Friday, March 03, 2017, 2:00PM - 3:00PM
Greg M. McFarquhar
Dept. Atmospheric Sciences, University of Illinois, Urbana-Champaign
4001 Discovery Dr. Boulder CO
Use of in-situ cloud microphysical observations to explore impact of ice clouds on radiation, climate and weather University of Illinois, Department of Atmospheric Sciences, Urbana, IL
Ice clouds currently reflect ~17 W m-2 of shortwave radiation and trap ~22 W m-2 of longwave radiation on global average. However, if the distribution of cloud heights and microphysical properties changes in response to increases in greenhouse gases and aerosols, associated changes in the radiative impact of clouds could feed back on Earth’s climate. Representations of ice particle density, scattering and sedimentation are needed for global and regional climate models that predict these effects. Parameterizations of other processes, such as riming, aggregation, sedimentation and evaporation, are also needed for numerical weather models that predict the destructive impact and quantitative precipitation forecasts for phenomena such as winter storms, hurricanes and mesoscale convective systems. To develop such parameterizations, accurate observations of ice particle sizes, shapes, phases and concentrations are needed.
Techniques for making measurements of ice crystal properties and sources of uncertainty in such observations are discussed using data collected over Alaska, Australia, and the continental United States. Techniques for using information from such studies to develop parameterizations of cloud properties are reviewed, highlighting the recent development of stochastic schemes that take into account instrumental and statistical uncertainty in derived parameters. It is shown that in-situ observations of small particles are especially uncertain due to potential shattering of large particles on probe tips and the limited resolution of state-of-the-art cloud particle imagers. Thereafter, examples on how combinations of in-situ and remote sensing observations can be used to understand processes occurring in winter storms and mesoscale convective systems are discussed. Finally, new projects underway and planned to further clarify the importance of cloud microphysical processes are reviewed.
Free and open to the public.