Spatiotemporal distribution of the Aura-OMI aerosol index and dust storm case studies over Iraq

Aerosol index (AI) is qualitatively indicating the presence of suspended aerosol particles in the air. The major sources of these particles are desert dust, biomass burning, and volcanic ash plumes. The AI observations derived from the ozone monitoring instrument (OMI) on Aura satellite were analyzed over Iraq for the period 2005–2018. The results showed that the long-term spatiotemporal distribution of AI was significantly variable, with lower values (< 1.5) at the north mountain area and western highland and higher at the central and southern parts of the country. Two distinct spots of very high AI were observed over the two major source areas of dust storms, in the northwest and south of Iraq. In general, AI was increasing from northwest to south and southeast suggesting that the main source of the aerosols is regionally not locally and coming from west and northwest side. The results also indicated that AI has an annual cycle over the entire country: minimum in winter (< 0.5 during January in the northeast) and maximum in summer (~ 4.0 during June in the south). The analysis of monthly AI revealed that maximum monthly AI (= 4.1) occurred in the northwestern town of Anah and the minimum AI (~ 0) happened in the northern city of Mosul. Statistical test of AI seasonal time series exhibited a significant decreasing trend in AI in the central and southern parts of the country. Analysis of daily AI showed that annual number of days with AI > 2 may reach more than 140 days in Basra and more than 90 in Anah and Baghdad. Comparisons of Moderate Resolution Imaging Spectroradiometer (MODIS) true color images and AI for five different types of dust storms occurred over Iraq showed that AI is maximum at the core of the storm and the gradation of decreasing AI was consistent with the spread of dust out of the core. Maximum AI was > 5.5 during summer Shamal storm, > 3.0 during winter Shamal and frontal cases, and > 2.0 for the Haboob case. The HYSPLIT trajectories calculations showed that the dust plume in the MODIS image was significantly similar to the computed trajectories and the majority of air masses were coming from north and northwest. © 2021, Saudi Society for Geosciences.