Climatology
vahideh abtahi; Saeed jahanbakhsh; hashem rostamzadeh; hasan lashkari
Abstract
Heavy rainfall is considered one of the climatic features of precipitation that can occur in any climate, but its occurrence in arid and semi-arid climates, due to the lack of adequate and appropriate infrastructure, is associated with greater damage. These rains occur under different synoptic conditions. ...
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Heavy rainfall is considered one of the climatic features of precipitation that can occur in any climate, but its occurrence in arid and semi-arid climates, due to the lack of adequate and appropriate infrastructure, is associated with greater damage. These rains occur under different synoptic conditions. In this study, the role of atmospheric rivers in the formation of heavy rainfall has been investigated. For this purpose, heavy rainfall data from stations in the west and northwest of the country were extracted for a 33-year period. Then, precipitation systems were separated in conjunction with atmospheric rivers. In the next step, using weather maps and the troposphere's underlying layer levels, synoptic patterns that lead to the formation of atmospheric rivers were identified. The results showed that atmospheric rivers were responsible for heavy rainfall in the study area, following three general patterns. The Sudanese low-pressure pattern and the combined pattern of Sudanese low-pressure and Mediterranean cyclone were responsible for the most significant role in the formation of atmospheric rivers leading to heavy rainfall, respectively. In the Sudanese low-pressure pattern, two to three days earlier, a broad tongue of Siberian high pressure spreads over the warm waters of the Oman, Arabian, and Aden seas, passing through Afghanistan, Pakistan, and the eastern part of Iran. This tongue, with the rotation of moisture, escapes from the Sudanese system. The Mediterranean trough deepens over western Asia and northeast Africa, and this moisture is strengthened along the southern currents and, by passing over the mountains,leads to the formation of atmospheric rivers. In the combined pattern, with the expansion of the Sudanese low-pressure tongue to the eastern Mediterranean and western Asia, the southern warm waters' moisture is released onto this region with the transport of moisture from the Mediterranean, it is strengthened, leading to the formation of atmospheric rivers.
Climatology
behrouz sobhani; minoo ahmadyan; Saeed jahanbakhsh
Abstract
the statistics of the ECMWF database were used for the observation data of the two stations of Semiram and Urmia during a 21-year period (1996-20016).In order to investigate the effects of climate fluctuations, the daily data of dynamic micro-rotation of the CORDEX project was used for the output of ...
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the statistics of the ECMWF database were used for the observation data of the two stations of Semiram and Urmia during a 21-year period (1996-20016).In order to investigate the effects of climate fluctuations, the daily data of dynamic micro-rotation of the CORDEX project was used for the output of the ICHEC-EC-EARTH model under the RCP8.5 and RCP4.5 radiative forcing (RCP) scenarios for the period (2017-2037). By using the data of the stations and the outputs of the micro scale model, and by using the perceptron neural network and linear regression, the performance was simulated. Then, to evaluate the efficiency of the models, R, R2, MSE, RMSE, and NRMSE statistics were used, and the non-parametric Menkendall test and age slope were used for the performance trend. The result of comparing the output of artificial neural networks with the linear regression model shows that the error rate of the neural network is less and the simulated results are close to the real observations to a very acceptable extent. The phenological stages, including bud blooming to fruit ripening in the stations under both scenarios, and in all the phenological stages in the future period will be completed earlier than the base period, and the length of the growth period will also decrease. The amount of future yield in Urmia station under RCP4.5 and RCP8.5 scenarios respectively yield 3.7 and 2.2 tons per hectare and in Semiram station yield 1.4 and 3 respectively tons per hectare will decrease. The results show that in the future in the study areas, with the change in the time of occurrence of the length of the growth period, all the phenological stages as well as the declining performance of apple trees will be subject to climatic fluctuations
Climatology
shahnaz Rashedi; Saeed jahanbakhsh; Ali Khorshiddoust; Gholam Hasan Mohammadi
Abstract
For this purpose, data on the type, amount, and height of different cloud layers and daily precipitation of 36 synoptic stations located on the southern coast of the Caspian Sea were received from the Meteorological Organization. MODIS images were used to investigate the relationship between precipitation ...
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For this purpose, data on the type, amount, and height of different cloud layers and daily precipitation of 36 synoptic stations located on the southern coast of the Caspian Sea were received from the Meteorological Organization. MODIS images were used to investigate the relationship between precipitation and cloud microphysical parameters (CTT, CTH, COT, CER, CWP). ERA5 and NCEP/NCAR data were also used to identify synoptic patterns leading to cloud formation. Finally, HYSPLIT model and regression method were used to identify the path of moisture flow. The results of observational data showed that Caspian clouds were observed in the form of low Stratus clouds and middle clouds of Altocumulus type in the region. So that among the low clouds, the heights of 750 and 900 meters and among the middle clouds, the heights of 2700 meters had the highest frequency. The results of Caspian clouds rainfall showed that in most areas, 1 to 5 mm of precipitation has occurred. Correlation results showed that precipitation was positively correlated with CTH,COT, CER and CWP, and negatively correlated with CTT. Multivariate regression predicted 17% of precipitation by cloud parameters. The results of the study of synoptic maps showed that with the establishment of a 1012 hPa high pressure core in the north of the Caspian Sea, the north-south wind flow along with the transfer of sea moisture to the south shore of the Caspian Sea, ascending the air mass and the formation of clouds and limited rainfall in the region. Vertical profiles showed maximum specific humidity in the lower levels of the atmosphere (1000 to 900 hPa). The results of HYSPLIT model moisture flow path showed that the main source of regional moisture was the Caspian Sea.
