Abrupt equatorial wave-induced cooling of the Atlantic cold tongue in 2009

Between May and August 2009 sea surface temperatures (SSTs) in the eastern equatorial Atlantic dropped 5 C, from 1 C above normal to 1 C below normal. The magnitude of this cooling is unprecedented since satellite SST measurements began in 1982. In this study, observations and a linear equatorial wave model are used to examine the causes of the sharp decrease in SST. It is found that the anomalous cooling along the equator can be traced to an anomalous meridional gradient of SST and associated northwesterly anomalous winds that developed in the equatorial Atlantic the preceding spring. The anomalous winds forced upwelling equatorial Rossby waves that propagated westward during boreal spring and reflected at the western boundary into upwelling Kelvin waves during late spring and summer. The upwelling Kelvin waves propagated eastward along the equator, anomalously decreasing sea level and SST during May-August. Citation: Foltz, G. R., and M. J. McPhaden (2010), Abrupt equatorial wave-induced cooling of the Atlantic cold tongue in 2009, Geophys. Res. Lett., 37, L24605, doi: 10.1029/2010GL045522.