Sunspots not good measure of solar impact

BOULDER, Colo., Sept. 17 (UPI) -- U.S. scientists say they've found using just sunspots provides an incomplete measure of changes in the sun's impact on Earth during the 11-year solar cycle.

Researchers at the National Center for Atmospheric Research in Boulder, Colo., and the University of Michigan said Earth was bombarded last year with high levels of solar energy despite the sun being in an unusually quiet phase and sunspots virtually non-existent.

"The sun continues to surprise us," said Sarah Gibson of NCAR's High Altitude Observatory, the lead author of the study. "The solar wind can hit Earth like a fire hose even when there are virtually no sunspots."

The study that included University of Michigan Professor Janet Kozyra, Giuliana de Toma, Barbara Emory, Terry Onsager and Barbara Thompson appears in the Journal of Geophysical Research.