[HCDX] Current Solar and Geomagnetic Conditions

[Tomas Hood - NW7US <nw7us@xxxxxxxxxxx>]

At the time of writing this e-mail, the Solar Wind is at 736.0 km/s
at 1.6 protons/cm3 - under typical conditions during the Solar
Cycle Maximum years, the average Solar Wind is around 400 km/s. 
So, today's speed is a lot higher than "normal."  What does this
mean?

I'll try to keep this short and sweet.

First, let me tell you a few things about the Sun.

1.  The atmosphere above the Sun's surface is called the "corona,"
under which is the chromosphere and the photosphere.  On the
photosphere exist several types of features.  Sunspots are the most
obvious.  But, using a certain type of instrument called a
coronagraph, we can see the corona.  The coronagraph is a man-made
eclipse aboard a space vehicle (satellite), that allows us to see
the pearly white crown surrounding the Sun.  Features then can be
seen, like coronal holes, solar flares, and popping bubbles called
coronal mass ejections.

Let's first talk about coronal holes.  Coronal holes are regions
where the corona is dark.  It is not a real "hole" as in a dip in
some surface.  The corona is not part of the sun's surface.  The
corona, again, is part of the sun's atmosphere (like our
troposphere, stratosphere, and so on).  These features were
discovered when X-ray telescopes were first flown above the earth's
atmosphere to reveal the structure of the corona across the solar
disc.  Coronal holes are associated with "open" magnetic field
lines and are often found at the Sun's poles.  A coronal hole
simply means an area where a break-down in the magnetic fields in
the solar corona have occurred.  It is not part of the sun "burning
out" or anything close to this.  It is a normal part of the way the
sun's corona acts.  Often, high-speed solar wind is known to
originate in coronal holes.  This escape of solar plasma and energy
streams outward away from the sun.  When this outward stream, or
solar wind, is directed toward Earth, we see an increase in the
Solar Wind speed and intensity.  More on this in a bit.

When a bubble of plasma (formed by the strong magnetic fields of
the sun) originating in the break-down of the corona (the coronal
hole)  bursts, and spews outward away from the sun the huge cloud
of plasma, we call it a "Coronal Mass Ejection."  It once was
thought that Coronal Mass Ejections were initiated by solar
flares.  Although flares accompany some CMEs, it is now known that
most CMEs are not associated with flares.  CMEs can occur at any
time during the solar cycle, but their occurrence rate increases
with increasing solar activity and peaks around solar maximum. 
Since the Sun completes a full rotation every 27 to 28 days, the
same CMEs may recur every month.  The exact processes involved in
the release of CMEs are not known, but we do know a lot about how
they affect the Earth. 

So, what is a sunspot?  Sunspots are magnetic regions on the Sun
with magnetic field strengths thousands of times stronger than the
Earth's magnetic field.  Remember, plasma flows in the magnetic
field lines of the sun.  Sunspots appear as dark spots on the
surface of the Sun.  Temperatures in the dark centers of sunspots
drop to about 3700 K (compared to 5700 K for the surrounding
photosphere).  This difference in temperatures makes the spots
appear darker than elsewhere.  Sunspots typically last for several
days, although very large ones may live for several weeks.  They
are seen to rotate around the sun, since they are on the surface,
and the sun rotates fully every 27.5 days.

Sunspots usually come in groups with two sets of spots.  One set
will have positive or north magnetic field while the other set will
have negative or south magnetic field.  The field is strongest in
the darker parts of the sunspots (called the "umbra").  The field
is weaker and more horizontal in the lighter part (the "penumbra").

Galilea Galileo made the first European observations of Sunspots in
1610.  The Chinese and many other early civilizations have record
of sunspots.  Daily observations were started at the Zurich
Observatory in 1749.  By 1849 continuous observations were
obtained.  

