Old Solar Cycle Returns
03.28.2008

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*March 28, 2008:* Solar Cycle 23, how can we miss you if you won't go away?

Barely three months after forecasters announced the beginning of new Solar
Cycle 24, old Solar Cycle 23 has returned. (Actually, it never left. Read
on.)

"This week, three big sunspots appeared and they are all old cycle spots,"
says NASA solar physicist David Hathaway. "We know this because of their
magnetic polarity." On March 28th the Solar and Heliospheric Observatory
(SOHO) made this magnetic map of the sun:

[image: A magnetic map of the sun]

It shows the north and south magnetic poles of the three sunspots. All are
oriented according to the patterns of Solar Cycle 23. Cycle 24 spots would
be reversed.

What's going on? Hathaway explains: "We have two solar cycles in progress at
the same time. Solar Cycle 24 has begun (the first new-cycle spot appeared
in January 2008), but Solar Cycle 23 has not ended."

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Strange as it sounds, this is perfectly normal. Around the time of solar
minimum--*i.e.*, now--old-cycle spots and new-cycle spots frequently
intermingle. Eventually Cycle 23 will fade to zero, giving way in full to
Solar Cycle 24, but not yet.

Meanwhile, on March 25th, sunspot 989, the smallest of the three sunspots,
unleashed an M2-class solar flare. Flares are measured on a "Richter scale"
ranging from A-class (puny) to X-class (powerful). M-class flares are of
medium intensity. This one hurled a coronal mass ejection or "CME" into
space
(movie<http://science.nasa.gov/headlines/y2008/images/oldcycle/cme_c3_med.gif>),
but the billion-ton cloud missed Earth.

While the CME was still plowing through the sun's atmosphere, amateur radio
astronomer Thomas Ashcraft heard "a heaving sound" coming from the
loudspeaker of his 21 MHz shortwave receiver in New Mexico:
listen<http://science.nasa.gov/headlines/y2008/images/oldcycle/s20080325_1855ut_\
TypeII_Ashcraft.mp3>.
It was a Type II solar radio burst generated by shock waves at the leading
edge of the CME. A thousand miles away in Virginia, David Thomas recorded
the same emissions on a chart recorder he connected to his 20 MHz ham rig:
look<http://spaceweather.com/submissions/large_image_popup.php?image_name=David-\
Thomas-080325182456_1206534597.jpg>.
"What a pleasant surprise," says Thomas.

[image: see
caption]<http://science.nasa.gov/headlines/y2008/images/oldcycle/ssn_predict_l.g\
if>

*Above:* Sunspot counts vs. year: 2008 is a low point in the solar cycle.
Smoothed curves are predictions of future activity.
[More<http://solarscience.msfc.nasa.gov/predict.shtml>
]

We could get more of this kind of activity in the next 7 to 10 days. It will
take about that long for the sunspots to cross the face of the sun. The
sun's rotation is turning the spots toward Earth, which means the next CME,
if there is one, might not miss. CME strikes do no physical harm to Earth
but they can cause Northern Lights, satellite glitches and, in extreme
cases, power outages.

The real significance of these spots is what they say about the solar cycle,
says Hathaway. "Solar Cycle 24 has begun, but we won't be through solar
minimum until the number of Cycle 24 spots rises above the declining number
of Cycle 23 spots." Based on this latest spate of "old" activity, he thinks
the next Solar Max probably won't arrive until 2012.

Stay tuned to Science@NASA for solar cycle updates.


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