Atmos. Chem. Phys. Discuss., 13, 27019-27052, 2013
© Author(s) 2013. This work is distributed
under the Creative Commons Attribution 3.0 License.
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Ice particles in the upper anvil regions of mid-latitude continental thunderstorms: the case for frozen-drop aggregates
J. L. Stith1, L. Avallone2,*, A. Bansemer1, B. Basarab3, S. W. Dorsi4, B. Fuchs3, R. P. Lawson5, D. C. Rogers1, S. Rutledge3, and D. W. Toohey6
1National Center for Atmospheric Research, Boulder, Colorado, USA
2Laboratory for Atmospheric and Space Physics, University of Colorado Boulder, Colorado, USA
3Colorado State University, Fort Collins, Colorado, USA
4CIRES, University of Colorado and NOAA-ESRL, Boulder, Colorado, USA
5SPEC Incorporated, Boulder, Colorado, USA
6Department of Atmospheric and Oceanic Sciences, University of Colorado Boulder, Colorado, USA
*now at: National Science Foundation, Arlington, Virginia, USA

Abstract. This study examines the occurrence and morphology of frozen drop aggregates in thunderstorm anvils from the US Midwest and describes the environmental conditions where they are found. In situ airborne data collected in anvils using several particle imaging and sizing probes and bulk total water instrumentation during the 2012 Deep Convective Clouds and Chemistry Experiment are examined for the presence of frozen drop aggregates. These types of particles, especially chains of frozen drops, have been only rarely reported before and are hypothesized to aggregate due to electrical forces in the clouds. They were identified in nine of the anvil cases examined to-date, suggesting that they are common features in Midwestern anvils. High concentrations of individual frozen droplets occurred on the tops and edges of one particular set of anvils, while regions closer to the center and bottom of the anvils exhibited fewer frozen drops and more frozen drop aggregates. Bulk ice water content measurements across these anvils could only be explained by contributions from both small particles (frozen droplets) and large particles (large aggregates of frozen droplets). Dual Doppler radar analysis confirmed the presence of deep and strong (> 15 m s−1) updrafts in the parent cloud of one of the anvils. These features contrast with previous anvil measurements in tropical/maritime anvils that evidently do not exhibit the same frequency of frozen drop aggregates.

Citation: Stith, J. L., Avallone, L., Bansemer, A., Basarab, B., Dorsi, S. W., Fuchs, B., Lawson, R. P., Rogers, D. C., Rutledge, S., and Toohey, D. W.: Ice particles in the upper anvil regions of mid-latitude continental thunderstorms: the case for frozen-drop aggregates, Atmos. Chem. Phys. Discuss., 13, 27019-27052, doi:10.5194/acpd-13-27019-2013, 2013.
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