Multiplicative Noise and Non-Gaussianity: A Paradigm for Atmospheric Regimes?

Philip Sura

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The extent to which multiple atmospheric regimes may be due to the nature of unpredictable weather noise, rather than to nonlinearities internal to the atmosphere is explored.

First, the response of the linearized barotropic vorticity equation to stochastic perturbations of the frictional damping and the zonal mean flow is studied. The stochastic parameterizations lead to multiplicative stochastic forcing. It is found that the qualitative behavior of the system is a function of the multiplicative noise level if the frictional damping is perturbed. In particular, the effect of multiplicative noise in the damping is not simply a smoothing of the probability density function (PDF). Rather, multiplicative noise leads to a highly non-Gaussian distribution due to an intermittent behavior of the Rossby waves. This effect is not observed if the zonal mean flow is perturbed stochastically. This simple, yet realistic stochastic model can serve as a null hypothesis for the non-Gaussian behavior of atmospheric PDFs. Second, it is shown from an analysis of 750 hPa streamfunction data that the non-Gaussian regime behavior in the leading Empirical Orthogonal Functions (EOFs) is not induced by nonlinearities in the deterministic part of the motion, but is rather due to multiplicative noise. Thus, non-Gaussianity does not always imply that a system has nonlinear multiple regimes.

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19 Nov, 2003
2 PM/ DSRC 1D 403
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