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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 17, issue 12 | Copyright
Atmos. Chem. Phys., 17, 7435-7444, 2017
https://doi.org/10.5194/acp-17-7435-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 20 Jun 2017

Research article | 20 Jun 2017

Time-dependent, non-monotonic response of warm convective cloud fields to changes in aerosol loading

Guy Dagan, Ilan Koren, Orit Altaratz, and Reuven H. Heiblum Guy Dagan et al.
  • Department of Earth and Planetary Sciences, The Weizmann Institute of Science, Rehovot 76100, Israel

Abstract. Large eddy simulations (LESs) with bin microphysics are used here to study cloud fields' sensitivity to changes in aerosol loading and the time evolution of this response. Similarly to the known response of a single cloud, we show that the mean field properties change in a non-monotonic trend, with an optimum aerosol concentration for which the field reaches its maximal water mass or rain yield. This trend is a result of competition between processes that encourage cloud development versus those that suppress it. However, another layer of complexity is added when considering clouds' impact on the field's thermodynamic properties and how this is dependent on aerosol loading. Under polluted conditions, rain is suppressed and the non-precipitating clouds act to increase atmospheric instability. This results in warming of the lower part of the cloudy layer (in which there is net condensation) and cooling of the upper part (net evaporation). Evaporation at the upper part of the cloudy layer in the polluted simulations raises humidity at these levels and thus amplifies the development of the next generation of clouds (preconditioning effect). On the other hand, under clean conditions, the precipitating clouds drive net warming of the cloudy layer and net cooling of the sub-cloud layer due to rain evaporation. These two effects act to stabilize the atmospheric boundary layer with time (consumption of the instability). The evolution of the field's thermodynamic properties affects the cloud properties in return, as shown by the migration of the optimal aerosol concentration toward higher values.

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Large eddy simulations with bin microphysics are used to study cloud fields' sensitivity to changes in aerosol loading and the time evolution of this response. We show that the mean field properties change with a non-monotonic trend, with an optimum aerosol concentration for which the field reaches its maximal water mass or rain yield. The evolution of the mean thermodynamic properties is studied and shown to cause the migration of the optimal aerosol concentration toward higher values.
Large eddy simulations with bin microphysics are used to study cloud fields' sensitivity to...
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