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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/acp-2016-1057
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
05 Dec 2016
Review status
A revision of this discussion paper was accepted for the journal Atmospheric Chemistry and Physics (ACP) and is expected to appear here in due course.
How do changes in warm-phase microphysics affect deep convective clouds?
Qian Chen, Ilan Koren, Orit Altaratz, Reuven H. Heiblum, Guy Dagan, and Lital Pinto Department of Earth and Planetary Sciences, Weizmann Institute of Science, Rehovot, Israel
Abstract. Understanding aerosol effects on deep convective clouds and the derived effects on the radiation budget and rain patterns can largely contribute to estimations of climate uncertainties. The challenge is difficult in part because key microphysical processes in the mixed and cold phases are still not well understood. For deep convective clouds with a warm base, understanding aerosol effects on the warm processes is extremely important as they set the initial and boundary conditions for the cold processes. Therefore, in this study the focus is on the warm phase, which can be better resolved. The main question is: ''How do aerosol-derived changes in the warm phase affect the properties of deep convective cloud systems?'' To explore this question, we used the weather research and forecasting (WRF) model with spectral bin microphysics to simulate a deep convective cloud system over Marshall Islands during the Kwajalein Experiment (KWAJEX). The model results were validated against observations, showing similarities in the vertical profile of radar reflectivity and the surface rain rate. Simulations with larger aerosol loading resulted in a larger total cloud mass, a larger cloud fraction in the upper levels, and a larger frequency of strong updrafts and rain rates. Enlarged mass both below and above the zero temperature level (ZTL) contributed to the increase in clouds’ total mass (water and ice) in the polluted runs. Increased condensation efficiency of cloud droplets governed the gain in mass below the ZTL, while both enhanced condensational and depositional growth led to increased mass above it. Moreover, the polluted runs showed increased upward transport (across the ZTL) of liquid water, driven by two main processes: 1) larger updrafts and 2) larger droplet mobility. These aerosol effects were reflected in the larger ratio between the masses located above and below the ZTL in the polluted runs. When comparing the net mass flux crossing the ZTL in the clean and polluted runs, the difference was small. However, when comparing the upward and downward fluxes separately, the increase in aerosol concentration was seen to dramatically increase the fluxes in both directions, indicating the aerosol-amplification effect of the convection and affecting cloud-system properties such as cloud fraction and rain rate.

Citation: Chen, Q., Koren, I., Altaratz, O., Heiblum, R. H., Dagan, G., and Pinto, L.: How do changes in warm-phase microphysics affect deep convective clouds?, Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2016-1057, in review, 2016.
Qian Chen et al.
Qian Chen et al.

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