Environmental & Climate Sciences Department Seminar

Clouds are collections of droplets and ice crystals, formed on aerosol particles, all interacting within a turbulent environment. Understanding these interactions is challenging, especially because the atmosphere is ever changing and the initial and boundary conditions are poorly constrained. Turning to the laboratory is one way to make progress. In the "Pi convection-cloud chamber", a pi-cubic-meter turbulent cloud is generated by feeding aerosols into a water-supersaturated environment created by moist Rayleigh-Benard convection. All microphysical processes that are usually considered "sub-grid-scale" even in detailed models, are fully represented. The resulting cloud microphysical and optical properties are similar to those observed in stratocumulus, and the Pi chamber has provided insight into the role of turbulence on cloud droplet activation and growth, the formation of persistent mixed-phase clouds, and the cloud dispersion indirect effect. A consortium of 12 universities, national laboratories, and industry/international partners, with support from DOE and NSF, has been developing a design for a much larger convection-cloud chamber that will allow droplet growth by collision-coalescence in addition to growth by condensation. That capability will allow interactions within a fully-coupled aerosol-cloud-precipitation system to be explored and directly compared to detailed models. We envision that this would exist as a national user facility available to the atmospheric research community for advancing our understanding of cloud processes relevant key uncertainties in weather and climate models.