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Volume 11, issue 8 | Copyright
Geosci. Model Dev., 11, 3215-3233, 2018
https://doi.org/10.5194/gmd-11-3215-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Model evaluation paper 10 Aug 2018

Model evaluation paper | 10 Aug 2018

Intraseasonal summer rainfall variability over China in the MetUM GA6 and GC2 configurations

Claudia Christine Stephan1,a, Nicholas P. Klingaman1, Pier Luigi Vidale1, Andrew G. Turner1,2, Marie-Estelle Demory1,3, and Liang Guo1 Claudia Christine Stephan et al.
  • 1National Centre for Atmospheric Science – Climate, Department of Meteorology, University of Reading, P.O. Box 243, Reading RG6 6BB, UK
  • 2Department of Meteorology, University of Reading, P.O. Box 243, Reading RG6 6BB, UK
  • 3Center for Space and Habitability, University of Bern, Gesellschaftsstrasse 6, 3012 Bern, Switzerland
  • aMax Planck Institute for Meteorology, Bundesstrasse 53, 20146 Hamburg, Germany

Abstract. The simulation of intraseasonal precipitation variability over China in extended summer (May–October) is evaluated based on six climate simulations of the Met Office Unified Model. Two simulations use the Global Atmosphere 6.0 (GA6) and four the Global Coupled 2.0 (GC2) configuration. Model biases are large such that mean precipitation and intraseasonal variability reach twice their observed values, particularly in southern China. To test the impact of air–sea coupling and horizontal resolution, GA6 and GC2 at horizontal resolutions corresponding to  ∼ 25, 60, and 135km at 50°N are analyzed. Increasing the horizontal resolution and adding air–sea coupling have little effect on these biases. Pre-monsoon rainfall in the Yangtze River basin is too strong in all simulations. Simulated rainfall amounts in June are too high along the southern coast and persist in the coastal region through July, with only a weak northward progression. The observed northward propagation of the Meiyu–Baiu–Changma rainband from spring to late summer is poor in all GA6 and GC2 simulations. To assess how well the MetUM simulates spatial patterns of temporally coherent precipitation, empirical orthogonal teleconnection (EOT) analysis is applied to pentad-mean precipitation. Patterns are connected to large-scale processes by regressing atmospheric fields onto the EOT pentad time series. Most observed patterns of intraseasonal rainfall variability are found in all simulations, including the associated observed mechanisms. This suggests that GA6 and GC2 may provide useful predictions of summer intraseasonal variability despite their substantial biases in mean precipitation and overall intraseasonal variance.

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Summer precipitation over China in the MetUM reaches twice its observed values. Increasing the horizontal resolution of the model and adding air–sea coupling have little effect on these biases. Nevertheless, MetUM correctly simulates spatial patterns of temporally coherent precipitation and the associated large-scale processes. This suggests that the model may provide useful predictions of summer intraseasonal variability despite the substantial biases in overall intraseasonal variance.
Summer precipitation over China in the MetUM reaches twice its observed values. Increasing the...
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