Valerio Lucarini, Salvatore Pascale
We want to extend the analysis of the thermodynamics of the climate system to the investigation of the role of its various scales of variability, which is achieved by performing coarse graining of the climate fields. We show that the coarser is the graining, the lower is the estimate of the material entropy production. In other terms, all the spatial and temporal scales of variability of the thermodynamic fields provide a positive contribution to the material entropy production. This may be interpreted also as that, at all scales, the temperature fields and the material heating fields have a negative correlation, while the opposite holds between the temperature fields and the radiative heating fields. The latter correlations are stronger, which confirms that radiation acts as primary drive for the fluctuations in the thermodynamic properties of the climatic fields, while the material fluxes dampen such fluctuations through dissipative processes. Using specific coarse-graining procedures, one can separate the contributions to the material entropy production coming from the dissipation of kinetic energy, the vertical heat fluxes, and the large scale horizontal fluxes, without resorting to the high-resolution fields. Most of the entropy production is associated to irreversible exchanges occurring along the vertical direction, and neglecting the horizontal and time variability has a small impact on the estimate of the material entropy production. These findings deserve to be explored in a more general context, because they provide a way for understanding forced fluctuations and dissipative processes in fluids at various spatial and temporal scales. The approach presented here seems promising specifically for studying the atmosphere of exoplanets, because it allows for evaluating the error in the estimate of their thermodynamical properties due to the lack of high-resolution data.
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http://arxiv.org/abs/1304.3945
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