Parameterizing the competition between homogeneous and heterogeneous freezing in cirrus cloud formation –  monodisperse ice nuclei

Barahona, D.; Nenes, Athanasios

doi:10.5194/acp-9-369-2009

Cited by 78 publications

(141 citation statements)

References 53 publications

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“…In BN09, S i,max is explicitly calculated, accounting for the competition between water vapor deposition onto ice crystals and supersaturation generation by expansion cooling. S i,max (hence N s i,nuc ) thus depends on dynamics, temperature and the concentration of ice nuclei; i.e., S i,max = S i,max (w sub , T , N het ) (Barahona and Nenes, 2009b). Since homogeneous freezing quickly depletes supersaturation, S i,max is limited, so that S i,max ≤ S hom , S hom being the saturation threshold for homogeneous freezing (Ren and Mackenzie, 2005;Koop et al, 2000).…”

Section: Ice Nucleationmentioning

confidence: 99%

“…Heterogeneous ice nucleation is described through a generalized ice nucleation spectrum, N het = N het (S i , T , m 1...n ), so that N het = N het (S i,max ), with S i being the saturation ratio with respect to ice, and m 1...n the moments of the aerosol number distribution. N het depends on the aerosol composition, and in principle can have any functional form (Barahona and Nenes, 2009b). The usage of N het (S i , T , m 1...n ) also obviates the need for prescribing fixed nucleation thresholds, which may carry uncertainty (Barahona, 2012).…”

Section: Ice Nucleationmentioning

confidence: 99%

“…If no IN are present, then S het approaches the saturation threshold for homogeneous freezing, S hom (Barahona and Nenes, 2009b). S het and S hom represent the minimum saturation ratio required for cloud formation by heterogeneous and homogeneous freezing, respectively.…”

Section: Ice Nucleationmentioning

confidence: 99%

“…2.3.1). The new scheme uses the CCN activation and ice nucleation parameterizations of Fountoukis and Nenes (2005) and Barahona and Nenes (2009b), respectively (Sects. 2.3.2 and 2.3.3).…”

Section: Microphysics Of Stratiform and Anvil Cloudsmentioning

confidence: 99%

“…2.3.1). According to BN09, the ice saturation ratio at which most IN freeze in a polydisperse aerosol population, S het , is given by (Barahona and Nenes, 2009b)…”

Section: Ice Nucleationmentioning

confidence: 99%

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Development of two-moment cloud microphysics for liquid and ice within the NASA Goddard Earth Observing System Model (GEOS-5)

et al. 2014

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Abstract. This work presents the development of a twomoment cloud microphysics scheme within version 5 of the NASA Goddard Earth Observing System (GEOS-5). The scheme includes the implementation of a comprehensive stratiform microphysics module, a new cloud coverage scheme that allows ice supersaturation, and a new microphysics module embedded within the moist convection parameterization of GEOS-5. Comprehensive physically based descriptions of ice nucleation, including homogeneous and heterogeneous freezing, and liquid droplet activation are implemented to describe the formation of cloud particles in stratiform clouds and convective cumulus. The effect of preexisting ice crystals on the formation of cirrus clouds is also accounted for. A new parameterization of the subgrid-scale vertical velocity distribution accounting for turbulence and gravity wave motion is also implemented. The new microphysics significantly improves the representation of liquid water and ice in GEOS-5. Evaluation of the model against satellite retrievals and in situ observations shows agreement of the simulated droplet and ice crystal effective radius, the ice mass mixing ratio and number concentration, and the relative humidity with respect to ice. When using the new microphysics, the fraction of condensate that remains as liquid follows a sigmoidal dependency with temperature, which is in agreement with observations and which fundamentally differs from the linear increase assumed in most models. The performance of the new microphysics in reproducing the observed total cloud fraction, longwave and shortwave cloud forcing, and total precipitation is similar to the operational version of GEOS-5 and in agreement with satellite retrievals. The new microphysics tends to underestimate the coverage of persistent low-level stratocumulus. Sensitivity studies showed that the simulated cloud properties are robust to moderate variation in cloud microphysical parameters. Significant sensitivity remains to variation in the dispersion of the ice crystal size distribution and the critical size for ice autoconversion. Despite these issues, the implementation of the new microphysics leads to a considerably improved and more realistic representation of cloud processes in GEOS-5, and allows the linkage of cloud properties to aerosol emissions.

