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Modelling the diurnal cycle of tropical convection across the ‘grey zone’
Author(s) -
Pearson K. J.,
Lister G. M. S.,
Birch C. E.,
Allan R. P.,
Hogan R. J.,
Woolnough S. J.
Publication year - 2013
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1002/qj.2145
Subject(s) - diurnal cycle , parametrization (atmospheric modeling) , convection , environmental science , climatology , meteorology , atmospheric sciences , atmospheric models , atmospheric convection , geostationary orbit , mixing (physics) , atmospheric model , geology , radiative transfer , atmosphere (unit) , physics , satellite , quantum mechanics , astronomy
We present the results of simulations carried out with the Met Office Unified Model at 12, 4 and 1.5 km resolution for a large region centred on West Africa using several different representations of the convection processes. These span a range of resolutions from much coarser than the size of the convection processes to 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 12 km model without convective parametrization, using Smagorinsky‐style subgrid‐scale mixing in all three dimensions, and a 1.5 km simulation with two‐dimensional Smagorinsky mixing. Of these, the 12 km model produces a better match to the magnitude of the total cloud fraction but the 1.5 km one 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 organization in the 4 km model compared with the standard 12 km configuration is principally a result of the convection scheme employed rather than the improved resolution per se . The details of this result and implications for high‐resolution model simulations are discussed.