EXPERT REACTION: Second coronal hole detected on the sun in one week

The idea of a hole on the surface of the Sun that is 20 times the size of the Earth might sound terrifying at first glance but it is nothing to be feared. What we are seeing is a region of the Sun, which is cooler and less dense on the surface, appear darker in UV images. These regions allow for high-speed solar wind to escape. When directed at the Earth these winds can increase geomagnetic storms and sites of Aurora at our poles.

Events like these are of great interest to us scientifically to further understand our Sun's 11-year solar cycle, but also important for us to evaluate how these winds might affect our technology in orbit like GPS. We can study how current satellites are affected by the increased geomagnetic activity, and work to produce future satellites better positioned to handle extreme space weather which is an unavoidable consequence of living around the Sun.

The solar wind is a stream of plasma coming off the Sun that spreads out to fill the solar system. The Earth is embedded in the wind all the time, and changes in the wind speed and properties can trigger magnetic storms in near-Earth space. Particularly fast winds come from the heart of ‘coronal holes’ - dark regions in the Sun’s atmosphere where the magnetic field structure allows plasma to escape.

Usually these coronal holes are located around the Sun’s poles (and therefore not pointed towards the Earth). However, during times of high solar activity they can form at low latitudes near the Sun’s equator, as has been seen in recent days. One type of event that can cause strong disruptions in Earth’s upper atmosphere occurs when the Earth transitions between slow and fast streams of solar wind. With fast wind escaping from low-latitude coronal holes into the ecliptic plane (where the Earth orbits), such events are increasingly likely. We don’t yet have reliable models that can predict what the wind speed will be at Earth, but this is an active topic of research and is presently being explored in part through flagship NASA and ESA missions (Parker Solar Probe and Solar Orbiter).

The Sun reaches a new period of high activity every 11 years, and we are a year or two away from the latest maximum now, meaning that there will likely be higher numbers of flares and eruptions on the Sun - as well as larger numbers of coronal holes releasing fast wind stress towards Earth - causing more disruptions in near-Earth space over the next few years.

The Sun is the starting point of everything, and it will also mark the end of Earth. For decades, astronomers have been monitoring the Sun, and thanks to that today we were able to detect these newfound 'Coronal Holes'. Such structures show how our Sun is nearing the peak of its activity: they are astonishing and are a product of a cycle that takes 11 years to occur.

They reveal the complexity and greatness of our host star, and while most of the time these coronal holes are harmless and do not represent a direct hazard for our daily life, we must take them seriously and continuously study them to predict their impact on Earth.

Coronal holes, which are cooler areas in the Sun’s atmosphere, allow the plasma to escape into space and that is why we need to know where they are located: if an alignment of Earth’s orbit with such holes occurred, and we add to that mix a Coronal Mass Ejection, a perfect storm could break down satellites and other important instruments. On the other hand, we might also witness a rain of charged particles interacting with our atmosphere (the so-called auroras), something to remind us who we owe our existence to and that the constant study of the Sun could save our lives in the future.

A space weather event may be imminent. A large coronal hole has appeared on the surface of our Sun, indicating we could see increased solar wind activity shortly. These holes allow supercharged plasma to jet towards Earth at speeds of close to three million kilometres-an-hour along the solar wind.

While not guaranteed, the increased activity could signal a geomagnetic storm that could potentially disrupt satellites and communications on Earth. The growing area of space weather will closely track the Sun’s activity and look for early signs of disruptive events. Hopefully the extent of this event will be more beautiful aurora as the charged particles crash into our atmosphere at the north and south poles.

Our Sun is an active star in the sense that it follows a cycle of increasing and decreasing magnetic activity. This cycle has a roughly 11-year period. The Sun is continually emitting a 'wind' of charged particles into space which carries with it some of the solar magnetic field. Usually Earth's magnetic field shields us from the impact of that 'solar wind'. However, near the peak of the solar cycle, disturbances on the Sun such as coronal holes and coronal mass ejections, result in great bursts of charged particles and magnetic field blasting into space.

If these intercept Earth in its orbit then magnetic storms and other disturbances are triggered. These in turn cause a range of effects broadly called 'space weather'. The effects include bright auroral displays, enhanced and sometimes damaging radiation to spacecraft, disruptions to radio and sometimes GPS networks, and electric currents induced on power lines and long pipelines.

Our Sun is now approaching the next solar maximum so we can expect such activity to be more common over the next couple of years. Various instruments are used to monitor solar activity and therefore we have a reasonable idea if a major magnetic storm is likely, and potential impacts: this is the task of the Bureau of Meteorology's Space Weather Prediction Centre. However, the science does not yet exist for precise prediction of solar disturbances.

