Haze Particle Nucleation Simulations in Cirrus Clouds, and Applications for Numerical and Lidar Studies

Sassen, Kenneth; Dodd, Gregory C.

doi:10.1175/1520-0469(1989)046<3005:hpnsic>2.0.co;2

Cited by 104 publications

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“…Although it remains a subject of debate under which atmospheric conditions homogeneous freezing of supercooled aerosols leads to the formation of cirrus clouds, the relevance Correspondence to: W. Haag (Werner.Haag@dlr.de) of this process has been emphasized in many previous studies (Heymsfield and Sabin, 1989;Sassen and Dodd, 1989;Jensen and Toon, 1992;Heymsfield and Miloshevich, 1993;Jensen et al, 1998;Lin et al, 1998;Field et al, 2001). It has been shown that the special class of orographic ice clouds predominantly forms at large supersaturations with respect to ice at temperatures below the spontaneous freezing point of pure water (∼ 235 K), and it seems likely that homogeneous freezing of supercooled solutions is the dominant ice particle formation mechanism for this cloud type, given the large cooling rates of air parcels induced by atmospheric waves.…”

Section: Introductionmentioning

confidence: 96%

Numerical simulations of homogeneous freezing processes in the aerosol chamber AIDA

et al. 2003

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Abstract.The homogeneous freezing of supercooled H 2 SO 4 /H 2 O aerosols in an aerosol chamber is investigated with a microphysical box model using the activity parameterization of the nucleation rate by Koop et al. (2000). The simulations are constrained by measurements of pressure, temperature, total water mixing ratio, and the initial aerosol size distribution, described in a companion paper (Möhler et al., 2003). Model results are compared to measurements conducted in the temperature range between 194 and 235 K, with cooling rates in the range between 0.5 and 2.6 K min −1 , and at air pressures between 170 and 1000 hPa. The simulations focus on the time history of relative humidity with respect to ice, aerosol size distribution, partitioning of water between gas and particle phase, onset times of freezing, freezing threshold relative humidities, aerosol chemical composition at the onset of freezing, and the number of nucleated ice crystals. The latter four parameters can be inferred from the experiments, the former three aid in interpreting the measurements. Sensitivity studies are carried out to address the relative importance of uncertainties of basic quantities such as temperature, total H 2 O mixing ratio, aerosol size spectrum, and deposition coefficient of H 2 O molecules on ice. The ability of the numerical simulations to provide detailed explanations of the observations greatly increases confidence in attempts to model this process under real atmospheric conditions, for instance with regard to the formation of cirrus clouds or polar stratospheric ice clouds, provided that accurate temperature and humidity measurements are available.

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Section: Introductionmentioning

confidence: 96%

Numerical simulations of homogeneous freezing processes in the aerosol chamber AIDA

et al. 2003

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“…For detailed process studies, cloud resolving models (Starr and Cox, 1985;Jensen et al, 1994;Lin et al, 2005;Kärcher, 2005) and box models (Sassen and Dodd, 1989;Lin et al, 2002;Gierens, 2003;Haag and Kärcher, 2004;Hoyle et al, 2005;Bunz et al, 2008) were used. Many box models and cloud resolving models have very detailed microphysics schemes which require high spatial and temporal resolution.…”

Section: Introductionmentioning

confidence: 99%

Modelling of cirrus clouds – Part 1a: Model description and validation

2009

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Abstract.A double-moment bulk microphysics scheme for modelling cirrus clouds including explicit impact of aerosols on different types of nucleation mechanism is described. Process rates are formulated in terms of generalised moments of the underlying a priori size distributions in order to allow simple switching between various distribution types. The scheme has been implemented into a simple box model and into the anelastic non-hydrostatic model EULAG. The new microphysics is validated against simulations with detailed microphysics for idealised process studies and for a well documented case of arctic cirrostratus. Additionally, the formation of ice crystals with realistic background aerosol concentration is modelled and the effect of ambient pressure on homogeneous nucleation is investigated in the box model.The model stands all tests and is thus suitable for cloudresolving simulations of cirrus clouds.

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“…The importance of haze particles for cirrus is that concentrated solutions inhibit the particles from freezing until dilution occurs. The solution drop temperature is thus transformed into a warmer effective temperature Te• for evaluating the nucleation rate [Sassen and Dodd, 1988 hereafter SD88], Although the relative importance of the two nucleation mechanisms in cirrus is a matter of debate [Khvorostyanov and Sassen, 1998a], both processes should be affected by the freezing point depression effects of concentrated solutions.…”

Section: Introductionmentioning

confidence: 99%

Ice nucleation in cirrus clouds: A model study of the homogeneous and heterogeneous modes

Sassen

Benson

2000

Geophysical Research Letters

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Abstract. Parcel cloud model simulations have explored the feasibility of a unified approach to describe the homogeneous and heterogeneous ice nucleation mechanisms in cirrus clouds. It was assumed that the ice crystal generation process involved the freezing of ammonium sulfate haze particles, as modulated by an effective temperature proportional to molality in both cases. Treated as variables in the -36 ø to -60øC model domain are the updraft velocity, and the terms in a modified Fletcher equation used to approximate heterogeneous freezing. Parameterizations drawn from the homogeneous freezing runs are provided for the threshold relative humidity and number of crystals nucleated, as functions of both temperature and updraft velocity. We find that heterogeneous nucleation can compete or dominate at relatively weak updrafts, but only for unusually high ice nuclei concentration and temperature activation terms.

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Haze Particle Nucleation Simulations in Cirrus Clouds, and Applications for Numerical and Lidar Studies

Cited by 104 publications

References 0 publications

Numerical simulations of homogeneous freezing processes in the aerosol chamber AIDA

Numerical simulations of homogeneous freezing processes in the aerosol chamber AIDA

Modelling of cirrus clouds – Part 1a: Model description and validation

Ice nucleation in cirrus clouds: A model study of the homogeneous and heterogeneous modes

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