This blog will contain posts Nathan has written on other sites (such as aurorasaurus.org), updates on publications Nathan has authored, or press clippings from articles that Nathan (or his work) have appeared in. Some original posts about Nathan’s activities (such as outreach or public engagement) may also be posted.
The article “AuroraWatch UK: an automated aurora alert service” was recently accepted to the American Geophysical Union (AGU) journal Earth and Space Science. The article, for which Nathan was the lead author, describes how the incredibly popular AuroraWatch UK is run and presents an analysis of a historical merged auroral activity data set.
The AuroraWatch UK aurora alert service uses a network of magnetometers from across the United Kingdom to measure the disturbance in the earth’s magnetic field caused by the aurora borealis (northern lights). The service has been measuring disturbances in the earth’s magnetic field from the UK, and issuing auroral visibility alerts to its subscribers, since September 2000. These alerts have four levels, corresponding to the magnitude of disturbance measured, which indicate from where in the UK an auroral display might be seen. In the following, we describe the AuroraWatch UK system in detail and reprocess the historical magnetometer data using the current alert algorithm to compile an activity database. This data set is comprised of over 150,000 hours (99.94% data availability) of magnetic disturbance measurements, including nearly 9,000 hours of enhanced geomagnetic activity.
The article is open source and free to download from the publisher’s site.
Whale strandings: could solar storms that cause the northern lights be to blame?
A series of sperm whale strandings saw 29 of the animals beached across the North Sea in early 2016. As these whales are not normally found in the North Sea, the strandings were a bit of a mystery. But a study is now proposing that the solar storms that cause the northern and southern lights (aurora) could be to blame for the ill-fated whales ending up on the beaches.
In their seasonal migrations between warmer equatorial waters and the squid-rich Norwegian Sea, sperm whales generally don’t travel through the North Sea. Instead, they migrate along the western coast of the British Isles. The North Sea is far too shallow for the whales and their favourite squid prey (Gonatus fabricii) generally isn’t found there either.
So once the whales entered the North Sea, it’s likely that they became disorientated, trapped in the shallow waters and ultimately beached. Necropsies performed on the whales suggested that they were healthy and well nourished, and so why they had entered the North Sea at all was a mystery.
It is thought that some animals can get a sense of direction from the Earth’s magnetic field. Indeed, cetaceans, which includes whales and dolphins, are thought to be able to navigate using “magnetoreception” just like migrating birds and bats. The recent study suggests that the whales’ detour into the North Sea was the result of a geomagnetic storm interfering with the whales’ magnetic navigation system.
The authors propose that these storms, which are the result of explosions of particles from the sun, created disturbances in the Earth’s magnetic field. They specifically identify two geomagnetic storms – occurring on December 20/21, 2015, and December 31 and January 1, 2015/2016 – which they argue could have caused disturbances strong enough to confuse the whales into travelling down the east coast of Shetland, rather than the west.
They suggest that a series of magnetic mountains, which have a magnetic field that is stronger than the surrounding area, would normally act as a barrier to the whales – preventing them from straying into the North Sea. During the storms, however, the local magnetic field was altered so much that these magnetic mountains appeared invisible to the whales – allowing them to pass into the North Sea.
The idea that geomagnetic storms cause navigational issues for animals is somewhat new but previous studies have shown that homing pigeons and migrating birds, for example, have trouble navigating through regions of magnetic anomalies. One study has found that the number of honey bees returning to their hive seems to drop significantly during geomagnetic storms, though the exact link remains unknown.
We have known for a long time that the sun’s activity, and the space weather it produces, can have a significant impact on us here on Earth. Not only does space weather produce the beautiful aurora that lights up the night sky, it can also cause serious damage to our technical systems.
In fact, space weather has already resulted in damage to satellites, interference with the Global Positioning System (GPS) and power grid failure. And it is estimated that a serious space weather event could cost the global economy US$40 billion per day.
While there’s increasing evidence that space weather can also affect biological organisms, it’s important to remember that a correlation is not the same as proof.
Further scientific analyses, such as actually monitoring a large number of whales to see if, and how, their travel paths change during geomagnetic storms, will be needed to prove this link for sure. After all, geomagnetic storms happen fairly often, so it could simply be a coincidence that these two events happened around the same time.
While space weather scientists are working hard to prepare our technological systems for future space weather events, it seems as though we may have to let nature take its course for the whales – at least for now.
