Solar Indices
As a summary of the training topic during the BARC net on 1,30,2007 the solar indices were the topic of discussion along with solar sunspots. The solar indices consist of solar flux, A-index and K-index. As a refresher the solar indices are updated every three hours and broadcast on WWV out of Denver at 18 minutes after the hour on 2.5, 5, 10 and 15 mhz. They are also found on many websites such as http://dx.qsl.net/propagation/.
The solar flux index mainly affects the F layer of the ionosphere in its ability to reflect radio waves. The higher the Solar Flux the higher the MUF (Maximum Usable Frequency) generally is. Also the higher the solar flux generally makes for better HF conditions especially DX (Other Countries). In simple words the higher the better.
The A-index is a logarithmic number from 0 to 200 which is calculated by a formula derived from the previous 24 hours of the K-index, or in other words the previous 8 K-index readings since they are only updated every 3 hours. HF conditions are normally better when the A-index is 15 or less. One of the big reasons to track the A-index is because of the suns 27-28 day rotational cycle, the A-index somewhat repeats itself about every four weeks since the sunspots generally remain in the same area on the sun, so by tracking the A-index over a period of time you can create a trend or somewhat predict the upcoming A-index and/or hf conditions. The A-index is a slightly delayed smoothed out version of the K-index, which makes it much easier to be use in trend observation. In other words the lower the A-index the better.
The K-index is a linear number from 0 to 9 that is mainly affected by Solar Flares and Solar Coronal Mass Ejections hurling x-rays and solar particles towards earth. These are the same particles that create the solar winds, and also the Northern Lights when the particles react with the earth’s magnetic field. When the particles are traveling 400 km/s (c=300,000km/s) that gives them about 4.3 days to reach the earth from the 93 million mile journey from the sun. Like the A-index the lower the K-index is the better hf communications normally are. Any number 3 or less is considered good. Or in other words the lower the K-Index the better.
Sunspots are magnetically active storms on the sun. And like hurricanes and tropical storms here on earth they spin one direction in the northern hemisphere and the opposite direction in the southern hemisphere with one exception of twin sunspots. When twin sunspots are observed they act like a magnet with one north and one south pole. Thus two opposite polarized sunspots in the same hemisphere produce opposite spins from one another. The number of sunspots are highest when the peak of the magnetic field intensity is greatest. The sun has a 22-year cycle which the magnetic field of the sun switches polarity every 11 years. So the beginning of a cycle is at the beginning of a solar magnetic shift or solar minimum, with nearly zero sunspots for a short period of time. Then as the field increases in magnetic intensity to its maximum over the next approximate 5.5 years the number of sunspots will at an average increase along with it. A number of sunspots reaching near 300 is possible. The sunspots affect the solar flux index. The higher the sunspot number is, the higher the Solar Flux number normally gets. Right now we are more or less at the beginning of a new cycle with the lower sunspots and lower solar flux index numbers.
Even though we are in the solar minimum there is still great HF fun happening. There are several people I talk to on a daily basis on 40 and 80 meters. In Oregon, California, Nevada, Idaho and Utah. So don’t let the bottom of the cycle discourage you from upgrading your license. There is still a lot going on. One big secret behind it is a good antenna. So good luck to all of you on the HF side of Amateur radio. 73
KB7ZNH
Ernie
