Texas Emergency Management ONLINE 2014 Vol. 61 No. 9

El Niño: The Basics

By Meteorologist Aaron Treadway
National Weather Service, New Braunfels, TX

What Is El Niño?
El Niño is half of ENSO, or the El Niño Southern Oscillation. This is an ocean and atmosphere interaction where El Niño is the ocean part and the Southern Oscillation is the atmosphere part. El Niño is characterized by warmer than normal ocean temperatures in the Eastern Pacific.

El Niño Conditions in the Pacific (pmel.noaa.gov)

Typically, pressure is higher on the eastern side of the Pacific than on the western side and that leads to winds blowing to the west across the Pacific. During El Niño pressures over Australia are higher than normal leading to less of a pressure gradient and weaker trade winds. When the trade winds relax, the thermocline (a layer in the ocean where the temperatures change rapidly with depth) becomes more balanced in depth across the Equatorial Pacific between 120°E to 80°W. This leads to a decrease in upwelling, and as a result sea-surface temperatures rise, causing the El Niño. Rainfall shifts eastward toward the warmer waters. These changes alter the atmospheric circulation, including changes in the location of the jet stream, which alters the weather around the globe (pmel.noaa.gov).

Typical Weather Impacts during El Niño (climate.gov)

What are the impacts to Texas?
While some areas of the United States experience drier weather from El Niño, Texas benefits during El Niño events. During 80% of the El Niño events over the last 100 years, Texas (and most of the Gulf Coast) has seen wetter than normal conditions.

El Niño also produces slightly cooler temperatures during the December through February winter period.

The reason that Texas is wetter and cooler than normal during El Niño  years is because the southern part of the jet stream, called the Pacific or Subtropical Jet, is farther south. This results in the storm track of weather systems being right over Texas (climate.gov).

What is the status of the 2014 El Niño?
The Climate Prediction Center (CPC), located in College Park, Maryland, is responsible for issuing ENSO forecasts. The current August forecast is for a 65% chance of El Niño conditions for the Northern Hemisphere during the fall and early winter. Because of this the CPC has issued an El Niño Watch (cpc.noaa.gov). However, the August updated forecast of 65% is down from 80% in July. Neither the ocean nor the atmosphere have taken on the characteristics yet of El Niño, so the status remains ENSO neutral (neither El Niño or La Niña). There were signs earlier this summer that the oceans were warming, but now the temperatures in the Eastern Pacific are actually below average. Part of the reason for this is the atmosphere never reacted to the warming temperatures earlier this summer. At this time, though, computer models continue to indicate that an El Niño will develop later this fall (climate.gov).

To get updates on the status of El Niño, refer to the Climate Prediction Center’s webpage here:
http://www.cpc.noaa.gov/products/precip/CWlink/MJO/enso.shtml

Links and sources:


Share |