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Study Uses in Situ Measurements of Summertime Convective Clouds to Understand Precipitation Processes in Arid and Semi-arid Regions

Mineral dust aerosols in the atmosphere in arid and semi-arid regions can impact precipitation depending on the spatial distributions of aerosols, humidity, geographical conditions, cloud dynamics, and cloud types, among other factors. Mineral dust aerosols act not only as Ice Nucleating Particles (INPs), but also as efficient Cloud Condensation Nuclei (CCN) due to their large sizes.

Thus, the knowledge of aerosol physicochemical properties is key to reliably simulate cloud formation and precipitation development because different microphysical properties of aerosols and clouds can yield varying seeding effects. Therefore, a reliable numerical model is necessary to understand precipitation processes in arid and semi-arid regions to evaluate the effect of optimal hygroscopic or glaciogenic cloud seeding against natural clouds for rain enhancement. This model should be validated in terms of the microphysical properties based on observational data to improve simulation performance.

To characterize the microphysical properties of diurnal convective clouds over the UAE in the summertime, a team led by Professor Masataka Murakami, a First Cycle Awardee of the UAE Research Program for Enhancement Science (UAEREP), and a scientist at Japan’s Meteorological Research Institute, conducted aircraft observations over the eastern mountainous areas of the UAE in 2017.

The field campaign involved several microphysical observations, where the aircraft penetrated summertime diurnal convective clouds and performed 14 flights. Two cases were selected for case studies, both of which included mixed-phase clouds with relatively cold cloud base temperatures (3.1°C to −1.4°C) and top temperatures (approximately −12°C), where graupel particles were the dominant type of solid precipitation.

Aerosol particle and CCN measurements indicated that the air mass had a continental nature, leading to high cloud droplet concentrations of 600-800 cm−3. Based on the microphysical measurements of the aerosols and clouds, the team concluded that background (BG) aerosols larger than approximately 0.1 μm are activated into cloud droplets at an SS between 0.1% and 0.5%. The team also recommended the need to focus future researches on integrated field programs involving in situ measurements, remote sensing observations, modeling, and laboratory studies to improve our understanding of rainfall mechanisms under specific conditions in the atmosphere.

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