Diagnostic study of spring dusty days over the southwest region of the Kingdom of Saudi Arabia

摘要

Three classes of dust over the southwest region of the Kingdom of Saudi Arabia were classified based on both the values and distribution of the TOMS Aerosol Index. These classes include a narrow spread class (i.e., a weak class), a moderate spread class, and a wide spread class (i.e., a strong class). A diagnostic study of these classes indicated that there are common atmospheric features for dust cases, and the intensity of these features increases with the characteristic strength of the dust cases. These features are the horizontal circulation of anticyclonic wind flow associated with lower layer upward motion through the zonal stripe between 17A degrees N and 25A degrees N through the meridional cross-section in addition to a vertical circulation, especially for the layers above 850 hPa. These two circulation patterns merge to form an unstable atmosphere and a deep cyclone. Furthermore, there are areas of convergence and divergence at the points of deepening upward motion and shallow upward motion, respectively. Finally, all these features collectively force the dust from the Arabian Desert to move into the southwest region of the Kingdom of Saudi Arabia.