Article Type:
Research Article

Low-Frequency Modulation of Intraseasonal Equatorial Kelvin Wave Activity in the Pacific from SODA: 1958–2001

Boris Dewitte IRD/LEGOS, Toulouse, France, and IMARPE, Callao, Peru

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Sara Purca IMARPE, Callao, Peru

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Serena Illig IRD/LEGOS, Toulouse, France, and JPL, Pasadena, California

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Lionel Renault IRD/LEGOS, Toulouse, France

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Benjamin S. Giese Texas A&M University, College Station, Texas

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Print Publication:
15 Nov 2008
DOI:
https://doi.org/10.1175/2008JCLI2277.1
Page(s):
6060–6069
Restricted access

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Abstract

Intraseasonal equatorial Kelvin wave activity (IEKW) at a low frequency in the Pacific is investigated using the Simple Ocean Data Assimilation (SODA) oceanic reanalyses. A vertical and horizontal mode decomposition of SODA variability allows estimation of the Kelvin wave amplitude according to the most energetic baroclinic modes. A wavenumber–frequency analysis is then performed on the time series to derive indices of modulation of the IEKW at various frequency bands. The results indicate that the IEKW activity undergoes a significant modulation that projects onto baroclinic modes and is not related in a straightforward manner to the low-frequency climate variability in the Pacific. Linear model experiments corroborate that part of the modulation of the IEKW is tightly linked to change in oceanic mean state rather than to the low-frequency change of atmospheric equatorial variability.

Corresponding author address: Boris Dewitte, IRD/LEGOS, 14 av. Edouard Belin, Toulouse 31400, France. Email: bxd@imarpe.gob.pe

Abstract

Intraseasonal equatorial Kelvin wave activity (IEKW) at a low frequency in the Pacific is investigated using the Simple Ocean Data Assimilation (SODA) oceanic reanalyses. A vertical and horizontal mode decomposition of SODA variability allows estimation of the Kelvin wave amplitude according to the most energetic baroclinic modes. A wavenumber–frequency analysis is then performed on the time series to derive indices of modulation of the IEKW at various frequency bands. The results indicate that the IEKW activity undergoes a significant modulation that projects onto baroclinic modes and is not related in a straightforward manner to the low-frequency climate variability in the Pacific. Linear model experiments corroborate that part of the modulation of the IEKW is tightly linked to change in oceanic mean state rather than to the low-frequency change of atmospheric equatorial variability.

Corresponding author address: Boris Dewitte, IRD/LEGOS, 14 av. Edouard Belin, Toulouse 31400, France. Email: bxd@imarpe.gob.pe

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