National Solar
Observatory
What's Down with
the Sun? Major Drop in Solar Activity Predicted
|
|
THE FOLLOWING RELEASE WAS
RECEIVED JOINTLY FROM THE NATIONAL SOLAR OBSERVATORY IN SUNSPOT, NEW
MEXICO, AND THE SOLAR PHYSICS DIVISION OF THE AMERICAN ASTRONOMICAL
SOCIETY AND IS FORWARDED FOR YOUR INFORMATION (FORWARDING DOES NOT IMPLY
ENDORSEMENT BY THE AMERICAN ASTRONOMICAL SOCIETY). Rick Fienberg, AAS
Press Officer: rick.fienberg@aas.org, +1 202-328-2010 x116.
** This release was
previously distributed to journalists under an embargo that has since
expired. {RTF} **
June 14, 2011
Contacts:
Dave Dooling
NSO Education and Public Outreach
+1 575-434-7015 (office); +1 575-921-8736 (cell)
dooling@nso.edu
Craig DeForest
AAS/SPD Press Officer
+1 303-641-5679 (cell)
deforest@boulder.swri.edu
Text & Images:
http://www.boulder.swri.edu/~deforest/SPD-sunspot-release
WHAT'S DOWN WITH THE SUN?
MAJOR DROP IN SOLAR ACTIVITY PREDICTED
A missing jet stream,
fading spots, and slower activity near the poles say that our Sun is
heading for a rest period even as it is acting up for the first time in
years, according to scientists at the National Solar Observatory (NSO) and
the Air Force Research Laboratory (AFRL).
As the current sunspot
cycle, Cycle 24, begins to ramp up toward maximum, independent studies of
the solar interior, visible surface, and the corona indicate that the next
11-year solar sunspot cycle, Cycle 25, will be greatly reduced or may not
happen at all.
The results were announced
at the annual meeting of the Solar Physics Division of the American
Astronomical Society, which is being held this week at New Mexico State
University in Las Cruces:
http://astronomy.nmsu.edu/SPD2011/
"This is highly unusual and
unexpected," Dr. Frank Hill, associate director of the NSO's Solar
Synoptic Network, said of the results. "But the fact that three completely
different views of the Sun point in the same direction is a powerful
indicator that the sunspot cycle may be going into hibernation."
Spot numbers and other
solar activity rise and fall about every 11 years, which is half of the
Sun's 22-year magnetic interval since the Sun's magnetic poles reverse
with each cycle. An immediate question is whether this slowdown presages a
second Maunder Minimum, a 70-year period with virtually no sunspots during
1645-1715.
Hill is the lead author on
one of three papers on these results being presented this week. Using data
from the Global Oscillation Network Group (GONG) of six observing stations
around the world, the team translates surface pulsations caused by sound
reverberating through the Sun into models of the internal structure. One
of their discoveries is an east-west zonal wind flow inside the Sun,
called the torsional oscillation, which starts at mid-latitudes and
migrates towards the equator. The latitude of this wind stream matches the
new spot formation in each cycle, and successfully predicted the late
onset of the current Cycle 24.
"We expected to see the
start of the zonal flow for Cycle 25 by now," Hill explained, "but we see
no sign of it. This indicates that the start of Cycle 25 may be delayed to
2021 or 2022, or may not happen at all."
In the second paper, Matt
Penn and William Livingston see a long-term weakening trend in the
strength of sunspots, and predict that by Cycle 25 magnetic fields
erupting on the Sun will be so weak that few if any sunspots will be
formed. Spots are formed when intense magnetic flux tubes erupt from the
interior and keep cooled gas from circulating back to the interior. For
typical sunspots this magnetism has a strength of 2,500 to 3,500 gauss
(Earth's magnetic field is less than 1 gauss at the surface); the field
must reach at least 1,500 gauss to form a dark spot.
Using more than 13 years of
sunspot data collected at the McMath-Pierce Telescope at Kitt Peak in
Arizona, Penn and Livingston observed that the average field strength
declined about 50 gauss per year during Cycle 23 and now in Cycle 24. They
also observed that spot temperatures have risen exactly as expected for
such changes in the magnetic field. If the trend continues, the field
strength will drop below the 1,500 gauss threshold and spots will largely
disappear as the magnetic field is no longer strong enough to overcome
convective forces on the solar surface.
Moving outward, Richard
Altrock, manager of the Air Force's coronal research program at NSO's
Sunspot, NM, facilities has observed a slowing of the "rush to the poles,"
the rapid poleward march of magnetic activity observed in the Sun's faint
corona. Altrock used four decades of observations with NSO's 40-cm
(16-inch) coronagraphic telescope at Sunspot.
"A key thing to understand
is that those wonderful, delicate coronal features are actually powerful,
robust magnetic structures rooted in the interior of the Sun," Altrock
explained. "Changes we see in the corona reflect changes deep inside the
Sun."
Altrock used a photometer
to map iron heated to 2 million degrees C (3.6 million F). Stripped of
half of its electrons, it is easily concentrated by magnetism rising from
the Sun. In a well-known pattern, new solar activity emerges first at
about 70 degrees latitude at the start of a cycle, then towards the
equator as the cycle ages. At the same time, the new magnetic fields push
remnants of the older cycle as far as 85 degrees poleward.
"In cycles 21 through 23,
solar maximum occurred when this rush appeared at an average latitude of
76 degrees," Altrock said. "Cycle 24 started out late and slow and may not
be strong enough to create a rush to the poles, indicating we'll see a
very weak solar maximum in 2013, if at all. If the rush to the poles fails
to complete, this creates a tremendous dilemma for the theorists, as it
would mean that Cycle 23's magnetic field will not completely disappear
from the polar regions (the rush to the poles accomplishes this feat). No
one knows what the Sun will do in that case."
All three of these lines of
research to point to the familiar sunspot cycle shutting down for a while.
"If we are right," Hill
concluded, "this could be the last solar maximum we'll see for a few
decades. That would affect everything from space exploration to Earth's
climate."
In response to news
inquiries and stories, Dr. Frank Hill issued a follow-up statement:
"We are NOT predicting a
mini-ice age. We are predicting the behavior of the solar cycle. In my
opinion, it is a huge leap from that to an abrupt global cooling, since
the connections between solar activity and climate are still very poorly
understood. My understanding is that current calculations suggest only a
0.3 degree C decrease from a Maunder-like minimum, too small for an ice
age. It is unfortunate that the global warming/cooling studies have become
so politically polarizing."
|