Clues to “;space weather”;—produced by energetic solar particles that pummel Earth—are under study by Hawaii scientists using orbiting observatories.

The newest is NASA's Solar Dynamics Observatory, launched Feb. 11, which occupies a geosynchronous orbit that allows it to continuously monitor the sun as it is wracked by magnetic storms.

It should achieve greater accuracy than SOHO, the Solar Heliospheric Observatory satellite launched by NASA with the European Space Agency on Dec. 2, 1995, said University of Hawaii solar astronomer Jeff Kuhn.

Astronomers want to know how the sun's magnetic energy is converted and released into space in the form of the solar “;wind”; and how that relates to changes on the solar surface and the 11-year solar cycle.

“;The mystery is, Why does the sun change in time?”; said Kuhn, associate director of the UH Institute for Astronomy, which operates the Haleakala solar observatories on Maui. “;Can we use observations of the surface of the sun to infer what the change is?”;

When the sun's particles hit Earth's magnetic field, they result in such stunning phenomena as auroras but also can disrupt satellite electronics and aircraft navigation and communications.

Kuhn is participating in a worldwide effort to understand the sun's effects on Earth's climate. “;We can't predict the climate on Earth until we understand these changes on the sun,”; he said in an interview.

The sun's recent 11-year cycle “;was an interesting time period to do this,”; he said, explaining his group “;got 11 years of good data from an instrument that really was designed for other things.”;

He and his collaborators—Rock Bush of Stanford University, Marcelo Emilio of Brazil, a former postdoctoral researcher in the UH Institute for Astronomy, and Isabelle Scholl of the IFA—monitored the sun with the Michelson Doppler Imager on SOHO.

Their intriguing finding: The sun's diameter has changed by less than one part in a million over the last 12 years despite its turbulent activity.

“;This constancy is baffling, given the violence of the changes we see every day on the sun's surface and the fluctuations that take place over an 11-year solar cycle,”; said Kuhn.

The Solar Dynamics Observatory has a successor to the SOHO image that should provide “;another factor of 10 improvement,”; he said.

“;We're learning how to use that instrument to do even more sensitive measurements, so we know when we find these tiny changes in the shape of the sun, we will be able to infer something about what causes this solar cycle.”;

Even more definitive answers are anticipated with the proposed Advanced Technology Solar Telescope, scheduled for completion on Haleakala in 2017, in combination with the space observatories, Kuhn said.

“;The ATST gives us a microscopic view of what goes on,”; he said. It has been described as a solar “;magnetometer,”; designed to allow precise measurements of the solar magnetic field.

“;With the ATST we will finally have a tool that can measure the magnetism that we believe controls solar fluctuations,”; Kuhn said earlier.

“;To be able to predict what the sun will do, we need both the big picture and the details. Just as powerful hurricanes on Earth start as a gentle breeze, the analogs of terrestrial storms on the sun start as small kinks in the sun's magnetic field.”;