The changing pattern of sea surface heights as conditions go from normal, to El Niño, to La Niña, to normal again is quite remarkable. The movie below shows how sea surface height changes over three years.

  !   Click the image to view the movie. Drag the slider back and forth or step through the animation frame by frame to see the timing of El Niño and La Niña events.

2. During which months do ocean surface elevations begin to rise along the equator, indicating the beginning of an El Niño?

3. During which months does the El Niño end and the La Niña begin?