Climatology
saeid Jahanbakhshasl; Behrouz Sari Sarraf; Hossein asakereh; soheila shirmohamadi
Abstract
Introduction Climate extreme events have expanded and intensified during the 21st century. Extreme precipitation event annually leads to severe damage in agriculture, environment, infrastructures and even the human loss. Therefore, identification of the behavior of such events is one of the pivotal aspects ...
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Introduction Climate extreme events have expanded and intensified during the 21st century. Extreme precipitation event annually leads to severe damage in agriculture, environment, infrastructures and even the human loss. Therefore, identification of the behavior of such events is one of the pivotal aspects of climatic change and the increase of information about extreme precipitation is tangibly necessary for the society especially with regard to those, living in the areas with high risk of flood. extreme precipitation events can be defined as significant deviations from the precipitation mean. As a result, to identify such precipitations, a criterion was needed to evaluate the rate of precipitation values’ deviation from mean. Importantly, given the different types of indicators and thresholds proposed for extracting extreme precipitation, choosing an appropriate threshold with climatology conditions of the study region which could also be capable of identifying extreme precipitation optimally in terms of amount and frequency, requires high precision. The present study aimed at identifying the extreme precipitation events in the west of Iran through introducing the appropriate threshold and spatial scale for the extraction and investigation of these events.Data and MethodsThe west of Iran with the areaof 230760 square kilometers includes about 14% of total area of Iran. Zagros Mountains, stretching from northwest to southeast, are the most important feature of the west of Iran. Two databases have been used in this study. The first database regardsthe precipitation data of 1129 synoptic stations, climatology and rain gauge in the west of Iran. The stations statistics have been checked in terms of existence of any outlier. Ultimately 823 stations out of 1129, were used for producing gridded data. The gridded data, are the results from the interpolation of daily precipitation observations since January 1st 1965 to December 31st 2016, using Kriging interpolation method and spatial separation of 6*6 kilometers. the final base, a matrix possessing the dimensions of18993*6410 (representing time on the rows and place on the columns) was developed. The second database referred to the Sea-level pressure patterns (Hectopascal).To identify such precipitations, in addition to the main threshold that includesthe mean of precipitation more than 75th percentile for each pixel per day of a year, a second threshold including the standard deviation of these precipitations (with the values of one, two, and three times more) has been also added to the mean. Accordingly, three groups of extreme precipitation were identified in the region which were separated according to the spatial zone that had been covered. Moreover, the sea-level pressure patterns were extracted with regard to these precipitations for each zone andthen classified using clustering analysis technique.Results and Discussionthree groups of precipitations with different coverage zoneswere identified: 1- 83 days with equal to or more precipitation than the mean of precipitations more than 75th percentile plus one time standard deviation which cover more than 40% of the region. 2- 144 days with equal to or more precipitation than the mean of precipitations more than 75th percentile plus two times standard deviation which cover more than 20% of the region. 3- 82 days with equal to or more precipitation than the mean of precipitations more than 75th percentile plus three times standard deviation which cover more than 20%The maps of 7 participation groups of the first type in comparison with 6 precipitation groups of the second and third type contain common and repetitive patterns. Each precipitation maps of the second and third types explains a type of patternand there is minimum overlapping in the maps. Therefore, the precipitations are obtained from the most particular and distinct atmospheric patterns. considering the three properties of 1- equality of precipitation groups of type two and three (both include 6 groups of atmospheric patterns). 2- repeating the atmospheric patterns of precipitation of type two prominently in the precipitations of type three. 3- the formation of the most optimum atmospheric modeling for the precipitations of both thresholds in the zones of 20% and higher, in the west of Iran, the extreme precipitations refer to those with higher means of recipitations more than 75th percentile plus two times standard deviations,have mostly occurred in the zone of 20% and higher of the region.
Climatology
Mohammad Hossein Aalinejad; Saeed jahanbakhsh; Ali Mohammad Khorshiddoust
Abstract
Introduction
Determining the temporal change of snowmelt or agriculture water equivalent of snow, predicting flood, and managing the reservoirs of a region is of utmost importance. Some major parts of the western sections of the country are located in the mountainous region and most of the precipitations ...
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Introduction
Determining the temporal change of snowmelt or agriculture water equivalent of snow, predicting flood, and managing the reservoirs of a region is of utmost importance. Some major parts of the western sections of the country are located in the mountainous region and most of the precipitations of this region occur in the form of snow in winter. The runoff resulting from snowmelt has an important role in feeding the rivers of this region and it has a significant share in developing agriculture and the economy.
Scientific studies have shown that climate change phenomena have significant effects on precipitations, evaporation, perspiration, runoff, and finally water supply. As the demand increases, climate changes, greatness, frequency, and the damage resulting from extreme weather events, as well as the costs of having access to water increase, as well. Therefore, evaluating the runoff resulting from snowmelt and the effect of climate change seems necessary for managing water resources.
Methodology
Gamasiab basin is located in the northeast part of the Karkheh basin originating from the springs in the vicinity of Nahavand. Its basin has an area almost equal to 11040 square kilometers that have been located in the east part having 47 degrees and 7 minutes to 49 degrees and 10 minutes geographical longitude and from the north part, it has 33 degrees and 48 minutes to 34 degrees and 54 minutes geographical latitude. This basin has an altitude between 1275 to 3680 meters.
