Wait and see for El Niño
El Niño is in the news again. Headlines started over the airwaves and on
the newsstands in February after NOAAs Climate Prediction Center (CPC) forecasted
an El Niño for this spring. They announced that ocean and atmosphere circulation
patterns as well as sea-surface temperatures were ripe for an El Niño to
develop over February, March and April.
With forecasts continuing into March, the headlines also continued some
cautious, some alarming, but all pointing toward an imminent change in our air
and seas. But not all climate researchers agree an El Niño is coming, and
some scientists are looking toward new signals to help better predict El Niños
in the future. These opposing viewpoints represent uncertainty surrounding an
If the waters
become warmer than normal beneath the surface or across the equatorial Pacific,
then we have the conditions that are normally present prior to or during the early
stages of an El Niño. Thats what weve been seeing over the
last two to three months, says Vern Kousky of CPC. He adds that this event
will likely be weaker than the last El Niño event in 1997 and 1998. Kousky
says making predictions is tough in March and April, during the so-called spring
barrier. All of the systems have difficulty in predicting conditions at
this time of year, he says. Being a transition season, spring, almost
anything can happen. Its a tough time of year to make forecasts anywhere,
even for our own backyard.
Satellite data during January 2002 for the
Indian and Pacific Oceans show precipitation anomalies, with wet regions in green
to red colors and dry regions in blue. Over 15 days, a seesaw of precipitation
occurred in the eastern Indian Ocean, a possible signal for El Niño development.
An experimental prediction indicates that by July to October 2002, the western
Pacific (left box) will be drier than normal, and the central Pacific (right box)
will be wetter than normal conditions of an El Niño event. Image
is courtesy of Scott Curtis.
And for that reason, David Adamec, an oceanographer at the NASA Goddard Space
Flight Center, thinks CPC announced a forecast too soon. I thought it took
a lot of guts to issue a forecast like that, Adamec says. Kousky explains,
however, that it is in NOAAs mission to provide information to the public
as soon as it is available, and that their available data showed the right warm
What CPC was relying on, Adamec says, was a strong, persistent, anomalous gust
of wind starting from Indonesia in the western Pacific and moving to the Americas
in the eastern Pacific. Pacific trade winds usually blow from east to west. It
is these anomalous westerlies that climate researchers believe trigger an El Niño,
pushing the warm pool of water in the western waters east, where the waters are
usually cold. This warm pool of water affects weather globally rains that
normally soak the western Pacific slide toward the Americas.
Adamec says, however, that westerlies are common in winter and early spring, bringing
some warm waters to the coast of Peru, and do not represent all the necessary
precursors. It certainly gets the ocean going and the ocean is in a state
for an El Niño to happen. But that is not enough, he says. The atmosphere
also has to change its state on a large scale. We are at the spring barrier
when things are supposed to take hold and the atmosphere hasnt bitten off
on that yet. The ocean has to go along and the atmosphere has to go along too,
and if either one of them decides they dont want to dance, there is no dance.
Indeed, Shawn Smith, a wind researcher at Florida State University, says that
he has yet to see the necessary atmospheric signs. He and his colleagues create
FSU winds, a dataset of the monthly mean of winds over the tropical Pacific that
many El Niño scientists use in their models. A lot of the models
are predicting an El Niño, but our group still is on the 50/50 fence, where
it may happen or may not happen. The indicators in terms of the winds have not
shown a signal yet.
Adamec says that until researchers better understand the genesis mechanisms behind
the phenomenon, predicting an El Niño will continue to prove difficult.
Fortunately, climate scientists are working toward a better physical understanding
of El Niño, developing new predictive tools.
Bob Adler and Scott Curtis of NASA-Goddard are looking at the Indian Ocean for
early signs of El Niño. In work that will be published in an upcoming Geophysical
Research Letters, Adler and Curtis present a statistical relationship between
precipitation changes in the Indian Ocean and the initiation of an El Niño.
Using global precipitation data that date back to 1979, they observed a pattern
that precedes El Niño event by six to nine months.
Turns out the climate of the Indian Ocean can sometimes be characterized
by a gradient of precipitation between the center of the basin and the coast of
Sumatra Indonesia, says Curtis, also a professor at the University of Maryland-Baltimore
County. In January, Curtis observed that the gradient had been oscillating over
the winter months, as seen by large and rapid changes in precipitation between
the two areas. At the same time, over the previous six months, the eastern Indian
Ocean near Indonesia was receiving excess rain while the central Indian Ocean
was remaining drier overall. And that pattern of precipitation, Curtis says, has
preceded the past five out of six El Niños, missing the weakest event.
Curtis and Adlers observations of this pattern in January corroborate the
CPC prediction for the current El Niño.
Its interesting that our oscillation for this year coincided with
flooding events that occurred in Indonesia. Its also interesting that a
regional climate phenomenon seems to be affecting the global weather pattern and
the El Niño development, he says.
Right now, their hypothesis is that this precipitation pattern in the Indian Ocean
could drive the wind shifts that stand at the center of El Niño development.
This seesaw of precipitation is telling you a little bit about the winds,
he says. It appears to be a bridge between the Indian Ocean and the western
Pacific. And I think researchers are beginning to realize that we need to also
monitor the Indian Ocean to better understand how and why El Niños occur.
Like the forecasters, Curtis says he is in a wait and see mode. While
he and Adler think they have found a good statistical relationship, they still
dont fully understand the physics. They hope to work with other researchers
to better understand the mechanisms that start El Niños in order to create
better forecasts. Ours is just one small project where we found some interesting
results and I hope we can open up those channels of communication.
Lisa M. Pinsker
NOAA El Niño Web page
NASA -- El Niño Watch