ARLA/CLUSTER: Novas previsões para o Ciclo Solar

[Salomao Fresco]

Boas,

Novas previsões para o Ciclo Solar 24.
Original em:
http://science.nasa.gov/headlines/y2009/29may_noaaprediction.htm

Cumprimentos

Salomão Fresco
CT2IRJ


New Solar Cycle Prediction
  05.29.2009

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*May 29, 2009:* An international panel of experts led by NOAA and sponsored
by NASA has released a new prediction for the next solar cycle. Solar Cycle
24 will peak, they say, in May 2013 with a below-average number of sunspots.


<http://science.nasa.gov/headlines/y2009/images/noaaprediction/296969main_flare_sxilabeled_HI.jpg>"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,"
says panel chairman Doug Biesecker of the NOAA Space Weather Prediction
Center.

*Right:* A solar flare observed in Dec. 2006 by NOAA's GOES-13 satellite.

It is tempting to describe such a cycle as "weak" or "mild," but that could
give the wrong impression.

"Even a below-average cycle is capable of producing severe space weather,"
points out Biesecker. "The great geomagnetic storm of 1859, for instance,
occurred during a solar cycle of about the same size we’re predicting for
2013."

The 1859 storm--known as the "Carrington Event" after astronomer Richard
Carrington who witnessed the instigating solar flare--electrified
transmission cables, set fires in telegraph offices, and produced Northern
Lights so bright that people could read newspapers by their red and green
glow. A recent report by the National Academy of Sciences found that if a
similar storm occurred today, it could cause $1 to 2 trillion in damages to
society's high-tech infrastructure and require four to ten years for
complete recovery. For comparison, Hurricane Katrina caused "only" $80 to
125 billion in damage.

*Above: *This plot of sunspot numbers shows the measured peak of the last
solar cycle in blue and the predicted peak of the next solar cycle in red.
Credit: NOAA/Space Weather Prediction Center.
[more<http://www.swpc.noaa.gov/SolarCycle/index.html>
]

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. Competing models gave different answers, and researchers
were eager for the sun to reveal which was correct.

"It turns out that none of our models were totally correct," says Dean
Pesnell of the Goddard Space Flight Center, NASA's lead representative on
the panel. "The sun is behaving in an unexpected and very interesting way."

Researchers have known about the solar cycle since the mid-1800s. Graphs of
sunspot numbers resemble a roller coaster, going up and down with an
approximately 11-year period. At first glance, it looks like a regular
pattern, but predicting the peaks and valleys has proven troublesome. Cycles
vary in length from about 9 to 14 years. Some peaks are high, others low.
The valleys are usually brief, lasting only a couple of years, but sometimes
they stretch out much longer. In the 17th century the sun plunged into a
70-year period of spotlessness known as the Maunder Minimum that still
baffles scientists.

<http://science.nasa.gov/headlines/y2009/images/noaaprediction/maunderminimum.jpg>

*Above:* Yearly-averaged sunspot numbers from 1610 to 2008. Researchers
believe upcoming Solar Cycle 24 will be similar to the cycle that peaked in
1928, marked by a red arrow. Credit: NASA/MSFC

Right now, the solar cycle is in a valley--the deepest of the past century.
In 2008 and 2009, the sun set Space Age records for low sunspot counts, weak
solar wind, and low solar irradiance. The sun has gone more than two years
without a significant solar flare.

"In our professional careers, we've never seen anything quite like it," says
Pesnell. "Solar minimum has lasted far beyond the date we predicted in
2007."

In recent months, however, the sun has begun to show timorous signs of life.
Small sunspots and "proto-sunspots" are popping up with increasing
frequency. Enormous currents of plasma on the sun’s surface ("zonal flows")
are gaining strength and slowly drifting toward the sun’s 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.

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  According to the forecast, the sun should remain generally calm for at
least another year. From a research point of view, that's good news because
solar minimum has proven to be more interesting than anyone imagined. Low
solar activity has a profound effect on Earth’s atmosphere, allowing it to
cool and contract. Space junk accumulates in Earth orbit because there is
less aerodynamic drag. The becalmed solar wind whips up fewer magnetic
storms around Earth's poles. Cosmic rays that are normally pushed back by
solar wind instead intrude on the near-Earth environment. There are other
side-effects, too, that can be studied only so long as the sun remains
quiet.

Meanwhile, the sun pays little heed to human committees. There could be more
surprises, panelists acknowledge, and more revisions to the forecast.

"Go ahead and mark your calendar for May 2013," says Pesnell. "But use a
pencil."
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