In this study, snow-related data required for simulation were derived from the daily images of the MODIS sensor. To this end, first, the snow-covered area of the Gamasiab basin was measured during the 2016-2017 water years using the process of satellite images obtained from the MODIS sensor in the google earth engine system. All geometric justifications and calibration processes of images were applied precisely in the mentioned system. In the next step, the output of the GCM model scenarios was utilized for calculating temperature and precipitation changes in future periods. These CMIP5 kind models were under the control of two RCP45 and RCP85 scenarios and were downscaled with LARS-WG statistical model.
Moreover, to investigate the uncertainty of models and scenarios, the best models and scenarios were selected for producing temperature and precipitation data of future periods; accordingly, the outputs of the models for future periods (2021-2040) having the basis period of (1980-2010) were compared using statistical indexes of coefficient of determination (R2) and Root Mean Square Error (RMSE). The results were entered into the SRM model as the inputs. In addition, temperature and precipitation data of meteorological station of the studied region as well as the daily discharge of the river flow of hydrometric station of Chehr Bridge (as located in the output part of Gamasiab basin) were used during the statistical period of October 2016 to May 2018.
Discussion
Using Digital Elevation Model (DEM) of the region and the appendage of Hec-GeoHMS in GIS software, firstly, flow direction map, flow accumulation map, and stream maps were drawn and the output point (hydrometric station of Chehr Bridge) was introduced to the border program of the identified basin and the basin was classified based on the three elevation regions.
Producing temperature and precipitation data of future periods requires a long-term statistical period; accordingly, the meteorological station of Kermanshahd was selected since it was in the vicinity of the studied region. To be confident in the ability of the model in producing data in future periods, the calculated data had to be compared with the observed model and data in the studied stations. The capabilities of the LARS-WG model in modeling the mentioned parameters of this station confirmed the observed data. Moreover, the ability of the model in modeling precipitation was very good and acceptable; however, the most modeling error was related to the precipitation in Mars.
In the next phase and compared to the basic periods, the mean of changes in average precipitation and temperature was measured in the studied stations during January and Juan of 2015 to 2017(for which simulation had occurred); as an index of changing the climate, this was entered into the SRM model under climate change conditions. During the simulation period (January to Juan), it had been predicted that the precipitation parameter would decrease and the temperature parameter would increase.
Conclusion
The results of this study indicated that using the MODIS sensor could provide an acceptable estimation of the snow cover level of the Gamasiab basin, which lacked snow gauge data. Moreover, the results of simulation with the SRM model showed that the model could simulate the snow runoff in the studied region. As the main purpose of the study, the effect of temperature and precipitation in future periods was well stated considering the uncertainty of CMP15 series models and scenarios. The results of temperature changes indicated an average increase of 1.8 C. the results of precipitation also indicated an average decrease of more than 5%. However, decreasing precipitation in the cold months of the years had been predicted severely so that the reduction of precipitation in February was of utmost importance for feeding the snow cover and rivers, which had been estimated to be 20%. This happened while increasing precipitation was mainly related to the hot months of the year whose amount was insignificant and didn`t have that much effect on the runoff. Accordingly, due to the increases in temperature and decreases in precipitation in cold seasons, the results of runoff simulation have indicated a 24% reduction for 2016-2017 and a 29% reduction for 2017-2018 water years.
Climatology
Saeed jahanbakhsh; saeideh ashrafi; Hosein Asakereh
Abstract
Introduction Cyclones constitute one of the major factors determining climatic conditions, especially precipitation in the middle latitudes. Changes in the properties of cyclones in a region may lead to variations in the precipitation conditions of that region. Therefore, studying major aspects in cyclones ...