The sunspot number is calculated by first counting the number of
sunspot groups and then the number of individual sunspots.  The
"sunspot number" is then given by the sum of the number of
individual sunspots and ten times the number of groups.  Since most
sunspot groups have, on average, about ten spots, this formula for
counting sunspots gives reliable numbers even when the observing
conditions are less than ideal and small spots are hard to see. 
Monthly averages (updated monthly) of the sunspot numbers show that
the number of sunspots visible on the sun waxes and wanes with an
approximate 11-year cycle.

And, what is a solar flare?  Solar flares occur near sunspots,
usually along the dividing line (neutral line) between the two sets
of spots, or areas of oppositely directed magnetic fields.  These
flares, tremendous explosions, heat material to many millions of
degrees and release as much energy as a billion megatons of TNT and
release many forms of energy.  Electro-magnetic energy (Gamma rays
and X-rays) are what affect ionospheric conditions within moments
of a flare, and energetic particles (protons and electrons) ride
the solar wind, to impact our magnetoshere.  Flares are
characterized by their brightness in X-rays (X-Ray flux).  The
biggest flares are X-Class flares.  M-Class flares have a tenth the
energy and C-Class flares have a tenth of the X-ray flux seen in
M-Class flares.

2.  Solar Wind.  Space is not a vacuum.  At least not in our solar
system.  The sun's atmosphere actually extends very far out from
the sun.  Space in our system is filled with plasma.  The
temperature of the corona is so high that the Sun's gravity cannot
hold on to it.  The solar wind streams off of the Sun in all
directions at speeds of about 400 km/s (about 1 million miles per
hour).  (So when you see the solar wind speed around 400 km/s, you
know that things are "normal" and our solar/geophysical "weather"
should be normal, for the most part).  The solar wind changes speed
and carries with it magnetic clouds, interacting regions where high
speed wind catches up with slow speed wind.  The solar wind speed
is high (800 km/s) over coronal holes and low (300 km/s) over
streamers.  These high and low speed streams interact with each
other and alternately pass by the Earth as the Sun rotates.  These
wind speed variations buffet the Earth's magnetic field and can
produce storms in the Earth's magnetosphere.  Many Coronal Mass
Ejections combine with the solar wind and cause shock waves which,
if directed to the Earth, can ignite the Aurora and major
ionospheric / geomagnetic storms.

3.  The Earth's magnetosphere - put up the force fields, Captain! 
The Earth has a magnetic field with north and south poles which is
enclosed in a region surrounding the Earth called the
magnetosphere.  As the Earth rotates, its hot core generates strong
electric currents that produce the magnetic field which reaches
36,000 miles into space.  The magnetosphere prevents most of the
particles from the sun, carried in solar wind, from impacting the
Earth.  The solar wind distorts the shape of the magnetosphere by
compressing it at the front and causing a long tail to form on the
side away from the Sun.  This long tail is called the magnetotail. 

4.  What does this all mean to me?  Radio wave propagation is
directly tied to the Ionosphere.  The more ionization occurring in
the F-layers, the higher the frequencies which refract back toward
the Earth.  The highest frequency that will refract back from the
Ionosphere over a selected point-to-point path is known as the
Maximum Usable Frequency, or MUF.  The other layers of the
Ionosphere can block our transmissions, and the earth's geomagnetic
field has an impact, as well.  The Lowest Usable Frequency, or LUF,
is the lowest frequency that can propagate via the Ionosphere over
a particular point-to-point path.   When the LUF increases to or
above the MUF, then communications are next to impossible over the
given path.

The Sunspots give us a general correlation to the sun's activity -
the overall energy that radiates out from the sun and causes the
ionization of the Ionosphere.  But, we have found that sunspot
numbers are not that accurate of a way to gauge this influence.  We
have adopted the measurement of the 10.7cm Wavelength Flux.  But,
even this does not always capture the direct impact of the solar
energy on the Ionosphere.

