The norlys model is an experimental model that aims to transcribe global magnetometer data into a dynamic map displaying the probable, near-real-time auroral activity in the northern hemisphere (aurora borealis) and by extension in the southern hemisphere (aurora australis). This is the first-ever public aurora map of its kind featuring near real-time magnetometer data across such an extensive area. On top of assessing the near real-time activity, our norlys model features an archive of this activity over the last two and twenty-four hours. Our model is not a forecast like the OVATION, it is a nowcast of the likely aurora activity on Earth.

The norlys model is derived from global magnetometer data, which are converted into a back-end ionospheric current map. This map works in the background and is updated every minute. It calculates the intensity and direction of equivalent ionospheric currents above an area of the world covering Europe, Iceland, Greenland and north America (‘model calculation area’). The ionospheric current vectors are assessed thanks to magnetometer stations provided by TGO, UAF, USGC, Carisma, BGS, IRF, FMI and DTU ; See credits later. The currents are then derived from associated magnetic field displacements in nanoTeslas. This intermediary map enables us to locate the position of the real-time auroral oval, as well as to determine the flowing direction and intensity of the auroral electrojet current.

The auroral electrojet (AE) current has been widely demonstrated to be closely associated to the auroral oval. In other words, it means that the auroral electrojet can be assimilated into the auroral oval, as the former is often near or inside the latter. Based on these scientific assumptions, our norlys model can give us a foundation to work out a relatively precise location and intensity for the auroral oval.

The norlys model gives a relatively accurate ‘nowcast’ of the location and intensity of the aurora activity. In addition, it enables users to go back in time to monitor the evolution of this activity over the last two hours and the past 24 hours.

Our model inputs data from unevenly located magnetometers around the globe, and there are large uncovered areas. We implemented a powerful algorithm that extrapolates the data over these less populated areas to fill in the blanks and produce a full auroral oval. This is better esthetically but it also introduces a source of bias that users need to make themselves aware of, especially over Russia, oceans and seas (see disclaimers). Moreover, due to the lack of magnetometer stations in the southern hemisphere, we could not create a full southern auroral oval that would be useful for norlys users. Our model still features the southern hemisphere auroral oval as a mirrored image of its northern hemisphere counterpart thanks to their conjugacy. There are caveats to this as well, which we develop in the disclaimers below.

NB: Our model favors the stronger auroras to the detriment of very weak ones, hence the scale displaying the probability of strong auroras. Weak aurora activity may still naturally arise along the oval and inside the polar cap whereas magnetometers- and so our model, don’t display the corresponding variations. (See disclaimers below).

By computing ionospheric current data, we are able to output a naturally realistic map of the tentative auroral oval, which evolves in latitude, longitude and intensity in near real-time. This is extremely useful for aurora chasing because users can rapidly locate where the oval is and where the maximum activity can be found along the oval. This is especially true when users monitor the evolution of the oval on our map continuously. With the ability to follow the auroral activity over the past two hours or 24 hours, users can easily identify how far they are from the oval, assess the sector of the oval they are crossing, understand the evolution of the auroral activity and eventually anticipate the type of auroral activity that will occur near them.

Please note that our model does not precisely determine all the different types of auroral behaviors along the oval. After all, magnetometer data can only serve as a proxy for the aurora activity and there is a gap between the two. With that being said, our model can still help greatly to anticipate the major types of behavior using the relative intensity and location of this activity.

As an example, early magnetic evening auroras are often quiet arcs and so the geographical locations passing under this sector of the auroral oval should on average only experience a thinner, dimmer activity in our model. In the same way, closer to magnetic midnight, the nightside of the Earth experiences more explosive auroras- most of them being substorms, which work in a dim build-up (growth), then bright release (expansion or onset), followed by a diffuse phase (recovery). Our model does show the real-time development of these spectacular substorms by sudden changes in intensity and location of the oval. The growth phase will often display a low intensity aurora slowly migrating equatorward on the nightside over several minutes or hours while the dayside oval will often display ‘dynamic activity’. The expansion phase typically features a sudden and intense brightening of the aurora activity on the nightside of the Earth, traveling from the equatorward oval towards a much more poleward location. On top of color brightening, our model will often display ‘dynamic’, ‘very dynamic’ or ‘extremely dynamic’ in these expansion areas to reflect how steep magnetometer deflections are. This often gives a good idea about how dynamically auroras dance in the sky. The recovery phase will generally show a moderate intensity but over a much larger oval in latitude span.

