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| Titel |
On scaling in spatial precipitation from radar |
| VerfasserIn |
Athanasios Paschalis, Peter Molnar, Paolo Burlando |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250083323
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| Zusammenfassung |
| The topic of self-similarity in precipitation in time and space has been prominent in
precipitation research for at least the last 3 decades. Data analysts have explored evidence for
self-similarity and reported departures from it. Modellers have developed stochastic models
that are based on self-similarity concepts or at least reproduce the observed scaling behaviour.
Physicists and meteorologists have argued why scale invariance should, or should not, exist in
precipitation. Although there appears to be consensus between these communities that
precipitation may exhibit scale invariance in some range of scales, most of us would probably
also agree that the scaling properties are connected to the precipitation generation
mechanisms (e.g. convection, orographic enhancement, etc.) and are not generally
valid. The demonstration of this variability in scaling properties of precipitation and
their relation to possible precipitation generating mechanisms is the focus of this
paper.
We analyse the spatial structure of radar precipitation for the orographically
complex environment of the Swiss Alps as a multi-scaling process. A reliable 7 year
long, high quality precipitation radar dataset, derived from the operational weather
radars of MeteoSwiss is used to conduct a comprehensive data analysis and to reveal
potential connections of the scaling processes of the precipitation structure and its
respective generating mechanisms. We use different analysis techniques to quantify
scale-dependent properties, from spectral analysis to multiplicative random cascades,
employing estimation techniques spanning from traditional moment scaling to wavelet
based estimators. We compare the results seasonally for radars in two different
locations, one north and one south of the main Alpine divide, with very different
topography.
The main result is that distinct seasonal and spatial patterns in precipitation
scaling properties exist which highlight the effect of topography on precipitation
formation. Our key findings are: (1) Topography and dominant wind flow patterns
can affect the isotropic/anisotropic structure of the precipitation fields. (2) Distinct
seasonal patterns for the scaling parameters of spatial precipitation exist, and some
analysis techniques are better than others to quantify those. (3) Scaling parameters are
related to precipitation large scale forcing, e.g. mean precipitation intensity, and
this relationship is seasonally dependent. (4) Our data suggest that precipitation
scaling in a topographically complex environment cannot be easily associated with
the thermodynamic descriptors of the state of the atmosphere, in contradiction to
what has been found in previous studies. (5) Topography and in particular different
enhancing/shadowing mechanisms at the two radar sites strongly influence the scaling
properties and spatial distribution of the precipitation fields. All of these findings
demonstrate that scaling properties in spatial rainfall should in fact be expected to
be variable, and the source of this variability is likely to be found in precipitation
generating mechanisms and the stochasticity in precipitation formation in general. |
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