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Mark Aguilar examines a solar tracker that follows the sun as part of the Atmospheric Radiation and Cloud Station (ARCS) outdoor sensor array.

Clouds Vs. The Sun: Clearing Up The Global Climate Forecast

Atmospheric monitoring station on its way to the tropics

ALBUQUERQUE, N.M. -- Even with satellite imagery and other high-tech tools, meteorologists have a difficult time forecasting tomorrow’s weather today. How, then, can atmospheric scientists be expected to predict with any accuracy worldwide climates 10, 50, even 100 years from now?

A team of scientists from Sandia National Laboratories have spent the last several months piecing together their own small contribution to humankind’s ability to predict long-term global climate changes. In mid-May, their Sandia-integrated Atmospheric Radiation and Cloud Station (ARCS) will be shipped to the tropical western Pacific Ocean, where it will spend the next 10 years watching clouds as they drift over a remote spot on the equatorial island of Manus, Papua New Guinea.

The project is a part of the Department of Energy’s Atmospheric Radiation Measurement (ARM) Program, which is seeking to understand how sunlight and infrared radiation interact with clouds and, in particular, whether varying levels of atmospheric moisture could influence Earth’s radiative energy budget to the point of causing long-term, worldwide climate changes.

Data from the program are expected not only to help atmospheric researchers understand climate mechanisms in specific regions of the world, they also should lead to improved numerical models, called General Circulation Models (GCMs), that may one day help researchers and policy makers study the likelihood that Earth’s climate could undergo a warming effect caused by emissions of man-made greenhouse gases.

Understanding El Niño

The ARM Program’s goal is to establish groupings of atmospheric measurement stations in three primary regions of the world. Each region was selected because researchers believe weather mechanisms in the area play critical or not-yet-well-understood roles in the overall global climate picture.

The Tropical Western Pacific (TWP) region where Manus is located, for instance, is known in climate circles as the “warm pool” for its unusually warm ocean surface temperatures. The warm ocean supplies heat and moisture to the atmosphere above it, resulting in the formation of high-altitude cirrus clouds that disperse over the entire region and help regulate atmospheric temperatures. (See below: “Hot or Not? What’s Water Got to Do With It?”) In addition, the region is thought to play a critical role in the phenomenon known as El Niño-Southern Oscillation — a cyclic variability in the global climate system, marked by warming of the eastern Pacific Ocean every two-to-seven years and a southerly shift in the tropical rain belt — that is thought to have far-reaching implications for weather patterns over much of the Northern Hemisphere and perhaps the planet.

“The locale is best for understanding El Niño,” says Mark Aguilar of Sandia’s Environmental Characterization/Monitoring Systems Department, “and for helping improve our understanding of climate processes near the equator and on the open ocean.”

The Tropical Western Pacific will become the second operational ARM region when the Sandia ARCS station arrives on Manus this summer. (The US Southern Great Plains site, in south-central Kansas and north-central Oklahoma, became the first active ARM region in 1992.) In addition to the primary station on Manus, simpler ARCS stations will be installed at various other locations in the TWP region, including on the islands of Banaba and Christmas Island.

Aguilar and Sandian Mark Ivey plan to meet the ARCS equipment when it arrives on Manus in late August or early September to assist with its setup and resolve any last-minute technical difficulties. The station then will be left alone to do its job for several months at a time, with only periodic maintenance visits by local operators.

A Gigabyte A Day

Sandia was selected to do the integration work on the Manus station by Los Alamos National Laboratory, which manages the ARM Tropical Western Pacific Program Office for DOE. Aguilar says integrating the system was a challenge because most of the atmospheric monitoring equipment was fresh out of the laboratory, with instruments contributed by various research facilities in the United States and around the world. Many of the instruments were either new designs or designs modified for harsh tropical environments.

“Sandia’s job was to integrate the instrumentation into a working, semi-autonomous data-gathering station that will operate reliably for 10 years or more,” he says.

