Temperature Anomalies

El Niño and La Niña

Graphic depicting pactific ocean surface heights

Images Courtesy NASA/JPL/CNES

Global weather patterns are infinitely complex and are affected by factors like solar radiation, volcanic activity, and sea surface temperatures. One well-documented sea-surface temperature feature that affects the weather in the United States and elsewhere is named "ENSO", an acronym meaning the El Niño Southern Oscillation. In this instance, "oscillation" refers to the multi-year cycle of temperature change in the surface waters of the eastern Pacific near the equator. El Niño and La Niña are the names of the two parts of this oscillation.

A graphic illustrating ocean temperatures during El Niño and La Niña.

Graphic Courtesy NOAA/CPC

During an El Niño period of the ENSO cycle, eastern Pacific waters become warmer than the observed long-term average. During a La Niña period, the reverse happens, with these same waters being cooler than average. The differences between these two portions of the ENSO cycle are depicted above. In these charts, land masses are represented in black, and the shaded areas represent the Pacific Ocean. Note the contrast between the images on the left and the images on the right, specifically in the region west of Equador. During the period from January through March of 1989, this region is 7°C (almost 13°F) cooler than the same region in the same portion of the year in 1998.

How does this impact the weather? As the prevailing winds traverse the waters of the Eastern Pacific, the temperature, humidity and pressure of the air in this region are influenced by the water beneath it. This not only affects the weather at sea, but as these air masses interact with land their behavior depends on the characteristics they take on over water. The impact of this sea surface temperature anomaly is broad and complex such that regions impacted by El Niño may see record flooding, while thousands of miles away others may experience record drought. More information about this topic can be obtained by visiting the ENSO F.A.Q.

Sources: