Synoptic-Dynamical Analysis of Garmesh Wind as an Atmospheric Hazard over the Alborz Mountains

Synoptic-Dynamical Analysis of Garmesh Wind as an Atmospheric Hazard over the Alborz Mountains Abstract Garmesh as an atmospheric hazard is dry, warm and down-slope wind in the leeward slope of Alborz Mountains range. It has major effects on rapid snow-melting and spread of wildfires in northern slope of Alborz Mountains. In this study, for the first time, daily, monthly and seasonal variations of Garmesh wind were analyzed by observed data (SCDATA) of several meteorological stations in northern slope of Alborz Mountains during 1982-2010. Then dynamical and synoptic patterns of Garmesh wind were studied using atmospheric parameters like sea level pressure, temperature, specific humidity, Geo-potential height, U-wind, V-wind , vortisity, vertical velocity, stream, humidity advection and temperature advection by data of NCEP/NCAR. Results indicated Garmesh wind occurrence was extreme in the cold months and Coupling of the two air masses, high pressure air mass on south slope of Alborz Mountains and low pressure air mass on north slope of Alborz Mountains south is essential factor to form southern(northward) streams (positive component of V-wind) and orographic lifting. Dynamical sub-polar low pressure and Mediterranean low pressure over southern coastal of the Caspian Sea and high pressure air with different origins like the Siberia high pressure and sub tropical high pressure belt over Iran central plateau led to pressure gradient and also wind speed increase. In 850 hPa level, temperature and humidity advections patterns confirmed positive temperature advection and negative humidity advection over North Slope of Alborz Mountains in the low-troposphere. Negative vortisity and positive omega represented air Subsidence in the leeward of the Alborz Mountains. Observation data and images of Modis sensor on Terra and Aqua satellite indicated 3 states of weather conditions over windward slope for different atmospheric patterns, clear sky, semi cloudy and precipitation conditions. Keywords: Garmesh wind, Alborz Mountains, synoptic patterns, warm advection