The fluctuations in ocean temperatures during El Niño and La Niña are accompanied by even larger-scale fluctuations in air pressure known as the Southern Oscillation. The negative phase of the Southern Oscillation occurs during El Niño episodes, and refers to the situation when abnormally high air pressure covers Indonesia and the western tropical Pacific and abnormally low air pressure covers the eastern tropical Pacific. In contrast, the positive phase of the Southern Oscillation occurs during La Niña episodes, and refers to the situation when abnormally low air pressure covers Indonesia and the western tropical Pacific and abnormally high air pressure covers the eastern tropical Pacific. These opposite phases of the Southern Oscillation are shown above.