ATMOSPHERIC OPTICAL DEPTH PROPERTIES OF THE 10 MARCH 2009 DUST STORM IN CENTRAL SAUDI ARABIA

摘要

Dust particles play a very important role in the Earth's climate system, air quality and environmental health. They affect both solar and terrestrial radiation by scattering and absorption, thus they are considered significant climate-forcing factors. Dust storms are considered natural hazards that affect daily life for short-time intervals ranging from a few hours to a few days, and they are a very frequent phenomenon in Saudi Arabia, especially in pre-monsoon season. A severe dust storm occurred on 10 March 2009 in the northeast region of Saudi Arabia. It is considered one of the largest recorded dust events in Saudi's history. In this study, sun photometer data obtained during March, the atmospheric optical depth, and Angstrom exponent, α, over Riyadh, Saudi Arabia were investigated and presented. We evidenced exceptionally high turbidity values during the event day in comparison to the previous days. The Atmospheric Optical Depth AOD (340 nm) on the dusty day ranged between 1.642 and 0.350, with an average value of 1.102 ± 0.50, whereas on the previous day the AOD (340 nm) ranged between 0.353 and 0.225, with an average value of 0.290±0.04. The Angstrom exponent, α, for the wavelength range (340-440 nm) during the event day, varied between 0.130 and -0.117, with an average value of 0.012 ± 0.01, whereas before the event, it varied between 0.093 and 0.386, with an average value of 0.212±0.03. Theoretical simulations using the SMART model were conducted to investigate how the turbidity conditions affected the solar irradiances during the event. That analysis suggested that the turbid conditions on the 10th significantly decreased the background global and direct-beam irradiances by about 53% and 139%, respectively, increasing the diffuse component by 39% compared with the previous day. We also found that this storm had a great effect on several meteorological variables; there was a great drop in air temperature and visibility and an increase in both wind speed and relative humidity due to its impact.