Solar activity drop to affect shortwave communication

February 28th, 2018, Published in Articles: EngineerIT

Fig. 1:  Montage of solar images taken between August 1991 and September 2001 [Credit: Yohkoh/ISAS/Lockheed-Martin/NAOJ/U. Tokyo/NASA].

Over the past few years there have been mutterings about another solar Maunder Minimum which could serious affect shortwave communication. While at the time many solar scientists did not support the notion, they now agree that the world can expect an extended solar minimum period. This is bad news for radio amateurs but good news for satellite operators who prefer a stable solar environment with no or low solar flare activity from the sun.

The Maunder Minimum, also known as a prolonged sunspot minimum, occurred for almost 70 years from 1645 until about 1715. During this low solar activity period, Europe also experienced lower than average temperatures. This finding set scientists on another direction of research: Is there a connection between the level of solar activity and Earth’s climate? Was the lower temperature due to the absence of solar activity? Right now it is a controversial subject. If it is truly a factor, is it being masked by climate change?

In 2015 Prof. Valentina Zharkova, professor in mathematics at Northumbria University in the UK, dropped a bombshell at the National Astronomy Meeting in Llandudno, when she presented a new model to forecast the length and intensity of the sun’s solar cycles. The new model is producing unprecedentedly accurate predictions of irregularities within the sun’s eleven-year heartbeat.

The model draws on dynamo effects in two layers of the sun, one close to the surface and one deep within its convection zone. Predictions from the new model suggest that solar activity will fall by 60% during the 2030s to conditions last seen during the “mini Ice Age” that began in 1645.

Ean Retief (ZS1PR), a Cape Town-based radio amateur who has studied radio propagation for many years, said that while scientists have generally accepted that a solar cycle is eleven years in duration, every cycle is slightly different. Up until now none of the models have fully explained these fluctuations. Many solar physicists have put the cause of variations in solar cycles down to a dynamo caused by convection fluid deep within the sun. Prof Zharkova and her colleagues have found that adding a second dynamo, close to the surface, completes the picture with surprising accuracy.

At the 2015 conference, Prof. Zharkova said they found magnetic wave components appearing in pairs, originating in two different layers in the sun’s interior. They both have a frequency of approximately eleven years, although this frequency is slightly different, and they are offset in time. During the cycle, the waves fluctuate between the northern and southern hemispheres of the sun. Combining both waves and comparing to real data for the current solar cycle, they found that their predictions showed an accuracy of 97%.

Prof. Zharkova and her colleagues derived their model using a technique called “principal component analyses”, where they analysed the magnetic field observations from the Wilcox Solar Observatory in California. They examined three solar cycles’ worth of magnetic field activity, covering the period from 1976 to 2008. In addition, they compared their predictions to average sunspot numbers, another strong marker of solar activity. All the predictions and observations were closely matched.

Looking ahead to the next two solar cycles, the model predicts that the pair of waves become increasingly offset during cycle 25, which peaks in 2022. During cycle 26, which covers the decade from 2030 to 2040, the two waves will become exactly out of synch and this will cause a significant reduction in solar activity.

In cycle 26, the two waves exactly mirror each other – peaking at the same time but in opposite hemispheres of the sun. Their interaction will be disruptive, or they will nearly cancel each other. Prof. Zharkova predicts that this will lead to the properties of a “Maunder Minimum”. Effectively, when the waves are approximately in phase, they can show strong interaction, or resonance, and there is strong solar activity. When they are out of phase, we have solar minimums. According to Prof. Zharkova, when there is full phase separation, we have the conditions last seen during the Maunder Minimum, 370 years ago.

Some UK newspapers misinterpreted the findings and led with scary headlines like “Earth heading for mini Ice Age within 15 years.” (The Telegraph, 11 July 2015); and “Is a mini Ice Age on the way? Scientists warn the sun will ‘go to sleep’ in 2030 and could cause temperatures to plummet.” (Daily Mail 10 July 2015).

While many scientists were sceptical of the findings that solar activity will drop by 60% during Cycle 26, today they are not so sure – with many now agreeing that the next few solar cycles will be lower than the current Cycle 25.

According to Retief, radio amateurs and shortwave enthusiasts should not despair. Even when the next two solar cycles are predicted to be much lower, and there will still be HF communication although the maximum useable frequencies (MUF) will be lower.

The ionosphere is not formed only by solar activity;cosmic rays also ionise the ionosphere. These high energy rays originate from sources throughout our galaxy and the universe su,ch as rotating neutron stars, supernovae, radio galaxies, quasars and black holes. This means that there will always be propagation of high frequency signals although the frequencies may be lower. Commercial users of the high frequency bands and shortwave broadcasters will select frequencies which are below the predicted MUF to ensure that they have a stable circuit but there will be many times when HF propagation occurs above the MUF. This provides opportunities for radio amateurs to explore unusual short-lived propagation conditions. This is what amateur radio is all about: exploring the unusual. Retief advises using the MUF predictions as a guide and then stepping up to the next higher frequency band.

The MUF is determined by ionospheric sounding, a technique that provides real-time data on high-frequency ionospheric-dependent radio propagation, using a basic system consisting of a synchronised transmitter and receiver.

The time delay between transmission and reception is translated into effective ionospheric layer altitude. Various organisations offer propagation forecasts. In South Africa the information is available from www.spaceweather.sansa.org.za.