ARRL

ARRL Satellite Bulletin ARLS004 (2009)

SB SPACE @ ARL $ARLS004
ARLS004 NASA Releases New Predictions for Solar Cycle 24

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Space Bulletin 004  ARLS004
From ARRL Headquarters  
Newington, CT  June 2, 2009
To all radio amateurs

SB SPACE ARL ARLS004
ARLS004 NASA Releases New Predictions for Solar Cycle 24

An international panel of experts -- led by the National Oceanic and
Atmospheric Administration (NOAA) and sponsored by NASA -- has
released a new prediction for the next solar cycle: Solar Cycle 24
will peak in May 2013 with a below-average number of sunspots. "If
our prediction is correct, Solar Cycle 24 will have a peak sunspot
number of 90, the lowest of any cycle since 1928 when Solar Cycle 16
peaked at 78," said panel chairman Doug Biesecker of NOAA's Space
Weather Prediction Center (SWPC). This report clarifies a NOAA
report from earlier this month that stated that Solar Cycle 24 would
bring "90 sunspots per day on average."

The latest forecast revises an earlier prediction issued in 2007. At
that time, a sharply divided panel believed solar minimum would come
in March 2008 followed by either a strong solar maximum in 2011, or
a weak solar maximum in 2012. "It turns out that none of our models
were totally correct," said Dean Pesnell of the Goddard Space Flight
Center (GSFC) and NASA's lead representative on the panel. "The Sun
is behaving in an unexpected and very interesting way."

In 2007, experts varied in their predictions on when the solar cycle
would peak and how strong it would be. In April of that year, NOAA,
in coordination with an international panel of solar experts,
predicted that the next 11-year cycle of solar storms "would start
in March 2008, plus or minus six months, and peak in late 2011 or
mid-2012." In the cycle forecast issued in April 2007, half of the
panel predicted a "moderately strong cycle of 140 sunspots, plus or
minus 20, expected to peak in October 2011. The other half predicted
a moderately weak cycle of 90 sunspots, plus or minus 10, peaking in
August 2012. An average solar cycle ranges from 75 to 155 sunspots.
The late decline of Cycle 23 has helped shift the panel away from
its earlier leaning toward a strong Cycle 24. The group is evenly
split between a strong and a weak cycle."

At a meeting of the American Geophysical Union in San Francisco in
December 2007, David Hathaway of NASA's Marshall Space Flight
Center, along with colleague Robert Wilson, said that Solar Cycle 24
"looks like it's going to be one of the most intense cycles since
record-keeping began almost 400 years ago." They said they believe
the next solar maximum should peak around 2010 with a sunspot number
of 160, plus or minus 25. "This would make it one of the strongest
solar cycles of the past 50 years -- which is to say, one of the
strongest in recorded history." Four of the five biggest cycles on
record have come in the past 50 years. "Cycle 24 should fit right
into that pattern," Hathaway said.

Right now -- June 2009 -- the solar cycle is in a valley, the
deepest of the past century. In 2008 and 2009, the Sun showed some
of the lowest sunspot counts on record, as well as weak solar winds
and a low solar irradiance, going more than two years without a
significant solar flare. "In our professional careers, we've never
seen anything quite like it," Pesnell said. "Solar minimum has
lasted far beyond the date we predicted in 2007."

In recent months, however, Pesnell said that the Sun has begun to
show some small signs of life: Small sunspots and "proto-sunspots"
are popping up with increasing frequency. Enormous currents of
plasma on the Sun's surface are gaining strength and slowly drifting
toward its equator. Radio astronomers have detected a tiny but
significant uptick in solar radio emissions. All these things are
precursors of an awakening Solar Cycle 24 and form the basis for the
panel's new, almost unanimous forecast.

Pesnell cautioned optimism, telling the ARRL that there is an "error
bar of +/- 20." This means Solar Cycle 24's sunspot number could be
as high as 110, or as low as 70. "Based upon my own personal
research, I don't think we'll see 90 [sunspots in Solar Cycle 24],"
he said.

When asked if such a low number foretold the beginnings of a Maunder
Minimum, Pesnell said that a Maunder Minimum takes several cycles to
appear: "Sunspots [in solar cycles] leading up to the Maunder
Minimum took several cycles to disappear. I really can't predict
what will happen in Solar Cycle 25. What we're seeing now is
something that look likes a sunspot, but it looks as if someone has
come along and 'stomped' on it, creating a multitude of little
things. We don't have a name for this and we've never seen anything
like it before."

There could be more surprises, panelists acknowledge -- and more
revisions to the forecast. "Go ahead and mark your calendar for May
2013," Pesnell said. "But use a pencil."
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