Aerosol-Cloud-Precipitation Interactions During STORMVEX

Principal Investigator(s):
Gannet Hallar, Desert Research Institute

The project will use data products that were obtained during the recent Storm Peak Lab Cloud Property Validation Experiment (STORMVEX, PI: Mace, Co-I: Hallar) field campaign. STORMVEX provides a wealth of data to investigate indirect aerosol effects on cloud droplet formation, ice crystal formation, snow growth, and precipitation in mixed-phase cloud systems. There is abundant empirical evidence that pollution aerosols affect cloud microphysical properties. On the other hand, less is known about aerosol effects and feedback mechanisms associated with mixed-phase clouds, where both water and ice are present. The lack of knowledge pertaining to the aerosol indirect effect on mixed-phase clouds is due to the complexity introduced by the ice phase and the lack of availability of high quality observational data. It is well known from global observations that cloud phase (liquid water versus ice) exerts a fundamental control on precipitation formation and atmospheric radiation. Phase partitioning processes are complex in any environment, and many details of how these processes manifest in an orographic region with variable aerosol concentrations is largely unknown. The main objective of this study is to describe and explain the impact of aerosols on distributions of super-cooled liquid water and ice in mixed-phase clouds using the observations during STORMVEX. We will accomplish this broad objective using ground-based remote sensing, in situ aerosol and cloud particle measurements to focus on four fundamental questions:

  1. do soot particles significantly contribute to the formation of ice crystals?
  2. do higher concentrations of large, super-cooled cloud droplets promote heterogeneous ice nucleation?; and
  3. does an increase in CCN lead to smaller droplets, a reduction in riming, and a reduction in snowfall?

Each question will be addressed empirically using a two-tiered approach. The first involves identifying and analyzing specific case studies to illustrate the different potential aerosol effects on cloud properties and precipitation. Then, building upon these cases, the broader significance and impact of the aerosol-cloud interactions will be addressed with a longer-term statistical perspective using the full STORMVEX data sets. The result will be an improved understanding of the impact of aerosols on cloud microphysics and precipitation in a mixed-phase environment, which will complement planned studies using new instrumentation at the DOE ARM North Slope of Alaska site.