Scaling behavior in daily air humidity fluctuations

We show that the daily average air humidity fluctuations exhibit nontrivial 1/${\mathit{f}}^{\mathrm{\alpha }}$ behavior which is different from the spectral properties of other meteorological quantities. This feature and the fractal spatial structure found in clouds make is plausible to regard air humidity fluctuations as a manifestation of self-organized criticality. We give arguments why the dynamics in air humidity can be similar to those in sandpile models of self-organized criticality.