The model has been designed with the utmost care for user interface. It is integrated into an interactive 3-D globe that can be smoothly rotated, zoomed on and moved around. Use your mouse (desktop) or fingers (mobile) to drag and rotate the globe. Scroll forward (desktop) or pinch out (mobile) to zoom in. Scroll back or pinch in to zoom out. As you load the homepage, the model should center itself on your current location automatically, provided you allowed location service when you first downloaded the app / used the website. This location should appear as a blue dot on the map. After a certain time of inactivity on the page, our model goes into a ‘presentation mode’ where different webcams around the world are displayed. This mode deactivates as soon as you move your mouse and use the map. The ‘presentation mode’ and ‘full screen mode’ can also be selected manually in the left hand-side panel.

The map also shows cities for which we have online webcams. On the desktop version, hover over the city to reveal the webcam. On mobile devices, click on the city to reveal the webcam. Click again to close it down. You may have to zoom in to reveal more cities and webcams. Webcams are extremely important to confirm the presence, the type, the brightness and the behavior of the aurora. Having them together with theoretical aurora activity from magnetometers is currently the best field tool any aurora chaser can use.

The aurora is very easily washed out by the slightest sunlight. Therefore, our model displays where the sunset / sunrise terminator is, where the Sun sets below or rises above the horizon for an observer on Earth. On our model, this terminator line marks the transition between a light gray area (sunlit) and a darker gray band. This band of darker gray corresponds to a time after sunset or before sunrise where it is yet too bright to see any aurora, even if it is in the sky. If you are located in that band, the Sun is between 0 and 7 degrees of elevation under the horizon. You are in what we call civil twilight (0-6 degrees) or the beginning of nautical twilight (7-8 degrees). The darkest area corresponds to the surface of the Earth where it should be dark enough to see the aurora. In this zone, the Sun is below 8 degrees of elevation under the horizon. It includes the end of nautical twilight (8-12 degrees), astronomical twilight (12-18 degrees) and full nighttime with complete darkness (below 18 degrees). Please note that the twilight (Sun between 8 and 18 degrees) can affect aurora viewing in different ways. During big solar events resulting in strong auroral activity, the aurora may well be visible in the twilight. However, the best views of the aurora are most often during full nighttime or at least astronomical twilight.

In the dark area of the Earth, we also implemented a moonlit area, which appears in dark blue and delimited by a ‘moonrise/set line’. The illumination % of the moon is indicated along that line. Moonlight can sometimes greatly affect the aurora by altering its colors and washing it out. It may be important to know when and how the moon can affect your aurora experience.

The auroral activity is concentrated into a dynamic ring, roughly centered around the geomagnetic poles. It is called the auroral oval. This ring is therefore strongly connected to geomagnetic latitudes on Earth (MLAT). Using the quasi-dipole approach and data provided by the BGS (see credits), we integrated the main lines of geomagnetic latitude on Earth. The area comprised between 90° and 70° MLAT is commonly referred to as the ‘polar cap’ or ‘very high geomagnetic latitudes, with a 20 to 60% chance of seeing the aurora (generally fainter though). The thin band stuck between 70° and ~64° MLAT is called the ‘auroral zone’ or ‘high geomagnetic latitudes’, which features a staggering 80 to 100% chance to see the aurora on any given night throughout the solar cycle. It is the best place to see the aurora on Earth, on average. Below ~65-60° MLAT lies the ‘sub-auroral zone’ or ‘geomagnetic mid-latitudes’, where it may still be possible to catch the aurora, albeit with a 0 to ~20% rate throughout the solar cycle. Mid-latitudes can see the aurora more often than what is popularly believed, especially during strong solar wind events when the oval widens. These events are more frequent around the solar maximum phase of the Sun’s activity cycle.

