Yunes Khosravi; Hassan Lashkari; Aliakbar Matkan; Hossein Asakareh
Abstract
Introduction
Survey of spatial relationships of environmental data is considered as one of themost important goalsof spatial statistics for analyzing the spatial patterns and understanding the spatial dependencies. In this context, the Exploratory Spatial Data Analysis (ESDA) could well provide methods ...
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Introduction
Survey of spatial relationships of environmental data is considered as one of themost important goalsof spatial statistics for analyzing the spatial patterns and understanding the spatial dependencies. In this context, the Exploratory Spatial Data Analysis (ESDA) could well provide methods for distinguishing betweenspatialrandomandnon-random patterns. Using the ESDA for analyzing the spatial autocorrelation of climatic elements is necessary to distinguish their changes and spatial distribution. The present research is aimed at explaining the use of ESDA to describethe spatial patterns ofwater vapor pressureas one of the most important climatic parameters. Water vapor pressure plays a crucial role in climate system as an important feedback variable associated with the earth’s energy balance and hydrologic cycle. This climatic parameter has an important rolein explaining the climate change or changes in climatic parameters, because: 1) It is the main sourceof rainfall in allweathersystems, 2) It suppliesthe latent heatin this process and controls the heat inthetroposphere, 3) It is the booster of the storm's speed and 4) It plays a major role in the dynamics of atmospheric circulation. So, determination and interpretation of the likely reasons of Water vapor pressure changes and its variability are vitally important for human as well as other living-beings.
Materials & Methods
The studied area, with about 360,200 km2 area, is located in the South and the Southwest of Iran and approximately between 25° 00'N and 34° 25'N latitudes and between 45° 38'E and 59° 17'E longitudes. Southern and southwestern parts of the studied area are located beside two massive sources of moisture, i.e. Persian Gulf and Oman Sea. The main mountain chain in the studied area is Zagros that extends from the northwest to the Southern part of the studied area. The Zagros mountainrange is responsible for the major portion of rain-producing air masses that enter the region from the Western and Northwestern sides, with relatively high amounts of rainfall. In this study, water vapor pressure data in pixels (dimension of 9×9 km) inthe time interval of 1981-2010 were collected by the Iranian Meteorological data website (http://www.weather.ir).To interpolate the water vapor pressure, Kriging Inverse Distance Weighting (IDW) and Radial Basis Functions (RBF) were tested and so after theerror validation, the optimum method (Ordinary Kriging with Gaussian method) was chosen. Considering the aim of this study, analyzing the spatial variability of WV in regional and local scale, the most important geographical features such as elevation, longitude, latitude, slope and other aspects were chosen. Topographical maps of the studied area were collected by the Geological Survey of Iran (http://www.gsi.ir). The Digital Elevation Model (DEM)with a 10 Km cell size was derived by mosaicking, geo-referencing, and editing these maps in Arc GIS 10.2 software, and the geographical features were prepared based on it. Moran's I, local Moran'sAnselin, and LISA were used asESDA’s approaches to analyze the spatial autocorrelation of water vapor pressure patterns based on climate parameters.
Results & Discussion
According to the cross validation, it was cleared thatthe optimum method for interpolation of water vapor pressureis Ordinary Kriging with Gaussian method. The results of Moran’s Istatistic showed that the water vapor pressure hasspatial structure and is distributed in cluster patternin the South and the Southwest of Iran. The monthly surveys showed thatthe spatial autocorrelation of water vapor pressure in warm months is higher than the cold months and therefore hasa greater tendency to cluster. The results alsoshowedthat the water vapor pressure is tending to disperse and non-clusterinspace in the South and SouthWest of Iran. The bivariate Moran's Istatistic for relation of water vapor pressure and longitude showed thestrong and positive spatial autocorrelation and also clustered pattern.
