Dynamic subgrid heterogeneity of convective cloud in a global model: description and evaluation of the Convective Cloud Field Model (CCFM) in ECHAM6–HAM2
The Convective Cloud Field Model (CCFM) attempts to address some of the shortcomings of both the commonly used bulk mass-flux parameterisations and those using a prescribed spectrum of clouds. By considering the cloud spectrum as a competitive system in which cloud types interact through their envir...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2017-01-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | http://www.atmos-chem-phys.net/17/327/2017/acp-17-327-2017.pdf |
| _version_ | 1818273757020553216 |
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| author | Z. Kipling P. Stier L. Labbouz T. Wagner |
| author_facet | Z. Kipling P. Stier L. Labbouz T. Wagner |
| author_sort | Z. Kipling |
| collection | DOAJ |
| description | The Convective Cloud Field Model (CCFM) attempts to address some of the
shortcomings of both the commonly used bulk mass-flux parameterisations and
those using a prescribed spectrum of clouds. By considering the cloud
spectrum as a competitive system in which cloud types interact through their
environment in competition for convective available potential energy (CAPE),
the spectrum is able to respond dynamically to changes in the environment. An
explicit Lagrangian entraining plume model for each cloud type allows for the
representation of convective-cloud microphysics, paving the way for the study
of aerosol–convection interactions at the global scale where their impact
remains highly uncertain.
<br><br>
In this paper, we introduce a new treatment of convective triggering,
extending the entraining plume model below cloud base to explicitly represent
the unsaturated thermals which initiate convection. This allows for a
realistic vertical velocity to develop at cloud base, so that the cloud
microphysics can begin with physically based activation of cloud condensation
nuclei (CCN). We evaluate this new version of CCFM in the context of the
global model ECHAM6–HAM, comparing its performance to the standard
Tiedtke–Nordeng parameterisation used in that model.
<br><br>
We find that the spatio-temporal distribution of precipitation is improved,
both against a climatology from the Global Precipitation Climatology Project
(GPCP) and also against diurnal cycles from the Tropical Rainfall Measurement
Mission (TRMM) with a reduced tendency for precipitation to peak too early in
the afternoon. Cloud cover is quite sensitive to the vertical level from
which the dry convection is initiated, but when this is chosen appropriately
the cloud cover compares well with that from Tiedtke–Nordeng.
<br><br>
CCFM can thus perform as well as, or better than, the standard scheme while
providing additional capabilities to represent convective-cloud microphysics
and dynamic cloud morphology at the global scale. |
| first_indexed | 2024-12-12T22:03:02Z |
| format | Article |
| id | doaj.art-8a834480f3a64588873a942c12bcecc7 |
| institution | Directory Open Access Journal |
| issn | 1680-7316 1680-7324 |
| language | English |
| last_indexed | 2024-12-12T22:03:02Z |
| publishDate | 2017-01-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Atmospheric Chemistry and Physics |
| spelling | doaj.art-8a834480f3a64588873a942c12bcecc72022-12-22T00:10:27ZengCopernicus PublicationsAtmospheric Chemistry and Physics1680-73161680-73242017-01-0117132734210.5194/acp-17-327-2017Dynamic subgrid heterogeneity of convective cloud in a global model: description and evaluation of the Convective Cloud Field Model (CCFM) in ECHAM6–HAM2Z. Kipling0P. Stier1L. Labbouz2T. Wagner3Department of Physics, University of Oxford, Oxford, UKDepartment of Physics, University of Oxford, Oxford, UKDepartment of Physics, University of Oxford, Oxford, UKDepartment of Physics, University of Oxford, Oxford, UKThe Convective Cloud Field Model (CCFM) attempts to address some of the shortcomings of both the commonly used bulk mass-flux parameterisations and those using a prescribed spectrum of clouds. By considering the cloud spectrum as a competitive system in which cloud types interact through their environment in competition for convective available potential energy (CAPE), the spectrum is able to respond dynamically to changes in the environment. An explicit Lagrangian entraining plume model for each cloud type allows for the representation of convective-cloud microphysics, paving the way for the study of aerosol–convection interactions at the global scale where their impact remains highly uncertain. <br><br> In this paper, we introduce a new treatment of convective triggering, extending the entraining plume model below cloud base to explicitly represent the unsaturated thermals which initiate convection. This allows for a realistic vertical velocity to develop at cloud base, so that the cloud microphysics can begin with physically based activation of cloud condensation nuclei (CCN). We evaluate this new version of CCFM in the context of the global model ECHAM6–HAM, comparing its performance to the standard Tiedtke–Nordeng parameterisation used in that model. <br><br> We find that the spatio-temporal distribution of precipitation is improved, both against a climatology from the Global Precipitation Climatology Project (GPCP) and also against diurnal cycles from the Tropical Rainfall Measurement Mission (TRMM) with a reduced tendency for precipitation to peak too early in the afternoon. Cloud cover is quite sensitive to the vertical level from which the dry convection is initiated, but when this is chosen appropriately the cloud cover compares well with that from Tiedtke–Nordeng. <br><br> CCFM can thus perform as well as, or better than, the standard scheme while providing additional capabilities to represent convective-cloud microphysics and dynamic cloud morphology at the global scale.http://www.atmos-chem-phys.net/17/327/2017/acp-17-327-2017.pdf |
| spellingShingle | Z. Kipling P. Stier L. Labbouz T. Wagner Dynamic subgrid heterogeneity of convective cloud in a global model: description and evaluation of the Convective Cloud Field Model (CCFM) in ECHAM6–HAM2 Atmospheric Chemistry and Physics |
| title | Dynamic subgrid heterogeneity of convective cloud in a global model: description and evaluation of the Convective Cloud Field Model (CCFM) in ECHAM6–HAM2 |
| title_full | Dynamic subgrid heterogeneity of convective cloud in a global model: description and evaluation of the Convective Cloud Field Model (CCFM) in ECHAM6–HAM2 |
| title_fullStr | Dynamic subgrid heterogeneity of convective cloud in a global model: description and evaluation of the Convective Cloud Field Model (CCFM) in ECHAM6–HAM2 |
| title_full_unstemmed | Dynamic subgrid heterogeneity of convective cloud in a global model: description and evaluation of the Convective Cloud Field Model (CCFM) in ECHAM6–HAM2 |
| title_short | Dynamic subgrid heterogeneity of convective cloud in a global model: description and evaluation of the Convective Cloud Field Model (CCFM) in ECHAM6–HAM2 |
| title_sort | dynamic subgrid heterogeneity of convective cloud in a global model description and evaluation of the convective cloud field model ccfm in echam6 ham2 |
| url | http://www.atmos-chem-phys.net/17/327/2017/acp-17-327-2017.pdf |
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