Washington, September 18 A new study has found that Earth was bombarded last year with high levels of solar energy at a time when the Sun was in an unusually quiet phase and sunspots had virtually disappeared.
The study was led by scientists at National Center for Atmospheric Research (NCAR) and the University of Michigan, Ann Arbor, in cooperation with scientists at NOAA and NASA.
"The Sun continues to surprise us," said lead author Sarah Gibson of the NCAR. "The solar wind can hit Earth like a fire hose even when there are virtually no sunspots," she added.
Scientists for centuries have used the number of sunspots, which are dark patches of concentrated magnetic fields on the solar surface, to determine the approximately 11-year solar cycle.
At solar maximum, the number of sunspots peaks.
During this time, intense solar flares occur daily and geomagnetic storms frequently buffet Earth, knocking out satellites and disrupting communications networks.
Gibson and her colleagues focused instead on another process by which the Sun discharges energy.
The team analyzed high-speed streams within the solar wind that carry turbulent magnetic fields out into the solar system.
When those streams blow by Earth, they intensify the energy of the planet's outer radiation belt.
This can create serious hazards for weather, navigation, and communications satellites that travel at high altitudes within the outer radiation belts, while also threatening astronauts in the International Space Station (ISS).
For the new study, the scientists analyzed information gathered from an array of space- and ground-based instruments during two international scientific projects: the Whole Sun Month in the late summer of 1996 and the Whole Heliosphere Interval in the early spring of 2008.
The solar cycle was at a minimal stage during both the study periods, with few sunspots in 1996 and even fewer in 2008.
The team found that strong, long, and recurring high-speed streams of charged particles buffeted Earth in 2008.
In contrast, Earth encountered weaker and more sporadic streams in 1996. As a result, the planet was more affected by the Sun in 2008 than in 1996.s sunspots became less common over the last few years, large coronal holes lingered in the surface of the Sun near its equator.
The high-speed streams that blow out of those holes engulfed Earth during 55 percent of the study period in 2008, compared to 31 percent of the study period in 1996. (ANI)
