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Remote Cloud Observatory Tracks El Niño Changes

December 18, 1997
Penn State
Perhaps the largest El Niño of the century is currently underway, and a team of scientists is remotely watching the sky, hoping that they can learn from this event.

University Park, Pa. -- Perhaps the largest El Niño of the century is currently underway, and a team of scientists is remotely watching the sky, hoping that they can learn from this event.

"A year ago we set up a ground-based observing station in the Western Pacific on Manus Island in Papua New Guinea that is intended to last a decade," says Dr. Thomas P. Ackerman, professor of meteorology at Penn State. "The timing was near-perfect, we got measurements before El Niño, now we are getting measurements during El Niño, and I hope we will get measurements after it passes."

The observing station is part of the Department of Energy's Atmospheric Radiation Measurement (ARM) program. Another observing station already exists in rural Oklahoma and others are planned. The program will collect continuous cloud observations and measurements for a decade in an effort to evaluate and develop cloud property and radiation algorithms for the global climate models, and to better understand phenomena like El Niño.

"We have records of El Niño quite far back, but the largest in recent history occurred in 1982-83," says Ackerman who also is associate director of Penn State's Earth System Science Center. "Right now, the 1997 El Niño is the biggest we have on record, although it is expected to begin to contract in late fall."

El Niño is of serious concern because it affects weather patterns across the Pacific and in North and South America. During an El Niño, the western coasts of the Americas become very wet and hurricanes spawn off the Pacific coast of Mexico, track up through Southern California and dump rain on such normally arid states as Arizona and New Mexico. The northern tier of North America becomes warmer and the southern tier becomes colder. The Southwest, Midwest and Southeast become wetter. The Northeast is little affected by El Niño.

In the Western Pacific, El Niño causes severe drought, which is especially problematic for islands relying on rain for irrigation and drinking water.

"The situation in New Guinea and nearby islands is serious, as are the consequences of West Coast hurricanes," says Ackerman. "While we are pretty good at projecting the effects of El Nino once one begins, we really do not know how to predict the onset."

El Niño is a quasi-periodic event, meaning it appears regularly but not necessarily predictably. Hopefully, data collected by the observing station along with sea surface and air/sea atmospheric temperature readings collected from ocean buoys set out by the National Oceanographic and Atmospheric Agency will help meteorologists and climatologists recognize the onset of El Niño.

The observing station monitors water vapor and liquid water in the atmosphere and takes a digital picture of the sky through a fish-eye lens every 10 minutes. Measurements of the base of the clouds and their depth, the particulate content of the atmosphere and radiative fluxes through the atmosphere and reflected radiation from the Earth's surface are also collected. Local weather observers collect temperature, humidity, wind speed and direction, and precipitation data.

"We have great cooperation from the New Guinean weather service and after a year, the station is extremely successful," says Ackerman. "No one knew if these stations could work on their own and they do."

The main focus of the ARM program is cloud cover and the effect of clouds on the surface radiation budget, which is important in understanding El Niño and in refining the output of the global climate models currently used to understand worldwide events.

Normally the Pacific trade winds blow from east to west and push warm water across the Pacific Ocean and allow colder water to move in from the north, south and below, along the west coast of North and South America.

When El Niño begins, the trade winds slacken and the water stays put. The west coast water becomes 3 to 5 degrees Celsius warmer than usual and the western Pacific becomes about a degree cooler, equalizing the temperatures across the Pacific. The normally cloud-free west coast becomes cloudy and wet, and the Western Pacific, which has frequent cloud cover and rain storms, experiences drought.

"We do not know what makes the trade winds slack off, nor why the El Niño system eventually collapses," says Ackerman. "We do know that clouds play a part in El Niño and other system and we hope that the ARM program can provide information on their effects."

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Penn State. "Remote Cloud Observatory Tracks El Niño Changes." ScienceDaily. ScienceDaily, 18 December 1997. <>.
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