Citizen scientists discover new type of aurora
A collaboration between aurora-hunting citizen scientists and a team of professional researchers has resulted in the discovery of a completely new type of aurora. The finding was made possible thanks to photos taken by aurora enthusiasts from across the globe which scientists could then compare with data from satellites.
The aurora, more commonly known as the northern or southern lights, form when electrically charged particles collide with the gases in our upper atmosphere. These charged particles, which have been accelerated into our atmosphere by the Earth’s magnetic field, transfer their energy to the atmospheric gases (such as nitrogen and oxygen). This extra energy is then released in the form of light which gives us the majestic aurora.
The aurora varies in strength depending on how active the sun is. Normally, an aurora is only visible near the magnetic poles but, when particularly active, it can be seen from much further away.
We generally see the aurora as a band about the poles (known as the auroral oval). This band is often green, with tinges of red or purple thrown into the mix. But sightings of this new phenomenon were different – straight away people noticed it didn’t look like the “normal” aurora.
When pictures first starting appearing on social media, the odd aurora was widely assumed to be what is known as a “proton arc”, but scientists knew that this wasn’t right. Proton arcs are caused by protons (positively charged particles which make up the atomic nucleus along with neutrons) colliding with neutral gases in the atmosphere. Proton aurora are not visible by eye and are broad and diffuse. This new type of aurora, however, was visible by eye and was a bright, structured band of purple in the night sky. They knew it had to be something else – but what?
The Aurorasaurus citizen science project issued a call to arms to collect sightings of this as-yet-unnamed aurora. Over 50 sightings from countries including Canada, US, UK and New Zealand were reported during 2016 and 2017. Because this type of aurora didn’t yet have a name, the citizen scientists called it “Steve” (after the animated children’s film, Over the Hedge).
The biggest breakthrough in identifying “Steve” came when Eric Donovan, an associate professor of physics and astronomy at the University of Calgary in Canada, found an instance where a photo was taken of “Steve” at the same time as one of the European Space Agency’s Swarm satellites passed above it. Donovan found that as the satellite flew straight though Steve, data from the electric field instrument showed very clear changes.
Speaking at a recent scientific conference, Donovan said that “the temperature 300km above Earth’s surface jumped by 3000°C and the data revealed a 25km-wide ribbon of gas flowing westwards at about 6km per second compared to a speed of about ten metres per second either side of the ribbon.”
This result definitively proved that “Steve” is in fact a distinct feature from the normal aurora oval, as the ribbon was located south of the main aurora. It also showed that “Steve” is not a proton arc.
While we have now been able to measure “Steve”, we still aren’t sure what causes it. It seems that “Steve” is fairly common but it took the power of citizen science for it to really be noticed. Donovan says that research is still ongoing but that he thinks he is close to finding the cause.
Discoveries of new types of aurora are rare and this one highlights the importance of citizen scientists. If it weren’t for the dedication of amateur aurora hunters, we may never have started studying this new phenomenon. So if you think you’ve spotted “Steve”, make sure you submit your sighting to Aurorasaurus to help us learn more about this beautiful purple streak.
Nathan is extensively quoted in a story by the Daily Express, discussing AuroraWatch UK.
After solar winds arrive at our planet, Dr Case said: “The charged particles run into Earth’s atmosphere and collide with molecules.
“When they collide, they transfer energy. The atmosphere does not like this extra energy which is why give off light.”
He said that oxygen emits the famous green colour and some red, while nitrogen gives off the blue and purply lights.
The article “An analysis of magnetic reconnection events and their associated auroral enhancements” was recently accepted to the American Geophysical Union (AGU) Journal of Geophysical Research: Space Science. The article, for which Nathan was the lead author, describes how small scale processes in the earth’s magnetotail, called magnetic reconnection, is associated with enhancements of the aurora.
An analysis of simultaneous reconnection events in the near-Earth magnetotail and enhancements in the aurora is undertaken. Exploiting magnetospheric data from the Geotail, Cluster, and Double Star missions, along with auroral images from the IMAGE and Polar missions, the relationship between a reconnection signature and its auroral counterpart is explored. In this study of 59 suitable reconnection events, we find that 43 demonstrate a clear coincidence of reconnection and auroral enhancement. The magnetic local time (MLT) locations of these 43 reconnection events are generally located within ±1 h MLT of the associated auroral enhancement. A positive correlation coefficient of 0.8 between the two MLT locations is found. The enhancements are localized and short-lived (τ≤10 min) and are as likely to occur during the substorm process as in isolation of a substorm. No significant dependence of the reconnection or auroral enhancement location on the dusk-dawn components of the solar wind velocity (Vy), IMF (By) or local By or Vy, as measured by the reconnection-detecting spacecraft, is found.
