A huge sunspot has formed on the sun – big enough to make the “regular” news.

So, as an Amateur Radio operator you’ve heard about sunspots, you’ve read about sunspots, you may have even prayed for sunspots ……. but what do you KNOW about sunspots?

I have perused the Internet and have come across several articles by our own Paul Harden, NA5N of Very Large Array (and Zombie Shuffle) fame.  He’s our authority on things of the sun.  I have found the best of his words and are pasting them here for your edification:

From Paul Harden NA5N, some solar weather basics:

We all know the sun goes through a solar cycle about every 11 years. During the minimun, or QUIET SUN, there are few sunspots, the solar flux is very low ( less than100), which means the sun’s ionizing radiation is quite low. As a result, our upper atmosphere, where the E and F layers reside, are not well ionized. This means the E and F layers do not reflect HF radio waves very well … and most of your signals will pass right on through to space to be picked up by Jodie Foster in the sequel to “Contact.” One measure of how well ionized our E and F layers are is the MUF, or Maximum Usable Frequency. During the quiet sun, the MUF is often below 15-18MHz. This is why 15M and 10M are “dead” during the quiet sun, except for local (line-of-sight) communications.

However, during the solar maximum or ACTIVE SUN, there are many sunspots, the solar flux is high, and this highly ionizes our ionosphere. This in turn means our E and F layers become very reflective to HF signals. Virtually all the power hitting the E and F layers will be reflected back to Earth and Jodie Foster will hear nothing out in space. This high reflectivity causes the MUF to rise, often to above 30MHz. And when this occurs, 10M will be open all day long to support global communications by using “skip propagation” … in that your signals are skipping (or being reflected) off the ionosphere back to earth.

SOLAR FLUX (SF) is a number that attempts to describe the total power output of the sun at radio wavelengths, which in turn helps describe the total ionizing power delivered to our ionosphere. The higher the SF, the more ionization, and the more reflective our ionosphere is to HF.

An SF of less than 100 is fairly poor propagation, the MUF  will be lower than 15MHz.  An SF of more than 150 is fairly good propagation, the MUF will be greater than 25MHz

A general rule of the thumb is 10M is open when the solar flux is greater than 150.

IONIZATION. The solar radiation reaching the Earth contains IONIZING radiation. This means the incoming solar radiation can rip electrons away from the oxygen molecules high in our atmosphere. So now you have all these “free electrons” roaming around that makes the upper atmosphere (or ionosphere) more dense. Now the mass or weight doesn’t change, it’s just denser. This density causes your RF signal to not pass onto space. In the real case, your RF signal strikes all these free electrons, and that is what reflects them back to earth … DURING DAYLIGHT HOURS when ionization occurs.

This is why the higher bands, such as 15M and 10M, are open (that is, signals being reflected back to earth) during the DAYLIGHT HOURS, but these same bands go dead (no reflective propagation) nearly as soon as the sun sets – because the sun’s ionizing radiation goes away.

This is also why these same bands tend to be completely dead during the quiet sun, because there is insufficient ionizing radiation to cause ionization for reflection. This is a phenomenon of the active sun, the period we are well into right now. And, during a quiet sun, the ionization can be so low, that the MUF drops below 14MHz at night, which is why even 20M can go dead at night. During an active sun, the MUF almost always remains above 15MHz even at night, which is why 20M often becomes a ’round-the-clock band during the active sun.

So what about 40M? Truth is, the solar cycle has virtually no effect on 40M or below. Propagation on 40M remains pretty much the same during the active sun as it does the quiet sun, because the MUF seldom drops below 10MHz. This is why 40M is the main nighttime band, year in and year out. Even with low ionization, the very long wavelengths of the lower frequencies will be reflected by the ionosphere. This would be like rolling a basketball through the popcorn balls … while the high frequency RF (the marbles) pass through pretty easy, certainly the low frequencies (basketball) would not. Quiet sun or active sun.

The active sun DOES effect 40M in that absorption to RF can be very good to very bad, or very high noise levels from geomagnetic storms … both due to solar flare activity that occurs only during an active sun. A large solar flare sends an extra dose of ionizing radiation to the Earth. This can raise the MUF to very high frequencies (greater than 100MHz), but this radiation can also penetrate far into our atmosphere to ionize the lower D-layer. RF signals must pass through the D-layer on their way to the upper E and F layers, where the reflection occurs. The more ionized the D-layer is, the more collisions that will take place with your RF signal, absorbing or attenuating some of its power. Thus, high absorption to HF signals can occur during and after a solar flare. Your poor little QRP signals just vanish on their way to the E and F layers!

80M signals are almost always highly or fully attenuated by the D-layer, and what “propagation” that occurs on 80M is actually by the signals traveling across the Earth’s surface, or “ground wave” propagation. The wave front is confined between the Earth’s surface and the D-layer, which causes attenuation to the power as it travels along the ground, skims the D-layer, and propagates through the dense atmosphere near the surface. This is why QRP on 80M is challenging at best since the absorption rates are fairly high – day and night, quiet sun or active.

The other major effect to HF propagation during the active sun is geomagnetic storms. Very briefly, this is caused by a shock wave from a solar flare hitting the Earth’s magnetic field, causing it to compress and wiggle for awhile. And while it’s wiggling, it’s generating huge electrical currents, which in turn creates gobs of noise on HF.

….80M…. Seldom has skip propagation…..Seldom has skip propagation
….40M…. Open around the clock……………..Open around the clock
….30M…. Open daylight hours………………….Open around the clock
….20M…. Open daylight hours………………….Open around the clock (usually)
….15M…. Dead – no skip propagation……….Open – daylight hours only
….10M…. Dead – no skip propagation……….Open – daylight hours only

See also –  This link explains the A and K Indices and other phenomena associated with solar weather. It also contains other pertinent links to other valuable solar weather sites.

Thank you, Paul!

So to recap (and this is a very general nutshell, and in W2LJ’s words)

High Solar Flux and sunspot numbers = increased ionization of the ionosphere =  good propagation = happy Hams.

Keep in mind that giant sunspots can be too much of a good thing, though, causing geomagnetic disturbances and solar flares which can muck everything up.

High A and K Index values = higher noise level on the bands and higher chance for signal absorption and a lowering of the MUF = bad propagation = sad Hams.

In the end, like everything else in nature, it’s all a fine balance.

72 de Larry W2LJ
QRP – When you care to send the very least!

Larry Makoski, W2LJ, is a regular contributor to and writes from New Jersey, USA. Contact him at [email protected].

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