Representing the ice fall speed in climate models: Results from Tropical Composition, Cloud and Climate Coupling (TC4) and the Indirect and Semi-Direct Aerosol Campaign (ISDAC)

Mitchell, David L.; Mishra, Subhashree; Lawson, R. Paul

doi:10.1029/2010jd015433

Cited by 42 publications

(62 citation statements)

References 36 publications

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“…This is what was observed from aircraft measurements of anvil cirrus (Mitchell et al, 2011a) and mid-latitude synoptic cirrus (Mitchell et al, 2011c) in the absence of liquid water, suggesting the retrieved change in modality could be partly due to the onset of homogeneous freezing nucleation. However, low levels of liquid may also be responsible for the retrieved β eff values.…”

Section: Summary and Concluding Remarkssupporting

confidence: 63%

Satellite retrieval of the liquid water fraction in tropical clouds between −20 and −38 °C

Mitchell

d’Entremont

2012

Atmos. Meas. Tech.

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Abstract. This study describes a satellite remote sensing method for directly retrieving the liquid water fraction in mixed phase clouds, and appears unique in this respect. The method uses MODIS split-window channels for retrieving the liquid fraction from cold clouds where the liquid water fraction is less than 50 % of the total condensate. This makes use of the observation that clouds only containing ice exhibit effective 12-to-11 µm absorption optical thickness ratios (β eff ) that are quasi-constant with retrieved cloud temperature T . This observation was made possible by using two CO 2 channels to retrieve T and then using the 12 and 11 µm channels to retrieve emissivities and β eff . Thus for T < −40 • C, β eff is constant, but for T > −40 • C, β eff slowly increases due to the presence of liquid water, revealing mean liquid fractions of ∼ 10 % around −22 • C from tropical clouds identified as cirrus by the cloud mask. However, the uncertainties for these retrievals are large, and extensive in situ measurements are needed to refine and validate these retrievals. Such liquid levels are shown to reduce the cloud effective diameter D e such that cloud optical thickness will increase by more than 50 % for a given water path, relative to D e corresponding to pure ice clouds. Such retrieval information is needed for validation of the cloud microphysics in climate models. Since low levels of liquid water can dominate cloud optical properties, tropical clouds between −25 and −20 • C may be susceptible to the first aerosol indirect effect.

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Section: Summary and Concluding Remarkssupporting

confidence: 63%

Satellite retrieval of the liquid water fraction in tropical clouds between −20 and −38 °C

Mitchell

d’Entremont

2012

Atmos. Meas. Tech.

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“…8 E and F). The significant reduction in ice fall velocity as ice particle size decreases has been documented based on recent in situ aircraft measurements (30). Due to slow fallout, the stratiform/anvil clouds remain longer, and the strong horizontal advection in the upper troposphere further spreads them out over larger areas.…”

Section: Resultsmentioning

confidence: 96%

Microphysical effects determine macrophysical response for aerosol impacts on deep convective clouds

