The surface of the sun is covered with transient storms, high and low pressure zones and swirling wind flows that vary from day to day like weather patterns on Earth's surface, according to new results by University of Colorado at Boulder researchers using the Solar and Heliospheric Observatory, or SOHO.
The results are being presented at the spring American Astronomical Society meeting held in Albuquerque, N.M., June 2 to June 6. SOHO is a joint satellite mission between NASA and the European Space Agency.
The results include the first large-scale weather maps of wind patterns evolving daily across the entire visible solar surface, said the researchers. The results also may overturn a longstanding theory of solar activity.
"For the first time, we can see large-scale weather systems developing on the surface of a star," said CU-Boulder researcher Deborah Haber. "That is important because the sun's surface weather patterns steer larger effects like the sun's rapidly changing magnetic field, the mysterious 1 million-degree corona and the violent interplanetary storms that arise from solar coronal mass ejections."
The new weather maps show flow patterns and jet streams twisting through the background turbulence, with typical speeds of up to 100 mph, she said. They also show "storm systems" with spinning flow similar to terrestrial hurricanes, but large enough to swallow Jupiter, forming and dissipating in less than three weeks.
In addition, the maps show a startling global weather pattern on the sun. A steady 45-mph "breeze" flows from the equator to the poles at the sun's surface, extending downward to depths of at least 15,000 km -- about the diameter of Earth.
The new weather maps reveal that in the sun's northern hemisphere the northward breeze stopped and reversed direction in 1998 and has retained the new direction since that time. "We are seeing a global weather shift on the sun like the El Ni帽o pattern here on Earth," said Haber.
CU-Boulder paper authors Haber, Brad Hindman and Juri Toomre also are members of JILA, a joint institute of CU-Boulder and the National Institute of Standards and Technology laboratory in Boulder.
The reversed flow is especially important because steady, "poleward" breezes play a crucial role in generating the solar magnetic field, said Haber, the paper聮s chief author. The reversed flow also helps cause the mysterious solar cycle that reverses the magnetic field every 11 years and gives rise to sunspots and space weather.
"Steady flows toward the poles are thought to disperse and transport the strong magnetic fields from sunspots to the poles, where they reverse the existing field every 11 years," said Alexander Kosovichev, a solar researcher at Stanford University. "The reversal of this flow is puzzling, and has important implications for our understanding of the solar activity cycle."
The research team created the maps from data produced by the Michelson Doppler Imager, or MDI, telescope aboard SOHO using a computationally efficient technique called "ring-diagram analysis." The technique measures the speed and direction of sound waves of different frequencies at many different locations on the sun to build a 3-D image of structures just under the sun聮s surface. Ring-diagram analysis is part of the growing field of helioseismology, or seismology of the sun.
"We observe ripples on the surface of the sun and measure how their speed varies in different directions," said Hindman. "Ripples traveling with the local wind move faster than ripples going against the wind, so we can tell the direction and speed that the material is moving."
Unlike ripples on a pond, the motions observed by MDI are caused by very deep solar sound waves with periods of 5 minutes -- about 14 octaves below the range of human hearing.
Other techniques such as "time-distance helioseismology" and "sonic holography" are used to identify detailed structures in individual regions of the sun. But ring-diagram analysis complements them because it is more computationally efficient and allows large areas of the sun to be mapped rapidly, said Hindman.
For downloadable maps of solar magnetic fields, wind flows and surface ripples, go to the Web site link: .