Monday, November 9, 2009

The New Solar Cycle and its Effects on Shortwave Radio Propagation

Over 100 years since the dawn of early radio there remains something magical about being able to transmit messages from one place to another, through the atmosphere and even into space, by using man-made electromagnetic waves. High frequency (HF) or "shortwave" wavelengths exist in the 3,000 to 30,000 kHz portion of the radiowave spectrum. They range anywhere from about 100 meters to 10 meters in length. Because they can be bounced off the earth's ionosphere, HF shortwaves are capable of traveling great distances around the planet. If you have spent much time listening to shortwave radio broadcasts then you might have noticed that reception of shortwave signals is highly variable. This variability is due at least in part to the condition of the earth's ionosphere.

The ionosphere is comprised of several layers itself but, in the grand scheme of things, it is simply the outermost portion of the earth's atmosphere which exists about 50 to 100 km above the earth. The ionosphere consists of various atoms, molecules, and subatomic particles including electrons. These components of the upper most reaches of the earth's atmosphere are easily affected by the activity of the sun. Therefore, the propagation, or ease and efficiency with which HF shortwave radio signals travel around the earth by bouncing off the ionosphere, is heavily dependent on solar conditions. The sun itself is dynamic and exhibits fluctuations in the amounts of charged particles that it emits into space in the form of a solar "wind". Effects of the solar wind can be seen in auroras, or natural light displays, which become visible at the northern and southern poles of earth. As solar winds and the earths geomagnetic properties contribute to the ever changing makeup of charged particles in the earth's ionosphere, they can alter or even disrupt the state of shortwave radio communications.

Solar storm activity has been discovered to occur in regular and somewhat predictable cycles. At present we are said to be at or near a low point in solar activity and a new solar cycle is set to begin or may already be beginning as solar storm activity increases. Scientific bodies such as NASA work to predict the future of solar cycles and forecast space weather. It has been proposed that the coming peak of Solar Cycle 24 may occur in early 2013. If NASA is correct then it seems quite probable that conditions for broadcasting and listening on the shortwave radio bands could be set to improve over the next couple of years, provided that the intensity of geomagnetic storms does not have a severe negative impact on shortwave propagation conditions.

While probably worthwhile pursuing, just like regional weather forecasting for terrestrial conditions, pinpointing just exactly what the sun has in store could easily prove to be not only challenging but also humbling. Common sense and experience should serve as a reminder that no matter what the weather report calls for, only time will tell for certain what awaits us. Either way, until proven wrong, shortwave radio listening through the new solar cycle looks to be a good way to harness some of the potentially fruitful space weather coming our way.

Additional links:

The Sun's sneaky variability (

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