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Introduction Cyclones constitute one of the major factors determining climatic conditions, especially precipitation in the middle latitudes. Changes in the properties of cyclones in a region may lead to variations in the precipitation conditions of that region. Therefore, studying major aspects in cyclones can clarify variations in precipitation conditions. In this research, changes of cyclones associated with precipitation in the Zard Rud basin (a Sub-basin of Jarahi basin in khozestan) has been reviewed decadal during a period ranging from the hydrological year of 1976-1997 to 2013-2014. In this research, daily precipitation maps during the studied period (13879 days) by using kriging method has been provided. Data and methods So the long-term precipitation mean of all days were extracted and by using 50 percentile, rainfall season detected. Upon identifying the precipitation season, Cyclones detected for this period. For identifying cyclones 1000 hPa hourly maps (NCEP/NCAR) were utilized. Two conditions were used to detect available cyclones: (1) the height values in each pixel of the 1000 hPa height map should be smaller than those of it 8 neighboring pixels and (2) the gradient mean of the height of the selected pixel and its 8 neighboring ones that was equal or smaller than 100 m/1000 km was regarded as the cyclone center. After identifying the cyclones on the map, the center of each cyclone was identified in consecutive maps to track the cyclone path. It was hypothesized that precipitation in the basin of the Zard Rud would be affected by the cyclones dominating the area as well as the trough of the cyclones that were far from the area, but could influence the region. Discussion Cyclones associated with precipitation in the basin were identified in the light of the presence of the cyclone or its troughs over the region during the occurrence of a precipitation. The results show that The extent of the area and frequency of cyclones in studied decades and consequently frequency of cyclonic rainy days and annual cyclonic precipitation in Zard Rud basin have decreased. Reduction in the frequency of cyclonic precipitations can be attributed to the place where the cyclones are formed. Indeed, in comparison with the past, a larger number of cyclones are formed over Saudi Arabia and Iraq, a phenomenon which has led to the entrance of dry or less humid air into the studied region. Masoudian (2012: 15-33) also indicated that a cyclonic center was formed over Iraq. Results Longitudinal extent area of cyclones decreases from 72.5˚ in first decade to 55˚ in fourth decade and Latitudinal extent decreases from 30˚ in first decade to 25˚ in fourth decade. Annual review on cyclones entry point to Iran show that minimum latitudinal extent from 1986-1987 hydrological year and maximum latitudinal extent from 1991-1992 hydrological year had fluctuation. So that, in 2011-2012 hydrological year, latitudinal extent of cyclones entry to Iran has reached the narrowest of its paths. Examining mean differences in the cyclone frequency of two halves of period (first half: 1976-1977 to 1994-1995 hydrological year and second half: 1995-1996 to 2013-2014 hydrological year) also revealed a noticeable shift in cyclones frequency. Result of surveying of cyclonic precipitation show that cyclonic total precipitation decreased during the studied decades. However, frequency of cyclones is less than first decade but second decade has the maximum amount of precipitation. It is may resulted of continuity of cyclones in this region. Taken together, a change was observed in geographical extent and frequency of cyclones associated with precipitation in the Zard Rud basin, which in turn affected precipitation in the area
Climatology
Yagob Dinpashoh; Saeid Jahanbakhsh-Asl; Leyla Mosavi Jahani
Abstract
Introduction One of the standard models for estimation of ET0 that accepted by all hydrologists and climatologists is the FAO Penman-Monteith (FAO56PM) method. Although this model is accurate in ET0 estimation, however, it has some limitations. The main limitation of this method in in its need for various ...
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Introduction One of the standard models for estimation of ET0 that accepted by all hydrologists and climatologists is the FAO Penman-Monteith (FAO56PM) method. Although this model is accurate in ET0 estimation, however, it has some limitations. The main limitation of this method in in its need for various meteorological data, including the solar radiation, air temperature, relative humidity, dew point temperature, wind speed and actual vapor pressure. Unfortunately, all of these parameters are not readily available in all the conditions. In this regard, many researchers interested to find a simple method for accurate ET0 estimation (Sentelhas et al., 2010; Dinpashoh, 2016; and many others). Based on our best knowledge there is no comprehensive study conducted in Urmia Basin for finding a simple and accurate method that needs less weather parameters for ET0 estimation. Therefore, the main aim of this study is estimation of ET0 that needs less weather parameters in Urmia Lake basin. Materials and Methods The area under study is the Urmia Lake Basin, located in North-West of Iran. This basin is approximately lied between the 35⸰ 40´ E to 38⸰ 29´ E latitudes and 44⸰ 07´ to 47⸰ 53 longitudes. The area of this basin is about 51700 km2 which is equal to about 3.2 percent of Iran's area. Data used in this research are the daily recorded values of maximum air temperature, minimum air temperature, wind speed at 10 m height, relative humidity, sunshine duration, and some geographic information such as altitudes, latitudes and longitudes. The nine stations were selected from different points of the basin in this study. The FAO56PM method (Allen, 1998) was selected as the bench mark for ET0 estimation in all the stations. In this method the following equation was used for ET0 in the chosen sites. (1) where ET0 is the reference crop evapotranspiration (mm/day), Rn is the net solar radiation at crop surface (MJ m-2 day-1), G is the soil heat flux (MJ m-2 day-1), T is the mean air temperature at 2 m height (°C), u2 is the wind speed at a 2 m height (m/s), the term (es-ea) is the saturation vapor deficit (kPa), Δ is the slope of the vapor pressure curve at the point of air temperature (kPa/°C) and g is the psychometric constant (kPa/°C). In order to convert U from 10 m height to u2 the following equation was used (Nandagiri and Kovoor, 2005; Sentelhas et al., 2010; Dinpashoh et al., 2011): (2) where Uz is the wind speed (m/s) at z m height, and zw is the height (m) at which wind speed measured. In this study, in order to find an alternative model, which uses less weather data in estimation of ET0 the three empirical models namely Hargreaves (HG), Kimberly Penman (KPM), Priestly Taylor (PT), and Multivariate Linear and non-linear regression were used. Evaluation of the models performed using the three metrics, coefficient of determination (R2), Root Mean Square Error (RMSE), and Mean Absolute Error (MAE). Results and Discussion Results showed that, the median of the R2 values for KP was more than 0.986. The median of the R2 values for PT and HG models were found to be equal to 0.902 and 0.40, respectively. The median of RMSE for HG model was about 0.9 (mm day -1). This value for KPM and PT models were about 1.3 and 2.1 (mm day -1). The median of MAE for the selected stations for KPM was less than 1 (mm day -1). This value for HG was equal to 0.7 (mm day-1) and in the case of PT was more than 1.5 (mm day -1). Therefore, considering the MAE values and RMSE, the HG model was detected to be the suitable method foe ET0 estimation in Urmia Lake basin.
