Stein, THM, Parker, DJ, Hogan, RJ et al. (5 more authors) (2015) The representation of the West-African Monsoon vertical cloud structure in the Met Office Unified Model: An evaluation with CloudSat. The Quarterly Journal of the Royal Meteorological Society, 141 (693). pp. 3312-3324. ISSN 0035-9009
Abstract
Weather and climate model simulations of the West African Monsoon (WAM) have generally poor representation of the rainfall distribution and monsoon circulation because key processes, such as clouds and convection, are poorly characterized. The vertical distribution of cloud and precipitation during the WAM are evaluated in Met Office Unified Model simulations against CloudSat observations. Simulations were run at 40 and 12 km horizontal grid length using a convection parametrization scheme and at 12, 4, and 1.5 km grid length with the convection scheme effectively switched off, to study the impact of model resolution and convection parametrization scheme on the organisation of tropical convection. Radar reflectivity is forward-modelled from the model cloud fields using the CloudSat simulator to present a like-with-like comparison with the CloudSat radar observations. The representation of cloud and precipitation at 12 km horizontal grid length improves dramatically when the convection parametrization is switched off, primarily because of a reduction in daytime (moist) convection. Further improvement is obtained when reducing model grid length to 4 or 1.5 km, especially in the representation of thin anvil and mid-level cloud, but three issues remain in all model configurations. Firstly, all simulations underestimate the fraction of anvils with cloud-top height above 12 km, which can be attributed to too low ice water contents in the model compared to satellite retrievals. Secondly, the model consistently detrains mid-level cloud too close to the freezing level, compared to higher altitudes in CloudSat observations. Finally, there is too much low-level cloud cover in all simulations and this bias was not improved when adjusting the rainfall parameters in the microphysics scheme. To improve model simulations of the WAM, more detailed and insitu observations of the dynamics and microphysics targeting these non-precipitating cloud types are required.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | © 2015 The Authors. Quarterly Journal of the Royal Meteorological Society published by John Wiley & Sons Ltd on behalf of the Royal Meteorological Society. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. |
Keywords: | CloudSat; West African monsoons; Cascade; clouds; convection; model evaluation |
Dates: |
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Institution: | The University of Leeds |
Academic Units: | The University of Leeds > Faculty of Environment (Leeds) > School of Earth and Environment (Leeds) > Inst for Climate & Atmos Science (ICAS) (Leeds) |
Depositing User: | Symplectic Publications |
Date Deposited: | 08 Jul 2015 10:15 |
Last Modified: | 10 Mar 2016 16:01 |
Published Version: | http://dx.doi.org/10.1002/qj.2614 |
Status: | Published |
Publisher: | Wiley |
Identification Number: | 10.1002/qj.2614 |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:87851 |