AbstractWhen subjecting ocean models to atmospheric forcing, the models exhibits two types of variability – a response to the external forcing (hereafter referred to as signal) and inherently generated (internal; intrinsic; unprovoked; chaotic) variations (hereafter referred to as noise). Based on an ensemble of simulations with identical atmospherically forced oceanic models which differ only in the initial conditions at different times, the signal-to-noise ratio of the atmospherically forced oceanic model is determined. In the large-scales, the variability of the model output is mainly induced by the external forcing and the proportion of the internal variability is small, so the signal-to-noise ratio is large. For smaller scales, the influence of the external forcing weakens and the influence of the internal variability strengthens, so the signal-to-noise ratio becomes less and less. Thus, the external forcing is dominant for large scales, while most of the variability is internally generated for small scales.