Climate Fact: Atlantic and Pacific Niños
It has long been known that what happens in the tropical Pacific doesn’t just stay in the tropical Pacific. Much of the year-to-year variability in America’s weather, particularly winter weather, can be explained by conditions there. All other things being equal, warm El Niño conditions off the coast of equatorial South America mean a wetter southern U.S., while cool La Niña conditions mean a wetter northern U.S. This switch between warm and cool conditions is influenced by the strength of the winds that descend from the upper atmosphere and blow over the surface of the tropical Pacific. These winds help to “pull” cool waters from the ocean depths to the surface where they upwell off the coast of South America. The strength of these descending winds is in turn influenced by temperatures in the eastern tropical Atlantic Ocean, which has its own “Niños” and “Niñas.” In contrast to the Pacific, where El Niño and La Niña are most pronounced during the winter, the Atlantic events are most pronounced during the summer months. During warm Atlantic phases, the convection in the eastern tropical Atlantic Ocean is stronger, which affects the upper atmospheric winds all the way over to the Pacific. This strengthening in turn strengthens the descending winds over the tropical Pacific, which makes the formation of La Niña conditions more likely there during the winter months. Thus, summertime ocean temperatures in the tropical Atlantic Ocean can help predict the wintertime ocean temperatures in the tropical Pacific.
Seasons: Summer, Fall, Winter
Source: Rodriguez-Fonseca, B et al. “Are Atlantic Niños enhancing Pacific ENSO events in recent decades?”Geophysical Research Letters 36 (2009): L20705.
