Greenhouse Warming, Decadal Variability, or El Niño? An Attempt to Understand the Anomalous 1990s
The dominant variability modes in the Tropics are investigated and contrasted with the anomalous situation observed during the last few years. The prime quantity analyzed is anomalous sea surface temperature (SST) in the region 30S-60N. Additionally, observed tropical surface wind stress fields were investigated. Further tropical atmospheric information was derived from a multidecadal run with an atmospheric general circulation model that was forced by the same SSTs. The tropical SST variability can be characterized by three modes: an interannual mode [the El Nin o-Southern Oscillation (ENSO)], a decadal mode, and a trend or unresolved ultralow-frequency variability.