Climatology
Majid Rezaei Banafsheh; saeid Jahanbakhsh; Shoaieb Abkharabat; Aliakbar Rasouli; Mostafa Karimi
Abstract
Introduction 120-day winds of Sistan are considered as one of the significant phenomenon which has a great impact on the morphology and environment of east and southeast of Iran (Figure.1). The common region for these winds is the border of monsoon region in south of Asia which mainly has sunny and cloudless ...
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Introduction 120-day winds of Sistan are considered as one of the significant phenomenon which has a great impact on the morphology and environment of east and southeast of Iran (Figure.1). The common region for these winds is the border of monsoon region in south of Asia which mainly has sunny and cloudless weather during monsoon period. This condition is due to lack of higher humidity divergence accompanied by tangible decrease of the air on the atmosphere (Salighe, 2010). These winds are the most famous advection system in northern hemisphere whose effects are visible in eastern regions of Iran, west and south of Afghanistan, and northwest of Pakistan(Khosravi, 2008). Data and Methodology In order to evaluate the role of the winds, data network of Geopotential height of 850 hPa (hectopascal) level during a 19-year period (1993-2012) from May to the end of September, the period of 120-day winds of Sistan, were found. These data were of those revisited data of 2.5*2.5 NCEO/NCAR during 2480 days. Then, factor analysis and clustering tests were applied on data network of Geopotential height to classify map patterns (Yarnal, translated by Masoudian, 2006: 100). As a matter of fact 5 clusters were recognized in this study presented in table 1. Dynamic method was used in GrADS software in order to find humidity flux of each region in the quintuplet patterns. Discussion Northern Wind Pattern (120-day wind of Sistan) As a matter of fact 120-day winds of Sistan are a part of northern Trade winds which are the most important source of Caspian Sea high pressure. After passing east of Iran, these winds reach Oman Sea and converge with southern Trade winds. Both of them moved toward Indian Subcontinent and finally enter atmospheric monsoon circulation of south of Asia. High pressure of north of Iran is also a tongue of high pressure Azores which is extended over northern regions of Iran and Caspian Sea by Mediterranean and Black sea Basin. Both existing Gang low during hot period of a year in south of Asia and spreading, its tongues over regions of Middle East make Azores high not be able to penetrate the zone in lower levels of atmosphere (from the earth surface to thelevel 850 hPa.). As a result, Azores high has to locate in northern parts especially north of Iran. Analyzing the curves of geo-potential height, figure (2) precisely shows this phenomenon. Gang low not only is weaken among middle levels of atmospheretongue, but also lost its appearance on Iran Plateau and Arabian Peninsula. Therefore, Azores high tongue also can locate in its normal position and appear with maximum pressure on Iran Plateau and Arabian Peninsula. Figure (3) presents the order of synoptic systems in level 500 hPa. of pattern 1. It shows that Gang low has lost its nature in this level, while Azores high tongue obviously is located on Middle East, especially Iran Plateau and Arabian Peninsula. As a matter of fact atmospheric levels of Geopotential height in pattern 1 (figures 2,3, 4) reveal that as we go away from lower levels of atmosphere to middle levels of atmosphere, Gang low gradually is weaken especially over Iran Plateau and Arabian Peninsula. This situation makes Azores high tongue locate in lower latitude. However, in lower levels (earth surface to level 850 hPa.), as a tongue of Gang comes into some parts of Middle East, expanded tongue of Azores high pressure has to locate on higher latitudes than normal latitudes; on north of Iran Plateau and Caspian Sea.Pattern (2) shows the same order as pattern (1), so it will not be repeated here. In the following, the effect of 120-day winds of Sistan on humidity of the region will be investigated, thus humidity flux is calculated between levels 925-1000 hPa. 850-925 hPa. and 850 -700hPa. Figure (5) shows sum of humidity flux for aforesaid levels of synoptic pattern (1). 120-day winds of Sistan with prevailing north direction in this pattern lead to the formation of a core of humidity flux divergence in east and center of Iran and decrease humidity of the region. As previously mentioned, after passing Iran, Sistan winds reach Oman Sea and north of Indian Ocean, and converge with southern Trade winds. Both of them move toward Indian Subcontinent. In fact, convergence of 120-day Sistan winds (northern Trade winds) and southern Trade winds leads to formation of a strong core of humidity flux convergence on Oman Sea and north of Indian Ocean (figure 5). The sum and average of humidity flux convergence and humidity flux divergence in studied region are presented in table (2). Eastern Wind Pattern The other clusters (3, 4, and 5) have different order from 120-day Sistan winds which are introduced as eastern wind pattern. Unlike clusters (1) and (2), in these clusters (table 1) the wind direction is not northern; in other words, the winds blow with prevailing east direction in east and northeast of Iran, however southeast of Iran experience mild weather at the same time. As synoptic order of pressure system and humidity flux system are mainly the same, pattern (3) will be analyzed precisely. The order of synoptic systems of level 850 hPa. in pattern (3) is presented in figure (5). This map reveals that the contrast between high pressure of north and Gang low differs from northern wind pattern, as on the one hand,the strength and breadth of Gang low increase, while on the other hand the strength and breadth of Azores high tongue (high pressure in north of Iran) decrease. In fact, this condition makes most regions of Iran Plateau in lower levels of atmosphere (1000 hPa, 925 hPa and 850 hPa.) be dominated by Gang low. Besides, this order of synoptic systems eliminates 120-day wind conditions of Sistan and make eastern wind conditions in east and northeast of Iran. Since the orders of synoptic systems of levels 925 hPa. and 1000 hPa are the same as level 850 hPa. they will not be presented here. The orders of synoptic systems in middle levels are different, as in level 700 hPa. Azores high tongue comes to Iran Plateau by Arabian Peninsula (figure 7). This layer of atmosphere is a transition layer from dominance of low pressure pattern in lower layers to high pressure pattern in middle levels and upper atmosphere. Moreover, in level 500 hpa. Azores high tongue dominates Iran Plateau and Arabian Peninsula with more power and breadth. The orders of synoptic systems of clusters 4 and 5 are the same as cluster 3. The sum of humidity flux divergence and humidity flux convergence of pattern 3 are presented in figure (9). In this figure, the core of humidity flux divergence, which covers eastern half and center of Iran, is omitted and a core of humidity flux convergence covers east and southeast of Iran. It can be said that both penetration of Gang low into Iran and lack of 120-day winds provide special conditions in which the zone of humidity flux convergence in north of Indian Ocean moves to southeast of Iran leading to moisture condensation. Conclusion In this study 2 patterns of synoptic systems of warm period in east and southeast of Iran were recognized. First pattern (northern wind pattern) makes 120-day winds of Sistan (cluster 1 and 2). In contrast to Gang low tongue, when high pressure of north of Iran and Caspian Sea are in strong mode, it provides the conditions for 120-day winds of Sistan. On the other hand,in contrast to Gang low tongue increasing its influence and spread over Iran Plateau, when the aforesaid high pressure rollbacks of north of Iran and it is weakened, 120-day winds of Sistan stop and second pattern (eastern wind pattern) starts. In this pattern the winds with prevailing east direction cover east and northeast of Iran (clusters 3, 4,and 5). High pressures of Caspian Sea and north of Iran are a tongue of Azores subtropical high pressure which has to move abnormally to higher latitudes due to coming Gang low into lower atmosphere layer. Since Gang low is an inter-tropical convergence zone moving abnormally to higher latitudes in south of Asia, 120-day winds of Sistan are part of northern Trade winds which are flowing from subtropical high pressure (Azores high tongue in north of Iran) to Gang low in south of Asia (inter-tropical convergence zone). After converging with southern Trade winds on north of Indian Ocean, they move toward Indian Subcontinent. 120-day winds of Sistan exclude the entranceof moisture from Oman Sea and Indian Ocean into southeast of Iran (figure 5). However, as 120-day winds of Sistan stop, a core of humidity flux is formed on southeast of Iran providing the entrance of moisture of water areas into southeast of Iran (figure 9). Generally, weakening of Azores subtropical high will help to provide rainfall conditions in southeast by 2 ways: on the one hand, as Azores high pressure is weakened, the influence of decent factors of this high pressure air in levels 700 hPa. and 500 hPa. decreases. As a result ascent conditions are provided in the zone, but on the other hand the weakening of subtropical high pressure in lower levels of atmosphere (1000 hPa to 850 hPa.) also makes expanded Azores tongue weaken and rollback over north of Iran and Caspian Sea leading to stop 120-day Sistan winds. This phenomenon provides appropriate condition to inject moisture from Oman Sea and Indian Ocean to southeast of Iran.
saeed jahanbakhsh; Ali Mohammad Khorshiddoust; Hamid Mirhashemi
Abstract
Introduction Due to their height, geometry and orientation, the mountains affect the atmospheric currents. Therefore, mountains cause the formation, intensification or weakening of many atmospheric phenomena. One of the most obvious of these phenomena is lee cyclogenesis whose formation and evolution ...
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Introduction Due to their height, geometry and orientation, the mountains affect the atmospheric currents. Therefore, mountains cause the formation, intensification or weakening of many atmospheric phenomena. One of the most obvious of these phenomena is lee cyclogenesis whose formation and evolution is subject to interaction between mountains and atmospheric currents. The lee sides of mesoscale or large-scale mountains, such as the Alps, Rocky Mountains, the East Asian mountains and the Andes, are favorable regions of cyclogenesis. This type of cyclogenesis is known as lee cyclogenesis, and can be defined as the formation of a cyclone with strong positive vertical vorticity or an appreciable fall in pressure with a closed circulation formed in the lee of a mountain that then drifts away (Chung. et al, 1976). In this regard, most studies have been made about the lee cyclogenesis of the Alps and the Rocky Mountains. As a result, the general understanding of mechanism of lee cyclogenesis is derived from studies conducted on these two mountains and partially due to the Alpine Experiment (ALPEX) field project held in 1982. In other words, the general framework of the mechanisms that exists today about lee cyclogenesis is based on the results obtained from the study of the Alps and the Rocky Mountains. Methodology The variables used in this study are consists of horizontal wind speed (u and v), vertical wind speed vertical pressure coordinates (w), temperature (T) geopotential pressure levels (z). The data variables used 1 and 0.5 degrees in the horizontal and vertical distance of 50 hPa from 1000 to 200 hPa. The data were extracting from the archival database ECMWF ERA Interim version with six-hour monitoring. Preliminary investigations showed that unstable systems under certain elevation models are located in the middle of the atmosphere