cycle on record
Hot gas flows cause sunspot lows
By Ron Cowen
Ne wly reported observations of gas flows
on the solar surface may explain why the
sun recently had such an extended case
of the doldrums.
From 2008 through the first half of
2009, the sun had a puzzling lack of sunspots, flares and other storms, extending
the usual lull at the end of the 11-year solar
activity cycle for an extra 15 months. Data
from the orbiting Solar and Heliospheric
Observatory, or SOHO, indicate that gas
flow affecting magnetic fields near the
sun’s poles may have been responsible for
the extended quiet. The findings also suggest a better way to forecast the intensity
and duration of future solar cycles.
Scientists want to improve predic-
tions because some solar outbursts can
blast Earth with massive, magnetized
clouds of charged particles capable of
knocking out electrical power grids and
cycle on record
The latest period of minimal solar activity
lasted longer than expected; data from
the SOHO spacecraft may explain why.
onal flow typically oppose much stronger flows of magnetized material on the
surface, Hathaway says. The faster the
meridional flow, the greater the opposition to other flows. As a result, the sun’s
polar magnetic field can’t become as
strong, the researchers propose.
“It is possible that the delayed start
of the present cycle, 2009 to 2010, was
caused by the relatively weak polar field
in 2007 to 2009,” comments Neil Sheeley
of the Naval Research Laboratory in
Polar magnetic field strength plays
a crucial role in the onset of each solar
cycle, Hathaway notes. These fields dive
beneath the solar surface, building up
deep sunspot-generating magnetic fields
that signal the start of the next cycle.
Weaker polar fields take more time to
reach the strength required to produce
sunspots, prolonging the lull in activity
from the previous cycle. And weaker-than-usual polar fields are likely to produce less activity during the next solar
cycle, Hathaway and Rightmire predict.
“The fact that the meridional flow plays
a key role in setting up the sun’s polar
fields for the next cycle suggests that
future observations will help us predict”
the duration and intensity of upcoming
cycles, Hathaway says.
Other models suggesting that a fast
meridional flow leads to strong polar
field and a shorter solar minimum may
now need to be revised, he says.
FROM TOP: NASA; G. NeukuM/Fu BeRliN, eSA, DlR