Chapter 3
Climate Spectra and
Stochastic Climate Models
by Claude Frankignoul
3.1 Introduction
As the power spectra of extratropical atmospheric variables are essentially
white on time scales between about 10 days and a few years, many climatic
fluctuations can be understood as the response of the slow climate variables
to stochastic forcing by the fast atmospheric fluxes (Hasselmann, 1976). The
stochastic climate model explains the statistical properties of mid-latitude
sea surface temperature anomalies on time scales of up to a few years, and
has been applied to long term climate changes, quasi-geostrophic ocean fluctuations, sea ice variability, soil moisture fluctuations, and ocean circulation
variability, providing a simple but powerful framework to investigate climate
variability. After briefly describing the spectral characteristics of the atmospheric variables, the concept of the stochastic climate model is introduced
in this chapter. Its application to climate variations is then illustrated in
the context of the midlatitude sea surface temperature anomalies. The other
applications are then briefly discussed.