München 2004 – scientific programme
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UP: Umweltphysik
UP 7: Hydrosph
äre und Boden I
UP 7.2: Fachvortrag
Monday, March 22, 2004, 14:30–14:45, HS 020
A nonlinear paradigm for tropical Pacific decadal variability — •Petra Friederichs1 and Keith Rodgers2 — 1Meteorologisches Institut, Auf dem Huegel 20, 53121 Bonn — 2Laboratoire d’Oceanographie Dynamique et de Climatologie, 4, Place Jussieu, 75252 Paris
A 1000-year integration of a coupled ocean/atmosphere model (ECHO-G) has been analyzed to describe decadal to multi-decadal variability in equatorial Pacific sea surface temperature (SST) and thermocline depth (Z20), and their relationship to decadal modulations of ENSO (El Niño-Southern Oscillation) behavior.
Our main finding is that the structures in SST and Z20 characteristic of Tropical Pacific Decadal Variability in the model are due to an asymmetry between the anomaly patterns associated with the model’s El Niño and La Niña states, this asymmetry reflecting a nonlinearity in ENSO variability. As a result, the residual (i.e. the sum) of the composite El Niño and La Niña patterns exhibits a dipole structure across the equatorial Pacific, with positive perturbation values in the east and negative values in the west for SST and Z20. During periods when ENSO variability is strong, this difference manifests itself as a change in the mean state through a rectifier effect.
For comparison, a similar analysis was applied to a gridded SST dataset spanning the period 1871-1999. The data confirms that the asymmetry between the SST anomaly patterns associated with El Niño and La Niña for the model are realistic.