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In this research the detection, frequency and quality of behavior of extratropical cyclones in different seasons of year within 1995-1996 are studied. To reach such a goal, data of geopotential height with six-hour temporal resolution and spatial resolution (2.5. 2.5) for different levels (500, 600, 700, 850, 925, 1000) were extracted from atmospheric databases and used (NCEP/NCER). Cyclones were identified by which two requirements were considered including 1- the places whose geopotential height is minimum in relation to the eight neighboring places, 2- regional geopotential height gradient in nine points present in at least 100m/1000km. The results show that in all levels, cyclones in winter and autumn have the highest frequency with very little difference. Frequency distribution in winter is more unified than other seasons and cyclonic areas intend to lower latitudes. One of the most evident features of this season is the presence of cyclonic areas in Mediterranean region. Spring is in the third level due to its cyclonic frequency. From frequency perspective summer cyclones have the least amount with the highest difference. Gang cyclone as the most evident features of other cyclones in 1000 and 925 HP levels are seen in spring and summer. Summer rainfalls and 120-day winds of Sistan in the southeast of Iran are related to the formation of such a system.

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1. Introduction

Urbanization has profoundly transformed natural landscapes throughout the world, which inevitably has resulted in various effects on the structure, function, and dynamics of ecological systems at a wide range of scales. For example, land transformations associated with urban expansion can significantly affect biodiversity, energy flows, biogeochemical cycles, and climatic conditions at local to regional scales. With accelerating urbanization throughout the world, therefore, it is becoming increasingly important for large-scale ecological research and applications (e.g., natural resource management, land use planning, and biodiversity conservation) to consider these most dramatic land transformations and their ecological consequences. Urban green spaces are fundamental ecological elements in urban structure that formed and transformed in city along time. Green spaces such as parks and sports fields as well as woods and natural meadows, wetlands or other ecosystems, represent a fundamental component of any urban ecosystem. Green urban areas facilitate physical activity and relaxation, and form a refuge from noise. Trees produce oxygen, and help filter out harmful air pollution, including airborne particulate matter. Therefore, sustainable green spaces can provide and enhance the ecological services and urban environment quality. In recent decades, landscape ecology approach has provided a theory and practical framework for assessment of landscape elements spatio patterns. One the most important tools are landscape metric that can quantify the pattern of landscape. In this study, we integrated gradient analysis with landscape pattern metrics to quantitatively characterize the urban green space patterns of Sabzevar urban area, Khorasan Razavi, Iran. We aimed to address several questions: 1) how do different green space types change with distance away from the urban center? 2) How green space sustainability change with distance away from the urban center? 3) What is a relationship between landscape metrics and sustainable properties? The gradient based landscape metrics analysis is now widely used to study the landscape pattern change in respond to urban area.

2. Material and Method

Study Area

City of Sabzevar is one of the cities of Khorasan Razavi province in Iran. It is located in west of Khorasan Razavi in north-east of Iran. The area of this city is 23322 he square kilometer (figure 1). 5500 square kilometer of the total area of Neyshabuor is desert and 3425 square kilometer of this city is heights. It is a part of central plateau climate and it is an arid climate and desert location.

Data and Method

For this study, methodology of research basically involves four steps :(1) to provide a patch layer in vector format (i.e., a polygon layer) was used to measure the composition and configuration of land cover features. It was created based on integrated land use map and calculating and extracting the K-Mean algorithm. (2) Land cover of study area was classified by land use map and combined with land cover map. Fragstate v.4.2 software was used in order to calculate metrics. (3) Landscape metrics were used in order to study quantitative features of vegetation cover, green spaces changes, relations of landscape structure and ecological sustainability. (4) To analysis relationship between sustainability and landscape metrics, gradient analysis was used form center away in two aspects: north-south and west-east. Combining gradient analysis with landscape metrics, we attempted to quantify the spatial suitability of urban green spaces.

Landscape Metrics

To select and application the landscape metrics, previous studies have introduced landscape metrics according to objectives and methodology of research. Although, a series of landscape metrics, have been developed to characterize the spatial patterns of landscapes and to compare ecological sustainability across the landscapes. However, the number of metrics can be used in evaluating the ecological sustainability, but not all landscape metrics can easily be classified as representing landscape composition or landscape configuration. For example, mean patch size and patch density of a particular patch type reflect both the amount of a patch type present (composition) and its spatial distribution (configuration).

3. Conclusion

Our study has demonstrated that the sustainable level and spatial patterns of urban green spaces can be quantified using a combination of landscape metrics and gradient analysis. The results from our study can adequately address the four research questions we defined earlier in Introduction: How does different green space sustainability change with distance away from the urban center? Results showed that green space sustainability decrees with moving from center in two aspects. In landscape levels, semi-public green spaces involved the highest sustainability. Also, Correlation analysis between landscape metrics and sustainability showed TE has the most R² (0.97) and MESH has the fewest R² (0.05). Therefore, urban green space developed along the streets and urban networks, which increase the edges of green patches. However, green spaces have the least amount of continuity; it is necessary the ecological approach in planning and design of green ecological networks .The changes in landscape pattern along the transect have important ecological implications, and quantifying the green space gradient, as illustrated in this paper, is an important first step to linking pattern with processes in urban ecological studies.

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In order to investigate the atmospheric mechanisms governing the occurrence of the Von phenomenon at the time of forest fires in northern Iran, four types of data were used in the research. First, by taking the statistics of fires, the forests of the north of the period were identified. The monitored data of temperature, pressure, and wind in the front and back slopes of the Alborz mountain range were examined, as well as the networked data related to the National Environmental Forecasting / Atmospheric Science Centers (NCEP / NCAR). The European Center for Atmospheric Prediction (ECMWF) was used to explain the structure of the atmosphere. Modis sensor images were used to investigate the surface temperature and a suspended particle regression model was used to track the air mass. Studies have shown that with the formation of hypertension in the south of the country and low pressure in the north of the Caspian Sea, a strong pressure gradient is created and causes the southern currents in the northern regions of Iran to be affected. So that with the rising of the air mass on the Alborz mountain range and evacuation of its moisture and then passing the air package over the mountain and the heatless heat resulting from that hot and dry air mass has entered the region, these conditions are accompanied by strong winds and areas Susceptible to fire. Studies show that there is a sharp temperature difference between the windward and backward areas of the mountains, which is due to the unreasonable decrease and increase of air closure in the region. Airborne tracking also indicates that the main source of current entering the region is in the northern Persian Gulf and Northeast Africa.