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The effect of increased convective entrainment on Asian monsoon biases in the MetUM General Circulation Model

Bush, S. J., Turner, A. G., Woolnough, S. J., Martin, G. M. and Klingaman, N. P. (2015) The effect of increased convective entrainment on Asian monsoon biases in the MetUM General Circulation Model. Quarterly Journal of the Royal Meteorological Society, 141 (686). pp. 311-326. ISSN 1477-870X

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To link to this article DOI: 10.1002/qj.2371

Abstract/Summary

We demonstrate that summer precipitation biases in the South Asian monsoon domain are sensitive to increasing the convective parametrisation’s entrainment and detrainment rates in the Met Office Unified Model. We explore this sensitivity to improve our understanding of the biases and inform efforts to improve convective parametrisation. We perform novel targeted experiments in which we increase the entrainment and detrainment rates in regions of especially large precipitation bias. We use these experiments to determine whether the sensitivity at a given location is a consequence of the local change to convection or is a remote response to the change elsewhere. We find that a local change leads to different mean-state responses in comparable regions. When the entrainment and detrainment rates are increased globally, feedbacks between regions usually strengthen the local responses. We choose two regions of tropical ascent that show different mean-state responses, the western equatorial Indian Ocean and western north Pacific, and analyse them as case studies to determine the mechanisms leading to the different responses. Our results indicate that several aspects of a region’s mean-state, including moisture content, sea surface temperature and circulation, play a role in local feedbacks that determine the response to increased entrainment and detrainment.

Item Type:Article
Refereed:Yes
Divisions:Faculty of Science > School of Mathematical, Physical and Computational Sciences > NCAS
Faculty of Science > School of Mathematical, Physical and Computational Sciences > Department of Meteorology
ID Code:36151
Publisher:Royal Meteorological Society

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