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.


Main Subjects

احمدی گیوی، ف.، سلطانزاده، ا. وایران نژاد، پ.، 1375 ،بررسی تأثیرکوهستان وکاربری اراضی اقلیم منطقه ایران با استفاده از مدل اقلیمی منطقه ای، م.فیزیک زمین و فضا، 33، 50-31.
بالالان فرد، ع.، 1392، بررسی اثر ارتفاعات شمالی و دمای سطح آب دریا در رخداد برف سنگین سال 2007 گیلان مطالعه موردی با استفاده از مدل پیش بینی عددی WRF، پایان نامه کارشناسی ارشد، دانشگاه آزاد اسلامی واحد تهران شمال.
درخشان، م.، 1379، مطالعه موردی نقش دریای خزر در دینامیک و تغذیة رطوبتی سامانه های جوی مؤثر بر سواحل جنوبی آن. پایان نامه کارشناسی ارشد، موسسه ژئوفیزیک دانشگاه تهران.
رنجبر سعادت آبادی، ع. و امینی، ن.، 1389، مطالعه بارش‌‌های شدید فصل تابستان استان گلستان(1380-1386)، نشریه پژوهش‌های اقلیم شناسی، 1،59-76.
علیزاده چوبری، ا.، آزادی، م. و علی اکبری بیدختی، ع.، 1376، بررسی نقش رشته کوه البرز در تقویت سامانه های همدیدی، همایش پیش بینی وضع هوا، تهران-ایران.
فراهانی، م.، احمدنیا، م. و علیزاده، ا.، 1376، کاربست مدل پیش بینی عددی ARPS برشبیه سازی توفان برف بهمن 1373 درتهران، م.فیزیک زمین وفضا، 34،165-155.
مرادی،م.، مشکواتی، ا. ح.، آزادی، م. و علی اکبری بیدختی، ع.، 1376، شبیه سازی عددی نقش کوهستان دریک سامانه بارش زا روی ایران، م.فیزیک زمین وفضا، 34،44 -25.
Alpert, P. and S. O. Krichak, 1996: The Relative Roles of Lateral Boundaries, Initial conditions, and Topography in Mesoscale Simulations of Lee Cyclogenesis. J. Appl. Meteor., 35, 1091-1099
Bluestein, H., 1992: Synoptic-Dynamic Meteorology in Midlatitude. Oxford university press., 608pp.
Chen C.C., D. R. Durran, and G. J. Hakim, 2005, Mountain-Wave Momentum Flux in an Evolving Synoptic-Scale Flow. J. Atmos. Sci.,62, 3213–3231.
Cole, B. A., 2003, Sensitivity of orographic precipitation to changing ambient conditions and terrain geometries: An idealized modeling precipitation. J. Atmos. Sci., 61, 588-606.
Durran, D. R., and Klemp, J. B., 1983, A compressible model for the simulation of moist mountain waves, J. Atmos. Sci., 111, 2341-4032.
Holton, J. R., 2004: An Introduction to Dynamic Meteorology. Elsevier Academic Press, 535pp.
Ivancˇan-Picek, B., K., Horvath, N., Strelec Mahovic, M., Gajic´-Cˇapka, 2014, Forcing mechanisms of a heavy precipitation event in the southeastern Adriatic area. Nat. Hazards, 72, 1231-1252.
Krichak, S. O., Alpert, P., and Krishnamurti, T.,1997, Interaction of topography and tropospheric flow possible generator for the red sea trough. Mete. Atmos. Phy., 63, 149-158.
Sun-Hee Jung, Eun-Soon Im, and Sang-Ok Han,2012, The Effect of Topography and Sea Surface Temperature on Heavy Snowfall in the Yeongdong Region A Case Study with High Resolution WRF Simulation, Asia-Pacific. J. Atmos. Sci., 48(3), 259-273.
Tosi, E., and Fantini, M., 1982, Numerical experiments on orographic cyclogenesis: Relationship between the development of the lee cyclone and the basic flow characteristics. Mon. Weather. Rev., 111, 799-814.