Showing 13 results for West of Iran
Rastegar Mohammadi, Mohammad Saligheh, Mohammad Hossein Naserzadeh, Mehri Akbari,
Volume 0, Issue 0 (3-1921)
Abstract
Extratropical cyclones according to the frequency, duration, and intensity, the major cause of mid-and high-latitude precipitation across the Mediterranean during winter and autumn. For this research using network data of ECMWF climatic variables with 6-hour time resolution and 0.25 × 0.25 spatial resolution from1979-2016 and were used of 4 Basin stations precipitation data from the Asfezari database from 1979-2016. The results showed that the first pattern is the Mediterranean trough pattern which has the highest frequency of 42%. In this pattern, the low-level due to the presence of a high-level that acts as a barrier have caused the deepening of the Mediterranean low-level and its axis extends to the Red Sea, and due to the collision of low-level and high-level on the region, instability is intensified and has caused the most rainfall among the patterns. In contrast to the first pattern, The fourth pattern has the lowest frequency of 10% Which is the trough pattern of western winds which is located on the Caspian Sea but due to high-level in the south of the region has prevented the entry of low-level and is located in the northern part of the study area due to this, the isobar in the north of the region have become orbital as a result, fewer cyclones enter the area, resulting in less rainfall between patterns. The results also showed that the frequency of cold-core cyclones was 60% in winter and 40% in autumn, but the frequency of hot core cyclones was 62% in winter and 38% in autumn, which in winter, the frequency of hot core cyclones has increased compared to cold-core cyclones, while in the fall the frequency of hot-core cyclones has decreased compared to cold-core. In the last decade, both the frequency of occurrence of cyclones and their intensity has decreased compared to the last two decades. In terms of cyclogenesis places, the western part of the study area has always been active, And with the onset of the cold season from autumn to winter, cyclogeneses places are gradually becoming more active.
Faramarz Khoshakhlagh, Mohammad Amin Heydary,
Volume 15, Issue 37 (9-2015)
Abstract
Climate control centers in each area are diverse and understanding how they relate to the atmospheric components of the Earth's surface contribute to prediction of climate fluctuations. In this study, by using Pearson's correlation and multivariate regression in a thirty-year period (1961-2010), the relationship between widespread rainfall anomalies in entire of Iran west with temperature and pressure of atmospheric centers in East and West of Mediterranean Sea in 5 atmospheric levels (SLP, 850, 500 and 300 Hpa) were analyzed and modeled. Based on the results, the correlation of atmospheric control centers in the East and West Mediterranean Sea with anomalies of rainfall in West of Iran is inverse and meaningful in 95% level. In this study, statistical indicators such as temperature differences and standardized pressure between West and East Mediterranean sea were identified as the most important indicators in relation to changes of rainfall in the study area. Based on the designed indicators, whenever indicators DT and DH is positive, this means higher temperature and higher atmospheric standardized pressure in the Western parts of Mediterranean sea in compare with its East and therefore the wet spells (Monthly) occur in the study area, and If the above mentioned index is negative, means that the occurrence of drought in West Iran. As for the indicators introduced for lower levels of the atmosphere, especially in the case of temperature, meaningful strong and direct correlation is seen with rainfall abnormalities in entire West of Iran. Modeling provided some indicator for Mediterranean region using multivariate regression that they showed a relatively strong correlation in this regard of the selected components that include the pressure difference in sea level, the temperature difference in 925 and 850 hPa level in the West (Compared to its East) Mediterranean sea. Also check the regression model using real data confirm the accuracy of the relative performance of the model.
Yousouf Ghavidel Rahimi, Manochehr Farajzadeh Asl, Solmaz Motalebizad,
Volume 16, Issue 40 (3-2016)
Abstract
This study tries to identify, classify, and analyze synoptic cold wave in North West region of Iran. This study applies standardized (z scores) index of Minimum Temperature in the period of 1951-2010.as such cold waves were classified based on the intensity of occurance. Out of occured cold wave in North West of the coldest identified wave pertaingt each class for synoptic analyzes were selected. This study suggests that the prevailing pressure pattern during the relevant wave indicates high pressure over the earth surface as well as deep trough in upper layer. From the continuing cold standpoint, the role of changing position from pavallel wind in to meridional corresponel to blocking is very offective. Blocking in turn leads to reduction in speed of cold air masses which are originating from higher latitude. They were assouclated with cold waves. More precipitation as so ciated with higher latitude as well as low speed flows will lead to strong and continious waves.