Conclusion
The monthly surveys showed that the spatial autocorrelation of water vapor pressure in warm months is higher than the cold months and is more tending towards clustering. The existence of such situation in most regions of the studied area in the warm seasons reflects the consistency and homogeneity in this seasons in relation to other seasons. The main reason for these circumstances may be the lack of non-diversification of input pressure systems in these seasons, climate uniformity and sustainability and effects of local systems. Over the time, the water vapor pressure in the South and Southwest of Iran has tended to be more dispersed and less clustering in space. The reason for this incident is not fully revealed but it may be attributed to topographical effects, changes in system positioning, land use changes, etc.Investigating the relationship between spatial distribution of water vapor pressure and geographical parameters showed that the relationship betweenwater vapor pressureand latitude,elevation and slope suggested adispersed and heterogeneousspatial distribution between them. The results of the bivariaterelationship betweenwater vapor pressureand other aspects suggested a discontinuous and random relation.
Mahmood Ahmadi; Hasan Lashkari; Ghasem Keikhosravi; Madjid Azadi
Abstract
Abstract
The present study was conducted to simulate precipitation and temperature with the RegCM4 and LARS dynamic model in two states, with and without using the statistical post-processing technique of direct model output in the north-east of Iran (Great Khorasan) and the statistical period of 1987-2011 ...
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Abstract
The present study was conducted to simulate precipitation and temperature with the RegCM4 and LARS dynamic model in two states, with and without using the statistical post-processing technique of direct model output in the north-east of Iran (Great Khorasan) and the statistical period of 1987-2011 in the annual time period. Based on the results, the annual bias average raw precipitation is equal to 53.63 millimeters and the post-processed is -11.25 in the LARS model in the study area during the 2007-2013 verification period. In summary, performing post-processing technique has been effective at 84% of the study stations in annual time scale and has reduced severely the bias error rate in most stations. Based on the results obtained from the RegCM4 model, the annual bias average raw rainfall of the RegCM4 model is calculated to be 85.3 millimeter and the post-processed to be 61.04 during the 2006-2011 verification period. Therefore, error values in most stations are very high before and after processing and the model results are not acceptable. In summary, performing post-processing technique has been effective at 75% of the research stations in annual time scale. Therefore, the absolute value of the bias error of the average annual rainfall post-processing of the LARS and RegCM4 models are equal to 13.6 and 61 respectively. The annual bias average raw temperature of the LARS model is equal to 0.096 degrees Celsius and the post-processed is -0.432. Practically, this is larger than the bias without post-processing, so post-processing operation is not effective in all stations and is only well defined in 46% of the stations. Simulation of 2 meter temperature data at the meteorological stations using the RegCM4 model as well as MA operations showed high efficiency.The annual bias average raw temperature of the RegCM4 model was -2.78 degrees centigrade which fell to -0.05 after applying post-processing technique. At all stations, the modelled annual temperature is different from observational data less than 0.1 ° C. Therefore, in the simulation of annual rainfall data, the LARS model is even more responsive than the RegCM4 model. And, in simulating the annual temperature data, the RegCM4 dynamic model shows a much better reality than the LARS statistical model.
Hasan Lashkari; Mahdi Khazaie
Volume 23, SEPEHR , July 2014, , Pages 70-79
Abstract
In order to investigate synoptic patterns of heavy precipitations in Sistan va Baluchestan province, 24 year (1987-2010) daily data of 6 synoptic stations was retrieved from meteorology organization. Moreover, data like sea level pressure, geo-potential elevation of 500 and 850 milibars were exploited ...
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In order to investigate synoptic patterns of heavy precipitations in Sistan va Baluchestan province, 24 year (1987-2010) daily data of 6 synoptic stations was retrieved from meteorology organization. Moreover, data like sea level pressure, geo-potential elevation of 500 and 850 milibars were exploited from NCAR/NCEP database and then required maps were prepared in Grads software. Generally, two patters have resulted in the heavy precipitations in this province.
In the first pattern which resulted in precipitations of December12, 1995, a cyclone with contour plot of 1017.5 and 1020 milibars crossed the Arabian Sea, 24 hours before the precipitation and caused humidity spreading toward the area. In 850 milibars, a cyclone above the country results in cold weather flow and a low pressure system with a 1500 geopotenial meter contour plot passed the Bangla Gulf and the Arabian Sea and supply the necessary humidity conditions for rising in this equilibrium level.
