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| Titel |
The role of marine organic ice nuclei in a global climate model |
| VerfasserIn |
Matthias Hummel, Jón Egill Kristjánsson |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250131910
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| Publikation (Nr.) |
 EGU/EGU2016-12363.pdf |
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| Zusammenfassung |
| Ice particle concentrations are a key parameter for cold clouds, exerting a strong
influence on cloud lifetime, precipitation release, and the cloud radiative effect. The
availability of ice-nucleating particles (INPs) and the temperature range in which they
become activated determine the rate of ice formation in clouds (Hoose und Möhler,
2012). Particles from marine sources may contribute to ice formation in clouds,
as they are abundant in the atmosphere and some of them have been found to be
ice-nucleating active, but the extent of their influence on clouds is not known (Wilson et al.,
2015).
Wilson et al. (2015) collected marine INPs from the sea surface microlayer and analyzed
their ice nucleation efficiency with a cold stage. Even in cirrus clouds, marine INPs may
play a role, as their ice nucleation surface site density as a function of RHice at
-40˚ C has been shown to be larger than for mineral dusts (ATD, kaolinite, and
feldspar).
In this study, we test the influence of marine organic aerosols on clouds via immersion
freezing with the earth system model NorESM2 (Version 2 of the Norwegian Earth System
Model; Bentsen et al., 2013). The model is based on the Community Earth System Model
(CESM1.2) and its atmospheric part (CAM5 Oslo) is based on the Community Atmosphere
Model (CAM5.3). The parameterization of ice nucleation of marine INPs is expressed as an
exponential function of temperature multiplied by the total organic content. Marine
organic aerosols are part of the sea spray aerosol and are ejected during bubble
bursting. INPs are associated with exudates or other macromolecules mainly from
diatoms. Hence, their concentration is related to the sea salt aerosols in the model
simulation.
Our first results indicate that the high marine INP concentrations at around 850 hPa occur
at high latitudes. These regions have low mineral dust concentrations, which might increase
the influence of marine INP on clouds. However, they do not coincide with regions of high
winds and therefore large sea spray aerosol concentrations, contrary to model simulations in
Wilson et al. (2015) with the global aerosol process model (GLOMAP), but are
shifted further polewards. Therefore, marine INP concentrations strongly depend on
temperature and do not necessarily coincide with large sea spray concentrations. At
mid-latitudes, marine INP concentrations rank below dust INP by at least one order of
magnitude.
Further, this presentation will describe the influence of marine INP on cloud properties
and give an estimate of the cloud radiative effect of marine INP.
Bentsen, M., I. Bethke, et al. (2013): The Norwegian Earth System Model, NorESM1-M
– Part 1: Description and basic evaluation of the physical climate, Geosci. Model Dev. 6(3):
687-720.
Hoose, C. und O. Möhler (2012): Heterogeneous ice nucleation on atmospheric
aerosols: a review of results from laboratory experiments, Atmos. Chem. Phys. 12(20):
9817-9854.
Wilson, T. W., L. A. Ladino, et al. (2015): A marine biogenic source of atmospheric
ice-nucleating particles, Nature 525(7568): 234-238. |
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