چکیده:
As widespread deserts is located in west and southwest of Iran plateau, dust storms form due to west and
southwest systems over Syria or Iraq as well as Arabian Peninsula. These systems severely affect west and southwest
regions. Sometimes the fine dusts transmit to central, north east, and east regions. In this study for investigating dusty
synoptical patterns, meteorological data at 5 synoptic stations were studied during recent ten years. Mean daily sea
level pressure data were selected from the NCEP reanalysis data encompassing the region from 20°-60°N latitude by
20°-80°E longitude, with a 2.5 spatial resolution and for the 10 year period 1961-2003 in dusty days. Selected
territory is located in a geographical situation that covers all the effecting systems on Iran. For classification and
delineate synoptical patterns Principal Component Analysis (PCA) and clustering method were used. Results showed
that in this region, days with dust have three general circulation patterns. Analyzing these patterns show that there is
a trough which restricted to 30-45°E longitude in 850 hPa chart, and at least one relatively strong low pressure over
Arabian Peninsula in sea level pressure extending to the west, south west and the study region. This study shows that
above aspects are the major specifications of dusty days.
خلاصه ماشینی:
Analyzing these patterns show that there is a trough which restricted to 30-45°E longitude in 850 hPa chart, and at least one relatively strong low pressure over Arabian Peninsula in sea level pressure extending to the west, south west and the study region.
Hematy, (1995) surveyed the frequency occurrence of dust storms in central and south west of Iran and found that the main factor in occurring sever storms is the existence of cyclonic systems in central regions of Iraq and north of Saudi Arabia.
In order to study and classifying dust storm synoptical patterns, daily data were extracted from National Center of Environmental Prediction (NCEP), in 850 hPa and sea level pressure at 1200 UTC, in days with dust.
Synoptical pattern governs at 850 hPa level in days with dust storm (first type pattern) CP2, sea level pressure: A low pressure center less than 1000 hPa is closed at the south west regions of Red Sea. Another low pressure center less than 1004 hPa is closed over east of Arabian Peninsula (Figure 5).
Synoptical pattern governs at sea level pressure in days with dust (second type pattern) pressure gradient is about 10 hPa between north and south of Iraq.
synoptical pattern governs at 850 hPa level in days with dust storm (second type pattern)CP3, sea level pressure: A low pressure center with less than 1004 hPa is seen at north east part of Arabian Peninsula.
Study of dust storm frequency occurrence in central and south west regions of Iran, M.