Dxers Unlimited
Dxers Unlimited weekend edition for Sept 30- Oct 1 2006
By Arnie Coro
Radio amateur CO2KK



Hi amigos radioaficionados around the world and in space ! Welcome to
the weekend edition of Dxers Unlimited reaching you when solar activity
is at at a really very low ebb… I am Arnie Coro, radio amateur CO2KK and
here is item one of today’s program, answering a question sent by no
less than twenty seven listeners of the show that formulated their
question in a more or less similar way….
They all want to now about the Sun, and why it is so important for short
radio wave propagation… Listen carefully, as I will be reading slowly an
excellent article written by Paul Harden radio amateur NA5N , an expert
in the field of radio astronomy.


This what you really NEED TO KNOW !!!
The sun is basically a thermonuclear reactor at it's core, producing
ionizing gamma and x-ray radiation. By the time this radiation reaches
the cooler surface of the sun, the wavelength is much longer ... in the
radio spectrum. This produces a wideband radio output from the sun,
which is measured on earth to represent the overall electromagnetic
energy being generated by the sun. It is measured at 2880MHz, or 10cm,
as a frequency to use as the standard reference, and a frequency for
which our ionosphere is fairly opaque and not generally effected by the
effects of solar flares. The solar radiation measured at 2880MHz is the
SOLAR FLUX, measured periodically and averaged over the 24-hour day. It
seldom changes much hour-to-hour (or even day-to-day).
During the quiet sun, solar flux in the 60-100 range is typical. During
the active sun, 150-200 is typical. The higher the solar flux, the more
ionizing radiation that is striking our ionosphere, producing free
electrons that stratify into the D, E and F layers. The more free
electrons in the E and F layers, the more reflective they are to HF
frequencies and the higher the MUF. Right now, with solar flux in the
60-100 range, the E and F layers are poorly ionized, yielding a lower
MUF and not acting as a very good mirror for bouncing HF signals back to
earth.
Very generally, when the solar flux is around 100, the 15 meters of 21
megaHertz amateur band and the adjancent 13 meters international
broadcast band will be open; above 150 solar flux will make frequencies
above 25 megaHertz propagate at long distances via the F2 layer, so the
12 meters amateur band , the 11 meters or 27 megaHertz Citizens Band and
the Ten meters amateur band will be open. When the solar flux is below
100 units the fourteen megahertz or 20 meters ham band will usually die
shortly after sunset.
More about the Sun and short wave propagation when Dxers Unlimited’s
weekend edition continues… I am Arnie Coro in Havana/…
………

Now continuing with the very detailed and very understandable
explanation about the SUN and short wave propagation there is an
IMPORTANT FACT: The Maximum useable frequency very rarely seldoms drops
below 10MHz. Therefore, the solar flux has very little effect on 30, 40
and 80M propagation, and the same holds for the 49 , 41 and 31 meters
international short wave broadcast bands. These bands are fairly immune
from the solar flux and the 11-year solar cycle.
Magnetic disturbances on the sun produce sunspots (cooler areas).
Occassionally, the magnetic field lines of the disturbance(s) grow to
such an intensity that it produces a small hole in the solar surface,
allowing hot solar mass to escape. This is a SOLAR FLARE.
While this hole is present (usually in the order of minutes to tens of
minutes), energetic electrons and ionozing radiation (that is, x-rays
and sometimes gamma rays) are allowed to escape. This, of course,
quickly increases the overall radiation output of the sun. The ionozing
radiation, when it strikes the earth 8 minutes later, will ionize the E
and F layers, making them more reflective to HF and raise the MUF,
usually for the rest of the day until local sundown. The radiation from
especially strong flares can penetrate into our ionosphere to the
D-layer. When the D-layer is highly ionized, it becomes very absorptive
to HF signals, and in extreme cases, can produce a temporary HF blackout.
This is known as the MOSS DILLINGER effect and it can be detected many
times during the peak years of a solar cycle, when suddenly your short
wave radio will go dead… and nothing is heard for minutes or even hours
at a time.
Most flares will not appreciably increase the daily solar flux;
therefore, the solar flux alone is not a good indicator following a
flare to increased E and F layer reflectivity (and hence, good skip DX).

……..