In the second pattern which resulted in precipitations of June 5, 2010, a large low pressure system is formed 24 hours before the precipitation over southern part of Asia, which also influence south eastern and southern parts of Iran. 24 hours before the precipitation, a low altitude center covers the area under study and supply humidity and instability. On the day of precipitations, study area in 850 and 500 milibars are affected by a trough of 1475 and 5850 geopotenial meter contour plot and results in precipitation of this pattern.
Hasan Lashkari; Maryam Sabuei
Volume 22, Issue 87 , November 2013, , Pages 32-38
Abstract
In order to investigate the dominant patterns in atmosphere during the occurrence of dust storm in Khuzestan province, time and date of occurrence were exploited from 11 synoptic stations during 1997 to 2006. Afterwards, 19 dust storm were exploited which involved at least 6 stations and lasted at least ...
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In order to investigate the dominant patterns in atmosphere during the occurrence of dust storm in Khuzestan province, time and date of occurrence were exploited from 11 synoptic stations during 1997 to 2006. Afterwards, 19 dust storm were exploited which involved at least 6 stations and lasted at least for 2 days, and their related 00, 850, 700 hectopascal pressure level maps were explored. The results identifies 4 dominant patterns during the occurrence of dust storm in Khuzestan province: a) Pakistani low pressure system at ground level, trough at 850 and 700 hectopascal level, b) low pressure system at ground level, trough at 850 and ridge at 700 hectopascal level, c) low pressure system at ground level, ridge at 850 and 700 hectopascal level, d) dynamic Mediterranean low pressure and Siberian high pressure system, trough at 850 and 700 hectopascal level.
Hassan Lashkari; Zahra Hojjati
Volume 21, Issue 82 , September 2012, , Pages 14-21
Abstract
In order to investigate synoptic-dynamic situations which results in thunder storms in South Western parts of the country, data were exploited from 16 synoptic stations in South West of Iran during a 10 year statistical period (1996-2005). Fitting the precipitation data, six types of severe storms were ...
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In order to investigate synoptic-dynamic situations which results in thunder storms in South Western parts of the country, data were exploited from 16 synoptic stations in South West of Iran during a 10 year statistical period (1996-2005). Fitting the precipitation data, six types of severe storms were identified. Exploring the exploited systems, two general patterns were identified for thunder storms with severe precipitation. The first pattern follows integrated systems pattern, so a ridge from North West Africa to Scandinavia causes cold weather falling on the Mediterranean Sea and deepens the Mediterranean trough, which in turn strengthen the East Mediterranean low altitude center. Continuous cold weather falling on this cyclone center increase pressure gradient in east Mediterranean area and makes penetration of 500 hecto Pascal trough toward middle Red Sea possible. Increased temperature gradient over North Africa and the Red Sea strengthen Sudanese system and while moving toward North of this system integrates with low pressure Mediterranean system and results in unsustainability in West and South West Iran. The Second pattern is a low pressure Sudanese one. Low pressure Scandinavian system result in cold weather of pole neighboring latitudes falling into lower latitudes. Azore anticyclone which is formed over North Africa transfers cold weather to North Africa, aggravates unsustainability, strengthen Sudanese system and creates a weather front. Thunder storms require access to hot and humid weather which is injected into the area due to the proximity of Southern seas.
Farideh Golvani; Hassan Lashkari
Volume 20, Issue 79 , November 2011, , Pages 31-36
Abstract
The purpose of this study was to determine the role of Foehn wind on forest fires in Gilan province and forest fire prediction methods. For this purpose, fire statistics of Gilan forests were selected during the statistical period (2002 - 2006) and synoptic maps of sea level were investigated during ...
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The purpose of this study was to determine the role of Foehn wind on forest fires in Gilan province and forest fire prediction methods. For this purpose, fire statistics of Gilan forests were selected during the statistical period (2002 - 2006) and synoptic maps of sea level were investigated during fire. The results of this study showed that the two cyclone patterns of northern Europe and migratory high-pressure have been effective in the Foehn phenomenon of the southern Alborz slopes. By studying the first method of prediction (Factor B of Angstrom risk) of fire caused by the Foehn phenomenon it is concluded that the migratory high-pressure system is the main cause of Foehn and fire in the region.