The article is open source and free to download from the publisher’s site.
Don’t panic: the northern lights won’t be turning off anytime soon
The northern lights are nature’s very own magnificent light show. They are the mesmerising end result of electrically charged particles from the sun colliding with the Earth’s upper atmosphere. Though more frequently witnessed from the polar regions, the UK and other places on similar latitudes are lucky enough for the aurora borealis to occasionally grace their night sky.
But recent reports now claim the phenomenon may no longer be visible from places such as the UK – instead confined to the North Pole. But is this correct?
The northern lights are driven by activity on the sun and the sun’s activity waxes and wanes over an 11-year period known as a solar cycle. The number of large-scale aurora events, the type that is visible from places such as the UK, tends to follow this cycle. But each solar cycle is different, with the maximum and minimum activity varying between each cycle.
Predicting solar activity
Current predictions suggest that we are headed for a period of particularly weak solar cycles, where the solar maximum of each cycle will not result in much solar activity. We call this a grand solar minimum.
Grand solar minimums can last for several decades or even centuries and have occurred throughout history. Although solar output does decline during these periods, it doesn’t mean that we are heading for a new ice age.
A study recently published in Nature has modelled the perhaps most well-known grand solar minimum, called the “Maunder minimum”. This particular grand solar minimum started in 1645 and finally ended 70 years later. During this time only 50 sunspots, structures on the sun that act as a measure of its activity, were observed. This is compared to the 40,000-50,000 that we would expect during a period of “normal” activity lasting that long.
The authors of the study found that during the Maunder minimum, the solar wind, which drives the aurora, dramatically weakened. They also illustrate that as the solar wind weakens, so too will the aurora.
If we are in fact heading into a new grand solar minimum, it stands to reason that we might see less of nature’s beautiful spectacle. But does that mean we’ll stop seeing it from the UK altogether as some have suggested?
Lessons from the past
Looking back at historical records of aurora sightings might provide the answer. Fortunately, a study has done just that. The authors analysed auroral observations during two grand solar minimums– including the Maunder minimum. They found that the number of aurora sightings from below 56° magnetic latitude (which is similar to geographic latitude but measured from the magnetic pole rather than the geographic pole) did indeed decrease. But they did not stop altogether.
That value of 56° magnetic latitude is actually quite important as it happens to coincide with the magnetic latitude of the UK (more specifically somewhere close to Lancaster, England).
So what’s my prediction for the aurora over the next century? If the models are correct and we do head into a grand solar minimum, then solar activity is going to decrease – and remain at very low levels for decades to come. With this decrease in solar activity, aurora sightings from outside the polar regions are going to become rarer. But that doesn’t necessarily mean they’ll stop altogether. It also isn’t certain that we are heading for a grand solar minimum or – even if we are – when it might occur.
So while that elusive light show might get even more elusive, don’t fret just yet: the northern lights aren’t going out anytime soon.
The article “Determining the accuracy of crowdsourced tweet verification for auroral research” was recently accepted to the journal Citizen Science: Theory and Practice. The article, for which Nathan was the lead author, describes the accuracy of citizen scientists at determining whether tweets relating to “aurora” were in fact sightings of the natural phenomenon.
The Aurorasaurus project harnesses volunteer crowdsourcing to identify sightings of an aurora (the “northern/southern lights”) posted by citizen scientists on Twitter. Previous studies have demonstrated that aurora sightings can be mined from Twitter with the caveat that there is a large background level of non-sighting tweets, especially during periods of low auroral activity. Aurorasaurus attempts to mitigate this, and thus increase the quality of its Twitter sighting data, by using volunteers to sift through a pre-filtered list of geolocated tweets to verify real-time aurora sightings. In this study, the current implementation of this crowdsourced verification system, including the process of geolocating tweets, is described and its accuracy (which, overall, is found to be 68.4%) is determined. The findings suggest that citizen science volunteers are able to accurately filter out unrelated, spam-like, Twitter data but struggle when filtering out somewhat related, yet undesired, data. The citizen scientists particularly struggle with determining the real-time nature of the sightings, so care must be taken when relying on crowdsourced identification.
The article is open source and free to download from the publisher’s site.
Beautiful green ‘airglow’ spotted by aurora hunters – but what is it?
