An aurora may often be viewed hundreds of kilometers equatorward of the auroral oval owing to its altitude. As such, the NOAA Space Weather Prediction Center (SWPC) Aurora Forecast product provides a “view-line” to demonstrate the equatorial extent of auroral visibility, assuming that it is sufficiently bright and high in altitude. The view-line in the SWPC product is based upon the latitude of the brightest aurora, for each hemisphere, as specified by the real-time Oval Variation, Assessment, Tracking, Intensity, and Online Nowcasting (OVATION) Prime (2010) aurora precipitation model. In this study, we utilize nearly 500 citizen science auroral reports to compare with the view-line provided by an updated SWPC aurora forecast product using auroral precipitation data from OVATION Prime (2013). The citizen science observations were recorded during March and April 2015 using the Aurorasaurus platform and cover one large geomagnetic storm and several smaller events. We find that this updated SWPC view-line is conservative in its estimate and that the aurora is often viewable further equatorward than is indicated by the forecast. By using the citizen reports to modify the scaling parameters used to link the OVATION Prime (2013) model to the view-line, we produce a new view-line estimate that more accurately represents the equatorial extent of visible aurora. An OVATION Prime (2013) energy-flux-based equatorial boundary view-line is also developed and is found to provide the best overall agreement with the citizen science reports, with an accuracy of 91%.
People in the polar regions of the world, such as Scandinavia and Canada, sometimes get to watch majestic, rainbow-coloured clouds drift across an otherwise grey winter sky. Over the past few days, observers from across the UK and Ireland have also been lucky enough to witness this phenomenon, known as “nacreous” (or polar stratospheric) clouds.
In fact, nacreous clouds are so unusual in Britain that AuroraWatch UK, a service that monitors the likelihood of auroal sightings, received reports that these colourful displays were “aurora borealis”, also known as the northern lights, which is caused by collisions of electrically charged particles from the sun colliding with particles in Earth’s atmosphere. However, the two phenomena are not related.
Nacreous clouds typically form in the winter polar stratosphere, a layer of our atmosphere around 15,000 to 25,000m in altitude. The stratosphere is generally very dry and so cloud formation is rare, but it seems as though recent storms may have driven moisture high into the atmosphere. Nacreous clouds will also only form when the temperature in the stratosphere is below a chilly -78°C, which turns any moisture in the air into super-cooled liquid or ice crystals. Such temperatures generally only occur in the winter at high latitudes.
During the hours of “civil twilight”, when the sun is between 1° and 6° below the horizon, the first or last rays of the day illuminate these high altitude clouds from below. This light is refracted by the ice crystals in the clouds, a process known as cloud iridescence, producing the shimmering rainbow effect.
As pretty as they may look, nacreous clouds have a darker side too. These clouds enhance the breakdown of the Earth’s ozone layer, a vital part of our atmosphere that provides protection from the sun’s harmful ultraviolet rays. The ice crystals in the clouds encourage a chemical reaction between the ozone layer, which is made up of a specific type of molecular oxygen (O3), and gases such as chlorine and bromine. In fact, it is estimated that just one atom of chlorine in the stratosphere can destroy over 100,000 ozone molecules.
The presence of these ozone-destroying gases in the stratosphere is a problem of our own making. Although phased out after the Montreal Protocol in 1987, the prime reason for their presence is our use of chlorofluorocarbons (CFCs) in products such as refrigerators and aerosol cans. While usage of CFCs has been significantly reduced, it is estimated that it may take another 50-100 years before the effects of CFCs in the atmosphere is diminished.
Current weather predictions suggest that further sightings of nacreous clouds may be possible in the UK until around Saturday. At this time, the polar vortex (which is responsible for the cold conditions currently in the stratosphere above the UK) moves northward to its usual position.
Nathan recorded the following clip for Lancaster University, and AuroraWatch UK, giving a few tips about how best to see the northern lights from the UK.
