El Niño Southern Oscillation (ENSO) describes the hand-in-hand relationship between tropical Pacific sea surface temperatures and pressure patterns (and hence rainfall). High sea surface temperatures across the central and eastern Pacific found during El Niño events tends to cause lower-than-normal air pressure. Convergence of winds within this zone causes air to rise and produce enhanced rainfall. Towards the western Pacific and Australasia, drier-than-normal conditions prevail. The opposite effect is seen during the La Niña events, when the pressure patterns oscillate to produce lower pressure and higher rainfall in the western Pacific and Australasia, while further east, drier conditions prevail.