Fan

Leung

Rosenfeld

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

313

305

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Deep convective clouds (DCCs) play a crucial role in the general circulation, energy, and hydrological cycle of our climate system. Aerosol particles can influence DCCs by altering cloud properties, precipitation regimes, and radiation balance. Previous studies reported both invigoration and suppression of DCCs by aerosols, but few were concerned with the whole life cycle of DCC. By conducting multiple monthlong cloud-resolving simulations with spectral-bin cloud microphysics that capture the observed macrophysical and microphysical properties of summer convective clouds and precipitation in the tropics and midlatitudes, this study provides a comprehensive view of how aerosols affect cloud cover, cloud top height, and radiative forcing. We found that although the widely accepted theory of DCC invigoration due to aerosol's thermodynamic effect (additional latent heat release from freezing of greater amount of cloud water) may work during the growing stage, it is microphysical effect influenced by aerosols that drives the dramatic increase in cloud cover, cloud top height, and cloud thickness at the mature and dissipation stages by inducing larger amounts of smaller but longer-lasting ice particles in the stratiform/anvils of DCCs, even when thermodynamic invigoration of convection is absent. The thermodynamic invigoration effect contributes up to ∼27% of total increase in cloud cover. The overall aerosol indirect effect is an atmospheric radiative warming (3-5 W·m ). The modeling findings are confirmed by the analyses of ample measurements made at three sites of distinctly different environments.aerosol-cloud interactions | aerosol indirect forcing D eep convective clouds (DCCs), particularly those associated with tropical convection, are significant sources of precipitation and play a key role in the hydrological and energy cycle as well as regional and global circulation (1). DCCs are organized into one or more convective cores characterized by strong updrafts that merge at the mature phase and anvil clouds that result from divergence of the updrafts from the convective cores just below the tropopause and spread over large areas. Cloud top height (CTH), cloud thickness, and microphysical properties are important properties of DCCs that influence their radiation effects. Satellite radar observations show a correlation between convective intensity and lifetime, size, and depth of the anvils (2). Because of their large coverage and long lifetime, anvils dominate the radiative effects of DCCs.Atmospheric aerosol particles can influence cloud properties and precipitation regimes through their impacts on cloud microphysical and macrophysical processes and consequently alter the radiation balance of the climate system. These so-called aerosol indirect effects remain a key uncertainty in understanding the current and future climate (3). Quantifying aerosol impacts on DCCs is exceptionally challenging because the interactions among cloud microphysics (liquid, ice, and mixed-phase), radiation, and atmospheric dynamics ar...

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“…However, there are still large variations of V t as a result of shape variations, even for the same ice particle dimension L. Mitchell (1996) proposed to relate V t with L, mass m, and projected area normal to the fall direction A and developed coefficients for different size ranges and ice crystal shapes. So far, Mitchell's parameterization has been widely used in cloud and climate models (Mitchell et al 2011;Sulia and Harrington 2011). Heymsfield and Westbrook (2010, hereafter HW10) suggested that Mitchell's parameterization overestimated the V t for open-geometry ice particles.…”

Section: B Parameterizations Of Ice Crystal Terminal Velocitymentioning

confidence: 99%

Ice Concentration Retrieval in Stratiform Mixed-Phase Clouds Using Cloud Radar Reflectivity Measurements and 1D Ice Growth Model Simulations

Zhang

Wang

Heymsfield

et al. 2014

Journal of the Atmospheric Sciences

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Measurements of ice number concentration in clouds are important but still pose problems. The pattern of ice development in stratiform mixed-phase clouds (SMCs) offers an opportunity to use cloud radar reflectivity (Z e ) measurements and other cloud properties to retrieve ice number concentrations. To quantify the strong temperature dependencies of ice crystal habits and growth rates, a one-dimensional (1D) ice growth model has been developed to calculate ice diffusional growth and riming growth along ice particle fallout trajectories in SMCs. The radar reflectivity and fallout velocity profiles of ice crystals calculated from the 1D ice growth model are evaluated with the Atmospheric Radiation Measurements (ARM) Climate Research Facility (ACRF) ground-based high-vertical-resolution radar measurements. A method has been developed to retrieve ice number concentrations in SMCs at a specific cloud-top temperature (CTT) and liquid water path (LWP) by combining Z e measurements and 1D ice growth model simulations. The retrieved ice number concentrations in SMCs are evaluated using integrated airborne in situ and remote sensing measurements and three-dimensional cloud-resolving model simulations with a bin microphysical scheme. The statistical evaluations show that the retrieved ice number concentrations in the SMCs are within an uncertainty of a factor of 2.

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Representing the ice fall speed in climate models: Results from Tropical Composition, Cloud and Climate Coupling (TC4) and the Indirect and Semi-Direct Aerosol Campaign (ISDAC)

Cited by 42 publications

References 36 publications

Satellite retrieval of the liquid water fraction in tropical clouds between −20 and −38 °C

Satellite retrieval of the liquid water fraction in tropical clouds between −20 and −38 °C

Microphysical effects determine macrophysical response for aerosol impacts on deep convective clouds

Ice Concentration Retrieval in Stratiform Mixed-Phase Clouds Using Cloud Radar Reflectivity Measurements and 1D Ice Growth Model Simulations

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