The tips include:
1 – Head north: the aurora will generally be visible on the northern horizon (in the northern hemisphere)
2 – Find an unobstructed view of the northern horizon: such as a hillside or a northward facing coast.
3 – Find dark skies: city light pollution will tend to be brighter than the aurora, especially when attempting to view by eye. Try seeking out local dark sky areas.
4 – Hope for clear skies: (this one is down to chance!) the aurora occur higher in altitude than clouds, so any clouds will obscure your view.
5 – Sign up to AuroraWatch UK for alerts of increased chance in auroral visibility from the UK.
Nathan also recorded a clip on “5 Surprising Facts about the Northern Lights” which you can watch below.
Witnessing an aurora first-hand is a truly awe-inspiring experience. The natural beauty of the northern or southern lights captures the public imagination unlike any other aspect of space weather. But auroras aren’t unique to Earth and can be seen on several other planets in our solar system.
An aurora is the impressive end result of a series of events that starts at the sun. The sun constantly emits a stream of charged particles known as the solar wind into the depths of the solar system. When these particles reach a planet, such as Earth, they interact with the magnetic field surrounding it (the magnetosphere), compressing the field into a teardrop shape and transferring energy to it.
Because of the way the lines of a magnetic field can change, the charged particles inside the magnetosphere can then be accelerated into the upper atmosphere. Here they collide with molecules such as nitrogen and oxygen, giving off energy in the form of light. This creates a ribbon of colour that can be seen across the sky close to the planet’s magnetic north and south poles – this is the aurora.
Gas giant auroras
Using measurements from spacecraft, such as Cassini, or images from telescopes, such as the Hubble Space Telescope, space physicists have been able to verify that some of our closest neighbours have their own auroras. Scientists do this by studying the electromagnetic radiation received from the planets, and certain wavelength emissions are good indicators of the presence of auroras.
Each of the gas giants (Jupiter, Saturn, Uranus, and Neptune) has a strong magnetic field, a dense atmosphere and, as a result, its own aurora. The exact nature of these auroras is slightly different from Earth’s, since their atmospheres and magnetospheres are different. The colours, for example, depend on the gases in the planet’s atmosphere. But the fundamental idea behind the auroras is the same.
For example, several of Jupiter’s moons, including Io, Ganymede and Europa, affect the blue aurora created by the solar wind. Io, which is just a little larger than our own moon, is volcanic and spews out vast amounts of charged particles into Jupiter’s magnetosphere, producing large electrical currents and bright ultraviolet (UV) aurora.
On Saturn, the strongest auroras are in the UV and infrared bands of the colour spectrum and so would not be visible to the human eye. But weaker (and rarer) pink and purple auroras have also been spotted.
Mercury also has a magnetosphere and so we might expect aurora there too. Unfortunately, Mercury is too small and too close to the sun for it to retain an atmosphere, meaning the planet doesn’t have any molecules for the solar wind to excite and that means no auroras.
The unexpected auroras
On Venus and Mars, the story is different. While neither of these planets has a large-scale magnetic field, both have an atmosphere. As the solar wind interacts with the Venusian ionosphere (the layer of the atmosphere with the most charged particles), it actually creates or induces a magnetic field. Using data from the Venus Express spacecraft, scientists found that this magnetic field stretches out away from the sun to form a “magnetotail” that redirects accelerated particles into the atmosphere and forms an aurora.
Mars’s atmosphere is too thin for a similar process to occur there, but it still has aurora created by localised magnetic fields embedded in the planet’s crust. These are the remnants of a much larger, global magnetic field that disappeared as the planet’s core cooled. Interaction between the solar wind and the Martian atmosphere generates “discrete” auroras that are confined to the regions of crustal field.
A recent discovery by the MAVEN mission showed that Mars also has much larger auroras spread across the northern hemisphere, and probably the whole planet too. This “diffuse” aurora is the result of solar energetic particles raining into the Martian atmosphere, rather than particles from the solar wind interacting with a magnetic field.
