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| Titel |
Ocean response to wind variations, the equatorial warm water volume, and simple models of ENSO in the low-frequency approximation |
| VerfasserIn |
A. Fedorov |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250022138
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| Zusammenfassung |
| Physical processes that control ENSO dynamics are relatively fast. For example, it takes
several months for an equatorial Kelvin wave to cross the Pacific basin (Tk = 2 months),
while Rossby waves travel the same distance in about half a year. Compared to such short
timescales the typical periodicity of El Nino is much longer (T = 3-6 years). Thus, ENSO is
fundamentally a low-frequency phenomenon in the context of these faster processes. Here,
we take advantage of this fact and use the smallness of the ratio Ék = Tk/T to expand
solutions of the ocean shallow-water equations into power series (the actual parameter of
expansion É is related to Ék but further modified by the oceanic damping rate). Using this
expansion, here referred to as the low-frequency approximation, we obtain simplified
formulations of ENSO dynamics and show how the meridional structure of wind
stress anomalies and oceanic damping rates affect the amplitude and periodicity
of El Nino, as well as the phase lag between variations in the mean thermocline
depth (related to the equatorial warm water volume) and temperature in the eastern
equatorial Pacific. This phase lag is a key feature of the recharge/discharge physics of
ENSO. A simple analytical expression is derived for the lag as a function of the
oscillation frequency, the oceanic damping rate, and the curl of wind stress anomalies. |
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