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| Titel |
Discriminating different El Niño and La Niña phases from evolving climate networks |
| VerfasserIn |
Marc Wiedermann, Alexander Radebach, Jonathan F. Donges, Jürgen Kurths, Reik V. Donner |
| 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 |
250127560
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| Publikation (Nr.) |
 EGU/EGU2016-7452.pdf |
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| Zusammenfassung |
| The variability of the El Niño Southern Oscillation (ENSO) can roughly be categorized into
El Niño (anomalously warm), La Niña (anomalously cold) and normal periods.
Additionally, at least the El Niño exhibits into two different types (Eastern Pacific
(EP) and central Pacific (CP)), which may be distinguished from each other by
different signatures in the Pacific sea surface temperature field. However, up to
now no generally applicable criterion to distinguish these different phases has been
introduced.
We present here a method based on complex network analysis to distinguish these EP and
CP events by utilizing a simple scalar-valued measure (the so-called climate network
transitivity) related to the third power of the cross-correlation matrix between grid points in a
daily global surface air temperature field. From a one-year running window analysis we
obtain the time-evolution of this measure and show that during EP events it displays a
strong peak, whereas its value during CP events is close to the baseline formed by
normal periods. This behavior is easily understood from the different impacts on
the global climate system displayed by the two different El Niño flavors as well
as the high synchronization of Pacific sea-surface temperatures during El Niño
events.
We compare our results with recent works on El Niño classifications and find that
for the years 1970-2000 (the main time interval covered by most past studies) our
method distinguishes correctly all existing events. By performing a network-based
dimensionality reduction of the correlation matrix, we show that our findings also display
high consistency with works that applied EOF analysis as a tool to discriminate
between both El Niño flavors. Ultimately, we apply our framework to La Niña
events and show that a similar discrimination into two types is not only possible
but again in good accordance with the few existing previous works regarding this
problem.
Our framework provides a powerful formalism to systematically detect and categorize
different types of ENSO periods. With our tools we derive generally applicable criteria for
discriminating EP and CP events purely based on the structural properties of the underlying
global cross-correlation matrix and thus complement existing tools from statistical
climatology. |
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