On the use of a Cloud Droplet Activation Parameterization for a Multi-Moment Bulk Microphysics Scheme in a Cloud-Resolving Model
Abstract
From a microphysical perspective, the droplet activation process is arguably the root of aerosol-cloud interactions as it is most susceptible to changes in atmospheric aerosol distribution properties. The initial droplet spectra produced upon activation should necessarily impact the chain of microphysical processes that follow and therefore play a role in determining the cloud's future state. This work re-examines the dependence of newly formed cloud droplet size distribution (CDSD) characteristics to environmental and aerosol properties via 1D parcel model simulations used to create look-up-tables (LUTs) that serve as the droplet activation parameterization for a multi-moment bulk microphysics scheme. It is shown that for conditions of high aerosol concentrations and low updraft speeds, applying a fixed cloud droplet size definition versus employing physical considerations of activated droplets can lead to erroneous activation of aerosol particles and overly broad CDSDs. Aerosol distributions characterized by larger sizes and/or more soluble particles generally result in greater activated droplet numbers, whereas the impact of these parameters on CDSD spectral width depends on both aerosol number concentration and updraft velocity. An expansion of the activation LUT to include CDSD spectral width is proposed as a preliminary step for extending high-order moment prediction to cloud droplet categories in CRMs for improved simulations of aerosol-cloud interactions.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2017
- Bibcode:
- 2017AGUFM.A22E..09L
- Keywords:
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- 3307 Boundary layer processes;
- ATMOSPHERIC PROCESSES;
- 3310 Clouds and cloud feedbacks;
- ATMOSPHERIC PROCESSES;
- 3311 Clouds and aerosols;
- ATMOSPHERIC PROCESSES;
- 3314 Convective processes;
- ATMOSPHERIC PROCESSES