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Geosci. Model Dev., 11, 2153-2173, 2018
https://doi.org/10.5194/gmd-11-2153-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Methods for assessment of models
12 Jun 2018
Automated model optimisation using the Cylc workflow engine (Cyclops v1.0)
Richard M. Gorman1 and Hilary J. Oliver2 1National Institute of Water and Atmospheric Research, P.O. Box 11-115, Hamilton, New Zealand
2National Institute of Water and Atmospheric Research, Private Bag 14901, Wellington, New Zealand
Abstract. Most geophysical models include many parameters that are not fully determined by theory, and can be tuned to improve the model's agreement with available data. We might attempt to automate this tuning process in an objective way by employing an optimisation algorithm to find the set of parameters that minimises a cost function derived from comparing model outputs with measurements. A number of algorithms are available for solving optimisation problems, in various programming languages, but interfacing such software to a complex geophysical model simulation presents certain challenges.

To tackle this problem, we have developed an optimisation suite (Cyclops) based on the Cylc workflow engine that implements a wide selection of optimisation algorithms from the NLopt Python toolbox (Johnson, 2014). The Cyclops optimisation suite can be used to calibrate any modelling system that has itself been implemented as a (separate) Cylc model suite, provided it includes computation and output of the desired scalar cost function. A growing number of institutions are using Cylc to orchestrate complex distributed suites of interdependent cycling tasks within their operational forecast systems, and in such cases application of the optimisation suite is particularly straightforward.

As a test case, we applied the Cyclops to calibrate a global implementation of the WAVEWATCH III (v4.18) third-generation spectral wave model, forced by ERA-Interim input fields. This was calibrated over a 1-year period (1997), before applying the calibrated model to a full (1979–2016) wave hindcast. The chosen error metric was the spatial average of the root mean square error of hindcast significant wave height compared with collocated altimeter records. We describe the results of a calibration in which up to 19 parameters were optimised.

Citation: Gorman, R. M. and Oliver, H. J.: Automated model optimisation using the Cylc workflow engine (Cyclops v1.0), Geosci. Model Dev., 11, 2153-2173, https://doi.org/10.5194/gmd-11-2153-2018, 2018.
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Short summary
We describe an optimisation suite ("Cyclops") that can be used to apply a selection of nonlinear optimisation algorithms to "tune" the parameters of a geophysical model. Based on the Cylc workflow engine, Cyclops can be used to calibrate any modelling system that has itself been implemented as a (separate) Cylc model suite, provided it includes computation and output of the desired scalar cost function.
We describe an optimisation suite ("Cyclops") that can be used to apply a selection of nonlinear...
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