This week’s unusual appearance of an enormous coronal hole near the Sun’s equator promises to deliver spectacular auroras, perhaps visible as far north as the Australian mainland. Large coronal holes tend to release a huge volume of magnetic particles—known as the solar wind—that will likely arrive on Earth by Friday evening. While the Earth’s protective magnetic field will channel those charged particles to the polar regions, satellites in orbit might suffer some damage. Although this is the second, pretty large coronal hole in a short time, it’s smaller than its cousin we saw earlier. And so the possible impact on mobile communications, the internet’s functionality and GPS is likely rather limited. Don’t change your travel plans, but if you are lucky enough, enjoy the mesmerising beauty of the ever-changing, brightly coloured light spectacle served up by Mother Nature!

Coronal holes are actually huge magnetic funnels, ejecting large amounts of ionised gas from the Sun. They are constantly changing and shifting in shape and size in response to the churning of the Sun’s magnetic fields. It’s important we study coronal holes as the ionised gases ejected from the Sun can interact with Earth’s magnetic sphere causing geomagnetic storms which can manifest as aurora borealis (in the north) and australis (in the south). Or in extreme cases cause trouble for our communications, aviation, navigation, and power infrastructure on Earth. Space weather forecasters use statistical (including machine learning) and physics-based models to predict geomagnetic storms, but there’s still much to learn and room for improvement.

The significance of the coronal hole that’s facing the Earth at the moment is, I think, a little over-stated in media reports so far. The size of the hole has gradually been decreasing over the past two days, and is only likely to have a minor impact on the near-Earth space environment. This view appears to be shared by the Bureau of Meteorology’s Space Weather Services, who in their daily space weather report state that “The solar wind speed is expected to begin to increase towards the end of 30-Mar due to a small equatorial coronal hole wind stream and remain elevated over 31-Mar and 01-Apr”. Further, their forecasts for geomagnetic activity only reaches a minor (i.e., “G1”) level over this period. Having said that, there is still a possibility for some aurora viewing from southern Australia and New Zealand once the high-speed solar wind arrives.
 
In terms of space weather forecasting, coronal holes are actually really nice! They’re relatively stable, and their impact (or their “geo-effectiveness”) can be well forecast ahead of time, particularly if the disturbance reaches spacecraft a few days before it hits Earth. Coronal mass ejections, on the other hand, are explosive events on the Sun’s surface that are highly unpredictable. For these, existing spacecraft up-wind (between the Sun and Earth in the solar wind) only give us about 30 min – 1 hr warning of the severity of the incoming storm.

Large holes can result in large flares, which usually hit Earth a day or two later.  Flares can affect the health of satellites and big ones can even cause fluctuations in power grids on the ground.  Many large satellites are well shielded, and our operators can handle that.  But most of Australia's satellites are smaller and less shielded.  They would have been zapped pretty hard on this one.

Every 11 years the Sun gets a bit grumpy, increases the number of black, cooler spots and some of them can be very large. These large dark areas are called coronal holes. They usually develop near the poles, and this one reached the sun’s equator. It is right now blasting solar winds that will reach us on Friday through the weekend. It will interact with our magnetic field producing purple and green skies at night, but also impact our satellites. Many CubeSats stop working after these events and we could see interruptions in telecommunication services or even disruption in powerlines. Coronal holes are a nightmare for satellite developers.

The Sun's magnetic activity is ramping up, with the peak expected in 2025. Coronal holes and X-class flares have started releasing enormous amounts of energy, and when directed towards the Earth can play havoc with anything that carries an electric current, the orbits of satellites, and, of course, they generate spectacular aurorae. 

Active regions are patches of strong magnetic field at the surface of the Sun, usually including sunspots. When the magnetic field loops rising above the surface touch and "reconnect", this causes a very bright flash of light, or a solar flare. 

Coronal holes are regions where these magnetic loops have been opened up and the magnetic field and charged particles are able to stream away from the Sun at very high speeds to escape into the solar wind.

The conditions of the magnetic field and charged particles in space are what we call 'space weather' and when it becomes turbulent, we call these 'solar storms'. All of this is driven by the Sun's magnetic field. At the moment, we cannot predict how or when a sunspot on the Sun might appear or a flare will occur, and so understanding the physics going on inside the Sun is essential to making forecasts for space weather.

Coronal holes represent normal behaviour of the Sun, and there is nothing particularly unusual about the ones recently reported.

Coronal holes are regions on the Sun where its magnetic field connects the Sun to interplanetary space. They show up as dark regions in X-ray images because they are locations with lower density of the gas close to the Sun. 

Coronal holes are sources of high-speed solar wind, which can interact with the Earth’s magnetic field, and cause enhanced geomagnetic activity. The formation of a coronal hole is determined by the location of sources of strong magnetic field at the surface of the Sun.