Blue Waters Professor
Dept. of Atmospheric Sciences
Univ. Illinois at Urbana-Champaign



Our most recent published study is entitled: Entrainment in a Simulated Supercell Thunderstorm. Part II: The Influence of Vertical Wind Shear and General Effects upon Precipitation.  J. Atmos. Sci., 79, 1429-1443.  In this study, we quantify the strength of the different entrainment mechanisms found in Part I (overturning ribbons, turbulent eddies, and the storm-relative air stream) as a function of environmental wind shear. The ascending “ribbons” of horizontal vorticity wrapping around the updraft contribute more to entrainment with increasing vertical wind shear, while turbulent eddies on the opposite side of the updraft contribute less. The storm-relative airstream introduces more low-level air into the storm core with increasing vertical wind shear. Thus, the total entrainment increases with increasing vertical wind shear, but the fractional entrainment decreases, yielding an increase in undiluted air within the storm core. As a result, the condensation efficiency within the storm core also increases with increasing vertical wind shear. However, due to the increase in hydrometeors detrained aloft and the resulting enhanced evaporation as they fall, the precipitation efficiency evaluated using surface rainfall decreases with increasing vertical wind shear, as found in past studies.

The article also has a supplement, with some animations of the various entrainment mechanisms acting on the 20 m/s core of a simulated supercell thunderstorm.

What can be seen in the animation below is the discrete “ribbons” of overturning motions introduce air into the core of the thunderstorm.  They do not reach all the way into the interior of the core, allowing part of the updraft to still remain unaffected (“undiluted”) by entrainment, as shown and discussed in the paper.  This work was supported by an award from NSF:  AGS17-25190, and used the Blue Waters Supercomputer, as well as the NSF/NCAR Cheyenne supercomputer, all supported by NSF.  The Blue Waters computer was also supported in part by the State of Illinois.



Group member Toby Ross successfully defended his M.S. in  May 2022.  He has decided to continue at the University of Illinois, working in our research group, to pursue his Ph.D.  The title of his thesis is AN INVESTIGATION INTO THE EFFECTS OF CCN
ON THE TIMING OF CONVECTIVE COLD POOL INITIATION.  A paper on his work is in preparation to submit to a journal.

Group member Enoch Jo successfully defended his Ph.D. in June 2022.  He has begun a postdoc position at PNNL (Pacific Northwest National Laboratory).  The title of his dissertation is ENTRAINMENT IN SIMULATED SUPERCELL THUNDERSTORMS.  The final paper based on his work is in review.

Group member Sophie Orendorf successfully defended her M.S. in July 2022.  She is currently pursuing employment opportunities.  The title of her thesis is A CONVECTIVE WINDSTORM IN A FUTURE CLIMATE: A PSEUDO-GLOBAL WARMING STUDY OF THE 10 AUGUST 2020 MIDWEST DERECHO. A paper on her work is in preparation to submit to a journal.



We welcomed Ms. Fitria Sari to our research group this fall.  Fitria is a Fulbright Fellow who intends to study hailstorms over Indonesia, using mainly numerical simulations.



Our group uses numerical modeling with observational analysis to investigate research problems associated with the development of clouds and precipitation. Our successes in the last decade, often with other collaborators, include demonstrating when giant aerosol particles are (or are not) important in warm rain formation, how the productivity of the warm rain process may change in a future warmer climate, the importance of variability resulting from entrainment and mixing upon accelerating or preventing warm rain formation, the influence of a strong warm rain process upon ice production in oceanic cumuli, and the behavior of clouds as shedding thermals that thus entrain air through their leading edges. We have published multiple articles in peer-reviewed journals and regularly present our work at the AMS Cloud Physics Conference and the International Conference on Clouds and Precipitation.

We have also contributed to the development of tools for visualization of ground-based and airborne radar data and high-resolution numerical simulations of clouds, evaluated the performance of aircraft-mounted cloud microphysical probes, and tested microphysical parameterizations in larger-scale cloud models. Finally, we have contributed to science education through studies on improving undergraduate understanding of the nature of science, and the development and evaluation of research-based laboratories for undergraduates in atmospheric science.



We continue to shift our emphasis toward microphysical processes in deep convection.  Current projects include using very high-resolution simulations on the NSF/NCAR supercomputer to investigate aerosol effects upon convective outflows and cold pools (DOE- ASR award), and studying the possible effects of climate change on severe weather, including hail storms and wind storms (NSF award, Jeff Trapp lead PI).