Illig Serena, Bachelery M. L., Cadier E. (2018). Subseasonal coastal-trapped wave propagations in the Southeastern Pacific and Atlantic Oceans : 2. Wave characteristics and connection with the equatorial variability. Journal of Geophysical Research : Oceans, 123 (6), p. 3942-3961. ISSN 2169-9275.
Titre du document
Subseasonal coastal-trapped wave propagations in the Southeastern Pacific and Atlantic Oceans : 2. Wave characteristics and connection with the equatorial variability
Journal of Geophysical Research : Oceans, 2018,
123 (6), p. 3942-3961 ISSN 2169-9275
The objective of this study is to compare the characteristics of the oceanic teleconnection with the linear equatorial dynamics of two upwelling systems along the southwestern South American and African continents at subseasonal time scales (<120 days). Altimetric data analysis shows that the coastal variability remains coherent with the equatorial signal until 27 degrees S in the southeastern Pacific (SEP), while in the southeastern Atlantic (SEA) it fades out south of 12 degrees S. To explain this striking difference, our methodology is based on the experimentation with twin regional model configurations of the SEP and SEA Oceans. The estimation of free Coastal-Trapped Waves (CTWs) modal structures and associated contribution to coastal variability allows inferring and comparing the characteristics of each CTW mode in the two systems; namely, their forcings, amplitude, dissipation rate, and scattering. Results show that the Pacific subseasonal equatorial forcing is only 20% larger than in the Atlantic, but important differences in the relative contribution of each baroclinic mode are reported. The first baroclinic mode dominates the eastern equatorial Pacific variability, while in the eastern equatorial Atlantic, the second mode is the most energetic. This leads to a drastic increase in the dissipation and scattering of the remotely forced CTW in the SEA sector, compared to the coastal SEP. Concomitantly, south of 15 degrees S, the subseasonal coastal wind stress forcing is substantially more energetic in the SEA and participates in breaking the link between the equatorial forcing and the coastal variability. Our results are consistent with the solutions of a simple multimode CTW model. Plain Language Summary The Humboldt and the Benguela upwelling systems are connected to the equatorial variability. Part of the incoming eastward equatorial wave energy is transmitted southward along the South American and African coasts as Coastal-Trapped Waves, where they imprint on the ecosystem variability. At subseasonal time scales (<120 days), altimetry reveals that the coastal variability remains coherent with the equatorial signal until 27 degrees S in the southeastern Pacific, while in the Atlantic counterpart it fades out south of 12 degrees S. To explain this striking difference, we compare the characteristics of coastal waves between the two systems: their forcing at the equator, their dissipation and scattering along their propagation, and the energization by the coastal wind stress. We use a variety of ocean models of different complexity ranging from regional general circulation models to simple linear coastal models. Results show that the difference between the two systems regarding the connection with the equatorial variability can be attributed to the distinct characteristics of their equatorial forcing. The latter favors fast and weakly dissipative coastal wave in the Humboldt. Off southwestern Africa, the equatorially-forced coastal-trapped waves dissipate at approximate to 13 degrees S and the subseasonal coastal wind stress forcing which is energetic south of 15 degrees S, participates in breaking the link between the equatorial and coastal variabilities.
Plan de classement
Sciences fondamentales / Techniques d'analyse et de recherche [020]
;
Limnologie physique / Océanographie physique [032]
Description Géographique
PACIFIQUE SUD EST ; ATLANTIQUE SUD EST ; ZONE EQUATORIALE