If an astronaut were to stand on the surface of Mars, they might still see an aurora but it would likely be rather faint and blue, and, unlike on Earth, not be necessarily near the planet’s poles.
Most planets outside our solar system are too dim compared to their parent star for us to see if they have auroras. But scientists recently discovery a brown dwarf (an object bigger than a planet but not big enough to burn like a star) 18 light years from Earth that is believed to have a bright red aurora. This raises the possibility of discovering other exoplanets with atmospheres and magnetic fields that have their own auroras.
Such discoveries are exciting and beautiful, but they are also scientifically useful. Investigating auroras gives scientists tantalising clues about a planet’s magnetic and particle environment and could further our understanding of how charged particles and magnetic fields interact. This could even unlock the answers to other physics problems, such as nuclear fusion.
Connor Gaffey from Newsweek.com today published an article about last night’s spectacular auroral display that was visible from across the UK. Connor spoke with Nathan about how best to see the aurora in the UK and why the display last night was so strong.
Newsweek spoke to Nathan Case, a member of the Aurora Watch U.K. team at Lancaster University, who track geomagnetic activity around the British Isles and sends alerts to users when sightings of the Northern Lights are possible, to find out the best way to see the lights.
On August 25, 2015 Nathan received the NASA Heliophysics Peer Award. The award was presented to Nathan in recognition and appreciation of superior performance of a special act, service, or achievement.
Nathan was the recipient of the NASA Heliophysics Peer Award on August 25, 2015
The full text of the award is as follows:
Nathan is a young PhD who has undertaken an unusual postdoc project and, through his innovation, has effectively opened up the analysis of citizen science aurora data for the space science community. He has submitted three first author papers in the past year (including a published GRL) and is working on a fourth. He has also been a co-author on numerous papers and presentations. He has worked with programmers, technical writers, educators, and human-computer interactions researchers, and is universally appreciated among a very diverse team. For these reasons, Nathan Case is presented with this 2015 Heliophysics Peer Award.
A new, citizen science based, aurora observing and reporting platform has been developed with the primary aim of collecting auroral observations made by the general public to further improve the modeling of the aurora. In addition, the real-time ability of this platform facilitates the combination of citizen science observations with auroral oval models to improve auroral visibility nowcasting. Aurorasaurus provides easily understandable aurora information, basic gamification, and real-time location-based notification of verified aurora activity to engage citizen scientists. The Aurorasaurus project is one of only a handful of space weather citizen science projects and can provide useful results for the space weather and citizen science communities. Early results are promising with over 2,000 registered users submitting over 1,000 aurora observations and verifying over 1,700 aurora sightings posted on Twitter.
Twitter data can even indicate where an Aurora Borealis may be spotted helping scientists have more sightings. After an electromagnetic storm in 2011 brought a flurry of Tweets with spottings of the Northern Lights even far down in the south, NASA scientist Elizabeth MacDonald created Aurorasaurus as a way to document sightings and to verify Tweets. A team of researchers led by Nathan Case found that Twitter data not only is a great indicator for where Aurora Borealis will be published but helps identify key characteristics of the light show including color.
Betsy Mason from Wired.com today published a story about how Aurorasaurus is using citizen science data to map the aurora. She and Nathan discussed the project via email and Nathan provided her with information about the project and an interesting new result:
“An interesting result is that, during our case study, around 60 percent of the reported sightings occurred equatorward (southward in the northern hemisphere, and northward in the southern hemisphere) of where our current best estimate predicted,” Case told me in an email.
As our users will know, we love Twitter here at Aurorasaurus. In addition to using the social media service ourselves (check out the Twitter list of Aurorasaurus Team Members here), we present aurora-related tweets for our users to verify them as aurora sightings (a process called crowdsourcing.) We then use these “verified tweets” in just the same way as the other observations reported via our website or apps, for example, by comparing their location with the modeled auroral ovals.