Dr. Greg McFarquhar earned a PhD in Atmospheric Physics in 1993 from the University of Toronto. Prior to moving to Illinois, he worked as a project scientist at NCAR and a postdoc at Scripps Institution of Oceanography. He joined the University of Illinois in 2001, becoming a full professor in 2009, and was also a visiting professor at the Universite Blaise Pascal in France in 2012. Greg's area of expertise is in cloud observations and microphysics. He is a member of the American Meteorological Society and served as the AMS committee chair on Cloud Physics from 2007 to 2012. He has been involved in a number of field campaigns including the upcoming Plains Elevated Convection at Night (PECAN) experiment and the Profiling of Winter Storms (PLOWS) experiment, which will be the focus of his keynote address.
The presentation will summarize analyses of the microphysical structure and processes producing precipitation in the comma-head region of wintertime continental cyclones using data collected by the W-band Wyoming Cloud radar and in-situ instrumentation installed on the NSF/NCAR C-130. Using data from 14 cyclones sampled during PLOWS, the microphysical properties (ice particle number concentrations, ice mass contents, median particle sizes) inside and outside of the generating cells and fall streaks are contrasted. It is shown that larger concentrations in the generating cells are consistent with enhanced ice production in convective updrafts, whereas the increased mass and size of particles within the cells show an environment favorable for enhanced particle growth. However, turbulent mixing between cells and surrounding regions lessens these differences, with supercooled water, similar particle habits and rimed particles observed both within and between cells.
Within stratiform regions below the generating cells, weak synoptic-scale ascent producing ice supersaturation occurs. The sizes and masses in the stratiform regions were larger relative to measurements in generating cells at similar temperatures, showing that the primary ice growth in these cyclones occurs below the generating cell level. Larger particle sizes and masses were observed within the fall streaks emanating from the generating cells compared to regions outside, with associated regions of enhanced reflectivity being traced all the way from the generating cells to the fall streaks and the ground. Further analysis shows the observations can be interpreted in terms of a seeder-feeder process, where the generating cells act to seed the stratiform layers below, whose large-scale moisture is able to support subsequent particle growth. Implications of the results for numerical modeling, and other ongoing activities with the PLOWS data will also be discussed.