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Study Investigates Role of Atmospheric Aerosol Concentration on Regional Cloud Precipitation Patterns

The Earth’s energy budget involves the exchange of energy between three levels: its surface, the top of the atmosphere and the atmosphere in between. In this system, aerosols - the small particles suspended in the Earth's atmosphere from sources such as desert dust, sea salt, volcanic ash, sulfate, and black carbon - play an important role in introducing uncertainties in weather and climatic predictions. Of all aerosol types, windblown mineral dust is one of the most mass abundant types of primary aerosol particles emitted into the atmosphere. Originating from soils in arid and semi-arid regions, mineral dust and other aerosol particle types can affect clouds and their microphysical properties and precipitation patterns by acting as cloud condensation nuclei (CCN) and ice nuclei (IN).

To better assess the role of mineral dust in the climate system, it is necessary to observe its composition and distribution, vertically as well as horizontally, and analyze its transport and emission processes. Professor Hannele Korhonen, the Director of the Climate Research Program at Finnish Meteorological Institute and a second cycle awardee of the UAE Research Program for Rain Enhancement Science (UAEREP), worked on a project involving the observation and retrieval of dust aerosol concentration profiles.

The study used the data of various instruments, including Infrared Atmospheric Sounding Interferometer (IASI) for aerosol retrieval, along with AErosol RObotic NETwork (AERONET) Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP), Cloud–Aerosol Transport System (CATS) and two ground-based lidar instruments based at M'Bour (Senegal) and Al Dhaid (United Arab Emirates) for the evaluation of the retrieved profiles.

To shed further light into atmospheric aerosol properties in the UAE region, Professor Hannele also conducted a one‑year field campaign from March 2018 to February 2019 at a location south‑west of Al Dhaid city, in the emirate of Sharjah in the UAE.

Titled ‘Optimization of Aerosol Seeding In rain enhancement Strategies (OASIS)’, the measurement campaign focused on the characterization of the geometrical and optical properties of atmospheric aerosol particles and their interaction with the regional/local meteorology and cloud precipitation patterns under different atmospheric conditions.

The project aimed to gain a more robust knowledge of the efficiency of the aerosol particles to act as CCN/IN in a challenging environment. A multi-instrument approach was used for this purpose including both in‑situ and remote sensing sensors along with model simulations.

The analysis of lidar observations suggests that aerosol particle populations over the UAE are sensitive to transport from Saudi Arabia, Iran, and Iraq but also from local sources. They observed up to seven distinct dust layers extending to altitudes of 8 km above frequent cloud bases. The study also suggests that the pure dust properties over the Middle East and western Asia, including the observation site, are comparable to those of African mineral dust regarding the linear particle depolarization ratios but not for the lidar ratios.

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