Abstract
Abstract. This paper describes a reduced-order quasi-geostrophic coupled ocean–atmosphere model that allows for an arbitrary number of atmospheric and oceanic modes to be retained in the spectral decomposition. The modularity of this new model allows one to easily modify the model physics. Using this new model, coined the "Modular Arbitrary-Order Ocean-Atmosphere Model" (MAOOAM), we analyse the dependence of the model dynamics on the truncation level of the spectral expansion, and unveil spurious behaviour that may exist at low resolution by a comparison with the higher-resolution configurations. In particular, we assess the robustness of the coupled low-frequency variability when the number of modes is increased. An "optimal" configuration is proposed for which the ocean resolution is sufficiently high, while the total number of modes is small enough to allow for a tractable and extensive analysis of the dynamics.
Highlights
The atmosphere at mid-latitudes displays a variability on a wide range of space scales and timescales, and in particular a low-frequency variability at interannual and decadal timescales as suggested by the analyses of different time series developed in the past years (Trenberth, 1990; Trenberth and Hurrell, 1994; Hurrell, 1995; Mantua et al, 1997; Li and Wang, 2003; Lovejoy and Schertzer, 2013)
This paper describes a reduced-order quasigeostrophic coupled ocean–atmosphere model that allows for an arbitrary number of atmospheric and oceanic modes to be retained in the spectral decomposition
The modularity of this new model allows one to modify the model physics. Using this new model, coined the “Modular Arbitrary-Order Ocean-Atmosphere Model” (MAOOAM), we analyse the dependence of the model dynamics on the truncation level of the spectral expansion, and unveil spurious behaviour that may exist at low resolution by a comparison with the higher-resolution configurations
Summary
The atmosphere at mid-latitudes displays a variability on a wide range of space scales and timescales, and in particular a low-frequency variability at interannual and decadal timescales as suggested by the analyses of different time series developed in the past years (Trenberth, 1990; Trenberth and Hurrell, 1994; Hurrell, 1995; Mantua et al, 1997; Li and Wang, 2003; Lovejoy and Schertzer, 2013). The presence of the seasonal radiative input favours the development of the coupled mode due to the amplification of the impact of the wind stress forcing in summer, associated with a drastic reduction of the mixed layer thickness at that period of the year. While these are encouraging results, which suggest the generic character of the coupled ocean–atmosphere mode, they need to be confirmed through the analysis of more sophisticated models, and in particular in higher-resolution coupled systems.
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