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| Titel |
Different contact angle distributions for heterogeneous ice nucleation in the Community Atmospheric Model version 5 |
| VerfasserIn |
Y. Wang, X. Liu, C. Hoose, B. Wang |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 14, no. 19 ; Nr. 14, no. 19 (2014-10-01), S.10411-10430 |
| Datensatznummer |
250119075
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| Publikation (Nr.) |
 copernicus.org/acp-14-10411-2014.pdf |
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| Zusammenfassung |
| 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 single-contact-angle
model with the probability-density-function-of-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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