Revisiting rainfall clustering and intermittency across different climatic regimes
One of the vexing questions in rainfall research is the role of intermittency and its nonuniversal signature in anomalous scaling functions. Whether this lack of universal behavior is due to the bursting patterns in rainfall intensity or the alternation between long dry periods and highly clustered wet phases (or both) remains an open issue. To progress on a narrower scope of this problem, the effects of intermittency originating from rainfall occurrence are first separated from rainfall intermittency induced by intensity variability. Across five climatic regimes considered here, it was shown that the rainfall occurrence process (OP) exhibits (1) a near-constant spectral slope, (2) a near-constant clustering exponent, and (3) a probability density function of dry phases displaying a power law behavior with an exponent β≈1.5, consistent with other studies for timescales commensurate with frontal and storm systems. Also for the OP, the scaling exponents of the normalized higher order structure functions reveal an extensive monofractal scaling at all five climatic regimes. When taken together, these intersite results are suggestive that rainfall intensity modulations are the main cause of the nonuniversal anomalous scaling and not the clustering properties associated with the support. The nature of these modulations is markedly different when comparing rainfall to a familiar and often interrelated process such as scalar turbulence. In the case of turbulence, amplitude variability of scalar dissipation rates appear to mitigate the intermittency effects connected with anomalous scaling, while for rainfall series, intensity fluctuations seem to amplify them. Copyright 2009 by the American Geophysical Union.
Molini, A; Katul, GG; Porporato, A
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