Estimating Atmospheric Response Using Fluctuation-Response Based Methods

Grant Branstator

For many problems of interest the atmospheric response to an external force is approximately a linear function of the source. One reason this is true is that, at equilibrium, mean values of some of the most important nonlinear terms in the governing equations, namely those associated with synoptic scale eddy fluxes, are nearly linear functions of the mean state. But these terms are not captured by a simple linearization of the equations. On the other hand, the fluctuation-dissipation theorem provides a means of finding linearized response equations that do include these effects. In this presentation we present an alternative derivation of the FDT to that offered by Leith (1975). This derivation makes it clear that this theorem is likely to be applicable to the atmosphere. We then test the theorem

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