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Volume 16, Issue 42 (9-2016)
Abstract
In Iran the issue of occurring natural disasters, particularly mesoscale convective systems. They are important on one hand, because of their increasing intimidations and causing damages and on the other hand, because of their increasing abundance, time of duration, and happening. Therefore life cycle, constituton condition and mesoscale convective systems features in west of Iran using satellite and extention area index and thresholds of brightness temperature 221 and 243 K have been studied. After their statistic analysis, based on mesoscale convective system importance, life and daily cycle, behavior parameters, and synoptic conditions of this system life cycle were analysed. Most of the systems have been formed in southeastern Iraq and in western Zagros hillsides. Wile puberty stages (the maturity) and their expandings were increased with the height increase; in turn, declining of the systems began by passing Zagros chain mountains. The system extention area at the system life cycle starting increases with a smooth process; whereas the reduction process of the system extention area at the declining stage was severe and sudden.
Hasan Zolfaghari, Jafar Masoompourv Samakosh, Shabnam Chahvari,
Volume 18, Issue 49 (3-2018)
Abstract
The purpose of this study is predicting climate changes and investigating the effect of probable climate change on the growing degree-days in the northwest of Iran. For this purpose the climatic data of seven synoptic stations during a 25 years period (1985-2009) was collected including Oroomieh, Tabriz, Zanjan, Sanandaj, Ghazvin, Kermanshah, and Hamedan were used as the base period and thus temperature variations periods (2030-2011 and 2065-2046) through HadCM3 model was simulated. For the little power of temporal and spatial distinction of this model, its outputs were downscaled using LARS-WG software and presented under Emission Scenarios including A1B (moderate scenario), A2 (maximum or pessimistic scenario), and B1 (minimum or optimistic scenario). Calibration, verification and Performance Model with the rate of the adaption of observed data and the simulated measures through statistics , RMSE and MAE were analyzed. Finally, using the simulated temperature growing degree-day was calculated and compared under 4 Base temperature including 0°,5°,10°, and 15° centigrade in the basic span (1985-2009) and future span (2011-2030 and 2046-2065). The results of simulation show that temperature change in north-west areas under all three A1B, A2, and B1 scenario are increasing in the future, but the differences among these three scenarios in each period is inconsiderable. In total the most temperature increasing was detected as 0/7 centigrade in A2 scenario for 2011-2030 period and 2/3 centigrade under A1B scenario for 2046-2065 period. Generally with the temperature increasing, the amounts of growing degree-day without exception increases in review periods and under the four Base temperature. Under studied scenarios, the Bases temperature of 0° centigrade had the most and 15° centigrade had the least impressibility from climate changes, so that the most increasing in calculated degree-day measures under 0° and 15° centigrade bases in the first period to the basic scenario (1985-2009) respectively was simulated as 207/4 and 120/6 degree-day under A2 scenario and for the second period to the 752/5 and 463/5 degree-day under A1B scenario.
Hossein Asakereh, Robab Razmi,
Volume 18, Issue 50 (3-2018)
Abstract
In the present study, the main aim was the spatial evaluation summer rainfall of northwest of Iran based on30 stations in northwest of Iran during 30 years of statistical period (1985-2014). An attempt, using geo-statistical modeling by ordinary least squares (OLS) and geographically weighted regression (GWR) procedures, was also made. The results represented that the GWR model with higher S2, lower residuals and lower RMSE is an optimized geo-statistical model for rainfall modeling of this area. This model can explain spatio-temporal rainfall distribution in northwest of Iran in a diversified topographical and geographical background. This model revealed that two spatial factors including elevation and slope, have the most important role in the summer rainfall behavior.Therefore Elevations in the mountainous and eastern parts of Lake Urmia, Latitude in the northern regions and slopes in the east of the region, have the most role in the spatial variations of summer precipitation in northwestern Iran.
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Volume 19, Issue 52 (3-2019)
Abstract
The heat waves today are one of the most important climatic hazards in the world. According to many scientists, the Severe and frequent occurrence of heat waves in recent years has been due to the emission of greenhouse gases and consequent increased global warming. The purpose of this study is to investigate changes in the frequency and intensity of heat waves As well as their relationship with Global land-ocean temperature anomalies and greenhouse gases in the north-west of Iran. At First, maximum temperature of two meters of the surface during the period from 1851 to 2014 for 164 years was obtained from NASA’s website, then the maps of heat waves was drawn and extracted. Then, we analyzed and evaluated the frequency and severity of the heat waves, as well as changes in the annual, decade, fifty years old fluctuations and their centenary were analyzed. To achieve the research objectives, Pearson and Spearman correlation methods, linear and polynomial regression and non-parametric Mann-Kendall test were used. The results showed that the frequency of occurrence of heat waves in the considered period interval is incremental and relevant, and the most frequency of occurrence was in decades. Also the intensity of the heat waves is associated with a relatively significant increase, and the most intense heat waves occurred in the decades of the late 20th and early 21st century until the present period. The results of the correlation coefficients indicated that the intensity and frequency of the heat wave incidence have a positive and significant correlation with the Global land-ocean temperature anomalies. The results of investigating the relationship between frequency and intensity of heat waves with 4 important greenhouse gases, including: (CO2, CH4, N2O, SF6), showed that, except for the positive and significant correlation of carbon dioxide gas with the most severe heat waves in June, There was no meaningful relationship between them. The results of the Mann-Kendall test indicate an incremental and significant increase in the frequency and intensity of heat wave events in the North-West region of Iran.
