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Study Uses Doppler Lidar and Cloud Radar to Observe Pre-convective Environment and Convection Initiation in UAE’s Al Hajar Mountains

With an annual precipitation ranging from 20–40mm to 140–150 mm, the UAE is one of the driest countries in the Middle East, making it highly vulnerable to climate change impacts in the future like the rest of the region. Furthermore, the UAE’s precipitation trends are projected to decrease by 20% by the year 2050 and 45% by 2100, compared to the period 1961 to 1990.

This has prompted the UAE Research Program for Rain Enhancement Science (UAEREP) to fund a project titled ‘Optimizing Cloud Seeding by Advanced Remote Sensing and Land Cover Modification’ (OCAL) as part of the program’s sustained efforts to enhance precipitation through innovative rain enhancement and weather modification methods. One of the aims of the OCAL project was to provide the UAE with unique observational capabilities, and eventual forecasting and cloud seeding guidance, particularly in the Al Hajar Mountains to the east of the UAE.

The project deployed a unique synergy of scanning Doppler lidar and cloud radar using coordinated scan patterns on a peak of the Al Hajar Mountains to study the clear-air pre-convective environment, convergence lines, and subsequent convection initiation (CI).

The observatory allowed the project team led by Prof. Volker Wulfmeyer, a First Cycle Awardee of UAEREP and Managing Director and Chair of Physics and Meteorology at the Institute of Physics and Meteorology of the University of Hohenheim in Stuttgart, to study seedable convective clouds. For approximately two years, the team identified and analyzed several convective cases in this extreme environment with a high vantage point for observing valley wind flows and convective cells.

The cloud radar Doppler images provided detailed observations of cloud hydrometeor dynamics. The study analyzed two cases of unstable conditions that occurred on 5 and 6 September 2018. In both convective cases, pre-convective signatures were apparent before convection initiation (CI) in the form of convergence, wind shear structures, and updrafts. These results demonstrate the potential of these synergetic observations for understanding convection initiation processes and providing cloud seeding guidance via early detection of CI events.

The study demonstrated the value of employing this synergy of instruments with synchronized scan patterns in a high elevation observatory for the assessment of clear air and cloud dynamics. The OCAL observatory has provided an excellent platform for studying the whole process chain of orographic CI within the Al Hajar Mountains, generating very useful statistics, and even showing potential as a timely forecasting system for convective clouds in the area.

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