Three studies predict that our sun is entering an unusually quiet period that could produce big changes in weather, both in space and on Earth.
The studies, announced Tuesday at a conference in Las Cruces, N.M., were all conducted by scientists affiliated with the National Solar Observatory, using telescopes on Kitt Peak near Tucson and Sacramento Peak in Sunspot, N.M., and other instruments across the globe.
They predict a weakening of the sun's magnetic field and a possible temporary disappearance of sunspots and the solar flares and mass eruptions that accompany them.
Frank Hill, associate director of the NSO's Solar Synoptic Network, said the solar cycle "may be going into hibernation."
Hill is lead author of a paper that compiles the observations of a network of data collectors known as GONG, or Global Oscillation Network Group, which operates six instruments, spaced across the globe to keep a 24-hour eye on the sun's activities.
Hill's group used helio-seismology to look beneath the sun's surface at its east-west wind flow, which moves as a band from the mid-latitudes to the equator and coincides with the formation of sunspots.
Those sunspots, in turn, presage the powerful eruptions that send additional solar radiation toward Earth.
Hill's group found a slowing in that movement that accurately predicted a late onset of current solar activity. Now, Hill said, the observations are predicting an even weaker cycle in the future, and its temporary disappearance.
Solar astronomers Bill Livingston and Matt Penn used a different type of measurement to predict decreased solar activity. They measured the magnetic strength of sunspots for 13 years, using the McMath-Pierce Telescope atop Kitt Peak.
Their data show sunspots decreasing in magnetic strength and predict their eventual disappearance. They first tried to publish their results in 2006, but the paper was rejected by reviewers. "It was controversial," said Penn, who said by telephone Tuesday that "it's nice to have company on the tree limb."
The third set of data presented this week at a conference of the solar-physics division of the American Astronomical Society used measurements of the sun's corona to document a slowing of the magnetic movement toward the poles.
That work was done by Richard Altrock, manager of the Air Force's coronal research program on Sacramento Peak in New Mexico. He said during a teleconference Tuesday that he, too, felt like a lonely voice for years.
Now, though, the "solar community" is pretty much in agreement that the sun is entering a prolonged period of reduced activity, said Tom Woods, associate director of the Laboratory for Atmospheric and Space Physics at the University of Colorado.
Five years ago, Woods said, "it was hard for the (solar physics) community to believe Bill Livingston's paper."
Woods, who was not associated with any of the studies, said the coming period of minimal activity will lower global temperatures, though its effect will be masked by human-caused heating.
Woods, who is also principal investigator for a NASA satellite that measures the Earth's total solar irradiance, said the effect of changes in that measurement are not well understood but could offset the warming currently predicted by climate scientists.
The overall difference between the peak of solar activity and its trough is believed to be about 0.5 percent.
If sunspots disappear for decades at a time, however, the effect could be greater, said Woods and Penn.
"The Earth can respond in a nonlinear way," Penn said.
In addition to heating the Earth, the sun's rays affect "the chemistry of the upper atmosphere," Penn said.
The change could increase the radiation danger in space for astronauts. An active sun blows off radiation sources from elsewhere in the galaxy.
The last time the sun entered a prolonged quiet period was the Maunder Minimum of 1645-1715, when virtually no sunspots were reported.
That loosely corresponds with historical accounts of unusually cold weather in parts of Europe.
"Whether these small tweaks can change climate - I guess we're going to find out," Penn said.
Contact reporter Tom Beal at firstname.lastname@example.org or 573-4158.