جستجوی مقالات مرتبط با کلیدواژه « خراسان بزرگ » در نشریات گروه « جغرافیا »

The Great Khorasan in northeast Iran has a variety of surface structures and plains and high peaks, but due to its vicinity to the deserts of Afghanistan and Turkmenistan, it is affected by dust all the time, especially in summer. The purpose of this study was to simulate summer dust in this region by RegCM model. For this purpose, during the period 2000 to 2017, three extreme dust events were selected. The satellite image used to confirmed dust mass presence and then the synoptic structure was analyzed. Finally, the simulation results of RegCM 4.6 model were compared with the observational data including the horizontal visibility and aerosol optical depth (AOD) of Aqua satellite. The synoptic analysis showed that during the summer, low thermal pressures form in the southern Afghanistan and high pressure in the north. This structure lead to the development of north and northeast winds with speeds of 12 to 21 m / s and dust emission on the eastern border of Iran and western Afghanistan. Investigation of RegCM accuracy done by visibility, Aquas’s AOD showed that model performance in South Khorasan is better as Razavi Khorasan. The highest correlation coefficients of AOD of model and horizontal visibility were obtained at Khorasan central stations including Gonabad, Ferdows, Nahaband and Ghaen at -0.82, -0.77 and -0.44 respectively. RegCM model performed a better dust simulation in severe dust with a horizontal visibility down to less than 1000 m, high continuity and horizontal extension. Overall, the RegCM model underestimates the AOD value for the Aqua satellite algorithm.

In this study, rainfall and temperature simulated annual in north-east of Iran (Great Khorasan) In the period 1987-2011. Basedon the results, in LARS model during verification period (2007-2013), average annual rainfall raw bias is equal to 53.63 millimeterand post- processed is -11.25. Shortly, in annual period, in 84% of studied stations, post-processing techniques have been effectiveand bias error rate has decreased heavily in more stations. Based on the results, in Reg-CM4 model during verificationperiod (2006-2011), average annual rainfall raw bias is equal to 85.3 millimeter and post- processed is 61.04. Shortly, in annualperiod, in 75% of studied stations, post-processing techniques havebeen effective and MA technique is more effective. So absolutebias error after processing an average annual rainfall of LARSequal to 6/13 and RegCM4 model is 61 .average annualtemperature raw bias is equal to 0.096 millimeter and post- processed is -0.432. This is more than bias without post-processing hence, post-processing is not effective in all stationsand only in 46% of stations are good. Simulation of 2--meter temperature data in climate stations with RegCM modeland MA technique show high effectiveness. Average annual temperature rawbias in RegCM4 model is equal to -2.78 millimeter andpost- processed is -0.05. In all stations modeled annual temperaturewith Observed data has difference less than 0.1. Also inrainfall simulation, LARS_WG model is more better than RegCMmodel and in simulation of annual temperature data, dynamic RegCM4model show more clear Objectivity of researched area rather thanLARS_WG model

Climate change with changing climate patterns and confounds Ecosystems discipline, imports Serious consequences on the environment. Changes in weather patterns Could Lead to severe flooding, extreme heat or cold, more frequent droughts. Each of these phenomena could put at risk the regional food reserves. North east of Iran due to the large area has very varied natural conditions and each of the areas included specific natural features. The extent of the area and factors such as mountains rising, desert areas. In this research, were use 25 year synoptic meteorological stations (14 stations) statistics from1/1/1987 to 31/12/2011? Result show that some station such an Ghochan and Sabzevar, show an decrease trend in the number of extreme temperature indices (CSDI, TR20,TNX,FD,TN10P). Other stations, in 90%, experience increase extreme temperature changes. Among the indicators, in the first order; the days of Summer, the warm days, The maximum temperature limit, the warm nights, the warm period duration Indicators Show an increase of 100% and cold days index shows an decreas of 100%. Also the minimum temperature of at least, maximum temperature of at least and tropical night indicators by more than 85% increasing trend and the cold night index by more than 85% are In second place. The maximum temperature of at least and the growing season duration indicators with 71% and 69% increasing trend and the ice days index with 71% decreasing trend, are In the third place. Hence we can derive the great Khorasan experience sever increasing temperature changes in last 25 years and based on behavior of indices, severity of this changes in coming decades will be multiple.

Atmospheric hazards are defined as any atmospheric event، which adversely affect or may adversely affect human life، property، or other aspects of the environment. The events can influence all aspects of human life. The main purpose of this research is zonation of atmospheric hazards in the northeast of Iran including North Khorasan، Khorasan Razavi and South Khorasan. In order to achieve the purpose، the spatial distribution of all atmospheric hazards، which occur over the area، has been investigated in terms of frequency and intensity. Study Area: Study Area is located in the northeastern of Iran with an area of 300000 Km between N30 21 to N38 17 latitudes and E55 28 to E61 14 Longitudes. The Study Area concludes three following provinces in the country: Khorasan Shomali، Khorasan Razavi and Khorasan Jonobi which have been separated from great Khorasan during the past decade. Extending the region from low latitudes to high latitudes and affected by different climatic systems resulted occurrence of a set climatic hazards throughout the study area. This paper is focused on atmospheric hazards zoning in the area using geographic information Systems (GIS). In order to identify the spatial distribution of each atmospheric hazard، the meteorological data of 17 weather stations in North Khorasan، Khorasan Razavi and South Khorasan is used for a 38-year (1971-2008) period. In this basis، 13 variables including precipitation، mean temperature، maximum temperature، minimum temperature، wind direction and intensity، visibility and weather conditions in terms of daily and monthly scales were used to investigate the frequency and the intensity of atmospheric hazards. In the first step، 13 major atmospheric hazards، including drought، heavy and extreme precipitation events، heavy snowfall، hail، thunderstorm، blizzard، fog، dust storm، dusty days، heat wave، frost and wind-chill events were identified in the scope of northeast of Iran. To make a general zonation map for atmospheric hazards، we analyzed each atmospheric hazard by a distinct method with regards to the characteristics of each hazard. Using the distinct methods، we determined the frequency and intensity of each hazard. Then، the Geography Information System (GIS) is applied to make a spatial analysis of the events and spatial distribution map is produced for each hazard by using ArcGIS tools. In the next step، all atmospheric hazards have been contained in three categories، with regards to their similarities and differences. Therefore، all atmospheric hazards categorized in temperature-based hazards، precipitation-related hazards and weather hazards related to visibility. As a final step، we combined all atmospheric hazards to make a general zonation map for the Northeast of Iran. The results indicate that the freezing and wind-chill events are the most frequent hazards in the northeast of Iran. It is found that، while the temperature-based hazards are increasing from north to south، the spatial distribution of precipitation-related hazards is showing an inverse mode، so that they are increasing from south to north. In contrast، the spatial distribution of atmospheric hazards related to visibility is more zonal than meridian direction. Therefore، they are showing a decrease from east to west. The final zonation map of atmospheric hazards which produced by combination of all elements confirm that the more hazards in northern part of the study area can be caused by the high frequency of eastward movement of extra-tropical systems as well as high mountains arrangement in northeastern part of Iran. The research showed that the north and northeastern parts of the study area hit by more atmospheric hazards and has the highest frequency of atmospheric hazards in regards to spatial analysis of the events. Therefore، we can conclude that the large parts of northern and northeastern Khorasan should be considered the most risky area over the whole domain. In contrast، the western and southern parts of Khorasan are the lowest risky areas as well. The results also indicate that the wind-chill event is the dominant atmospheric hazard over the entire domain in terms of frequency.