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Volume 16, issue 11
Atmos. Chem. Phys., 16, 7251–7283, 2016
https://doi.org/10.5194/acp-16-7251-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Atmos. Chem. Phys., 16, 7251–7283, 2016
https://doi.org/10.5194/acp-16-7251-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 10 Jun 2016

Research article | 10 Jun 2016

Derivation of physical and optical properties of mid-latitude cirrus ice crystals for a size-resolved cloud microphysics model

Ann M. Fridlind1, Rachel Atlas2, Bastiaan van Diedenhoven1,3, Junshik Um4, Greg M. McFarquhar4, Andrew S. Ackerman1, Elisabeth J. Moyer2, and R. Paul Lawson5 Ann M. Fridlind et al.
  • 1NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY, USA
  • 2University of Chicago, Chicago, IL, USA
  • 3Columbia University, New York, NY, USA
  • 4University of Illinois, Urbana-Champaign, IL, USA
  • 5Spec Inc., Boulder, Colorado, USA

Abstract. Single-crystal images collected in mid-latitude cirrus are analyzed to provide internally consistent ice physical and optical properties for a size-resolved cloud microphysics model, including single-particle mass, projected area, fall speed, capacitance, single-scattering albedo, and asymmetry parameter. Using measurements gathered during two flights through a widespread synoptic cirrus shield, bullet rosettes are found to be the dominant identifiable habit among ice crystals with maximum dimension (Dmax) greater than 100 µm. Properties are therefore first derived for bullet rosettes based on measurements of arm lengths and widths, then for aggregates of bullet rosettes and for unclassified (irregular) crystals. Derived bullet rosette masses are substantially greater than reported in existing literature, whereas measured projected areas are similar or lesser, resulting in factors of 1.5–2 greater fall speeds, and, in the limit of large Dmax, near-infrared single-scattering albedo and asymmetry parameter (g) greater by  ∼  0.2 and 0.05, respectively. A model that includes commonly imaged side plane growth on bullet rosettes exhibits relatively little difference in microphysical and optical properties aside from  ∼ 0.05 increase in mid-visible g primarily attributable to plate aspect ratio. In parcel simulations, ice size distribution, and g are sensitive to assumed ice properties.

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Images of crystals within mid-latitude cirrus clouds are used to derive consistent ice physical and optical properties for a detailed cloud microphysics model, including size-dependent mass, projected area, and fall speed. Based on habits found, properties are derived for bullet rosettes, their aggregates, and crystals with irregular shapes. Derived bullet rosette fall speeds are substantially greater than reported in past studies, owing to differences in mass, area, or diameter representation.
Images of crystals within mid-latitude cirrus clouds are used to derive consistent ice physical...
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