Hassan Lashkari; Ghasem Key Khosravi
Volume 19, Issue 75 , November 2010, , Pages 60-66
Abstract
Strong winds have been named storms, which, in various forms and at high speed, blow over for a short time and are usually accompanied by unstable air. If unstable air is humid, a thunderstorm, and if it is dry, a dust storm will form (Alijani, 2000). In all stations of Hamadan province the majority ...
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Strong winds have been named storms, which, in various forms and at high speed, blow over for a short time and are usually accompanied by unstable air. If unstable air is humid, a thunderstorm, and if it is dry, a dust storm will form (Alijani, 2000). In all stations of Hamadan province the majority of thunderstorms occur in the spring. In this season, the greatest number of thunderstorms have occurred due to increased solar radiation energy, which is characterized by significant atmospheric moisture content due to evaporation and vegetation cover, wet lands and transitional thermodynamic systems from the west and southwest of the country. The fall season is second in terms of the number of Thunder storms. In this season, due to the high radiation energy and the arrival of unstable systems with an appropriate moisture source, the number of thunderstorms is significant. The smallest number of thunderstorms belongs to winter. The maximum average of dust storms occurs mainly in dry areas without vegetation, and the number of these storms is less in the mountainous areas of Hamadan. The seasons with most frequent storms in the districts of Ekbatan, Hamadan, Noghe and Malayer are spring and summer, and at Nahavand station the summer season. The study of the trend of hourly changes in storms frequency shows that the maximum occurrence of these storms is from 9 am on, and at 6 p.m. their intensity and frequency decreases, and in all stations the frequency of these storms is higher in days than in nights. According to the conducted surveys, the most activity of dust storms is in the spring and summer. Although during this period of time the ground for local instability is provided due to the high radiation energy and suitable topographic conditions, but the energy of the systems is evacuated as dust storms because of the lack of adequate moisture.
Hushang Ghaemi; Hassan Lashkari; Tayyebeh Namdarian
Volume 19, Issue 74 , August 2010, , Pages 69-74
Abstract
Recognition of the country's precipitation regime and its spatial and temporal dispersion can be a better basis for proper planning to deal with damage and reduce the effects of abnormalities of water resources. In the present study, the monthly and annual data of 22 synoptic stations during the statistical ...
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Recognition of the country's precipitation regime and its spatial and temporal dispersion can be a better basis for proper planning to deal with damage and reduce the effects of abnormalities of water resources. In the present study, the monthly and annual data of 22 synoptic stations during the statistical period (1986-2005) have been used to determine the time and place indices of precipitation and its changes. (Table 2 shows the geographic position of the stations). The analysis shows that according to the average station precipitation of 20 years old, precipitation in the northwest of Iran is 354 mm, variation coefficient of precipitation 0.26, skewness 0.39 and bezel 0.86 respectively. Studies have shown that rainmaking systems that invade the area create different effects due to the geographic location of the stations.
Hassan Lashkari; Reza Davari
Volume 13, Issue 49 , May 2004, , Pages 21-25
Abstract
The province of West Azerbaijan, due to its geographical location, topographic conditions and governing atmospheric systems, experiences from cold to semi-cold weather over the main part of the year. Consequently, during five to eight months of the year, cold-to-cool bioclimatic conditions prevail in ...
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The province of West Azerbaijan, due to its geographical location, topographic conditions and governing atmospheric systems, experiences from cold to semi-cold weather over the main part of the year. Consequently, during five to eight months of the year, cold-to-cool bioclimatic conditions prevail in the province.Owing to these conditions, the main priority in the overall design of buildings is that of receiving the maximum radiation energy in residential areas, especially in the cold season. Considering the prevalence of cold and cool bioclimatic conditions in the province as well as the little need for the air flow to create comfortable conditions in the environment (less than 10% in year), the best direction for using solar energy to heat residential areas is “southeastern” in the southern and central parts of the province, and “southern” in the northen part of the province.
