Influence of El Niño on the Upper-Ocean Circulation in the Tropical Atlantic Ocean

Abstract

This study investigates the influence of El Niño on the upper-ocean circulation in the tropical Atlantic Ocean (via changes in the Atlantic trade winds) by analyzing observed sea surface temperature (SST) together with an ocean general circulation model integration forced by the NCEP-NCAR reanalysis. During periods with anomalously warm (cold) eastern equatorial Pacific SST, the southern Atlantic tropical cell is strengthened (weakened). The difference of the cell strength between El Niño and La Niña years is about 20% of the mean cell strength. However, the variability of the cell is not dominated by the remote forcing from the eastern equatorial Pacific but seems to be caused by intrinsic tropical Atlantic variability. A strengthening (weakening) for periods with anomalously warm (cold) eastern equatorial Pacific SST is also found for the zonal surface and subsurface currents. TOPEX/Poseidon altimetry data are used to validate the results based on the OGCM integration.

Observed Transport Variability of the Atlantic Subtropical Cells and Their Connection to Tropical Sea Surface Temperature Variability

“…The comparison between the results for the 2-and 5-year running mean time series suggests that the STCs are modulating equatorial SST rather on longer time scales which is consistent with model studies for the equatorial Pacific showing that while the SST variability on interannual time scales is predominantly driven by equatorial wind forcing, a significant part of the variability on decadal time scales is related to changes in the equatorward STC transport (Farneti et al, 2014;Lohmann & Latif, 2007;Lübbecke et al, 2008;Nonaka et al, 2002).…”

Tropical SST forcing on the anomalous WNP subtropical high during July–August 2010 and the record-high SST in the tropical Atlantic

“…We investigated whether this occurred in 2009-2010. Figure 6a displays the time series of the SSTA over the TA and Niño 3.4 regions; the warm TA-SSTA, initiated in the boreal winter and peaking in the following April, lagged the Niño 3.4 index by approximately 3-5 months, suggesting that the TA-SSTA was partially forced by the ENSO-induced large-scale subsidence, as suggested in previous studies (e.g., Enfield and Mayer 1997;Chiang and Sobel 2002;Huang et al 2002;Lohmann and Latif 2007). Conversely, the TA-SSTA might have a feedback on the fast decaying of 2009 El Niño (shown in Fig.…”

On the Inconsistent Relationship between Pacific and Atlantic Niños*

“…For example, positive SST anomalies in the eastern equatorial Atlantic were found to lag those in the equatorial Pacific by 6 months in a cross-spectral analysis of observational SST data by Latif and Grö tzner (2000). Lohmann and Latif (2007) found a boreal summer warming in the entire tropical Atlantic apart from weak cooling in the eastern equatorial basin in their composite analysis of observed SST data. On the contrary, a coupled general circulation model (CGCM) analysis by Huang (2004) argued for cold SST anomalies in the tropical Atlantic in the boreal summer following an El Niñ o because of the dynamical response to anomalous easterlies.…”