Coexistence of the Antarctic Circumpolar Wave and a Southern Annular Type Mode in the Southern Ocean?
Stephanie Artigues(1) , Claire Pottier(2) , Jean Pierre Ceron(3) , Joel Sudre(1) , and Veronique Garcon(1)
18 Avenue Edouard Belin,
31401 Toulouse Cedex 9,
(2) CLS and CNRS, 8-10 rue Hermès, 31520 Ramonville St Agne, France
(3) Météo France, 42 Avenue Gaspard Coriolis, 31057 Toulouse Cedex 1, France
We examine the time evolution over a 13 yr time series of the dominant modes of variability in sea level anomalies (SLA) from TOPEX/Poseidon and ERS-1/2 in the Southern Ocean (35-60°S). We use Hayashi's classical space-time spectral analysis and a newly developed method combining a Gabor analysis with Hayashi's method. Zonal wavenumbers 3 and 2 emerge unambiguously with null corresponding meridional wavenumber meaning that both associated modes have no meridional propagation. Their power spectrum density (PSD) is maximum within 50-55°S. The 2/0 pair is characterized by a ~4.4 yr period and exhibits a clear eastward propagation, with a maximal PSD just after the 1998 El Niño peak. It corresponds then probably to the Antarctic Circumpolar Wave. The discernible zonal wavenumber 3 pattern of variability in the SLA signal displays a westward propagation associated with a 1.04 yr period, and may be related to the atmospheric Southern Annular Mode (SAM). Simultaneously, we have investigated the presence of these two modes in the surface chlorophyll concentrations derived from the SeaWiFS sensor over the 1997-2004 period. It is delicate to resolve the 2/0 mode due to the limited temporal extent of the ocean color archive. Results show high correlation coefficients (up to 54%) between the power spectrum density of the ocean color signal and that of the altimetric signal associated to the 3/0 mode related to SAM. Links between the SAM index, the biological and the physical signals at the interannual scale will be discussed.