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Discussion papers
https://doi.org/10.5194/acp-2018-781
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2018-781
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 30 Aug 2018

Research article | 30 Aug 2018

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Core and margin in warm convective clouds. Part II: aerosol effects on core properties

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

Abstract. The effects of aerosol on warm convective cloud cores are evaluated using single cloud and cloud field simulations. As presented in Part I, the BcoreRHcoreWcore property is seen during growth of warm convective clouds. We show that this property is kept irrespective of aerosol concentration. During dissipation core fractions generally decrease with less overlap between cores. However, for clouds that develop in low aerosol concentrations capable of producing precipitation, Bcore and subsequently Wcore volume fractions may increase during dissipation (i.e. loss of cloud mass). The RHcore volume fraction decreases during cloud lifetime and shows minor sensitivity to aerosol concentration.

It is shown that a Bcore forms due to two processes: (i) Convection – condensation within supersaturated updrafts and release of latent heat, (ii) Adiabatic heating due to weak downdrafts. The former process occurs during cloud growth for all aerosol concentrations. The latter process only occurs for low aerosol concentrations during dissipation and precipitation stages where large mean drop sizes permit slow evaporation rates.

The aerosol effect on the diffusion efficiencies play a crucial role in the development of the cloud and its partition to core and margin. Using the RHcore definition, it is shown that the total cloud mass is mostly dictated by core processes, while the total cloud volume is mostly dictated by margin processes. Increase in aerosol concentration increases the core (mass and volume) due to enhanced condensation but also decreases the margin due to evaporation. In clean clouds larger droplets evaporate much slower, enabling preservation of cloud volume and even increase by dilution (detrainment while losing mass). This explains how despite having smaller cores and less mass, cleaner clouds may live longer and grow to larger sizes.

Reuven H. Heiblum et al.
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Reuven H. Heiblum et al.
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