
Estimating Atmospheric Response Using FluctuationResponse Based Methods
Grant Branstator
NCAR
Abstract
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
fluctuationdissipation 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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