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Aerosols and Greenhouse Gases

The IFS can consider the effects of several greenhouse gases and aerosol species that impact forecasts via their interaction Greenhouse gases and aerosols interact with short-wave and long-wave radiation, which .  The effects can heat or cool the atmosphere and surface and so can impact the surface. Aside from water vapour, the greenhouse forecasts.

Greenhouse gases considered are:

• water vapour.
• carbon dioxide

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• ozone

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• methane

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• nitrous oxide

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• four CFC compounds.

Aerosol The aerosol types considered are:

• sea salt (three different sized particles).
• desert dust (three different sized particles).
• organic matter.
• black carbon.
• ammonium sulphate.

, desert dust, organic matter, black carbon, and ammonium sulphate. In the case of sea salt and dust, three different sized particles are represented. Several of the aerosol species are hydrophyilic, which means that they would hydrophilic.  This means the particles swell as the relative humidity increases . This makes making the aerosol more optically thick and if .  If this process is activated in the model it can act to reduce visibility in humid conditions.

A prerequisite to a reliable For reliable treatment of the interaction with radiation the global distribution of greenhouse gases and aerosols with radiation is that their global distribution is needs to be well represented . There  There are two different configurations of the IFS that are used operationally, and which represent their global distribution in different ways:

• CAMS forecasts. In the model configuration used to produce air Air-quality forecasts for the Copernicus Atmosphere Monitoring Service (CAMS), including the CAMS reanalysis, gases and aerosols are represented by prognosticvariables. This means that they  These are advected around with the model winds, and source and sink processes are also represented. In the case of
  • For greenhouse gases, fluxes taken into account are from:
    • anthropogenic sources
  ,
  • • .
    • vegetation
  , wetlands and ocean are all taken into account, as well as
  • • .
    • wetlands.
    • oceans.
    • chemical reactions between gases.
  In the case of natural aerosol, the dependence of surface emissions on wind speed is represented

• • For aerosols, fluxes taken into account are from:
    • anthropogenic aerosols (e.g. from urban sources and biomass burning using a database of surface sources). 
    • natural aerosols (e.g. dust raised by wind and sea salt from breaking waves
). Anthropogenic aerosol emissions such as those from urban sources and biomass burning make use of a database of surface sources.  In addition to aerosol particles being advected by the mean wind, they are also affected by vertical diffusion and convective lofting, sedimentation, dry deposition, and wet deposition
• • • - depends on forecast wind speed).
  • Aerosol particles are advected by:
    • the mean winds.
    • vertical diffusion.
    • convective lofting.
    • sedimentation.
    • dry deposition.
    • wet deposition (by large-scale and convective precipitation).

• All other forecasts
: Since prognostic variables are computationally expensive, in all other configurations of the IFS (HRES, ENS
•  (medium range, extended-range and seasonal forecasts, and ECMWF
Reanalysis
• reanalysis products).  In all non-CAMS configurations of the IFS, gases and aerosols are represented by a monthly-mean climatology.
In the case of the different

For greenhouse gases

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the climatology varies with month, latitude and height, but not longitude.

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For aerosol species, the climatology varies with month, latitude and longitude, but the vertical structure of the aerosol mass mixing ratio follows a simple exponential decrease with height.

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For both gases and aerosols, the climatology has been derived from the CAMS reanalysis but with a slight tuning to account for known deficiencies in certain locations of the globe.

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Atmospheric chemistry is not yet included in the IFS.  

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Aerosol is not considered in the cloud microphysics (e.g. condensation nuclei) within the operational IFS -

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this may be important for weather is worth stressing

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but the impact is difficult to assess.

Users are advised to keep themselves updated about changes to the radiation scheme through the ECMWF Newsletter and web site.

Note that before the introduction of IFS Cycle 43R3 in July 2017, an older aerosol climatology was used that considered fewer aerosol species and did not include the dependence of optical properties on relative humidity.  

Additional Sources of Information

(Note: In older material there may be references to issues that have subsequently been addressed)

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