Preprints
https://doi.org/10.5194/acp-2021-597
https://doi.org/10.5194/acp-2021-597

  21 Jul 2021

21 Jul 2021

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

Convection-Aerosol Interactions in the United Arab Emirates: A Sensitivity Study

Ricardo Fonseca1, Diana Francis1, Michael Weston1, Narendra Nelli1, Sufian Farah2, Youssef Wehbe2, Taha AlHosari2, Oriol Teixido3, and Ruqaya Mohamed3 Ricardo Fonseca et al.
  • 1Khalifa University of Science and Technology, P. O. Box 54224, Abu Dhabi, United Arab Emirates
  • 2National Center for Meteorology (NCM), P. O. Box 4815, Abu Dhabi, United Arab Emirates
  • 3Environment Agency – Abu Dhabi (EAD), P.O Box 45553, Abu Dhabi, United Arab Emirates

Abstract. The Weather Research and Forecasting (WRF) model is used to investigate convection-aerosol interactions in the United Arab Emirates for a summertime convective event. Both an idealised and scaled versions of a 7-year climatological aerosol distribution are considered. The convection on 14 August 2013 was triggered by the low-level convergence of the circulation associated with the Arabian Heat Low (AHL) and the daytime sea-breeze circulation. The cold pools associated with the convective events, as well as the low-level wind convergence along the Intertropical Discontinuity (ITD) earlier in the day, explain the dustier environment, with Aerosol Optical Depths (AODs) in excess of two.

Due to a colder surface and air temperature, the AHL is incorrectly represented in WRF, which leads to a mismatch between the observed and modelled clouds and precipitation. Employing interior nudging in the outermost grids of the three-nested simulation has a small but positive impact on the model predictions of the innermost nest. This is because the higher temperatures from more accurate boundary conditions are offset by colder temperatures from locally enhanced precipitation, the latter arising from a shift in the position of the AHL. Numerical experiments revealed a high sensitivity to the aerosol properties. In particular, replacing 20 % of the rural aerosols by carbonaceous particles has an impact on the surface radiative fluxes comparable to increasing the aerosol loading by a factor of 10, with a daily-averaged reduction in the UAE-averaged net shortwave radiation flux of ~90 W m−2 and an increase in the net longwave radiation flux of ~51 W m−2. However, in the former, WRF generates 20 % more precipitation than in the latter, due to a broader and weaker AHL.

The surface downward and upward shortwave and upward longwave radiation fluxes are found to scale linearly with the aerosol loading, while the downward longwave radiation flux varies by less than ±12 W m−2 when the aerosol amount and/or properties are changed. An increase in the aerosol loading also leads to drier conditions due to a shift in the position of the AHL and rainfall occurring in a drier region, with a domain-wise decrease in the daily accumulated rainfall of 16 % when the aerosol loading is increased by a factor of 10. In addition, the onset of convection is also delayed.

Ricardo Fonseca et al.

Status: open (until 01 Sep 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse

Ricardo Fonseca et al.

Ricardo Fonseca et al.

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Short summary
High-sensitivity of summer convection and precipitation over the United Arab Emirates to aerosols properties and loadings.
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