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Unprecedented
warming on earth during a solar minimum
Mystery:
Sun grows strangely quiet, lowest activity in 100 years
11
December, 2013
The
sun’s current space-weather cycle is the most anemic in 100 years,
scientists say.
Our
star is now at “solar maximum,” the peak phase of its 11-year
activity cycle. But this solar max is weak, and the overall current
cycle, known as Solar Cycle 24, conjures up comparisons to the
famously feeble Solar Cycle 14 in the early 1900s, researchers said.
“None
of us alive have ever seen such a weak cycle. So we will learn
something,” Leif Svalgaard of Stanford University told reporters
here today (Dec. 11) at the annual meeting of the American
Geophysical Union.
The
learning has already begun. For example, scientists think they know
why the solar storms that have erupted during Solar Cycle 24 have
caused relatively few problems here on Earth. The sun often blasts
huge clouds of superheated particles into space, in explosions known
as coronal mass ejections (CMEs).
Powerful CMEs that hit Earth
squarely can trigger geomagnetic storms, which in turn can disrupt
radio communications, GPS signals and power grids.
But
such effects have rarely been seen during Solar Cycle 24, even though
the total number of CMEs hasn’t dropped off much, if at all.
The
explanation, researchers said, lies in the reduced pressure currently
present in the heliosphere, the enormous bubble of charged particles
and magnetic fields that the sun puffs out around itself.
This lower
pressure has allowed CMEs to expand greatly as they cruise through
space, said Nat Gopalswamy of NASA’s Goddard Space Flight Center in
Greenbelt, Md.
Indeed, Solar Cycle 24 CMEs are, on average, 38
percent bigger than those measured during the last cycle — a
difference with real consequences for folks here on Earth.
“When
the CMEs expand more, the magnetic field inside the CMEs has lower
strength,” Gopalswamy said. “So when you have lower-strength
magnetic fields, then they cause milder geomagnetic storms.”
