By Skip Rigney 

Some years it seems that every odd weather event anywhere in the world is blamed on El Niño. However, you may have noticed that there hasn’t been much mention of El Niño in the news lately.

One reason is that the flip side of El Niño, which is called La Niña has been going on for the past five months.

But, what are El Niño and La Niña anyway? The official name given to this oceanic and atmospheric phenomenon by climatologists, meteorologists, and oceanographers is the “El Niño – Southern Oscillation,” abbreviated as ENSO. The “Southern Oscillation” in the name refers to fluctuation of higher atmospheric pressure between the tropical western Pacific and central Pacific.

The oceanic component of ENSO shows up in the upper ocean temperatures of the eastern and central tropical Pacific. Variations from year-to-year are related to variations in the strength of the trade winds in the central and western Pacific.

When sea surface temperatures (SSTs) in the central and eastern Pacific become much warmer than average, this is called El Niño. The name arose because these anomalously warm waters often show up off the coast of Peru around the Christmas season. The Spanish term “El Niño” referring to “the boy,” became associated with this phenomenon because of the timing often being near the celebration of the birth of the Christ Child.

In some years, an opposite, much colder-than-normal upper ocean condition arises in the same regions of the Pacific. That phase ENSO is referred to as La Niña, literally “the girl” in Spanish, as a simple way to identify it as the flip side of El Niño.

When ocean temperatures in the tropical Pacific are not significantly warmer or cooler than the long-term average, scientists say that ENSO is in its “neutral phase.”

But, what do changes in SST or atmospheric pressure in the tropical Pacific have to do with weather in other parts of the world?

In the 1960s and 1970s scientists proved that changes in SSTs over large ocean regions affected more than just the nearby atmosphere. Those changes alter the atmospheric circulation in surrounding regions, and eventually influence weather patterns around the globe. One example is that El Niños are often associated with wind patterns over the tropical Atlantic that tend to inhibit the formation of hurricanes.

Although there are a number of other atmospheric and oceanic oscillations, ENSO is associated with the largest variations in global weather patterns from year to year.

The switch between El Niño, neutral, and La Niña phases happens on an irregular basis. The neutral phase may last for several years, then an El Niño or La Niña begins and lasts from one-half to two years.

The beginning of hurricane season is only three weeks away.

According to the National Oceanic and Atmospheric Administration, the La Niña (cool phase) that has been ongoing for the last five months is coming to an end, and NOAA expects the neutral phase of ENSO to be in place this summer.

To find out more about how this may influence the upcoming hurricane season, come out to a talk that I will be giving on hurricanes on May 20th at 2:00 PM at Crosby Memorial Library in Picayune, sponsored by the Friends of the Library.