Shadieh Heydari Tasheh Kaboud, Younes Khoshkhoo,
Volume 19, Issue 53 (6-2019)
Abstract
The aim of this research is the study of the climate change impacts on the seasonal and annual reference evapotranspiration time scales in some selected stations located in the West of Iran. To this purpose, four stations including Sanandaj, Saghez, Khorramabad and Kermanshah synoptic stations with enough long-term data were selected and the climate change impact on the reference evapotranspiration of these stations under two RCP2.6 and RCP8.5 scenarios in three future time periods including 2011-2040, 2041-2070 and 2071-2100 in comparison with the 1970-1999 base period was studied. The FAO-Penman-Montieth method was applied to calculating reference evapotranspiration and the CanESM2 general circulation model and SDSM downscaling method were used to simulating future climate conditions under the climatic scenarios. The results showed that the mean reference evapotranspiration in the annual and autumn and winter time scales in comparison to the base period will significantly increase for all of the studied stations under all of the scenarios and periods at the 0.01 confidence level. For spring season, the only significant change of the future period mean reference evapotranspiration compared to the base period in the all of the studied area will be a significant increase at the 0.01 confidence level in the 2071-2100 period under the RCP8.5 scenario and for the summer season, this significant increasing rate will occur in the 2041-2070 and 2071-2100 periods under the RCP8.5 scenario. The overall results of this research showed that the highest increasing rate of the future periods in comparison with the base period for all of the seasonal and annual time periods and for all of the studied area will under RCP8.5 scenario and in the 2071-2100 time periods. by comparing the reference evapotranspiration change rates between the different seasonal and annual scales, the results showed that the increasing rate of the mean reference evapotranspiration at the West of Iran will be very remarkably in the autumn and winter seasons compared to the other time scales.
Dr Mahmoud Hooshyar, Dr Behrouz Sobhani, Nader Parvin,
Volume 19, Issue 54 (9-2019)
Abstract
Early heat waves are extreme events that cause heavy losses in plant and animal life and cause many social and economic problems for communities. The purpose of this study was to identify synoptic patterns and statistical analysis of preterm heat waves in northwestern Iran. To do this, the maximum daily temperature data of March 14th was used for fourteen synoptic stations in the northwest of the country during the statistical period (1333-1393) Hijri Shamsi. Then, on the basis of the threshold, the Baldy index was selected for 61 days of heat wave. All statistical characteristics of the data were processed in SPSS software. They were The elevation data of the middle atmosphere of the atmosphere was extracted from a NCEP / NCAR database on a network with an arc 2/5 × 2/5 degree on the 0 to 70 degree eastern longitude and 0 to 60 degrees north latitude. The matrix was made up of 864 columns in 40 rows, with rows of days with thermal waves and elevation data on the columns on the middle of the atmosphere. The analysis of the basic components was performed on the algebraic data matrix matrix And 12 components that account for about 93 of the variations in pressure levels above 500 hp, were identified. To identify the coherent patterns, cluster analysis was performed on the scores of the components by the WARD integration method. Five types of pre-heat generation waveform patterns were identified. The results of this study showed that the premature heat waves in the northwest of Iran are due to high altitude formation in southern Arabia, the Aden valley and the center of Sudan at a level of 500 hpa and the formation of Sudan's low pressure in the sea level and the discharge of its tabs to the north and northeast of the region The case study (Northwest of Iran) also includes events occurring.
Ms Mahboobeh Pouratashi, Dr Mohammad Moradi, Dr Ebrahim Fattahi,
Volume 20, Issue 57 (6-2020)
Abstract
This research aims to study the impact of temperature and wind in the southern low-pressure system and its associated precipitation in the southern regions of Iran. As The southern low pressure system moves eastward, it crosses the southern regions of Iran, causing medium and heavy rainfall in these areas. In this study, two southern low-pressure systems that caused heavy rainfall on March 11, 2015 and January 17, 2000 in southern Iran were selected, analyzed and simulated using the numerical Weather Research and Forecasting (WRF) model. Since the wind and temperature fields play a significant role in the southern low-pressure systems, four experiments were performed for investigating the effects of temperature and wind on the intensification and weakening of the southern system. The simulation results showed that the simulation for the increased (decreased) temperature caused the weakened (intensified) the southern low pressure in the studied area. This result showed that the vertical structure of the southern low-pressure and its physical characteristics are similar to the mid-latitudes cyclones, and these systems were different from the thermal low pressures. The results of wind speed changes showed that the increased (decreased) wind speed simulation caused an increase (decrease) in relative vorticity, thus the southern low pressure was intensified (weakened). In both cases, the rainfall was decreased by the increased temperature simulation, and decreased temperature caused an increase in rainfall. It was also seen that the increase in wind speed caused the special humidity advection to be increased and then the rainfall increased. Also the amount of rainfall decreased when conditions did not provide for the advection of specific humidity or the wind speed reduced.
