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Geoscientific Model Development An interactive open-access journal of the European Geosciences Union
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Volume 11, issue 11
Geosci. Model Dev., 11, 4693-4709, 2018
https://doi.org/10.5194/gmd-11-4693-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Geosci. Model Dev., 11, 4693-4709, 2018
https://doi.org/10.5194/gmd-11-4693-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Model evaluation paper 27 Nov 2018

Model evaluation paper | 27 Nov 2018

The Indian summer monsoon in MetUM-GOML2.0: effects of air–sea coupling and resolution

Simon C. Peatman and Nicholas P. Klingaman Simon C. Peatman and Nicholas P. Klingaman
  • National Centre for Atmospheric Science–Climate and Department of Meteorology, University of Reading, Reading, UK

Abstract. The fidelity of the simulated Indian summer monsoon is analysed in the UK Met Office Unified Model Global Ocean Mixed Layer configuration (MetUM-GOML2.0) in terms of its boreal summer mean state and propagation of the boreal summer intraseasonal oscillation (BSISO). The model produces substantial biases in mean June–September precipitation, especially over India, in common with other MetUM configurations. Using a correction technique to constrain the mean seasonal cycle of ocean temperature and salinity, the effects of regional air–sea coupling and atmospheric horizontal resolution are investigated. Introducing coupling in the Indian Ocean degrades the atmospheric basic state compared with prescribing the observed seasonal cycle of sea surface temperature (SST). This degradation of the mean state is attributable to small errors (±0.5°C) in mean SST. Coupling slightly improves some aspects of the simulation of northward BSISO propagation over the Indian Ocean, Bay of Bengal, and India, but degrades others. Increasing resolution from 200 to 90km grid spacing (approximate value at the Equator) improves the atmospheric mean state, but increasing resolution again to 40km offers no substantial improvement. The improvement to intraseasonal propagation at finer resolution is similar to that due to coupling.

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We investigate the simulation of the Indian monsoon in the UK Met Office climate model. We simulate both the atmosphere and the ocean (which can interact with each other) and compare against simulating the atmosphere alone. Atmosphere–ocean interactions make the modelled average monsoon climate less realistic because the sea surface temperature is wrong in the model, but the interactions make individual rain events, in which storms propagate northwards over the Indian Ocean, more realistic.
We investigate the simulation of the Indian monsoon in the UK Met Office climate model. We...
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