Use of observed ice crystal sizes and shapes to calculate mean‐scattering properties and multispectral radiances: CEPEX April 4, 1993, case study

McFarquhar, Greg M.; Heymsfield, Andrew J.; Macke, Andreas; Iaquinta, Jean; Aulenbach, S.

doi:10.1029/1999jd900802

Cited by 66 publications

(51 citation statements)

References 28 publications

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“…Both simulations are compared with the same observational data from KWAJEX and TOGA-COARE, including some new cloud-related and thermodynamical statistics in the validation. Following Phillips et al (2007), the predicted properties of cirrus for TOGA-COARE are compared with observations from the Central Equatorial Pacific Experiment (CEPEX; McFarquhar et al, 1999), in view of the lack of flights above the freezing level during TOGA-COARE. Note that these maritime simulations (KWAJEX, TOGA-COARE) are not used for any biological sensitivity tests anywhere in the present paper.…”

Section: Appendix a Validation Of Simulations Of Maritime Convectionmentioning

confidence: 99%

Potential impacts from biological aerosols on ensembles of continental clouds simulated numerically

et al. 2009

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Abstract. An aerosol-cloud modeling framework is described to simulate the activation of ice particles and droplets by biological aerosol particles, such as airborne icenucleation active (INA) bacteria. It includes the empirical parameterisation of heterogeneous ice nucleation and a semi-prognostic aerosol component, which have been incorporated into a cloud-system resolving model (CSRM) with double-moment bulk microphysics. The formation of cloud liquid by soluble material coated on these partially insoluble organic aerosols is represented. It determines their partial removal from deep convective clouds by accretion onto precipitation in the cloud model. This "aerosol-cloud model" is validated for diverse cases of deep convection with contrasting aerosol conditions, against satellite, ground-based and aircraft observations.Simulations are performed with the aerosol-cloud model for a month-long period of summertime convective activity over Oklahoma. It includes three cases of continental deep convection simulated previously by Phillips and . Elevated concentrations of insoluble organic aerosol, boosted by a factor of 100 beyond their usual values for this continental region, are found to influence significantly the following quantities: (1) the average numbers and sizes of ice crystals and droplets in the clouds; (2) the horizontal cloud coverage in the free troposphere; (3) preCorrespondence to: V. T. J. Phillips (vaughanp@hawaii.edu) cipitation at the ground; and (4) incident solar insolation at the surface. This factor of 100 is plausible for natural fluctuations of the concentration of insoluble organic aerosol, in view of variability of cell concentrations for airborne bacteria seen by Lindemann et al. (1982).In nature, such boosting of the insoluble organic aerosol loading could arise from enhanced emissions of biological aerosol particles from a land surface. Surface wetness and solar insolation at the ground are meteorological quantities known to influence rates of growth of certain biological particles (e.g. bacteria). Their rates of emission into the atmosphere must depend on these same quantities, in addition to surface wind speed, turbulence and convection. Finally, the present study is the first attempt at evaluating the impacts from biological aerosols on mesoscale cloud ensembles in the literature.

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Section: Appendix a Validation Of Simulations Of Maritime Convectionmentioning

confidence: 99%

Potential impacts from biological aerosols on ensembles of continental clouds simulated numerically

et al. 2009

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“…The aspect ratio of the polycrystal remains invariant with respect to size. McFarquhar et al (1999) integrated the ice crystal shape distribution over the observed size distribution functions to obtain the bulk scattering properties to try to describe the reflectance properties of cirrus measured at four wavelengths between 0.664 µm and 2.142 µm obtained during the CEPEX (Central Equatorial Pacific Experiment) campaign. They found that the simulations of observed reflectances were highly sensitive to assumptions about which shapes to include in their shape distribution function, and a general description of cirrus reflectance would be difficult without prior knowledge of ice crystal shapes.…”

Section: Introductionmentioning

confidence: 99%

“…McFarquhar et al (1999) assumed an ensemble consisting of spheres, hexagonal ice columns, bulletrosettes and polycrystals. The polycrystal due to Macke et al (1996a) is a randomization of a second generation triadic Koch fractal and is supposed to represent the more irregular shapes that are observed in cirrus.…”

