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Impacts of aerosol chemical composition on microphysics and precipitation in deep convection

Lee, Seoung Soo; Donner, Leo J. and Phillips, Vaughan LU (2009) In Atmospheric Research 94(2). p.220-237
Abstract
Aerosols affect precipitation by modifying cloud properties such as cloud droplet number concentration (CDNQ. Aerosol effects on CDNC depend on aerosol properties such as number concentration, size spectrum, and chemical composition. This study focuses on the effects of aerosol chemical composition on CDNC and, thereby, precipitation in a mesoscale cloud ensemble (MCE) driven by deep convective clouds. The NICE was observed during the 1997 department of energy's Atmospheric Radiation Measurement (ARM) summer experiment. Double-moment microphysics with explicit nucleation parameterization, able to take into account those three properties of aerosols, is used to investigate the effects of aerosol chemical composition on CDNC and... (More)
Aerosols affect precipitation by modifying cloud properties such as cloud droplet number concentration (CDNQ. Aerosol effects on CDNC depend on aerosol properties such as number concentration, size spectrum, and chemical composition. This study focuses on the effects of aerosol chemical composition on CDNC and, thereby, precipitation in a mesoscale cloud ensemble (MCE) driven by deep convective clouds. The NICE was observed during the 1997 department of energy's Atmospheric Radiation Measurement (ARM) summer experiment. Double-moment microphysics with explicit nucleation parameterization, able to take into account those three properties of aerosols, is used to investigate the effects of aerosol chemical composition on CDNC and precipitation. The effects of aerosol chemical compositions are investigated for both soluble and insoluble substances in aerosol particles. The effects of soluble substances are examined by varying mass fractions of two representative soluble components of aerosols in the continental air mass: sulfate and organics. The increase in organics with decreasing sulfate lowers critical supersaturation (S,) and leads to higher CDNC. Higher CDNC results in smaller autoconversion of cloud liquid to rain. This provides more abundant cloud liquid as a source of evaporative cooling, leading to more intense downdrafts, low-level convergence, and updrafts. The resultant stronger updrafts produce more condensation and thus precipitation, as compared to the case of 100% sulfate aerosols. The conventional assumption of sulfate aerosol as a surrogate for the whole aerosol mass can be inapplicable for the case with the strong sources of organics. The less precipitation is simulated when an insoluble substance replaces organics as compared to when it replaces sulfate. When the effects of organics on the surface tension of droplet and solution term in the Kohler curve are deactivated by the insoluble substance, S, is raised more than when the effects of sulfate on the solution term are deactivated by the insoluble substance. This leads to lower CDNC and, thus, larger autoconversion of cloud liquid to rain, providing less abundant cloud liquid as a source of evaporative cooling. The resultant less evaporative cooling produces less intense downdrafts, weaker low-level convergence, updrafts, condensation and, thereby, less precipitation in the case where organics is replaced by the insoluble substance than in the case where sulfate is replaced by the insoluble substance. The variation of precipitation caused by the change in the mass fraction between the soluble and insoluble substances is larger than that caused by the change in the mass fraction between the soluble substances. (C) 2009 Elsevier B.V. All rights reserved. (Less)
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author
publishing date
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Contribution to journal
publication status
published
subject
keywords
Microphysics, Cloud condensation nuclei, Mesoscale cloud ensemble
in
Atmospheric Research
volume
94
issue
2
pages
220 - 237
publisher
Elsevier
external identifiers
  • wos:000270119400007
  • scopus:68949096592
ISSN
1873-2895
DOI
10.1016/j.atmosres.2009.05.015
language
English
LU publication?
no
id
fb6ce398-2bbb-4bfd-b196-f1780c9afac6 (old id 4587474)
date added to LUP
2014-08-15 10:29:01
date last changed
2017-01-01 05:19:14
@article{fb6ce398-2bbb-4bfd-b196-f1780c9afac6,
  abstract     = {Aerosols affect precipitation by modifying cloud properties such as cloud droplet number concentration (CDNQ. Aerosol effects on CDNC depend on aerosol properties such as number concentration, size spectrum, and chemical composition. This study focuses on the effects of aerosol chemical composition on CDNC and, thereby, precipitation in a mesoscale cloud ensemble (MCE) driven by deep convective clouds. The NICE was observed during the 1997 department of energy's Atmospheric Radiation Measurement (ARM) summer experiment. Double-moment microphysics with explicit nucleation parameterization, able to take into account those three properties of aerosols, is used to investigate the effects of aerosol chemical composition on CDNC and precipitation. The effects of aerosol chemical compositions are investigated for both soluble and insoluble substances in aerosol particles. The effects of soluble substances are examined by varying mass fractions of two representative soluble components of aerosols in the continental air mass: sulfate and organics. The increase in organics with decreasing sulfate lowers critical supersaturation (S,) and leads to higher CDNC. Higher CDNC results in smaller autoconversion of cloud liquid to rain. This provides more abundant cloud liquid as a source of evaporative cooling, leading to more intense downdrafts, low-level convergence, and updrafts. The resultant stronger updrafts produce more condensation and thus precipitation, as compared to the case of 100% sulfate aerosols. The conventional assumption of sulfate aerosol as a surrogate for the whole aerosol mass can be inapplicable for the case with the strong sources of organics. The less precipitation is simulated when an insoluble substance replaces organics as compared to when it replaces sulfate. When the effects of organics on the surface tension of droplet and solution term in the Kohler curve are deactivated by the insoluble substance, S, is raised more than when the effects of sulfate on the solution term are deactivated by the insoluble substance. This leads to lower CDNC and, thus, larger autoconversion of cloud liquid to rain, providing less abundant cloud liquid as a source of evaporative cooling. The resultant less evaporative cooling produces less intense downdrafts, weaker low-level convergence, updrafts, condensation and, thereby, less precipitation in the case where organics is replaced by the insoluble substance than in the case where sulfate is replaced by the insoluble substance. The variation of precipitation caused by the change in the mass fraction between the soluble and insoluble substances is larger than that caused by the change in the mass fraction between the soluble substances. (C) 2009 Elsevier B.V. All rights reserved.},
  author       = {Lee, Seoung Soo and Donner, Leo J. and Phillips, Vaughan},
  issn         = {1873-2895},
  keyword      = {Microphysics,Cloud condensation nuclei,Mesoscale cloud ensemble},
  language     = {eng},
  number       = {2},
  pages        = {220--237},
  publisher    = {Elsevier},
  series       = {Atmospheric Research},
  title        = {Impacts of aerosol chemical composition on microphysics and precipitation in deep convection},
  url          = {http://dx.doi.org/10.1016/j.atmosres.2009.05.015},
  volume       = {94},
  year         = {2009},
}