The primary component of the ARCS station is its outdoor array of sensors that measure such climate indicators as solar energy (sunlight), radiant energy emitted from the ground, cloud height and density, percentage of cloud cover, profiles of atmospheric moisture content, temperature, and wind direction and speed.

Four walk-in cargo shipping containers are outfitted with additional monitoring equipment. Unique data loggers store information until it can be transferred to tape in a nearby data van. Satellite communications equipment allows the researchers, from thousands of miles away, to monitor conditions inside the enclosures and shut down and restart the computers if necessary. A small amount of data can be transmitted to Sandia via satellite as well.

“We expect to be collecting between 400 megabytes and a gigabyte of data a day,” Aguilar says, “so most of it will have to be brought back on tape.”

A utility van provides power distribution and a backup generator that can keep the computers running for three hours in case of a power-grid failure. “The system is designed to operate on its own without a lot of maintenance,” he says.

Putting it all together into a working system was “like putting 10 pounds of stuff into a five-pound bag,” he adds.

Prototype For Alaskan Site

Eventually, each ARM site will provide intensive data about climate indicators in a particular region of the world. Researchers hope to use this data in their quest to develop GCMs that divide Earth’s atmosphere into a mesh comprising thousands of cells, then model climate dynamics on a worldwide scale. (Each ARM region, roughly 150 miles square, approximates the size of a cell in a typical GCM.)

Ultimately, it is hoped such models will allow humans to predict with some accuracy the long-term consequences of atmospheric changes, such as increasing levels of carbon dioxide and other man-made greenhouse gases, and aid decision makers in developing appropriate policies to deal with likely climate scenarios.

The Manus station also will serve as the prototype for later ARCS stations to be deployed at other ARM locales in coming years. Sandia is managing the next stage in the ARM program that will establish an ARCS station on the North Slope of Alaska, an area that interests climatologists because of its snow and ice cover, which is thought to reflect as much as 80 percent of the sun’s energy back into space.

“The global atmosphere is a highly complicated system to try to model,” says Bernie Zak, ARM Site Program Manager for the North Slope of Alaska/Adjacent Arctic Ocean region. “We want to determine how a snow- and ice-covered surface is influenced by warming, how it influences warming, whether melt caused by warming would result in increased cloud cover, and what the radiative influences of the area’s low-altitude ice clouds might be.”

Hot Or Not? What's Water Got To Do With It?

Scientists have long suspected that the addition of carbon dioxide and other man-made “greenhouse gases” into the atmosphere may cause a long-term warming of Earth’s atmosphere. But naturally occurring atmospheric moisture may prove to be a far more significant player on the global climate stage than all the greenhouse gases combined.

Because greenhouse gases are thought to slightly warm the atmosphere by absorbing heat in the form of infrared radiation from Earth’s surface, and because a warmer atmosphere can hold more water vapor, scientists suspect a feedback effect may occur — that increased water vapor in a warmer atmosphere might amplify the warming effect of an incremental increase of other greenhouse gases.

Water vapor is not, however, the only form of water in the atmosphere. It is present as a solid and a liquid in clouds, and the effects of clouds are thought to be a major factor in determining the potential for long-term climate change. Clouds themselves can reflect incoming sunlight and therefore contribute to cooling, but they can also absorb and retransmit infrared radiation leaving Earth and contribute to warming. High cirrus clouds, for instance, may help warm the atmosphere. Low-lying stratus clouds, which are frequently found over oceans, can contribute to cooling.

As part of the international effort to understand global climate change, DOE’s Atmospheric Radiation Measurement Program seeks both to describe the effects of clouds and moisture on the current climate and predict the complex chain of events that might influence the distribution and properties of clouds in an altered climate.

Chris Miller,

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Last modified: June 12, 2001

Sandia National Laboratories is operated by Lockheed Martin Corp. for the U.S. Department of Energy.