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Secondary ice production by fragmentation of freezing drops : Formulation and theory

Phillips, Vaughan T.J. LU ; Patade, Sachin LU ; Gutierrez, Julie and Bansemer, Aaron (2018) In Journal of the Atmospheric Sciences 75(9). p.3031-3070
Abstract

A numerical formulation is provided for secondary ice production during fragmentation of freezing raindrops or drizzle. This is obtained by pooling laboratory observations from published studies and considering the physics of collisions. There are two modes of the scheme: fragmentation during spherical drop freezing (mode 1) and during collisions of supercooled raindrops with more massive ice (mode 2). The empirical scheme is for atmospheric models. Microphysical simulations with a parcel model of fast ascent (8 m s-1) between -10° and -20°C are validated against aircraft observations of tropical maritime deep convection. Ice enhancement by an order of magnitude is predicted from inclusion of raindrop-freezing fragmentation,... (More)

A numerical formulation is provided for secondary ice production during fragmentation of freezing raindrops or drizzle. This is obtained by pooling laboratory observations from published studies and considering the physics of collisions. There are two modes of the scheme: fragmentation during spherical drop freezing (mode 1) and during collisions of supercooled raindrops with more massive ice (mode 2). The empirical scheme is for atmospheric models. Microphysical simulations with a parcel model of fast ascent (8 m s-1) between -10° and -20°C are validated against aircraft observations of tropical maritime deep convection. Ice enhancement by an order of magnitude is predicted from inclusion of raindrop-freezing fragmentation, as observed. The Hallett-Mossop (HM) process was active too. Both secondary ice mechanisms (HM and raindrop freezing) are accelerated by a positive feedback involving collisional raindrop freezing. An energy-based theory is proposed explaining the laboratory observations of mode 1, both of approximate proportionality between drop size and fragment numbers and of their thermal peak. To illustrate the behavior of the scheme in both modes, the glaciation of idealized monodisperse populations of drops is elucidated with an analytical zero-dimensional (0D) theory treating the freezing in drop-ice collisions by a positive feedback of fragmentation. When drops are too few or too small (≪1 mm), especially at temperatures far from -15°C (mode 1), there is little raindrop-freezing fragmentation on realistic time scales of natural clouds, but otherwise, high ice enhancement (IE) ratios of up to 100-1000 are possible. Theoretical formulas for the glaciation time of such drop populations, and their maximum and initial growth rates of IE ratio, are proposed.

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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Cloud microphysics, Clouds, Cumulus clouds
in
Journal of the Atmospheric Sciences
volume
75
issue
9
pages
40 pages
publisher
Amer Meteorological Soc
external identifiers
  • scopus:85052652428
ISSN
0022-4928
DOI
10.1175/JAS-D-17-0190.1
language
English
LU publication?
yes
id
cc6fb871-a043-46fb-959c-b09c3f484abc
date added to LUP
2018-09-25 12:40:55
date last changed
2019-06-09 04:52:40
@article{cc6fb871-a043-46fb-959c-b09c3f484abc,
  abstract     = {<p>A numerical formulation is provided for secondary ice production during fragmentation of freezing raindrops or drizzle. This is obtained by pooling laboratory observations from published studies and considering the physics of collisions. There are two modes of the scheme: fragmentation during spherical drop freezing (mode 1) and during collisions of supercooled raindrops with more massive ice (mode 2). The empirical scheme is for atmospheric models. Microphysical simulations with a parcel model of fast ascent (8 m s<sup>-1</sup>) between -10° and -20°C are validated against aircraft observations of tropical maritime deep convection. Ice enhancement by an order of magnitude is predicted from inclusion of raindrop-freezing fragmentation, as observed. The Hallett-Mossop (HM) process was active too. Both secondary ice mechanisms (HM and raindrop freezing) are accelerated by a positive feedback involving collisional raindrop freezing. An energy-based theory is proposed explaining the laboratory observations of mode 1, both of approximate proportionality between drop size and fragment numbers and of their thermal peak. To illustrate the behavior of the scheme in both modes, the glaciation of idealized monodisperse populations of drops is elucidated with an analytical zero-dimensional (0D) theory treating the freezing in drop-ice collisions by a positive feedback of fragmentation. When drops are too few or too small (≪1 mm), especially at temperatures far from -15°C (mode 1), there is little raindrop-freezing fragmentation on realistic time scales of natural clouds, but otherwise, high ice enhancement (IE) ratios of up to 100-1000 are possible. Theoretical formulas for the glaciation time of such drop populations, and their maximum and initial growth rates of IE ratio, are proposed.</p>},
  author       = {Phillips, Vaughan T.J. and Patade, Sachin and Gutierrez, Julie and Bansemer, Aaron},
  issn         = {0022-4928},
  keyword      = {Cloud microphysics,Clouds,Cumulus clouds},
  language     = {eng},
  month        = {08},
  number       = {9},
  pages        = {3031--3070},
  publisher    = {Amer Meteorological Soc},
  series       = {Journal of the Atmospheric Sciences},
  title        = {Secondary ice production by fragmentation of freezing drops : Formulation and theory},
  url          = {http://dx.doi.org/10.1175/JAS-D-17-0190.1},
  volume       = {75},
  year         = {2018},
}