Bob NM7M's "Propagation 101, 201, 301" is another good introduction to this
topic. I placed a copy in this group's Files area.
73,
Dave, AA6YQ
--- In [email protected], Tony <d...@...> wrote:
>
> All,
>
> Interesting read about solar output and HF propagation by Paul Harden, NA5N.
>
> Tony -K2MO
>
> ____________________________________________
>
>
> Paul wrote:
>
>
> 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, 15M will be open; above 150 10M will be open. Below 100, 20M will
> usually die shortly after sunset. IMPORTANT: The MUF seldoms drops below
> 10MHz.
>
> Therefore, the solar flux has very little effect on 30, 40 and 80M
> propagation. 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. 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). 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 28-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 28-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. IMPORTANT: 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 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
> For QRPers, a good time to operate is right after a solar flare. 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 for QRPers 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.
> Let's be honest. For a QRPer, if your propagation program says conditions are
> good to the Pacific and you end up in a QSO with Israel ... who's going to be
> disappointed over that! Heck, from New Mexico, I get excited when I work
> Alaska or Nova Scotia :-)
>
