A basic reference state suitable for anomaly-coupled ocean-atmosphere climate models

Abstract

A large class of ocean-atmosphere models exists in which the ocean state is coupled to the model of the atmosphere only through the anomalies of the ocean state. The sea surface temperatures are defined with respect to a mean reference state, i.e., they are the difference between the ocean state and a reference state. Due to coupled model drift, the choice of reference state is important and it can have a large impact on the variability in the model. The reference state can be calculated as an average throughout the coupled simulation and various methods of doing this (moving average, exponentially weighted moving average and accumulated mean) are compared in this note. The accumulated mean method appears to be the sole method of the three which gives both unbiased anomalies and a convergent reference state. It is recommended for use in anomaly-coupled models for improving variability and predictability.