Section: Introductionmentioning

confidence: 99%

A self‐consistent scattering model for cirrus. I: The solar region

Baran

C.‐Labonnote²

2007

Quart J Royal Meteoro Soc

129

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ABSTRACT:In this paper a self-consistent scattering model for cirrus is presented. The model consists of an ensemble of ice crystals where the smallest ice crystal is represented by a single hexagonal ice column. As the overall ice crystal size increases, the ice crystals become progressively more complex by arbitrarily attaching other hexagonal elements until a chain-like ice crystal is formed, this representing the largest ice crystal in the ensemble. The ensemble consists of six ice crystal members whose aspect ratios (ratios of the major-to-minor axes of the circumscribed ellipse) are allowed to vary between unity and 1.84 for the smallest and largest ice crystal, respectively. The ensemble model's prediction of parameters fundamental to solar radiative transfer through cirrus such as ice water content and the volume extinction coefficient is tested using in situ based data obtained from the midlatitudes and Tropics. It is found that the ensemble model is able to generally predict the ice water content and extinction measurements within a factor of two. Moreover, the ensemble model's prediction of cirrus spherical albedo and polarized reflection are tested against a space-based instrument using one day of global measurements. The space-based instrument is able to sample the scattering phase function between the scattering angles of approximately 60°and 180°, and a total of 37 581 satellite pixels were used in the present analysis covering latitude bands between 43.75°S and 76.58°N. It is found that the ensemble model phase function is well able to minimize significantly differences between satellite-based measurements of spherical albedo and the ensemble model's prediction of spherical albedo. The satellite-based measurements of polarized reflection are found to be reasonably described by more simple members of the ensemble. The ensemble model presented in this paper should find wide applicability to the remote sensing of cirrus as well as more fundamental solar radiative transfer calculations through cirrus, and improved solar optical properties for climate and Numerical Weather Prediction models.

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“…The larger cloud-ice mass increases the reflectivity of clouds and, hence, tends to increase the reflectivity of incident solar radiation on clouds in the control run than in the single-moment run. The in-cloud averaged generalized effective size of cloud ice is larger in the control run than in the single-moment run where the generalized size is prescribed as a function of air temperature following McFarquhar et al (1999) (Fig. 8d).…”

Section: Radiation (Arm-a Case)mentioning

confidence: 99%

“…Due to the absence of the particle-number prediction, the effective particle size diameter of a cloud droplet is assumed to be 20 μm, and that of cloud ice is given by empirical functions of height (McFarquhar et al 1999). The homogeneous freezing of all supercooled droplets and rain is performed at -36°C or below.…”

Section: Single-moment Microphysicsmentioning

confidence: 99%

Effects of Cloud Parameterization on Radiation and Precipitation: A Comparison Between Single-Moment Microphysics and Double-Moment Microphysics

Lee¹,

Donner²

2011

Terr. Atmos. Ocean. Sci.

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This study compares a single-moment microphysics scheme to a double-moment microphysics scheme using four observed cases of a mesoscale cloud system. Previous studies comparing a single-moment microphysics scheme to a doublemoment microphysics scheme have focused on microphysical processes or overall dynamics, precipitation and morphology of cloud systems. However, they have not focused on how the different representation of microphysical processes between a single-and double-moment microphysics scheme affects precipitation. This study shifts its focus from that of previous studies to the effect of the different representation of microphysics on precipitation. In addition, this study examines the effect of the different representation of microphysical processes on different radiation budgets between single-and double-moment microphysics schemes.The temporal evolution of precipitation simulated by a single-moment microphysics scheme is significantly different from that by a double-moment microphysics scheme in this study. This is mostly due to different physical representations of key processes (i.e., autoconversion, saturation, and nucleation). Also, a simulation by a single-moment microphysics scheme results in different radiation budgets compared to a double-moment microphysics scheme. More reflection of incident solar radiation in a simulation with a double-moment microphysics scheme than that with a single-moment microphysics scheme is simulated.

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Use of observed ice crystal sizes and shapes to calculate mean‐scattering properties and multispectral radiances: CEPEX April 4, 1993, case study

Cited by 66 publications

References 28 publications

Potential impacts from biological aerosols on ensembles of continental clouds simulated numerically

Potential impacts from biological aerosols on ensembles of continental clouds simulated numerically

A self‐consistent scattering model for cirrus. I: The solar region

Effects of Cloud Parameterization on Radiation and Precipitation: A Comparison Between Single-Moment Microphysics and Double-Moment Microphysics

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