Factors Affecting the summer rainfall in a region with complex topography (Case Study: Golestan Province)

Iran is a vast land of geographically specific features and the climate is quite different. Each year a number of times, short intense rains caused flooding in various parts of the southern coast of the Caspian Sea and river flood malicious conduct is falling. The rainfall intensity is greater and more destructive floods caused heavy damage. Severe flooding during the brutal summer precipitation in the region, notably Iran, which sometimes lead to large losses of life and property. Having the proper depth of the Caspian Sea and the north-south strain and temperature is relatively constant during the period of two to three days, thus having the potential to heat and high humidity, high impact weather system is feeding. Another factor influencing the occurrence of floods in Golestan province Alborz mountain range and its effect on the flow of the atmosphere and therefore the issue is complex. Factors such as height and width roughness, and the interaction of the Alborz mountains to heavy rainfall in the region and how the agent is effective. Here a summer torrential rainfall in Golestan province is simulated using the WRF model toinvestigate the effective factors. 30 vertical sigma levels are used in the network. To run the model horizontal resolution of 3 nesting range of 90, 30 and 10 km in length and latitude is used. During geographically considered the center latitude 54,15 and 35,51 respectively. Model of internal networks and the highest point is 27 × 27, 31 × 43 and 34 × 45 grid points are. Depending on the selected physical model microphysics scheme WSM5, longwave radiation scheme RRTM, shortwave radiation scheme Dudhia, cumulus parameterization scheme and Kian-Fritsch are YUS boundary layer.To investigate the role of vertical surface fluxes and effects of the Alborz mountains on rainfall intensity in the selected system, four experiments were conducted to test the model simulation with control (CTL), the physical model was used. In a second experiment was to delete the Elburz Mountains (NTO), in the third experiment, the vertical flux of moisture and temperature of the Caspian Sea has been removed (NFL) and the fourth test of the Elburz Mountains and vertical flux of moisture and temperature simultaneously removed the Caspian Sea (BOT) and the results of the first experiment (control) were compared. Using the output of the model, some parameters such as the effective rainfall floods the advection of temperature, convective available potential energy, vorticity advection in the simulations were calculated and analyzed.
The results show that the mechanisms of rainfall in the Golestan province depend to position of phenomena. So that the horizontal convergence of heat and humidity fluxes are the main causes of rainfall along the coastline of the Caspian Seawhile the rainfall over Northern part of Alborz mountains range is caused by the forcing ascent over the mountain. The heavy rains in the South East of the Caspian Sea occurred due to the horizontal convergence of heat flux, intense upward vertical flux and significant amount of CAPE.Convective instability in this area is due to the warm advection in surface and cold advection in middle troposphere. Upward motion and precipitation start with positive vorticity advection in 500-hPa level which is affected by Alborz Mountain strongly.