A previously unknown seasonal change on the sun is occurring every two years, according to a new study. Researchers have found that twisted bands of magnetic fuel reach the surface of the sun every two years - in addition to its existing 11-year cycle. And when the seasons combine, the activity of the sun can be amplified, producing mega storms that are even more dangerous to Earth than others. Scientists in Colorado have found evidence for a new solar season cycle. Every two years it appears 'bands' of magnetic field move to the surface. This combines with the existing 11-year solar cycle, causing even more powerful coronal mass ejections (CMEs), pictured, and solar flares that can endanger Earth . The study was carried out by a team of researchers led by the National Centre for Atmospheric Research (NCAR) in Colorado. They found that the changes seem to be driven by bands of strong magnetic fields in the sun's hemispheres which emanate from the solar interior. It was already known that the sun goes through a solar cycle of 11 years, during which its activity increases and decreases. Solar flares and coronal mass ejections (CMEs) can damage satellites and have an enormous financial cost. The charged particles can also threaten airlines by disturbing the Earth's magnetic field. Very large flares can even create currents within electricity grids and knock out energy supplies. A positive aspect, from an aesthetic point of view, is that the auroras are enhanced. Geomagnetic storms are more disruptive now than in the past because of our greater dependence on technical systems that can be affected by electric currents. But this shorter two-year season seems to also play a part in the sun's activity, on a similar scale to the 11-year cycle - despite being much quicker. The new solar season occurs when twisted, ring-shaped 'bands' of magnetic field rise from the solar interior and pass to the surface through the tachocline - a 'transition' region in the outer third of the sun. 'Much like Earth's jet stream, whose warps and waves have had severe impact on our regional weather patterns in the past couple of winters, the bands on the sun have very slow-moving waves that can expand and warp it too,' said co-author Dr Robert Leamon, a scientist at Montana State University. 'Sometimes this results in magnetic fields leaking from one band to the other. 'In other cases, the warp drags magnetic fields from deep in the solar interior, near the tachocline, and pushes them toward the surface.' The result of this motion is that the bands create turbulent regions of activity on the surface, causing solar flares and coronal mass ejections (CMEs). CMEs are the huge waves of material that are seen in images of the sun, and they can pose a threat to satellites in Earth orbit. Solar flares are flashes of energy on the surface of the sun, which are sometimes associated with CMEs - although their connection is not well understood. The new solar season discovery occurs when twisted, ring-shaped 'bands' of magnetic field rise from the solar interior and pass to the surface through the tachocline - a 'transition' region in the outer third of the sun. Shown in this illustration are the various different regions of the sun and a sunspot (top right) The bands, which appear in each hemisphere of the sun, cause the 11-year solar cycle to actually become a longer cycle that lasts 22 years. The 11-year solar cycle sees a periodic change in the sun’s activity - such as the number of ejections - in addition to changes in the number of sunspots, flares and other visible differences. A solar flare occurs when magnetic energy that has built up in the solar atmosphere is suddenly released. Radiation is emitted across virtually the entire electromagnetic spectrum, from radio waves at the long wavelength end, through optical emission to X-rays and gamma rays at the short wavelength end. The amount of energy released is the equivalent of millions of 100-megaton hydrogen bombs exploding at the same time . A flare occurs when magnetic energy that has built up in the solar atmosphere is suddenly released - mostly in the active regions around sunspots. Their frequency varies from several a day, when the sun is particularly active, to less than one a week during quiet periods. However, the cause of the 11-year cycle is poorly understood. And according to this new research, when the 11-year cycle combines with the two-year cycle, the solar storms that pummel Earth's atmosphere can be amplified. The bands  appear to take place separately in the northern and southern hemispheres, with activity peaking over 11 months, then dropping over another 11 months. The almost annual variations can be likened to regions on Earth that have two seasons, such as a rainy season and a dry season. 'What we're looking at here is a massive driver of solar storms,' said Dr Scott McIntosh, lead author of the new study and director of NCAR's High Altitude Observatory. 'By better understanding how these activity bands form in the sun and cause seasonal instabilities, there's the potential to greatly improve forecasts of space weather events.' The overlapping bands are fueled by the rotation of the sun's deep interior, according to observations by the research team. The study, published this week in Nature Communications, could help lead to better predictions of massive geomagnetic storms in Earth's outer atmosphere that sometimes disrupt satellite operations, communications, power grids and other technologies. The research was funded by Nasa and the National Science Foundation, which is NCAR's sponsor. The 11-year solar cycle sees a periodic change in the sun’s activity - such as the number of ejections - in addition to changes in the number of sunspots, flares and other visible differences. Shown here are images of the sun over one cycle showing changes in its activity . The surges of magnetic fuel from the Sun's interior catastrophically destabilise the corona, the sun's outermost atmosphere. They are the driving force behind the most destructive solar storms. 'These surges or "whomps" as we have dubbed them, are responsible for over 95 per cent of the large flares and CMEs - the ones that are really devastating,' Dr McIntosh said. The almost-annual variability can also help explain a cold-war era puzzle: why do powerful solar flares and CMEs often peak a year or more after the maximum number of sunspots? This lag is known as the Gnevyshev Gap, after the Soviet scientist who first reported it in the 1940s. The answer appears to be that seasonal changes may cause an upswing in solar disturbances long after the peak in the solar cycle. Researchers can turn to advanced computer simulations and more detailed observations to learn more about the profound influence of the bands on solar activity. Dr McIntosh said this could be assisted by a proposed network of satellites observing the sun, much as the global networks of satellites around Earth have helped advance terrestrial weather models since the 1960s. 'If you understand what the patterns of solar activity are telling you, you'll know whether we're in the stormy phase or the quiet phase in each hemisphere,' Dr McIntosh said. 'If we can combine these pieces of information, forecast skill goes through the roof.'
Scientists in Colorado have found evidence for a new solar season cycle .
Every two years it appears 'bands' of magnetic field move to the surface .
The sun was already known to have an 11-year solar cycle .
When the two combine it can create amplified and dangerous storms .