- Nesa Sepandar, Professor Kamal Omidvar,
Volume 21, Issue 61 (6-2021)
Abstract
In this study, we tried to identify the sources of moisture and its direction of heavy rainfall in south and southwest of Iran by using a new algorithm based on atmospheric rivers. For this purpose, daily rainfall of 17 synoptic stations in the period 1986 to 2015 in south and southwestern Iran that have a common time span and fully cover the study area is used.Also from the data set of the National Center for Environmental Prediction / National Center for Atmospheric Research (NCEP / NCAR) European Mid-Term Forecast Center (ECMWF) and ERA-interim data with spatial resolution of 0.75 It was used at 0.75 latitude and longitude with 6 hour resolution. The variables used are integrated water vapor (IWV), specific humidity (q), and orbital and meridional components (u, v). In this research, an algorithm based on the calculation of Vertical Horizontal Vapor Transfer Integral (IVT) is used to identify and navigate atmospheric rivers. The results show that the main source of rainfall moisture is in south and southwestern Iran, south of Red Sea and Gulf of Aden. Of course, the maps show that the Arabian Sea was not affected by the humidity.The Arabian Peninsula also, due to the high moisture transfer rate, as a transitional route, transmits a large amount of moisture to the study area.Finally, the path of moisture to the study area was mapped and identified, and thus considering the three main conditions for the atmospheric river, it can be said that the path obtained is the same as the atmospheric river.
Asal Falak, Reza Boran, Farideh Asadian,
Volume 21, Issue 62 (9-2021)
Abstract
This study aimed to investigate the temporal-spatial and synoptic features of thunderstorms in southwest of Iran (Khuzestan, Chaharmahal & Bakhtiari and Kohkiluyeh & Boyerahmad Provinces) It was compiled using volatility indices during the period 1985-2015. Results of Frequency Analysis of Thunderstorms at Dezful Station with 479 cases the highest frequency and Ramhormes with 252 days had the lowest frequency. In terms of seasonal distribution, spring was the most abundant with 39%. On a monthly basis, April had the lowest frequency with 21% and August with only 2 cases. In terms of thunderstorms the highest frequency of thunderstorms with no thunder was 21 percent. Synoptic analysis: Most of the time there is a nave (at level 500) or low pressure in the west of the region, east of the Mediterranean Sea with its tabs clockwise. From the Red Sea and the Persian Gulf, they entered the south, southwest, and west of Iran On the other hand, the high-pressure system on the Gulf of Aden in the east of the region is round in the clock It has injected moisture, especially at a level of 850 millibars. Interaction between the two systems over the course of the day, It has injected moisture from three sources of the Mediterranean Sea, the Red Sea and then the Persian Gulf into the rising systems of the region. The low-pressure counterclockwise movement of the eastern Mediterranean, Along with the high-altitude clock movement over the Gulf of Aden, it has injected moisture at levels of 850 to 700 degrees.
Seyed Hossein Mir Mousavi, Masoud Jalali, Enayet Asadolahi,
Volume 21, Issue 63 (12-2021)
Abstract
In this research, coding the rainfalls, prepares daily 45 stations with the statistical period of 20 years to zero and one codes to realize the daily dry periods in west and north west of the country and then, by establishing the main condition of occurrence of code one for 30 stations, we extracted the dry 4 to 10-day frequencies. And the results gained of considering the atmospheric weathering, shows that the most clear rotational pattern in sea level is related to Siberia-Europe high-pressure panels and sometimes both of them that increase the rotation on the region and also, the local high-pressure reinforcement and there is a high altitude in atmospheric middle level which is derived from sample patterns and is placed on the studied region and these sample patterns are from omega, bi-polar and rex models that they are on Russia and Scandinavian countries with some changes. The 500 level TAVA and omega shows well that in most regions, the air course, has decreasing case and so, we can result that placement of a high altitude in atmospheric middle and upper level on the high-pressures of the earth, causes the weather stability and lack of rainfall and as a result, the stability and durability of these conditions for several days, is related to sample patterns.
