Preprints
https://doi.org/10.5194/acp-2021-200
https://doi.org/10.5194/acp-2021-200

  06 Apr 2021

06 Apr 2021

Review status: this preprint is currently under review for the journal ACP.

Analysis of aerosol-cloud interactions and their implications for precipitation formation using aircraft observations over the United Arab Emirates

Youssef Wehbe1, Sarah A. Tessendorf2, Courtney Weeks2, Roelof Bruintjes2, Lulin Xue2, Roy M. Rasmussen2, Paul Lawson3, Sarah Woods3, and Marouane Temimi4 Youssef Wehbe et al.
  • 1National Center of Meteorology, Abu Dhabi 4815, UAE
  • 2Research Applications Laboratory, National Center for Atmospheric Research, Boulder, CO 80307, USA
  • 3Stratton Park Engineering Company, Boulder, CO 80301, USA
  • 4Department of Civil, Environmental, and Ocean Engineering, Stevens Institute of Technology, Hoboken, NJ 07030, USA

Abstract. Aerosol and cloud microphysical measurements were collected by a research aircraft during August 2019 over the United Arab Emirates (UAE). The majority of science flights targeted summertime convection along the eastern Hajar mountains bordering Oman, while one flight sampled non-orographic clouds over the western UAE near the Saudi Arabian border. In this work, we study the evolution of growing cloud turrets from cloud base (9 °C) up to the capping inversion level (−12 °C) using coincident cloud particle imagery and particle size distributions from cloud cores under different forcing. Results demonstrate the active role of background dust and pollution as cloud condensation nuclei (CCN) with the onset of their deliquescence in the sub-cloud region. Sub-cloud aerosol sizes are shown to extend from submicron to 100 µm sizes, with higher concentrations of ultra-giant CCN (d >10 µm) from local sources closer to the Saudi border, compared to the eastern orographic region where smaller size CCN are observed. Despite the presence of ultra-giant CCN from dust and pollution in both regions, an active collision-coalescence (C-C) process is not observed within the limited depths of warm cloud (< 1000 m). The state-of-the-art observations presented in this paper can be used to initialize modelling case studies to study the influence of aerosols on cloud and precipitation processes in the region and to better understand the impacts of hygroscopic cloud-seeding on these clouds.

Youssef Wehbe et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-200', Anonymous Referee #1, 27 Apr 2021
  • RC2: 'Comment on acp-2021-200', Anonymous Referee #3, 28 Apr 2021

Youssef Wehbe et al.

Youssef Wehbe et al.

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Short summary
The role of dust aerosols as ice nucleating particles is well established in the literature, whereas their role as cloud condensation nuclei is less understood, particularly in polluted desert environments. We analyze coincident cloud particle imagery and size distributions collected over the UAE using an instrumented aircraft. Despite the presence of large aerosol sizes associated with dust, fine-mode aerosols appear to suppress the formation of large droplets needed for rainfall production.
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