The behaviour of the sea surface temperature (SST) as a response to stochastic latent- and sensible heat forcing

Following Hasselmann's work on climate variability we consider a stationary stochastic process with two different time scales for the forcing (the weather variables) and the response (the climate variable). We extend the work of Hasselmann, and Frankignoul and Hasselmann by allowing for a more general equation for the sea surface temperature (SST) containing, besides a stochastic forcing term, a term with a stochastic coefficient (feedback), in order to describe wet bulb temperature and wind velocity as two stochastic variables. From this equation, expressions for the average, the variance and the spectrum of the climate variable are derived by means of a cumulant expansion. So the SST is thought to be the result of a stochastic forcing by latent and sensible heat fluxes. The expressions are applied to data. For this application the daily observations of the lightvessel Texel (53˚00?N, 4˚23'E) measured during the winters of 1965–1974 are used. It turns out that the SST variance near the lightvessel Texel is described better by our extended stochastic equation than by the equation of Frankignoul and Hasselmann, while the shape of the spectrum is almost the same. It is the wet-bulb temperature rather than the wind velocity that largely determines the variation of the SST near the Dutch coast in winter.