On the ice nucleation spectrum

Barahona, D.

doi:10.5194/acp-12-3733-2012

Cited by 39 publications

(59 citation statements)

References 62 publications

(133 reference statements)

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“…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). In this work, N het is described using the formulation of Phillips et al (2013) (hereafter Ph13), considering immersion and deposition ice nucleation on dust, black carbon, and soluble organics.…”

Section: Ice Nucleationmentioning

confidence: 99%

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%

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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“…We modify the original expression used in Hoose et al (2010) concerning J het (the rate of heterogeneous nucleation per aerosol particle and per second) with the form factor (f ) raised to the −1/2 power instead of 1/2 (see Eq. 1); this is done due to the unphysical behavior of the original expression which implies that J het →0 when f →0 (i.e., the ice nucleation rate will become smaller on more easily wettable materials) (Määttänen et al, 2005;Barahona, 2012).…”

Section: Single-contact-angle (α) Modelmentioning

confidence: 99%

“…Due to the uncertainty of assuming a spherical substrate (or any other simple geometry) (Barahona, 2012) and due to the fact that the difference between a flat surface and a spherical surface can be ignored when the diameter of a particle is larger than 100 nm, we calculate the compatibility parameter f with a flat surface instead of the convex surface. Thus, f has the form (Pruppacher and Klett, 1997) …”

Section: Y Wang Et Al: Different Contact Angle Distributionsmentioning

confidence: 99%

Different contact angle distributions for heterogeneous ice nucleation in the Community Atmospheric Model version 5

et al. 2014

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Abstract. In order to investigate the impact of different treatments for the contact angle (α) in heterogeneous ice nucleating properties of natural dust and black carbon (BC) particles, we implement the classical-nucleation-theory-based parameterization of heterogeneous ice nucleation (Hoose et al., 2010) in the Community Atmospheric Model version 5 (CAM5) and then improve it by replacing the original singlecontact-angle model with the probability-density-functionof-α (α-PDF) model to better represent the ice nucleation behavior of natural dust found in observations. We refit the classical nucleation theory (CNT) to constrain the uncertain parameters (i.e., onset α and activation energy in the single-α model; mean contact angle and standard deviation in the α-PDF model) using recent observation data sets for Saharan natural dust and BC (soot). We investigate the impact of the time dependence of droplet freezing on mixed-phase clouds and climate in CAM5 as well as the roles of natural dust and soot in different nucleation mechanisms. Our results show that, when compared with observations, the potential ice nuclei (IN) calculated by the α-PDF model show better agreement than those calculated by the single-α model at warm temperatures (T ; T > −20 • C). More ice crystals can form at low altitudes (with warm temperatures) simulated by the α-PDF model than compared to the single-α model in CAM5. All of these can be attributed to different ice nucleation efficiencies among aerosol particles, with some particles having smaller contact angles (higher efficiencies) in the α-PDF model. In the sensitivity tests with the α-PDF model, we find that the change in mean contact angle has a larger impact on the active fraction at a given temperature than a change in standard deviation, even though the change in standard deviation can lead to a change in freezing behavior. Both the single-α and the α-PDF model indicate that the immersion freezing of natural dust plays a more important role in the heterogeneous nucleation than that of soot in mixed-phase clouds. The new parameterizations implemented in CAM5 induce more significant aerosol indirect effects than the default parameterization.

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“…Connolly et al (2009) used linear and quadratic equations to describe the cumulative number of sites per unit surface area of different dust particles. The formulation of Barahona (2012) used the sum of several functions to define the activity spectrum. Such approximations are consistent with the emphasis (in Sect.…”

Section: Empirical Approachesmentioning

confidence: 99%

Interpretation of freezing nucleation experiments: singular and stochastic; sites and surfaces

2014

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Abstract. Publications of recent years dealing with laboratory experiments of immersion freezing reveal uncertainties about the fundamentals of heterogeneous freezing nucleation. While it appears well accepted that there are two major factors that determine the process, namely fluctuations in the size and configuration of incipient embryos of the solid phase and the role of the substrate to aid embryo formation, views have been evolving about the relative importance of these two elements. The importance of specific surface sites is being established in a growing number of experiments and a number of approaches have been proposed to incorporate these results into model descriptions. Many of these models share a common conceptual basis yet diverge in the way random and deterministic factors are combined. The divergence can be traced to uncertainty about the permanence of nucleating sites, to the lack of detailed knowledge about what surface features constitute nucleating sites, and to the consequent need to rely on empirical or parametric formulas to define the population of sites of different effectiveness. Recent experiments and models, consistent with earlier work, demonstrate the existence and primary role of permanent nucleating sites and the continued need for empirically based formulations of heterogeneous freezing. In order to clarify some aspects of the processes controlling immersion freezing, the paper focuses on three identifiably separate but interrelated issues: (i) the combination of singular and stochastic factors, (ii) the role of specific surface sites, and (iii) the modeling of heterogeneous ice nucleation.

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On the ice nucleation spectrum

Cited by 39 publications

References 62 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)

Different contact angle distributions for heterogeneous ice nucleation in the Community Atmospheric Model version 5

Interpretation of freezing nucleation experiments: singular and stochastic; sites and surfaces

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