Modelling the diurnal cycle of tropical convection across the "Grey Zone"

Pearson, K. J., Lister, G. M. S., Birch, C. E., Allan, R. P. ORCID: https://orcid.org/0000-0003-0264-9447, Hogan, R. J. ORCID: https://orcid.org/0000-0002-3180-5157 and Woolnough, S. J. ORCID: https://orcid.org/0000-0003-0500-8514 (2014) Modelling the diurnal cycle of tropical convection across the "Grey Zone". Quarterly Journal of the Royal Meteorological Society, 140 (679). pp. 491-499. ISSN 1477-870X doi: 10.1002/qj.2145

Abstract/Summary

We present the results of simulations carried out with the Met Office Unified Model at 12km, 4km and 1.5km resolution for a large region centred on West Africa using several different representations of the convection processes. These span the range of resolutions from much coarser than the size of the convection processes to the cloud-system resolving and thus encompass the intermediate "grey-zone". The diurnal cycle in the extent of convective regions in the models is tested against observations from the Geostationary Earth Radiation Budget instrument on Meteosat-8. By this measure, the two best-performing simulations are a 12km model without convective parametrization, using Smagorinsky style sub-grid scale mixing in all three dimensions and a 1.5km simulations with two-dimensional Smagorinsky mixing. Of these, the 12km model produces a better match to the magnitude of the total cloud fraction but the 1.5km results in better timing for its peak value. The results suggest that the previously-reported improvement in the representation of the diurnal cycle of convective organisation in the 4km model compared to the standard 12km configuration is principally a result of the convection scheme employed rather than the improved resolution per se. The details of and implications for high-resolution model simulations are discussed.

Item Type	Article
URI	https://reading-clone.eprints-hosting.org/id/eprint/31339
Item Type	Article
Refereed	Yes
Divisions	Science > School of Mathematical, Physical and Computational Sciences > Environmental Systems Science Centre Science > School of Mathematical, Physical and Computational Sciences > NCAS Science > School of Mathematical, Physical and Computational Sciences > Department of Meteorology Science > School of Mathematical, Physical and Computational Sciences > National Centre for Earth Observation (NCEO)
Uncontrolled Keywords	Africa;cascade;CRM;CSRM;GERB;OLR;parametrization;UM
Publisher	Royal Meteorological Society
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