On different microphysical pathways to convective rainfall

Sonia Lasher-Trapp, Shailendra Kumara, Daniel H. Moser, Alan M. Blyth, Jeffrey R. French, Robert C. Jacksonc, David C. Leon, David M. Plummer

Research output: Contribution to journalArticle

Abstract

The Convective Precipitation Experiment (COPE) documented the dynamical and microphysical evolution of convection in southwestern England for testing and improving quantitative precipitation forecasting. A strong warm rain process was hypothesized to produce graupel quickly, initiating ice production by rime splintering earlier to increase graupel production and, ultimately, produce heavy rainfall. Here, convection observed on two subsequent days (2 and 3 August 2013) is used to test this hypothesis and illustrate how environmental factors may alter the microphysical progression. The vertical wind shear and cloud droplet number concentrations on 2 August were 2 times those observed on 3 August. Convection on both days produced comparable maximum radar-estimated rain rates, but in situ microphysical measurements indicated much less ice in the clouds on 2 August, despite having maximum cloud tops that were nearly 2 km higher than on 3 August. Idealized 3D numerical simulations of the convection in their respective environments suggest that the relative importance of particular microphysical processes differed. Higher (lower) cloud droplet number concentrations slow (accelerate) the warm rain process as expected, which in turn slows (accelerates) graupel formation. Rime splintering can explain the abundance of ice observed on 3 August, but it was hampered by strong vertical wind shear on 2 August. In the model, the additional ice produced by rime splintering was ineffective in enhancing surface rainfall; strong updrafts on both days lofted supercooled raindrops well above the 0°C level where they froze to become graupel. The results illustrate the complexity of dynamical-microphysical interactions in producing convective rainfall and highlight unresolved issues in understanding and modeling the competing microphysical processes.

Original languageEnglish (US)
Pages (from-to)2399-2417
Number of pages19
JournalJournal of Applied Meteorology and Climatology
Volume57
Issue number10
DOIs
StatePublished - Oct 1 2018

Keywords

  • Cloud microphysics
  • Cloud resolving models
  • Clouds

ASJC Scopus subject areas

  • Atmospheric Science

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    Lasher-Trapp, S., Kumara, S., Moser, D. H., Blyth, A. M., French, J. R., Jacksonc, R. C., Leon, D. C., & Plummer, D. M. (2018). On different microphysical pathways to convective rainfall. Journal of Applied Meteorology and Climatology, 57(10), 2399-2417. https://doi.org/10.1175/JAMC-D-18-0041.1