's climate. In this study, the effect of the high altitude location of the sthp on the Mediterranean gyres during the droughts and wetness of Iran during 1979 to 2020 was analyzed. In this regard, two datasets were used. Station data were used to identify drought and wetness periods, and ECMWF-ERA5 grid data was used to identify the location of high pressure in the subtropical region. The results showed that STHP with 3 anticyclone cells (ridge) affects the position of atmospheric waves affecting Iran's rainfall. The STHP system, especially the Arabian Subtropical anticyclone (ASA) and North Africa, play a more important role in the location of the cyclone affecting Iran's rainfall, so that widespread droughts with the expansion of the ASA to the west and its integration with the African anticyclone, the lack of expansion of the Mediterranean trough to the sea Redness and reduction of Sudan low and Mediterranean integration systems occur. With the eastward movement of the ASA over the Arabian Sea and the northern Indian Ocean, the Mediterranean trough deepens and the amount of waves and consequently the rainfall of the country increases. Therefore, the eastward expansion of the Arabian Peninsula and the strengthening of the North African Ridge provide the conditions for the expansion of the Mediterranean Sea. Whenever the ASA is located in its easternmost position on the Oman Sea and the Arabian Sea, it will lead to the advection of moisture for Iran through the access to the large areas of southern water and eventually rainfall. The main cause of the occurrence of drought and wetness in Iran is the spatial variations of atmospheric waves due to the spatial variations in the ASA.
Sharifeh Zarei, Bohloul Alijani, Zahra Hejazizadeh, Bakhtiar Mohammadi,
Volume 13, Issue 1 (7-2026)
Abstract
In this research, the most important synoptic patterns of widespread snowfall in the western half of Iran have been investigated. For this purpose, the data of current weather code and snow depth of 36 synoptic stations during the statistical period of 1371-1400, for the months of October to March, were received from the Meteorological Organization of the country. In order to investigate wide snowfalls, the days when more than 70% of the studied area saw snowfall at the same time were extracted as a wide day. In order to perform synoptic-dynamic analysis of wide snowfalls in the western half of Iran, the classification method using cluster analysis was used and maps of representative days were drawn, including atmospheric temperature, moisture flux, geopotential height, tovai, front formation, jet stream, omega index, and orbital and meridian wind data. Trend analysis was also performed using the Mann-Kendall test. The results showed that 4 models justify the widespread snowfall in the studied area in the best way. According to the results in all the models, at sea level, the collision of cold and dry air of northern latitudes with warm and humid air of southern latitudes has caused the formation of frontal fields in the western half of Iran. At the level of 500 hectopascals, the intensification of the meridional currents in the western winds caused the creation of closed centers and as a result the flow changed in the direction of the westerly winds, and the location of the western half of Iran in the east of Naveh Al-Aghti and Sardchal has provided the necessary conditions for air to rise. Also, there was no trend in the number of snow days in the western half of Iran at the significant levels tested. But; The number of snow days has been decreasing over time. In general, it can be concluded that due to the warming of the earth and climate change, the number of snowy days has decreased and these changes have led to a significant shortening of the snow season.
