Interannual Variability of subsurface connection in Southeastern Tropical Pacific during 1999 – 2004. Ivonne Montes 1,a , C. Böning 2,b , F. Colas 3,c , W. Schneider 1,d and B. Blanke 4,e. EUC. SEC.
Interannual Variability of subsurface connection in Southeastern Tropical Pacific during 1999 – 2004
Ivonne Montes1,a, C. Böning2,b, F. Colas3,c, W. Schneider1,d and B. Blanke4,e
1: Departamento de Oceanografía. Universidad de Concepción. Casilla 160-C. Concepción - Chile. 2: Institut für Meereskunde, Universität Kiel, Kiel - Germany. 3: IGPP – UCLA, Los Angeles – USA. 4: Laboratoire de Physique des Océans, UMR 6523 CNRS-IFREMER-IRD-UBO, Brest-France.
Motivation and Objective
Methodology: Regional Ocean Model System (Roms) Configuration
Fig.3 (left) presents the monthly averaged sea level anomaly (SLA) maps from AVISO product and the model for a characteristic month during La Niña event and El Niño event. In terms of large-scale patterns and amplitudes, it shows the good agreement between the model and data for both events.
Fig.4 (below) presents AVISO and model SLA time series at an averaged area located between 2.5-3.5°N/79-80°W (a) and, Pathfinder/Reynolds product and model SST anomaly time series at an averaged area located between 2-3°S/85-86°W (b). The model SLA and SST time series are close to the observations.
The numerical data has been obtained from the high - resolution numerical model ROMS:
- 94º/70ºW - 4ºN/22ºS (East boundary closed)
- Bathymetry: ETOPO2.
- Surface conditions:
(1/2º - monthly climatology)
Fig. 2 shows a snapshot of the modeled surface currents and the sea surface temperature (SST, °C) for November of 2004. It can be notice that the model is able to reproduce the known dynamics representative of this region: the cold upwelled water along the shore, the upwelling filaments extending from the upwelling front, the equatorward flow along the shore and the westward South Equatorial Current.
b. El Niño
a. La Niña
Fig.5 Vertical sections of zonal velocity (m/s) at 88°W during La Niña event (a, ENSO cold phase) and El Niño event (b, ENSO warm phase); the most representative months of each event have been averaged (October, November and December for 1999 [Niña] and 2002 [Niño]). It is noticed that there are three eastern subsurface currents: EUC, pSSCC and sSSCC in both events however, the distribution in depth and intensity are different for each one.
Fig. 7 shows the horizontal streamfunction ψh related to the vertically integrated transport of the flow transmitted from 92°W (during the 1999 La Niña event <a> and the 2002 El Niño event <b> and, between 40 and 400 m depth) to 11°S (between 82°W and the coastline). The value of ψh is arbitrarily set to 0 in America. The contour interval is 0.01 Sv from 0 to 0.1 Sv, and is 0.05 Sv from 0.1 and beyond. We used the ARIANE Lagrangian model (Blanke and Raynaud, 1997; Blanke et al., 1999) with 27587 particles on the velocity outputs of our solution during La Niña event and 23156 particules during El Niño.
Fig. 8 shows the time evolution of the EUC flow transferred within 2 years to the South American coastline. The time series of the inflow at 92°W is shown in black whereas the outflow at 11°S is shown in red. The average tranfer is 0.14Sv over the model solution. The median time needed to achieve the connection is 450 days. Restricting the averaging process to the inflow over August – December 1999 (La Niña conditions) and August – December 2002 (El Niño conditions) gives a mean transfer of 0.14 Sv (see Fig. 7a) and 0.07 Sv (see Fig. 7b), respectively.
Fig.6. shows the subsurface circulation (m/s) during La Niña (140m) and El Niño event (100m). As previously have pointed out (Eden and Timmermann, 2004), the Galapagos Island is a topography barrier to the EUC causing it to split into two zonal branches, northward and southward. Our results reveal that, during El Niño, both branches are intense, well developed and it seems they have a better connection with the PCUC whereas, during La Niña, the southern branch is almost negligible. And also, there is indication of a possible pathway from the EUC to a southern eastward current during La Niña Event.
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