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Section: Ice Nucleationmentioning

confidence: 99%

Section: Ice Nucleationmentioning

confidence: 99%

Section: Ice Nucleationmentioning

confidence: 99%

“…2.3.1). The new scheme uses the CCN activation and ice nucleation parameterizations of Fountoukis and Nenes (2005) and Barahona and Nenes (2009b), respectively (Sects. 2.3.2 and 2.3.3).…”

Section: Microphysics Of Stratiform and Anvil Cloudsmentioning

confidence: 99%

“…2.3.1). According to BN09, the ice saturation ratio at which most IN freeze in a polydisperse aerosol population, S het , is given by (Barahona and Nenes, 2009b)…”

Section: Ice Nucleationmentioning

confidence: 99%

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Development of two-moment cloud microphysics for liquid and ice within the NASA Goddard Earth Observing System Model (GEOS-5)

et al. 2014

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Quantifying sensitivities of ice crystal number and sources of ice crystal number variability in CAM 5.1 using the adjoint of a physically based cirrus formation parameterization

et al. 2015

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(2015), Quantifying sensitivities of ice crystal number and sources of ice crystal number variability in CAM 5.1 using the adjoint of a physically based cirrus formation parameterization, J. Geophys. Res. Atmos., 120, 2834-2854, doi:10.1002 AbstractWe present the adjoint of a cirrus formation parameterization that computes the sensitivity of ice crystal number concentration to updraft velocity, aerosol, and ice deposition coefficient. The adjoint is driven by simulations from the National Center for Atmospheric Research Community Atmosphere Model version 5.1 CAM 5.1 to understand the sensitivity of formed ice crystal number concentration to 13 variables and quantify which contribute to its variability. Sensitivities of formed ice crystal number concentration to updraft velocity, sulfate number, and is sufficient but sulfate number concentration is low, indicating a sulfate-limited regime. Outside of the tropics, competition between homogeneous and heterogeneous nucleation may shift annually averaged sensitivities to higher magnitudes, when infrequent strong updrafts shift crystal production away from purely heterogeneous nucleation. Outside the tropics, updraft velocity is responsible for approximately 52.70% of the ice crystal number variability. In the tropics, sulfate number concentration and updraft jointly control variability in formed crystal number concentration. Insoluble aerosol species play a secondary, but still important, role in influencing the variability in crystal concentrations, with coarse-mode dust being the largest contributor at nearly 50% in certain regions. On a global scale, more than 95% of the temporal variability in crystal number concentration can be described by temperature, updraft velocity, sulfate number, and coarse-mode dust number concentration.

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Aerosol effects on cirrus through ice nucleation in the Community Atmosphere Model CAM5 with a statistical cirrus scheme

Wang

Liu

Zhang

et al. 2014

J Adv Model Earth Syst

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A statistical cirrus scheme that tracks ice saturation ratio in the clear-sky and cloudy portion of a grid box separately has been implemented into the Community Atmosphere Model CAM5 to provide a consistent treatment of ice nucleation and cloud formation. Simulated ice supersaturation and ice crystal number concentrations strongly depend on the number concentrations of heterogeneous ice nuclei (IN), subgrid temperature formulas, and the number concentration of sulfate particles participating in homogeneous freezing, while simulated ice water content is insensitive to these perturbations. Allowing 1-10% of dust particles to serve as heterogeneous IN is found to produce ice supersaturation in better agreement with observations. Introducing a subgrid temperature perturbation based on long-term aircraft observations produces a better hemispheric contrast in ice supersaturation compared to observations. Heterogeneous IN from dust particles alter the net radiative fluxes at the top of atmosphere (TOA) . Aerosol effects on cirrus exert an even larger impact on the atmospheric component of the radiative fluxes (2 or 3 times the changes in the TOA radiative fluxes) and therefore through the fast atmosphere response on the hydrological cycle. This points to the urgent need to quantify aerosol effects on cirrus through ice nucleation and how these further affect the hydrological cycle.

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Parameterizing the competition between homogeneous and heterogeneous freezing in cirrus cloud formation – monodisperse ice nuclei

Cited by 78 publications

References 53 publications

Development of two-moment cloud microphysics for liquid and ice within the NASA Goddard Earth Observing System Model (GEOS-5)

Development of two-moment cloud microphysics for liquid and ice within the NASA Goddard Earth Observing System Model (GEOS-5)

Quantifying sensitivities of ice crystal number and sources of ice crystal number variability in CAM 5.1 using the adjoint of a physically based cirrus formation parameterization

Aerosol effects on cirrus through ice nucleation in the Community Atmosphere Model CAM5 with a statistical cirrus scheme

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