## Solar Activity Report explanations

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• Maybe it would be a good idea if I explained some of the things I post! So, here is an ecplanation of some of the things you might see in my reports. NOAA
Message 1 of 1 , Sep 12, 2002
Maybe it would be a good idea if I explained some of the things I
post! So, here is an ecplanation of some of the things you might see
in my reports.

NOAA sunspot number - This is a number that is calculated from the
number of sunspots and the area they cover. Basically, its a measure
of how many sunspots there are and how big they are.

SFI (Solar Flux Index) - This is a measure of the sun's output on the
10.7 cm radio band. This wavelength is important because it is used
as a surrogate for the solar output in wavelengths that charge up the
Earth's ionosphere. The SFI is a good indicator of overall solar
activity. The higher the SFI, the more active things are. It usually
correlated with the sunspot number. When the sunspot number goes up,
the SFI will, too.

A index : A measure of geomagnetic activity over a 24 hour period. It
can run from 0 to 400.

K index : The same thing as the A index, but measured over a 3 hour
period. It can run from 0 to 10.

Solar wind speed and density - Pretty self explanatory. These and the
solar wind pressure measurements are taken by the Advanced Composition
Explored (ACE) satellite.

Solar wind pressure - Physical pressure exerted by the solar wind. It
is measured in nano-pascals (nPa)

Interplanetary Magnetic Field (IMF) - The interplanetary magnetic
field (IMF) comes from the sun's magnetic field, and is carried by the
solar wind. Therefore, the solar wind has a magnetic field associated
with it. The IMF is measured in nT (nano-telsas). It isn't very
strong. It usually runs at 15 nT or less. In contrast, Earth's
magnetic field is around 40,000 nT. The IMF can either be north or
south pointing. A south pointing IMF is pointing opposite from the
flow of Earth's magnetic field flow. The result is that a
south-pointing IMF will interfere with and weaken Earth's magnetic
field. When Earth's magnetic field gets weakened, its renders the
Earth more prone to the solar wind gusts, and geomagnetic storms (and
aurora) can be the result.

Geomagnetic storm - A major disturbance in Earth's magnetosphere.
They can range from G-1 to G-5.
http://www.sec.noaa.gov/NOAAscales/#GeomagneticStorms

Solar radiation storm - Basically this is what happens when the Earth
gets hit by a barrage of protons from the sun. They can range from
S-1 to S-5. Very strong solar radiation storms can be dangerous to
astronauts in orbit, and can expose people in high-flying airplanes to

Coronal Mass Ejection (CME) - This is a blast of a billion tons or
more of white-hot plasma from the sun's carona. They are often
associated with solar flares, but they don't have to be. They can
trigger solar radiation storms and geomagnetic storms if they hit Earth.

Full Halo CME - A CME that is coming directly at us, or directly away
from us. In the satellite images, it looks like a giant smoke ring,
or halo.

Solar Flare - A sudden and explosive release of magnetic energy.
Makes a nuclear warhead liike like a firecracker. They can release a
massive proton barrage that can make the trip from the sun to here in
less than 15 minutes. They can also cause CME's. They are quantified
by their X-ray flux as measured by the Goes 8 satellite. They are
classified as C, M, or X (weakest to strongest), with numeric
divisions within each letter category. Ex : M1.5, X2.0, etc.
Anything M1.0 or above is classified as a significant flare.

Coronal Hole : This is where the sun's magnetic field lines open up.
The high speed solar wind is known to originate from these. In
ultaviolet imagery, it looks like a big dark spot on the sun.
http://www.spaceweather.com/images2002/10sep02/coronalhole_soho.gif

Well, I think that's about it! I should add that that geomagnetic
science is a field of study in itself, and books have been written on
the subject. I'm far from an expert! I'll be glad to try, however,
to answer any questions anybody may have.
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