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Forecasters Design Better Ways To Track Space Weather

Solar storms have the potential to knock out satellites used for relaying everything from conference calls to sitcoms.

As the millennium approaches, a day at the office is bound to get more interesting for Mike Schmeiser and his co-workers at the Space Environment Center in Boulder, Colo.

It's the job of the SEC scientists to track solar storms and sound the alarm when outbursts of charged particles from the sun travel earthward.

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Those outbursts can damage or destroy satellites, disrupt electric-utility grids and communications, and represent a threat to astronauts, who will begin building the International Space Station later this year. Solar storms are expected to grow more frequent as the sun begins its climb toward the peak of its 11-year storm cycle, expected between 1999 and 2001.

Typically, the space weather forecasters in Boulder tap a network of telescopes, radar, and satellites to watch the sun and the flow of charged particles, or solar wind, it constantly sheds. This week, however, Mr. Schmeiser will begin hearing from a new sentinel orbiting a point 900,000 miles sunward from Earth.

Measurements get a boost

Known as the Advanced Composition Explorer, the spacecraft will send forecasters measurements of the solar wind as they are taken, 21 hours a day. In addition to its basic-research chores, ACE will be able to give about an hour's warning of an outburst's arrival. The craft's data will allow forecasters to more accurately estimate how much punch a solar storm will deliver when the particles hit Earth's magnetic field.

Up to now, commercial satellite operators or electric utilities have tended to take the SEC's space-weather warnings "under advisement," Schmeiser says. "ACE will definitely drive up the credibility of our forecasts."

ACE is the latest in a series of spacecraft designed to study the sun and track its influence on the region around Earth. More are under construction. Meanwhile, scientists are designing and refining complex computer programs that simulate space weather.

The effort to improve forecasts of solar storms and their effects is driven by a growing dependence on satellites for everything from long-distance phone calls and weekly visits with "Seinfeld" to finding directions in the woods.

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Yet for all their high-tech wizardry, satellites are vulnerable to a variety of sun-made mishaps, which can occur even during the sun's quiet periods. Last January, for example, a satellite carrying programming from ABC, PBS, and Fox fell silent following a solar storm.

Ordinarily, satellites are sheltered by Earth's magnetosphere, the region around the planet influenced by Earth's magnetic field. On the daylight side, the magnetosphere extends out to about 10 times the radius of the earth. On the night side, it stretches millions of kilometers in a comet-like tail stretched by the solar wind.

When a burst of highly energized particles erupts from the sun's surface and blows past Earth, it squeezes the sunward side of the magnetosphere, pushing its boundary below the altitude where many of the most valuable satellites orbit, exposing them to the full fury of the storm.

Life doesn't get much easier on the night side. Satellites swing back into the interior of the magnetosphere, which traps vast quantities of charged particles. When solar storms send a burst of charged particles, they carry a magnetic field. Under the right conditions, the solar wind's magnetic field couples strongly with that of Earth, pumping more energy and particles into the soup already present.

If the particles are electrons, they can accumulate on the surface of a spacecraft until "the charge gets so high it generates a lightning strike between parts," says Ernest Hildner, director of the SEC. Heavier protons will penetrate the craft, building excessive charges that lead to electrical discharges within cables and other circuits, damaging crystals used in circuits, or even changing data "bits" in computer chips.

Radio communications affected

Solar storms also can cause instabilities in the ionosphere, a high-altitude region of the atmosphere that plays a key role in radio communications. The instabilities cause scintillations in signals to and from satellites. If radio transmitters operate at low frequencies or are powerful enough, Dr. Hildner explains, they can beat the "twinkle" problem. But for satellites relaying digital data using high-speed modems, or for hand-held satellite cell phones, whose signals whisper with 1/60th or less the power of a standard household light bulb, scintillations can mean lost data and frustrated phone calls.

For all the progress scientists have made in forecasting, thorny problems remain to be solved. For example, researchers don't know what triggers the most disruptive solar events, known as coronal mass ejections. "We're making progress. We known what they look like, but we really don't understand how these are created," says David McComas, a space scientist at the Los Alamos (N.M.) National Laboratory.

Closer to home, key details of the magnetosphere's response to solar storms are lacking. To help fill in those details, Dr. McComas is heading a team building a pair of satellites to launch in 2002 that will allow him to build 3-D movies of the storms' impact on the magnetosphere. The $18 million project could help move space-weather forecasting from broad outlooks based on statistical averages to more specific forecasts based on the processes that drive space weather.