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This area of the web site is dedicated to any articles on most any subject a member may want to have posted.  We try to keep the subject matter related to amateur radio, but on occassion there may be an article not directly related to the hobby.  Please enjoy!


WHAT THE NUMBERS ARE ALL ABOUT?

Scientists have tried to evaluate sun activity for centuries. Initially, the only available technique was to visually count and record the observed spots. Continuous records of daily activity are available going back to 1880, with available values well into the previous century. This is the data that permits the curve fitting and exploration that are used to predict long-term trends and cyclic activity. For our purposes, we are more interested in predicting what will happen in intervals on orders of days -- What we expect in the next weekends DX contest--for example. Data that can assist in this effort includes:

DAILY SUNSPOT NUMBER-this number is based on the area of the sun's surface covered in spots and spot groups converted to an equivalent number of spots (See Table 1) so the number can be used to compare with earlier data. International solar observatories and standards of bodies, including our own NOAA , have developed a number of computational techniques. Often data is reported in terms of Smoothed Sunspot Numbers (SSN) that use averaging techniques to make the numbers more consistent. The numbers can range from zero during times of inactivity up to 100 during moderate activity and well above 100 in high activity periods. One of the most active periods in the 1950s had sunspot numbers up to 250.

TABLE 1

Effects of Magnetic Conditions on

HF Radio Communication

K	A	Observed Conditions
0	0	Undisturbed or Quiet
1	3	Quiet
2	7	Unsettled, Some Degradation
5	48	Minor Magnetic Storm
6	80	Major Storm
7	140	Large Storm
9	400	Major Storm with likely HF Blackout

SOLAR RADIO FLUX-- while most of the ionizing radiation from the sun is attributed to sun spots, a more direct measure of one form of radiation is taken by measuring the intensity of radio signals at a wavelength of 10.7 cm (2800 MHz) emanating from the sun. While the signals are only one portion of the total radiation, they provide a good indication of overall solar activity. The solar flux unit numbers are higher than the sunspot numbers, but the shapes of the curves correlate well. The numbers range from a low of about 60 to about 300.
GEOMAGNETIC INDICES -- An increase in solar activity not only increases the ionospheric ionization level, but also results in some effects that tend to reduce radio communication capabilities. These occur through magnetic disturbances resulting increased noise levels t and sometimes increase absorption. These are generally the results of Coronal Mass Ejection's CME. These appear as dark spots on the sun, which may also include CME which appear as a sun flare. The largest recorded over the last 25 years was on April 2, 2005.

There are two indices, the A and K that are measures of this effect. In addition, high levels of x-ray emission from a solar flare can heavily ionize the ionosphere’s D layer, resulting in almost total absorption of HF signals and a radio blackout. Since the x-rays travel at the speed of light, they arrive at the same time as the visible flare. Since there is no warning time, the effect is called a Sudden Ionospheric Disturbance or SID.

The K index is a short-term (3-hour average), logarithmic measure of the horizontal component of the Earth's magnetic field-- perpendicular to the usual field between the Earth's poles. A coordinated average of the K values from observatories around the world is called the planetary K index or Kp. Values of KP range from zero through nine. The effects on HF radio communications is summarized in table 1. The NOAA space weather prediction Center issues K index warnings when they predicted value of 4, 5, 6, 7 or greater while K index alerts are issued if the Boulder measured K index reaches 4, 5, 6, 7, 8 or 9 in a three-hour period.
The A index is a linear measure of similar magnetic activity averaged over an entire day rather than a 3 hour interval. The values during this storm may be as high as 100, with a severe geomagnetic storm reaching 400. Values of A index that correspond to K index values are also shown in table 1.

WHERE DO YOU FIND THEM?
ARRL members can subscribe to the weekly propagation forecast bulletin by Tad Cook, K7RA, via e-mail. It is free-just sign on to the AAR RL webpage, click EDIT YOUR PROFILE, then EDIT MAIL SUBSCIPTIONS and click on the PROPAGATION bulletin near the bottom of the list. You will get a weekly e-mail from Tad with up to the minute data, as well as commentary on what to expect. You can
also obtain the weekly bulletin from 1995 to the present directly from ARRL website at www.arrl.org/w1aw-bulletins-archive-propagation.
The solar flux index and K index are also available from a number of Internet locations on a daily basis including www.swpc.noaa.gov/index.html. www.n3kl.org/Sun/noaa.html and www.wm7d.net/hamradio/solar/index.shtml.

WHAT CAN WE DO WITH THEM?
In general, the higher the SFI, the better the HF propagation – the higher the A and K indices, the worse the HF propagation. The actual effects for you will depend in large measure on your geographical latitude, so you can’t make a detailed prediction by just looking at the numbers. Of course, an extreme blackout in progress trumps everything else.
Keep in mind that predictions are educated guesses just like weather forecasts; some bands are likely to be open to some areas much of the time – especially as we get further into cycle 24. No matter what the predictions, it is worth how well the HF beacons are coming in, just in case. 2 A recent DX contest coincided with the prediction of a major CME event – it didn’t wipe out W1ZR!

USE PREDICTIVE SOFTWARE
Listening, as described above, will tell you what’s happening at the moment you’re at the radio, but often it’s nice to know ahead of time when a good path to a particular location is likely to be available. This allows you to plan your operating schedule along with your other activities. Unlike listening, which provides the real story, propagation forecasting can only provide a probabilistic prediction – much like weather forecasting. Still, having an idea of the most likely time to make a contact can save a lot if wasted effort.
There are a number of propagation prediction programs available – just try a Google search on “propagation prediction software,” and you will get a bunch.

1 www.aavso.org/dances-wolfs-short-history-sunspot-indices
2 S. Sant Andrea, AG1YK, “Use Beacons to Spot Band Openings” QST, Nov 2010, p 75
Joes R. Hallas, W1ZR, is QST Technical Editor, he can be reached at W1ZR@arrl.org.