Sunday, August 10, 2008 La Niña about to end, El Niño is unlikely By Stella A. Estremera
THE La Niña phenomenon is drawing to a close and El Niño-Southern Oscillation (Enso)-neutral conditions or more popularly known as just El Niño have been observed last month as "sea surface temperatures (SSTs) in the central equatorial Pacific Ocean remained near-average."
The US Climate Prediction Center/National Centers for Environmental Predictions reported that mixed atmospheric and oceanic indicators have been observed during the duration.
Increase in above-average temperatures, particularly in the eastern Pacific, and certain areas in equatorial Pacific Ocean suffering a lingering influence of La Niña were also manifested.
These manifestations are but typical of Enso-neutral conditions, the report said.
It further noted that Enso-neutral conditions are predicted to continue till sometime around March in 2009.
But, "due to the positive heat content anomalies in the Pacific Ocean, the development of El Niño cannot be ruled out during the later part of the year, although chances remain low."
Should the positive heat content anomalies not develop into an El Niño, then Enso-neutral conditions that is predicted further this month will continue through this yearend.
Enso is an ocean-atmosphere phenomenon in the Pacific Ocean. It is named after the Christ child because El Niños are usually noticed around Christmas time.
Both El Niño and La Niña are "sustained sea surface temperature (SST) anomalies of magnitude greater than 0.5 degrees Centigrade across the central tropical Pacific Ocean."
When this anomaly is met for less than five months, then it's referred to as either El Niño or La Niña conditions.
An anomaly that persists for five months or longer is classified as an El Niño or La Niña episode.
Episodes come less often than conditions.
Historically, it has occurred at irregular intervals of 2-7 years and has usually lasted one or two years.
The first signs of an El Niño as:
1. Rise in air pressure over the Indian Ocean, Indonesia, and Australia
2. Fall in air pressure over Tahiti and the rest of the central and eastern Pacific Ocean
3. Trade winds in the south Pacific weaken or head east
4. Warm air rises near Peru, causing rain in the northern Peruvian deserts
5. Warm water spreads from the west Pacific and the Indian Ocean to the east Pacific. It takes the rain with it, causing extensive drought in the western Pacific and rainfall in the normally dry eastern Pacific.
