Dave, > Bob NM7M's "Propagation 101, 201, 301" is another good introduction to > this topic
Thanks for posting that. Have a copy of Bob's book "The Little Pistol's Guide" and had the pleasure of speaking to him some time ago. His health was up and down last time I heard so I hope he's doing well. Tony -K2MO ----- Original Message ----- From: "Dave Bernstein" <[email protected]> To: <[email protected]> Sent: Monday, April 13, 2009 12:33 AM Subject: [digitalradio] Re: HF and the Spotless Sun 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 :-) >