With an increase of solar sunspot counts during the Solar Cycle
Maximum, an increase in solar flares, and coronal holes also
happens.  When those X-rays from these increased number of Flares
pass by Earth, they, in part, increase the ionization of the D
Layer.  When this happens, we experience degradation of radio
signal strength.  The D Layer begins to absorb the radio waves,
causing Radio Blackouts, as the LUF is raised to the MUF.

Let's look at the relationship between coronal material and
magnetic fields.  The Corona is so hot that the gases in it loose
some of their electrons in the powerful collisions between atoms. 
This plasma is a mixture of positively-charged ions and
negatively-charged electrons.  Take a look at a Neon light.  You
are looking at plasma.  Because plasmas are electrically
conductive, they can steer magnetic fields.  And they are steered
by magnetic fields.  CMEs drag a piece of the Sun's magnetic field
with it.  These loops of magnetic force are stretched and dragged
into interplanetary space by the inertia of the expanding plasma. 
When these magnetic forces impact the Earth they are either
diverted by or combined with Earth's magnetic field.

The speed of a CME ranges from less than 50 to about 2000
kilometers per second. As the CME moves outward from the Sun, it
generates a shock wave that can accelerate particles in
interplanetary space to high energies. When a CME or its shock wave
passes the Earth, geomagnetic storms are triggered.  The majority
of large and major geomagnetic storms are generated by the
encounter with both the interplanetary shock and the CME that
drives it.  Their ability to disturb the Earth's magnetosphere is a
function of their speed, the strength of their magnetic field, and
the presence of a strong southward magnetic field component.

The Earth's magnetosphere is formed from two essential ingredients,
the Earth's magnetic field (which has much the same form as that of
a bar magnet, and is from pole-to-pole), and the solar wind.   When
the CME combines with the Earth's magnetic field, it alters the
shape and intensity of this shield around the Earth.  The
Ionosphere is affected by these changes, either by an increase of
ionization, or a decrease or even a depletion of ionization. 
Depressions in ionospheric density cause major communications
problems because radio frequencies that previously had been
refracting off the ionosphere now punch through.  The MUF can be
decreased by a factor of two during an ionospheric storm event. 
Storm effects are more pronounced at high latitudes.

When a CME is directed toward Earth and arrives after the two- to
three-day journey, the interaction between the CME, solar wind, and
the magnetosphere and ionosphere causes Aurora.  Propagation off of
Aurora is an exciting activity.  At the same time, we bemoan the
loss of communication caused by the degraded ionization of the
Ionosphere.  But hang in there!  While CMEs affect us year-round,
they are not as common as solar flares and solar wind.

SUMMARY:

We are in a high-speed solar wind storm.  This solar wind is coming
out of a coronal hole (not a real hole and not a burned out part of
the sun that need reigniting), and is causing the magnetosphere to
compress, which is setting off a bit of a geomagnetic storm.  Kp
readings are therefore high.  Conditions on HF are degraded.

What's in store for the next few days and the rest of next week? 
Expect an X-Class flare from some NEWLY developing BIG sunspots. 
The magnetic field around these new spots appear very complex and
they have the potential to break down and spew out great amounts of
plasma and energy.  The resulting flare will likely head toward
Earth.  We'll have some radio blackouts.  Maybe some Aurora.  We
are in the Aurora season.

Also:  We just saw the Flux rise above 200 again.  The sunspot
number has not climbed as much.  This shows you that the Flux is a
more accurate reading of sun activity.  Look for some good DX in
the next few days on the HIGHER bands (above 15 MHz).

I have a lot of resources at http://hfradio.org/propagation.html -
if you are interested.

73 de Tomas, NW7US // AAR0JA

(This e-mail is in copyright, 2002, by Tomas Hood.  No part may be
reproduced, in whole or part, without permission -- except in
quoting this e-mail as part of the discussion of this e-mail. 
Parts of this e-mail are already published, and parts are due to be
published, by Tomas Hood.)

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