in the region of the west, northwest of the west and west to the upstream slopes of the Zagros Mountains. so that the study of middle - level maps showed how the trough and the ridge of such systems has played an important role in determining the direction and movement of these systems towards zagros because it is different in terms of the confluence or diffluence system, curvature and sheer vorticity advection and ageostrophic wind of the trough, and finally the direction in the trough. In general, the conditions prevailing on these systems and the it direction they pass through to the Zagros have an important role in how they interact with the zagros. Therefore, it is necessary to examine how these systems approach to Zagros. For this purpose, this important issue was further investigated using the ageostrophic wind equation. Because the ageostrophic wind indicates the imbalance of geostrophic, and in fact the change of wind both in space and time causes this imbalance of geostrophic and the creation of the ageostrophic wind (Lynch and Cassano 2006, 123). Also used curvature vorticity in the natural coordinates, quasi-geostrophic height tendency equation and divergence of the isallobaric wind. Results and discussion An examination of the maps of the lower atmospheric levels shows that in some cases the cyclones approaching the windward slopes of the Zagros, under the baroclinic wave’s atmosphere, lead to the formation of a secondary rotation in the lee ward Zagros. Therefore, it is necessary to have a primary cyclone on the windward slope of the Zagros Mountains to form the lee cyclone. So the detection of cyclone approaching windward of the Zagros Mountains shows that cyclones which move and even higher than the Mediterranean latitude to the east, would have approached the Zagros in a way that was accompanied by a pattern of confluence ridge - diffluence trough in the middle of the atmosphere. While the cyclones, accompanied by a trough, were moving northward along the path of their eastward before reaching the Zagros in the north east. On the other hand, the cyclons, formed in the Red Sea region or Sudan, were required to reach the Zagros Mountains (the maximum velocity at the base of the trough) or the diffluence trough to approach the zagros. At the same time, the cyclones that were located in the area were under a confluence trough, never moved to the Zagros Mountains. So, according to the latitude of the primary cyclone and how the stack - trough is the level of 500 hpa, the path of the approaching Zagros is different. However, in many cases the nature of the trough and the level of the level of 500 hpa on the path of the eastward movement changes from difflunce to confluence and vice versa, which occurs due to the changing location in the baroclinic wave Conclusion Because The Zagros Mountains create changes in approaching baroclinicity waves causes advent thermal anomaly and consequently cause the occurrence of cyclone, so, such cyclogenesis is interpreted adjust according to the theory modify baroclinicity waves. Because this theory clearly states that mountain lead to lee cyclogenesis by modify baroclinicity. It is worth noting that many of the much complexities of the relationship between the Zagros Mountains and baroclinicity waves that may cause the occurrence of cyclones are a variety of other theories proposed in the literature to be more consistent Atmospheric Sciences. In any case, this study is based on small portions and a special kind of cyclogenesis can be in the Zagros leeward.
Climatology
Nafiseh Rahimi; Saeed jahanbakhsh; Brooman Salahei
Volume 23, Issue 70 , March 2020, , Pages 145-167
Abstract
Strong winds are one of natural disasters that sometimes cause enormous Financial and physical damages. Since northwest of Iran and specially Ardabil Province is one of windy regions, this study tried to identify synoptic patterns which bring strong winds. Through considering equal and threshold wind ...
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Strong winds are one of natural disasters that sometimes cause enormous Financial and physical damages. Since northwest of Iran and specially Ardabil Province is one of windy regions, this study tried to identify synoptic patterns which bring strong winds. Through considering equal and threshold wind speeding over 28 knots per second, 783 days identified as wind crashing days in Ardabil province. Then by data component- based analysis of 500hPa geo-potential height of the 783-days detected seven components which explain 92% of variance. Finally by clustering seven components identified ten patterns as synoptic patterns that are responsible for Strong wind of Ardabil province. The survey of topographic arrangement of these patterns indicates the rise of trough and ridge levels to these patterns. This means that the patterns consists of, mainly, trough, ridge, or combination of both and aren’t observed other systems such as cut off, block systems, etc. Although mentioned systems may be observe in individual patterns of each of the 783 days, but the systems aren’t responsible for the dominance and influence. The temporal distribution patterns show that two patterns, 6 and 7which occurs in the summer, has a similar system at 1000 hPa level when it compares with other models which occur in winter, spring, fall. What's notable, reversal of location position of pressure systems, 1000 hPa, in two patterns of summer, so that a low pressure instead of high pressure is over the Zagros and a high pressure instead of low pressure is over the Caspian Sea.
Climatology
Saeed jahanbakhsh; yagob din pazhoh; mohammad hossein aalinejhad
Volume 23, Issue 67 , April 2019, , Pages 91-107
Abstract
According to the importance of snowfall in supplying water of different regions especially mountainous areas, accurate estimation of snow water equvallent and changes of its coverage would be effective in agriculture, energy, management of reservoir and flood warnings. In this study runoff orginated ...