Amateur astronomers and aurora hunters alike have been reporting a green glow across the UK sky. Easily confused with the aurora borealis, or northern lights, the sightings were of another phenomena called “airglow”.
Airglow is the natural “glowing” of the Earth’s atmosphere. It happens all the time and across the whole globe. There are three types of airglow: dayglow, twilightglow and nightglow. Each is the result of sunlight interacting with the molecules in our atmosphere, but they have their own special way of forming.
Dayglow forms when sunlight strikes the daytime atmosphere. Some of the sunlight is absorbed by the molecules in the atmosphere, which gives them excess energy. They become excited. The molecules then release this energy as light, either at the same or slightly lower frequency (colour) as the light they absorbed. This light is much dimmer than daylight, so we can’t see it by eye.
Twilight glow is essentially the same as dayglow, but only the upper atmosphere is sunlit. The rest of the atmosphere and the observer on the ground are in darkness. So, unlike day glow, twilightglow is actually visible to us on the ground with the naked eye.
The chemistry behind nightglow is different. There is no sunlight shining on the nighttime atmosphere. Instead, a process called “chemiluminescence” is responsible for the glowing atmosphere.
Sunlight deposits energy into the atmosphere during the day, some of which is transferred to oxygen molecules (e.g. O₂). This extra energy causes the oxygen molecules to rip apart into individual oxygen atoms. This happens particularly around 100km in altitude. However, atomic oxygen isn’t able to get rid of this excess energy easily and so acts as a “store” of energy for several hours.
Eventually the atomic oxygen does manage to “recombine”, once again forming molecular oxygen. The molecular oxygen then releases energy, again in the form of light. Several different colours are produced, including a “bright” green emission.
In reality, the green nightglow isn’t particularly bright, it’s just the brightest of all nightglow emissions. Light pollution and cloudy skies will prevent sightings. If you’re lucky though, you might just be able to see it by eye or capture it on long-exposure photos.
Not to be confused with aurora
The green night glow emission is very similar to the famous green we see in the northern lights. This is unsurprising since it is produced by the same oxygen molecules as the green aurora. But the two phenomena are not related.
Aurora form when charged particles, such as electrons, bombard the Earth’s atmosphere. These charged particles, which started off at the sun and were accelerated in the Earth’s magnetosphere, collide with the atmospheric gases. They transfer energy, forcing the gases to emit light.
But it isn’t just the process behind them that is different. The aurora form in a ring around the magnetic poles (known as the auroral oval); whereas nightglow is emitted across the whole night sky. The aurora are very structured (due to the Earth’s magnetic field); whereas airglow is generally quite uniform. The extent of the aurora is affected by the strength of the solar wind; whereas airglow happens all the time.
Why then did we get a lot sightings from the UK recently, rather than all the time? The brightness of airglow correlates with the level of ultraviolet (UV) light being emitted from the sun – which varies over time. The time of year also seems to have an impact on the strength of airglow.
To maximise your chances of spotting airglow, you’ll want to take a long-exposure photograph of a clear, dark, night sky. Airglow can be spotted in any direction that is free of light pollution, at about 10⁰-20⁰ above the horizon.
The article “A real-time hybrid aurora alert system: combining citizen science reports with an auroral oval model” was recently accepted to the American Geophysical Union (AGU) journal Earth and Space Science. The article, for which Nathan was the lead author, describes how citizen science reports are combined with the Ovation auroral forecast product to produce accurate and localised aurora alerts.
Accurately predicting when, and from where, an aurora will be visible is particularly difficult, yet it is a service much desired by the general public. Several aurora alert services exist that attempt to provide such predictions but are, generally, based upon fairly coarse estimates of auroral activity (e.g., Kp or Dst). Additionally, these services are not able to account for a potential observer’s local conditions (such as cloud cover or level of darkness). Aurorasaurus, however, combines data from the well-used, solar wind-driven, OVATION Prime auroral oval model with real-time observational data provided by a global network of citizen scientists. This system is designed to provide more accurate and localized alerts for auroral visibility than currently available. Early results are promising and show that over 100,000 auroral visibility alerts have been issued, including nearly 200 highly localized alerts, to over 2000 users located right across the globe.
The article is open source and free to download from the publisher’s site.
“Without the citizen science observations, Aurorasaurus wouldn’t have been able to improve our models of where people can see the aurora,” said the study’s lead author, Nathan Case, a previous Aurorasaurus team member and now a senior research associate at Lancaster University, United Kingdom. “The team is very thankful for our community’s dedication and are excited to have more people sign up.”
The full article can be read here