Understanding ENSO, the climate systems that trigger drought, precipitation

It seems someone is always complaining about the weather; it is too wet or it is too dry—like right now for much of the High Plains. However, if we can understand the systems that cause our weather conditions, the weather can be more predictable when making agriculture decisions.

Gary McManus, state climatologist for the Oklahoma Mesonet, explained the El Niño-Southern Oscillation, or ENSO as it is often called, is one of the main influences of the weather that impacts our planet. Although El Niño is in the title, this system actually has three phases: El Niño, La Niña and neutral conditions.

“Southern Oscillation refers to seesaw changes in equatorial Pacific surface pressures,” McManus said. “ENSO is one of the most important climate phenomena on Earth since it can change the global circulation pattern, which includes the planet’s temperature and precipitations patterns. Since the Earth’s atmosphere is just one gigantic fluid, it does translate through the whole globe eventually.”

McManus said scientists like using ENSO because it can be predicted several months or even seasons in advance of weather impacts, which allows people to plan ahead. However, he stressed there are uncertainties with using ENSO, and the weather patterns are not always as expected.

He went on to explain that ENSO switches irregularly between the three phases every two to seven years. The three phases are based partly on the sea surface temperature changes in the equatorial pacific routes.

“El Niño is the warming of those waters between Indonesia and the West Coast of South America at least by 0.5 degrees Centigrade,” McManus explained. “La Niña is the cooling by minus 5 degrees C in the eastern part of the equatorial pacific.”

In between El Niño and La Niña is the neutral phase when normal patterns kick in. ENSO is a coupled phenomenon so it requires a certain change in the atmosphere to be classified as El Niño or La Niña. McManus said it starts with the change in the sea surface temperatures, but then there needs to be a Southern Oscillation change in atmospheric pressure and precipitation patterns. However, a sea surface anomaly without the atmospheric component is just an anomaly.

ENSO changes weather patterns around the globe through teleconnections—a underlying correlation between meteorological or other environmental phenomena which happen a long distance apart.

“It changes the pressure and storm patterns along the equator, which changes the trade winds—also known as the Walker Circulation,” McManus said. “It then influences the Hadley Circulation, which leads to changes in the circulation patterns worldwide, including the position of the jet stream over North America.”

Effects of ENSO

El Niño causes significant droughts in Australia and northern South America. However, it often benefits the southern United States. McManus said during El Niño, hurricane season is usually worse in the Pacific Ocean, but better in the Atlantic Ocean. On the North American continent, El Niño often causes warmer weather across the northern tier of the U.S., but wetter weather across the southern tier.

“It is often dry in the upper Midwest and into the southeast from October to March, which is the bulk of the cool season,” he added.

La Niña usually causes opposite weather conditions to that of El Niño. Australia and Central America often benefit during La Niña and the southern U.S. and parts of Asia and South America often struggle. Hurricane season is worse in the Atlantic Ocean and better in the Pacific Ocean. Conditions are drier and warmer along the southern tier of the U.S. and wetter in the Pacific Northwest and Ohio Valley.

“La Niña impacts are usually seen from October to April, but the strongest effects are in January, February and March,” McManus said. “Strength of the sea surface temperature change has a significant influence on weather pattern changes in both El Niño and La Niña.”

McManus said impacts are more likely to occur during ENSO events, but not certain to transpire.

“The stronger the ENSO events, the more likely the teleconnection impacts become,” he said. “There is some correlation between strength of the event and the severity of the effects. Scientists have low confidence in exactly what will happen to ENSO in the future even while they have high confidence that ENSO itself will continue. Climate change could strengthen or weaken the typical weather patterns associated with ENSO.”

The next time you hear the weather man reference El Niño, don’t just think of Chris Farley in a Weather Channel Saturday Night Live skit, wearing a ruffled shirt saying “El Niño is Spanish for the Niño.” Remember it is also part of ENSO, a recurring climate pattern that sets the stage for the weather conditions that effect your farm or ranch.

Lacey Vilhauer can be reached at 620-227-1871 or [email protected].