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According to the importance of snowfall in supplying water of different regions especially mountainous areas, accurate estimation of snow water equvallent and changes of its coverage would be effective in agriculture, energy, management of reservoir and flood warnings. In this study runoff orginated from snow melting in ShahrChay basin under the terms of climate change calculated. For this purpose, snow cover for water year of 2012-2013 were extracted in ENVI software by using daily images of Modis satellite.Then, GIS software the physiographic specification of the basin was obtained. In the next step, data of snow cover, meteorological variables and other necessary parameters to SRM model provided as an input of model and run_off from snow melt was simulated. Then output of the 6 models of atmospheric general circulation with title of 3 scenarios nomely A1B , A2 and B1 converted to a downscaleing by using LARS-WG model. By comparing the output of 6 models in the future period to period based on monthly statistical, the best model and scenario for generation of air temperature and precipitation data in the period 2030-2011 were selected. As a result the HADCM3 model under the scenario A1B was used for generation of precipitation and the MPEH5 under scenarios A2 was used for generation of temperature data. In order to estimate the rate of change of runoff orginated from snowmelt rate of change of monthly data of air temperature and precipitation of the base time period as well as future time period under selected model and scenarios was entered to SRM model in simulation time period. Results for all of the scenarios show that runoff orginated from snowmelt in late spring will be reduced. The peak flow appeared earlier in comparison with base time period and its value would be larger than base time period.
Climatology
Saeid Jahanbaksh; Gholam Hasan Mohammadi; shahnaz rashedi; Atefeh Hoseini Sadr
Abstract
In this study, non-parametric Mann-Kendall test was used to analyze the trend of monthly mean minimum temperature in the Northwest of Iran. For this purpose, the data from 35 synoptic stations in the cold part of year including November, December and January-to-April have been used in the period of 24 ...
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In this study, non-parametric Mann-Kendall test was used to analyze the trend of monthly mean minimum temperature in the Northwest of Iran. For this purpose, the data from 35 synoptic stations in the cold part of year including November, December and January-to-April have been used in the period of 24 years (1987-2010). Kriging interpolation method was used to obtain spatial distribution of mean minimum temperature over study area. The results showed that the minimum temperature in most parts of study area is rising so that in the months of February, March and December respectively in 22, 19 and 17 stations of the 35 stations were determined an increasing trend. While only in April, at 6 weather stations decreased and this parameter is relatively stable in November and January. Spatial distribution of monthly mean minimum temperature indicated that this element is lower in the mountainous parts of study area (including Northwest and Southeast) and whiles in lowlands (including Northeast and Southwest parts), is higher than its regional average. It was also found that regional minimum temperature and its trend in the Northwest of Iran Does not have the same characteristics in different months, so that this parameter in January and in April increased and decreased in November and December. Finally, in November and December minimum temperature has not substantially changed.
Saeed Jahahnbakhsh Asl; Hamid Mirhashemi; Masoomeh Tadayyon
Volume 19, Issue 51 , April 2015, , Pages 107-125
Abstract
In this study to identify the synoptic patterns causing heavy rainfall in East Azarbaijan province used with Environment- circulation pattern. Thus, beginning with the use of statistical methods limit type with return periods of ten-thousand-year, precipitation index for the 9 synoptic stations and climatology ...
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In this study to identify the synoptic patterns causing heavy rainfall in East Azarbaijan province used with Environment- circulation pattern. Thus, beginning with the use of statistical methods limit type with return periods of ten-thousand-year, precipitation index for the 9 synoptic stations and climatology located at the province was determined and finally 25 days was analyzed as day's high Heavy. The clustering of the 1000 hPa geopotential height level these days, were identified three patterns of spring cyclone, deformation and winter cyclone as the creator of this precipitation patterns. Synoptic analysis of this patterns showed that the low pressure at polar latitudes move to down and troughs on the Mediterranean and the Middle East that it has spread. Next to the tropical high pressure and subsequent ridge are moved to higher latitudes. There are conditions in the planetary patterns, increased temperature and pressure gradient zonal and meridional circulation of establishing Cut-off low and blocking high system is in the region. Research area within the affected system has been up and down simultaneously. Thermodynamic analysis using data from the radio station of Tabriz probe showed that the potential instability in the event of heavy rain on the atmospheric vertical profile has prevailed. In fact, because the study area in this period of low and high latitudes is dominated systems and the systems at different height levels of temperature and humidity differences are great together, a stratification of temperature, moisture in the atmosphere will be created and established conditions of potential instability
Saeed Jahanbakhsh Asl; Ali . Mohammad Khorshiddoost; yaghoob Din Pazhooh; Fatemeh Sarafroozeh
Volume 18, Issue 50 , February 2015, , Pages 107-133
Abstract
Trend analysis of 27 indices related with extreme temperature and precipitation during 1961-2011 were conducted in Tabriz using the non-parametric Mann-Kendall test and Sen’s Estimator Slope methods. Furthermore Generalized Extreme Value distribution fitted to observational extreme events. Values ...
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Trend analysis of 27 indices related with extreme temperature and precipitation during 1961-2011 were conducted in Tabriz using the non-parametric Mann-Kendall test and Sen’s Estimator Slope methods. Furthermore Generalized Extreme Value distribution fitted to observational extreme events. Values of quantiles of the variables were estimated for different return periods. Results indicated that during the past half century, trends of indices for summer days, tropical nights and warm nights were upward and statistically significant. Trends of indices related to ice days and cool days were downward and significant. Minimum values of daily minimum and maximum temperature in year indicate significant increasing trends. Indices of number of days with precipitation greater or equal to 10 and 15 mm, consecutive wet days, total precipitation in wet days and total precipitation when rainfall is greater than 95 and 99 percentiles have experienced significant decreasing trends. After fitting GEV distribution to annual values of daily minimum and maximum temperature as well as daily maximum precipitation in Tabriz Growth curves and Q-Q plats were illustrated. Investigation of plots indicated that this distribution function has more capability in fitting of time series of extreme value even in tails of the distribution.
