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| Titel |
Time scaling properties of rainfall from 1.5 year to 15 s and applications to the study of the extreme values |
| VerfasserIn |
Sebastien Verrier, Laurent Barthes, Cécile Mallet, Louis de Montera |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250036237
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| Zusammenfassung |
| Rain, as many geophysical processes, exhibits a scale invariant behavior over a wide range of
space/time scales. In this presentation, the scaling and fractal properties of rainfall
are investigated in the time domain, using high-resolution observations. Rainfall
intensities were obtained from measurements performed in Palaiseau (France) by a
disdrometer- the Dual-Beam Spectropluviometer (DBS). The dataset consists in time series
covering a period of 1,5 year long (July 2008- December 2009) that yields a wide
range of scales due to the high resolution of the series (15 s). The power spectrum
E(Ï) displays distinct regimes of different behaviors: a spectral plateau is found at
time scales greater than 2 weeks and is followed by a transition regime at scales
comprised between 2 weeks and 3 days. Then, two scaling regimes obeying power-laws
E(Ï) - Ï-β are found at the smaller scales, separated by a break at the 0.5-1 h scale. The
spectral exponents are estimated respectively at β=0.97 from 3 days to 0.5-1 h and
β=1.51 from 0.5-1 h to 1 min. Consistently, multifractal analysis techniques show
the existence of two multiscaling regimes, respectively extending from about 3
days to 1 h and from 1 h to 0.5 min. Both scaling regimes may be described by
using the three-parameter (fractionally integrated) Universal Multifractal (UM)
model and differ from each other by the values of the three fundamental exponents
α,C1,H. Whereas the breaks at 2 weeks and 3 days scales may be explained by
meteorological considerations, it is suggested that the break at 0.5-1 h scale is an
artefact due to the presence of numerous zeroes in the series. In order to improve
the estimation of the three parameters, multifractal analysis is also performed on
uninterrupted rain events extracted from the DBS full series. This approach provides a
’corrected’ set of parameters that applies in the interior of rain events. These ’corrected’
fundamental exponents are estimated to be close to α=1.7, C1=0.1, H=0.3-0.5, differing
noticeably from the parameters usually reported in the literature (e.g. Lilley et al., 2006.
J. Hydrol. 328, 20-37): the effect of the zero rain rates on multifractal analysis
is likely to underestimate α and H and to overestimate C1. However, the results
of this new approach confirm recently published work (de Montera et al., 2009.
J. Hydrometeor., AMS, 10, 493-506) devoted to analysis of rain data previously
collected at different locations with the same instrument. In particular, the comparison
of both studies suggests that the parameter H could be the most sensitive to the
local climate. However, H is found strictly greater than zero at small scales in both
studies, meaning that the absolute increments of the series- rather than the series
itself- should be considered in analysis. Then, the extreme values of the normalized
absolute increments of the selected rain events are shown to follow a power-law
of the scale ratio, as predicted by the multifractal model. The estimated scaling
exponent remains almost constant regardless of the duration of the event and is
coherent with the ’corrected’ parameters. Finally, the CDFs of the whole series (and
of their increments) are considered. The issue of the behavior of the tails of the
distributions is discussed, taking into account the predictions of the UM model. |
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