Now part three of the comprehensive , detailed explanation about how the
Sun impacts upon the Earth’s upper atmosphere generating the ionization
required for radio wave propagation…
Incidentally and for your information, space scientists have found that
planet MARS also has a ionosphere, but its characteristics have yet to
be fully investigated by space probes…
Let’s see what happens here on Earth when the solar cycle begins its
upward phase, due to start sometime by the end of 2007 or early 2008
according to researchers…
As the number of sunspots increases, there is a higher chance of solar
flares, and the daily solar flux tends to increase. However, there is
*no* direct mathematical relationship between sunspot count and the
solar flux.
They follow the same trend when plotted, but no one can say 10 sun spots
equals xxx solar flux units.
The solar flux will vary from a minimum to maximum value over 27-days,
related to the solar rotation. It also varies from minimum to maximum
over the 11-year solar cycle. Thus, it is a slowly varying indicator
that is used to show the general trend of the sun for the current 27-day
cycle, and for the current solar cycle. It is not used for an hourly or
daily predictor. Propagation programs use solar flux values primarily
for calculating the MUF and what bands will be open, or closed, at
different times of the day.
When a solar flare occurs, it often produces a shockwave carrying
electrons and other solar mass away from the sun.
This is called a coronal mass ejection or CME. If the solar flare is
located towards the center of the sun (as opposed to the limbs or
edges), the trajectory of the shockwave will intercept with the earth,
usually about 50-55 hours later. When this happens, the shockwave will
compress the Earth's geomagnetic field, triggering a GEOMAGNETIC STORM,
generating huge electric currents flowing along the Earth's magnetic
field lines, causing increased noise levels.
A VERY IMPORTANT FACT: This effect is more pronounced on the lower
frequencies, such that 30M, 40M, 80M are more effected by the "noise
storm" than is 20, 15 and 10M.
The amount of "wiggling" or disturbance to our magnetic field is the
K-Index. It is measured every 3 hours to show what the present state of
our geomagnetic field is. K=1 to 3 is fairly quiet to unsettled.
Higher numbers (K>4) is a geomagnetic storm. K>7 is a severe to extreme
storm.
The K-Indices throughout the day are averaged over the UTC day to form
the A-Index. It basically tells you what our geomagnetic field did
YESTERDAY.
It is usually expressed as the "Ap," or planetary A-index, being
averaged over 24 hours and from all the reporting stations.
THEREFORE,

The SOLAR FLUX reading tells you the general radiation output of the
sun. But, don't expect it to make a sudden jump to open up 15 or 10M.
That takes years ... or an M or X-class solar flare.
The A-Index tells you what our geomagnetic field did YESTERDAY. It
tells you almost nothing about what the bands sound like TODAY. For
that, find out what the current K-Index is. The lower the number, the
better. Above about 6 or 7, conditions on the LOWER bands will be very
rough.
WHEN TO OPERATE YOUR HAM RADIO STATIONS OR LISTEN FOR RARE DX IF YOU ARE
A SHORT WAVE LISTENER
In case a solar flare do happens, the good time to operate is right
after a the solar flare is detected. Once the solar flare is over, our
E and F layers are highly ionized for good reflectivity and higher MUF,
and will stay that way for the duration of your local sunlight. This
can cause several hours of unexpected openings on the higher bands and
fairly quiet signals on 20M.
Conditions will be normal the following day or two ... until the
shockwave from the flare arrives, triggering a geomagnetic storm. This
can last from a few hours to over a day.
Once the geomagnetic storm is over (when the K-Index falls back to 1-3),
our geomagnetic field tends to get very quiet for a day or two (unless
triggered by another CME, though unlikely where we are right now in the
solar cycle). Therefore, another good time to operate is following a
geomagnetic storm when conditions can often be fairly quiet on 30 and
40M, and sometimes even 80M. Especially at night.
This is really all you need to know to understand the effects of HF
propagation due to solar flux and the K- and A-Indices. The only other
real variable is throughout the year, our sun "shines" on the earth at
different latitudes (higher in the summer, lower in the winter for
northern hemisphere). This changes the paths signals bounce off the E
and F layers ... whether the "skip" is more east-west from your
location, or other directions. This changes throughout the day and
throughout the year.
This is what the propagation programs primarily exploit to determine
good times to work South America or the Middle East from your QTH.
AND… do remember that real life is much richer and fascinating that the
best ever made computer simulations, so even when the computer software
used for forecasting HF propagation conditions tell you that signals
will be weak or non existent on a given path, go ahead and listen…. You
may be surprised by the results, just as I was not too long ago when
looking for a amateur radio DX expedition , that according to my best
propagation forecasting software could not be heard here in Havana at
all during practically the whole day, … listening to the pile ups , I
was finally able to spot the rare station and work it using my 5 Watts
QRP rig on 20 meters amigos…
And now just before going QRT, let me tell you that we are seeing
disturbed propagation conditions now and for the next two days or so,
caused by the effects of a solar coronal hole… Solar flux has increased
a bit as three active sunspot regions have emerged on the solar disk, so
be prepared for much better propagation after Tuesday or Wednesday…
Send your comments about this program , signal reports and QSL requests
to arnie@rhc.cu, or VIA AIR MAIL to Arnie Coro, Radio Havana Cuba,
Havana, Cuba