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Vaughan Phillips

Research in the Area of Clouds, Aerosols and Climate

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New Empirical Formulation for the Sublimational Breakup of Graupel and Dendritic Snow

Author

  • Akash Deshmukh
  • Vaughan Phillips
  • Aaron Bansemer
  • Sachin Patade
  • Deepak Waman

Summary, in English

Ice fragments are generated by sublimation of ice particles in subsaturated conditions in natural clouds. Conceivably, such sublimational breakup would be expected to cause ice multiplication in natural clouds. Any fragment that survives will grow to become ice precipitation that may sublimate and fragment further. As a first step toward assessing this overlooked process, a formulation is proposed for the number of ice fragments from sublimation of ice particles for an atmospheric model. This is done by amalgamating laboratory observations from previously published studies. The concept of a “sublimated mass activity spectrum” for the breakup is applied to the dataset. The number of ice fragments is determined by the relative humidity over ice and the initial size of the parent ice particles. The new formulation applies to dendritic crystals and heavily rimed particles only. Finally, a thought experiment is performed for an idealized scenario of subsaturation with in-cloud descent. Scaling analysis yields an estimate of an ice enhancement ratio of about 5 (10) within a weak deep convective downdraft of about 2 m s−1, for an initial monodisperse population of dendritic snow (graupel) particles of 3 L−1 and 2 mm. During descent, there is a dynamic equilibrium between continual emission of fragments and their depletion by sublimation. A simplified bin microphysics parcel model exhibits this dynamical quasi equilibrium, consistent with the thought experiment. The fragments have average lifetimes of around 90 and 70 s for dendrites and graupel, respectively. Sublimational breakup is predicted to cause significant secondary ice production.

Department/s

  • Dept of Physical Geography and Ecosystem Science
  • MERGE: ModElling the Regional and Global Earth system
  • eSSENCE: The e-Science Collaboration

Publishing year

2022-01-19

Language

English

Pages

317-336

Publication/Series

Journal of the Atmospheric Sciences

Volume

79

Issue

1

Document type

Journal article

Publisher

Amer Meteorological Soc

Topic

  • Meteorology and Atmospheric Sciences

Keywords

  • Diffusion; Ice crystals; Ice particles; Sublimation; Clouds

Status

Published

Project

  • Secondary ice production: An empirical formulation and organization of mechanisms among simulated cloud-types
  • Mechanisms for the Influence from Ice Nucleus Aerosols on Clouds and their Indirect Effects: Cloud Modelling

ISBN/ISSN/Other

  • ISSN: 1520-0469