عنوان مقاله [English]
Thunderstorm rainfall is one of the most important climatic phenomena in the northwest of Iran that has specific variability in spatial distribution. These rains have an important role in case study area climates. The purpose of this study is investigation of spatial distribution of Thunderstorm rainfall of Mountainous Areas of the Northwest of Iran to modeling Thunderstorm in northwest. Because of that TRMM images precipitation data from 2009 to 2012 is selected & in the software Arc Gis ,ENVI and EDRISI, have been processed.
Precipitation is one of the crucial elements of climate that Temporal and spatial variation can control a variety of geographical area. In this case thunderstorm is one of the most important climatic phenomena of area. Sometimes these rains provide waters to crops & especially in summer leave catastrophic effects on the natural environmental and agricultural economy. Thunderstorm is related to the warm months of the year. In some cases thunderstorm rainfall can cause flooding and destructive disaster in all over the area. Therefore, this type of precipitation can be considered as a representative of regional climate, especially in spring and summer).
Identification of geographic factors including elevation with precipitation of the study area and access to the regression model, the aim of this paper.
Conrad (1996) in a study had shown high correlation between height and distance from the source of heat, humidity, Cold and warm precipitation in Blorych Mountainous of America.
Johansson (2003) in a study about the effect of topography on precipitation distribution on Sweden slopes concluded that, precipitation increases with increasing elevation in windward slopes.
Case stydy area
The study area is located in the range of 40 to 36 degrees north latitude and 49-40 degrees east longitude, Sahand Mountainou and Arasbaran ,sabalan Bozghoush, misho, and Zagros Mountainous in West of Lake Urmia are the most important features in case study area. . Urmia Plain, moghan, plains of Tabriz, Ardabil, Sarab, Ahar are the most regions of the Northwest of iran( Motalab faed ,1386). Overall, the area climate is affected by two major factors, such as the topographic features, synoptic. The first and most important factor that affected the climatic zone, climate system in Synoptic-scale that has main role in Explanation of region climate in long-term (Masuodian , 2003).
Materials and Methods
To modeling thunderstorm rainfall, TRMM images of precipitation days from 2010 to 2012, has been downloaded from the site http://lake.nascom.nasa.gov/tovas/
This method is mainly a mathematical method that is based on the distance between points of observation that interpolated. The method of inverse distance weighting approach which is an advanced proximity of neighboring stations to estimate of the weight issue uses. in This way nearest station has more weight than the other stations.
DEM is a simply statistical representation of the continuous ground By the large number of selected points with coordinates x, y and z of a range of optional coordinates. In the other words, DEM is a digital or numerical display of the true ground
Results and Discussion
Study of Rainfall Fluctuations to height and determine the regional gradient rainfalls relation to estimate the amount of rainfall points , Due to high levels, especially in areas without weather station is important .this is usually done as parametric methods in whether studies ( Jahanbakhsh s.2011).
The image height as the independent variable and the dependent variable was selected asTRMM images rainfall. The Average rainfall of TRMM images from 2010 to 2012 is used as the dependent variable.
The correlation confident above 63/0, which shows a positive correlation, Because of more than 5/0, it has a good correlation& shows high positive correlation .It means that it increased with increasing altitude, Residual sum of squares is smaller than the, Regression sum of squares .This indicates that the model has high explanatory power . The Model 99/0 is significant .T-test of the model is more than 33/2 ,as a result, T-test of model at 99/0 is meaningful.
In this study has shown a high correlation between trmm rain & dem & thunderstorm rainfall is raining in spring & summer too.
Keyword: thunderstorm rainfall, Modeling, spatial distribution, Mountainous Areas of the Northwest of Iran.