Dynamics of El Ni

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Dynamics of El Niño Southern Oscillation

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Persistence of marine tropical climate and El
Niño historical reconstructions

• Alexey Kaplan and Daniel Gombos
• LDEO Cornell University

In collaboration with J.CH. Chiang (U of CA,
Berkeley),
Y.Kushnir, R.Seager, H.-P.Huang (LDEO)
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Outline

• Why climate persistence is important for
  historical analyses of instrumental data?
• Surprising persistence of tropical wind and
  pressure anomalies.
• What drives it?
• Additional benefit of equatorial wind persistence
  for ocean modeling.
• New horizons opening to us.

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EOFs of zonal wind anomaly
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Independent ENSO indices
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Persistence in SST anomalies is
traditionally used to constrain historical
analyses, but there is no persistence in monthly
wind or pressure anomalies, right?
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Persistence Anomaly autocorrelations with 1
month lag
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Persistence Anomaly autocorrelations with 1
month lag
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Persistence with longer lags
Zonal wind in Reanalysis 160E-120W averages
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Verification by satellite data
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Persistence in AMIP experimentszonal wind
anomaly
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John Chiangs et al., 2001 approach to
surface wind modelinglinearized dynamical core
of a GCM Seager and Zebiak, 1995 is set up to
take both sea surface temperature and elevated
atmospheric heating as forcings.The latter is
parameterized via precipitation.
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Persistence of the actual forcings
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Simulation skill
Consistency of persistence pattern in ERS
(colors) and simulation (contours)
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What is a good wind product from Oceanographers
point of view?
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Why equatorial persistence?
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RMS of sea level response to the wind noise in a
single location
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Conclusions

• Within 10 degree of Equator there is a
  persistence of surface wind and pressure
  anomalies.
• It is driven by the persistence in SST and
  precipitation (via elevated heating).
• It can be used in historical analyses of
  instrumental data by either fitting AR model to
  wind or pressure data or by including temperature
  and precipitation in the analysis.
• Wind analyses suitable driving ocean models must
  be persistent near Equator.

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