The spectra of a general class of stochastic climate models
Seminar Room 1, Newton Institute
The simplest class of stochastic models relevant to geophysical applications consist of a linearization of the dynamical system and the addition of constant multivariate stochastic forcing. Such stochastic systems are known as finite dimensional Ornstein Uhlenbeck systems and have wide application. In this talk we describe a general decomposition of the equilibrium spectrum of such processes. This is of interest in applications since spectra of long time series are commonly robustly defined from observations.
We apply this formalism to the case of ENSO where it is often argued that there is a dominant normal mode. Here we argue that the decadal part of the ENSO spectrum can be simply explained by the stimulation of the cross spectrum of the dominant normal mode. The cross spectrum is dependent on the ENSO cycle phase meaning that this mechanism implies that the different ENSO phases have different spectral strengths at decadal frequencies.