عنوان مقاله [English]
To study the atmospheric structure at the time of Thunder storm occurrence in Kermanshah province, were used the transmitted codes from synoptic stations of the province. To study the atmospheric structure, the sea level pressure parameters, geopotential heights, specific humidity, Uwnd and Vwnd were obtained from the NCEP / NCAR Web site, and Radio sonde data was used for intermediate studies. To illustrate this phenomenon, the WRF model was used with a resolution of 15 km. Finally, in order to evaluate the model output in the rainfall section, the estimated rainfall values of the TRMM sensor. The results showed that the cold weather and the formation of a deep cave on the west of Iran, the emergence of severe pressure gradient in the northwest and west of the country and the formation of a cold front in the region, were the main synoptic factors during the storm. Also, the role of the Arabian Sea, Red Sea and Persian Gulf can be mentioned in providing rain water resources. On the other hand, extreme climbs of the air have played a major role in the formation of bubble clouds and hailstones. The review and evaluation of the WRF model output (Estimated precipitation is 18 mm) and TRMM sensor (Estimated precipitation is 19 mm) compared to reported rainfall from stations (Estimated precipitation is 17 mm) showed that this model with RMSE=1 mm is suitable for exploring the structure of atmosphere in the region to dynamically visualize intermediate scale phenomena such as thunder storms.
Keywords: Thunderstorm, Synoptic, WRF model, TRMM sensor, Kermanshah province.
Thunder storm is one of the most important, most abundant and most severe atmospheric hazards that due to its combination with rainstorms, hail and lightning, its effective role in creating sudden floods, both in terms of agriculture and in terms of financial and life damage, this phenomenon has always been of interest to researchers. Hail from grains or pieces of ice with a diameter of 5 to 50 mm and sometimes more. Hail intensive growth is the result of intense and frequent vertical movements of the air in the clouds of the cumulonimbus, which causes hailstones to absorb water droplets around them and freeze them. Creating and hailing, the presence of hot and humid air at the bottom of the atmosphere and climbing clouds accumulated with high altitude and high temperature combined with the continuation of the conditions of maximum instability of the air. Because of the importance of the hail event, studies have been conducted on its formation and growth in different countries in order to anticipate them. This can be cited by Sterling (2003) Prosenjit et al. (2008) by Litta et al. (2012).
Materials and methods
The Advanced Modeling System (WRF) is an interdisciplinary and flexible model with many capabilities that can be used to simulate different atmospheric conditions. This model has been developing over the past few years, the model is available on a variety of computer systems, including a computer cluster, its range is very wide and covering a range between several meters to thousands of kilometers and by varying the different modes of physical parameters in the model, a wide range of performances can be achieved. In the course of this investigation and to simulate real thunderstorm was used from version 3.8 Medium scale WRF model. For this purpose, the network was considered with a horizontal resolution of 15 km with a moderate resolution in a network with dimensions of = 316x, = 451y. Also, FNL-type data were used with a one-degree separation as three hours.
Discussion and results
In Fig. 2, the arrangement of pressure patterns is such that a high pressure masses with a central pressure of 1016 hPa in the south of the Black Sea causes an hourly flow to occur in this region. On the other hand, in central Iran, a low-pressure cell with a central pressure of 1004 hPa has caused pressure gradient on the country. With an increase in the pressure gradient of about 12 hPa, a fracture in the pressure lines in the south of the Caspian region has occurred, which continues to the west of Iran. The formation of the fronts with extreme high currents has made it possible to provide conditions for incidental precipitation and thunderstorms in the region. On the other hand, in the middle of the atmosphere and on the west of Iran, the cold weather of the troposphere with the loss of geopotential has led to an ever-increasing upturn in air and instability. With 5450 geopotential meters placed on the area, a very powerful rotating core has affected all of the western and northwest regions of the country. This cold weather has caused the formation of a cold front in the region resulting in heavy rains and heavy storms along with hail in the area.
The results showed a high pressure masses with a central pressure of 1016 hpa in the south of the Black Sea, causing an hourly flow in this area. . On the other hand, in central Iran, a low-pressure cell with a central pressure of 1004 hPa has caused pressure gradient on the country. The model output also showed the highest positive vortices in the mid-range in the Iraq-Turkey region, which includes another core of the south-west. The existence of instabilities at all levels in the western regions has caused the conditions for storms in the region. The results of the total precipitation also showed that by eliminating the initial 6 hours of the output of the model, the maximum changes and the region's potentiality from the atmospheric systems referred to the east of Kermanshah province. Therefore, it is needed to demonstrate this phenomenon from the previous day and use more hours to explain the behavior and structure of the Thunder storm in the WRF model. On the other hand, it can be pointed out that simultaneous use of satellite data and dynamic model can be a good way to monitor and predicting thunderstorms with hail.