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Rivers Under the Sun
29 August 1997 9:00 pm
WASHINGTON, D.C.--"Rivers" of solar material are flowing beneath the surface of the sun, researchers announced yesterday at a NASA press conference. Data from the Solar and Heliospheric Observatory (SOHO) spacecraft has revealed doughnut-shaped zones of relatively rapid flow near the solar north and south poles.
The results came from SOHO's Michelson Doppler Imager (MDI), one of 12 instruments on board the European Space Agency craft, which watches the sun continuously from a vantage point more than 1.5 million kilometers sunward of Earth. "We would never have seen [the subsurface flows]" from ground based observations, says Douglas Gough, a University of Cambridge astrophysicist. The MDI makes sensitive measurements of the undulations on the sun's surface at about 700,000 points at once. This wiggling shows where acoustic waves traveling through the sun emerge at its surface, and their frequencies and patterns tell the researchers about conditions in the subsurface regions that the waves have passed through.
These rivers are about 30,000 kilometers across and 40,000 kilometers below the surface, and they carry material around the sun at nearly 200 kilometers per hour, some 10% faster than the surrounding material moves. Gough had no explanation for these unexpected features but thinks they might be similar to Earth's jet streams--narrow, high-speed air flows that encircle the globe, high in our atmosphere
Other SOHO findings reported at the conference reinforced the metaphor. The scientists described broader, slower bands of gas flow at the surface, which they compared to the trade winds on Earth. Astronomer Jack Harvey of the National Solar Observatory in Tucson, Arizona says these features had been glimpsed from Earth, but the SOHO data confirm "that the surface effect actually does go deeper into the sun; it's not some skin effect." That makes it more likely the bands are related to the puzzling 11-year cycle of solar magnetic activity, which sometimes affects communications and power grids on Earth and is thought to be driven by events below the surface.
Says Gough, "We're getting these fantastic measurements, and if things [go] the way they went with terrestrial meteorology, this is going to enable us to have a much deeper understanding of the dynamics of the sun and is going to hail what I believe will be a new era of solar meteorology."