Washington Post/Philadelphia Inquirer

Health & Science

Monday, September 8, 1997

Suddenly, the job of forecasting weather on the sun has become interesting. New instruments have revealed huge ``trade winds,'' fiery currents and storms not visible on the surface.

By Curt Suplee

You might think that the weather forecast for the surface of the sun would be a pretty dreary affair: Hot and dry. High 10,000 degrees. Outlook: continued sunny with intermittent spots and flares for the next 4 billion years.

But recently scientists have learned that our local star is beset by its own kind of incendiary tempests, seasonal squalls and rogue currents of fire. And now new instruments that can peer beneath the outer luminous layers have revealed an utterly unexpected meteorological feature in the form of titanic ``jet streams'' of electrically charged gases that circle the poles, churning the atmosphere where it was thought to be most calm.

They also detected several mysterious ``trade wind'' bands of high-speed plasma 40,000 miles wide that ring the solar perimeter like the belts on Jupiter, as well as a global pattern of upper-level current flow north and south from the equator. Many of these effects, said Jesper Schou of Stanford University, exhibit ``motion similar to weather patterns in the Earth's atmosphere.''

The findings, reported by Schou, Craig DeForest and other Stanford researchers using the Solar and Heliospheric Observatory (SOHO) spacecraft ``herald a new era of solar meteorology,'' said Douglas Gough of Cambridge University in England.

Researchers are hoping that the SOHO data will help explain such persistent enigmas as the origin and life cycle of sunspots, which influence the torrents of solar emissions that blast toward Earth, deranging radio communications.

``One of our ultimate goals,'' said John W. Harvey of the ground-based National Solar Observatory in Tucson, ``is to learn enough about the sun to predict activity'' accurately enough to warn earthlings days in advance that a solar storm is on the way. ``Any sort of insight,'' DeForest said, ``could give us more lead time.''

But in the short term, most solar scientists will settle for anything that makes clearer the nature of our familiar, but often inscrutable, star.

The sun, 98 percent of which is hydrogen and helium, is a perfectly ordinary middle-aged representative of the 100 billion stars in our galaxy. It can thus serve as ``a Rosetta stone'' for understanding others large and small, said George Withbroe of NASA's solar-research program.

But first scientists need to understand its baffling quirks.

To that end, NASA and the European Space Agency launched SOHO in December 1995. The two-ton, 12-by-12-foot spacecraft, positioned 930,000 miles sunward from Earth, carries many instruments, some of which detect regional speed differences in sound-wave pulses that propagate through the solar gases. Such regions reveal their locations and relative velocities via the Doppler effect: Waves moving toward an observer appear closer together (that is, seem to have higher frequency and shorter wavelength); those moving away appear just the opposite.

That's how the Stanford group found the polar jet stream (invisible on the surface) and the fast-track horizontal bands. The bands' existence had been postulated in the 1980s, but the new data show they extend at least 12,000 miles deep.

Scientists also had long suspected that there was a general flow in both hemispheres from the equator to the poles. SOHO confirmed that the upper layer of the solar surface (down to a depth of at least 15,000 miles) drifts poleward at 50 m.p.h. At that speed, it takes about a year to make the trip. Apparently when it reaches the higher latitudes, it descends and ``we assume that the flows will return at some depth,'' Schou said, ``though we haven't observed that yet.''

That means surface currents are heading toward the poles at the same time that sunspot clusters are moving toward the equator. According to present theory, those seemingly contradictory events are possible because the big magnetic kinks that cause sunspots are thought to originate at the bottommost boundary of the convection layer, where currents are probably flowing toward the equator.

``Do we really understand'' all the patterns? Gough asked. ``The answer is no. But we will. That is the faith of the scientist.''

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Health & Science -- Copyright Monday, September 8, 1997