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| Titel |
Dynamical Analysis of Blocking Events: Spatial and Temporal Fluctuations of Covariant Lyapunov Vectors |
| VerfasserIn |
Sebastian Schubert, Valerio Lucarini |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250134793
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| Publikation (Nr.) |
 EGU/EGU2016-15559.pdf |
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| Zusammenfassung |
| One of the most relevant weather regimes in the mid latitudes atmosphere is the
persistent deviation from the approximately zonally symmetric jet stream to the
emergence of so-called blocking patterns. Such configurations are usually connected to
exceptional local stability properties of the flow which come along with an improved
local forecast skills during the phenomenon. It is instead extremely hard to predict
onset and decay of blockings. Covariant Lyapunov Vectors (CLVs) offer a suitable
characterization of the linear stability of a chaotic flow, since they represent the full
tangent linear dynamics by a covariant basis which explores linear perturbations at
all time scales. Therefore, we will test whether CLVs feature a signature of the
blockings. We examine the CLVs for a quasi-geostrophic beta-plane two-layer model
in a periodic channel baroclinically driven by a meridional temperature gradient
ΔT. An orographic forcing enhances the emergence of localized blocked regimes.
We detect the blocking events of the channel flow with a Tibaldi-Molteni scheme
adapted to the periodic channel. When blocking occurs, the global growth rates of the
fastest growing CLVs are significantly higher. Hence against intuition, globally the
circulation is more unstable in blocked phases. Such an increase in the finite time
Lyapunov exponents with respect to the long term average is attributed to stronger
barotropic and baroclinic conversion in the case of high temperature gradients,
while for low values of ΔT, the effect is only due to stronger barotropic instability.
For the localization of the CLVs, we compare the meridionally averaged variance
of the CLVs during blocked and unblocked phases. We find that on average the
variance of the CLVs is clustered around the center of blocking. These results show
that the blocked flow affects all time scales and processes described by the CLVs. |
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