Nonlinear statistics of daily temperature fluctuations reproduced in a laboratory experiment.

The near-global statistics of daily mean temperature changes reveals a robust asymmetry. Warming steps have significantly higher frequency and lower average magnitude than those of cooling steps for most weather stations. This is a markedly nonlinear feature: Fourier surrogate time series exhibit completely symmetric increment statistics. The obtained geographic distribution of asymmetry parameters suggested an experimental test in a classical rotating tank setup. Temperature measurements in the dynamical regime of geostrophic turbulence reproduce quantitatively the strong asymmetry and spatial dependence of field observations. The statistics might be relevant in other systems of nonequilibrium steady states.