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| Titel |
Inter-Scale Statistical Analysis of Fine-Resolution Rainfall Datasets over the Japanese Islands |
| VerfasserIn |
Martín Gómez García Alvéstegui, Toshio Koike |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250108626
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| Publikation (Nr.) |
 EGU/EGU2015-8389.pdf |
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| Zusammenfassung |
| The continuous improvement of remotely-sensed precipitation estimates has greatly favored
the inter-scale statistical study of rainfall fields and its potential applications. One of the
expected results of this type of analysis is intended to provide the guidelines to effectively
reproduce at finer scales (downscaling) the characteristic geometrical structure. Intermittency
(no-rain areas contained within large rainfall fields), slow-varying gradients of intensity,
and sudden sharp rises of intensity (high-intensity regions enclosed, or rapidly
followed, by lower-intensity fields) are within the structural properties that define
the rainfall fields. The concept of intermittency, indicates a positive probability of
having no rain at some point, and for that reason the actual magnitude of rainfall
intensity is not compatible with some scaling operations. However, the deviations of
local means (local fluctuations) proved to be a process with noteworthy inter-scale
statistical properties. Previous research revealed that local fluctuations can be well
adjusted to stable distributions, in which the characteristic exponent α defines the
thickness of the tails. If so, it can be inferred that this parameter should be related to
the type of rainfall (rate of variation of intensity). However, the abovementioned
research showed that in order to portray a self-similar relationship between scales the
fluctuations needed to be divided by their correspondent local mean (standardization). The
distribution of these standardized values was observed to be almost Gaussian (α = 2),
and even though remarkable, with this operation becomes more challenging to
relate the frequency of extreme values with the type of rainfall. In our study the
local fluctuations of rainfall were analyzed by fitting the data to a folded stable
distribution which is a distribution of absolute values. This approach not only allowed to
reveal a somewhat invariance of the characteristic exponent between scales, but also
depicted a clear inter-scale exponential tendency of the scale parameter γ of the
distributions.
In this study we utilized the highly-accurate fine-resolution (1 km) Radar-AMeDAS
datasets available over the Japanese islands and surrounding ocean waters. With the purpose
of having a broad idea of the parameter range of the characteristic exponent and its
relationship with the type of rainfall, different locations were selected to perform this
inter-scale analysis for several events between 2006 and 2009. Japan’s geographical location
in the northwest Pacific Ocean and the long latitudinal extent (from 26.0oN to 45.5oN
approximately) permits to observe the outcome of different patterns of rainfall, which include
stratiform structures caused by warm fronts, narrow bands of high-intensity rainfalls caused
by cold fronts, isolated convection activity, and severe storms caused by the activity of
tropical cyclones. The results reported in this study are intended to serve as a basis for further
research that, among other topics, may be able to relate the parameters of the folded
distribution to other measurable environmental parameters that describe the rainfall patterns. |
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