relative humidity and moisture flux convergence during the dusty days in alvand mountain

the moisture flux convergence (mfc) and relative humidity in dusty days at different times and levels over the alvand mountain was investigated. the required basic data for the years 2009-2012, including relative humidity, visibility and synoptic codes, were gathered from hamadan synoptic station, while sea level pressure, uwind, vwind and specific humidity data were gathered from ncer/ncar site. the dusty days were categorized into four groups, according to wmo protocol. sea level pressure (slp) patterns were classified using cluster analysis (ca). mfc function, jet stream and omega maps were computed using special moisture and horizontal and vertical components of wind, slp and omega data in various levels and times for each sea level pressure pattern. the results showed 6 categorized patterns of sea level pressure. the highest values of mfc were observed at 1000, 925 and 850 hpa levels and at 12:00 and 18:00 utc. mfc value strongly decreased in dusty days at the 700, 600 and 500 hpa and at 06:00 utc. the relative humidity significantly decreased at 12:00, while the maximum increase was recorded at 18:00 and 00:00 utc.