During normal years in the Equatorial Pacific, trade winds push warm water to the west creating a deep pool of warm water in the western Equatorial Pacific. The warm water leads to deep convection in the atmosphere and heavy rains in the west. When the trade winds relax, a pulse of warm water moves from west to east along the Equator as a Kelvin wave. In some years this leads to an El Nino, heavy rains spread into the central Equatorial Pacific, and warm water covers the eastern Equatorial Pacific.
Sea level is a useful indicator of processes in the equatorial Pacific.
Pools of warmer than normal water associated with tropical rain in the central Pacific and El Nino conditions in the east Pacific produce sea levels that are higher than normal. Conversely, cold conditions in the eastern Pacific associated with La Nina produce below normal sea levels. We are using data from the satellite to monitor conditions in the Equatorial Pacific. The figure shows anomalies of sea level as a function of time along the Equator from 150 degrees east off New Guinea to 90 degrees west at the Galapagos Islands. Such a plot is called a time-longitude plot.