One thing is certain: the closer you are to the auroral zone, the more chances of seeing any aurora.

Please note that these geomagnetic latitude lines do not describe perfect circles around the Earth because this model does not follow the perfect dipole approach, revealing therefore a more realistic picture of the Earth’s magnetic field. The geomagnetic latitude lines are represented by thick, light gray lines. We also represented the geographic latitudes in the background by thinner and dimmer lines. Superposing these two coordinate systems are quite interesting from an aurora chasing standpoint, because it reveals how two identical geographic latitudes on Earth may not at all have the same chances to see the aurora at equal activity.

The scale of probability of strong aurora goes from low to high (0-10/10). Very low to moderate activity (0-3/10) would correspond to fainter aurora, often encountered when the geomagnetic activity is generally quiet, or during substorm growth. This type of aurora is often encountered in the daytime oval (dayside aurora), in the afternoon oval (discrete quiet arcs), the early evening oval (discrete quiet arcs), the late evening and nighttime oval (substorm growth arcs or substorm recovery pulsating aurora). Moderate probability (3-5/10) often describes situations like more intense evening auroras, more intense substorm growth and substorm recovery. High and very high intensities (>5/10) typically correspond to the most active auroras, occurring generally during substorm expansion or other types of explosive auroral activity in the nighttime oval, at the beginning of the recovery phase or anywhere along the oval under a unusually active magnetosphere. The latter state is called ‘geomagnetic storming’, during which many different sectors of the oval can intensify. At times when magnetometer register a steep H/x slope, our model will show an area with ‘dynamic’, ‘very dynamic’ and ‘extremely dynamic’. These areas are independent from the model score and often indicate how dynamic the auroral activity is in the sky. These zones may appear before the model changes colors during substorm expansions and can sometimes be used as an early warning sign that the aurora is getting more active.

Clicking on any point of the globe will reveal a lot of useful information about that location. For example, you’ll find the model score and strong aurora probability, the geographic and magnetic latitude (MLAT), the magnetic zone, the magnetic local time (MLT), the local time, sunrise, sunset, moonrise and most times. The closest magnetometer station to the clicked location will appear as a dashed-line and a cross (with distance and confidence level), whereas the closest webcam to the clicked point should come up as a plain line ended by a dot.

Users can utilize the time slider to reveal the state and location of the aurora activity at any time during the last 2 hours or 24 hours. Click on the ‘2 hours’ box to change to the ’24 hours’ mode. You can also let it play as a timelapse movie by pressing on ‘play’ on the left-hand side of the slider. Using the slider may introduce a little lag in displaying the aurora data, as there are more than 200 data points to retrieve per minute. Please allow some time for data retrieval before playing. NB: the ‘play’ option will only display rougher boundaries for countries and aurora activity because of the amount of data. You can come back to the nowcast by clicking on ‘latest’ on the right-hand side of the slider.

Our model is not a forecast. While you can use the model by spotting where the current aurora activity is at a glance, we recommend that you monitor it closely over several minutes (or dozens of minutes). As magnetometer data can display very quick changes or errors, our model may therefore underestimate or overestimate the auroral activity at times, resulting in gaps, discrepancies or sudden drastic changes. These are almost always erased naturally in the course of a few minutes, hence the need to monitor the map on a regular basis and not just punctually. The time bar makes it much easier to study how the auroral oval evolves over the past hours, enabling you to better anticipate what is likely to occur next.

We are eternally indebted to Dr. M. G. Johnsen, head of the Tromsø Geophysical Observatory (https://www.tgo.uit.no/), along with his team for providing us with geomagnetic data from Norway, Greenland and Svalbard, as well as helping in the construction of several aspects of the model. We would also like to thank the FMI (the Finnish Meteorological Institute, https://en.ilmatieteenlaitos.fi/) for providing geomagnetic data in Finland. In the same way, we thank the IRF (Swedish Institute of Space Physics, https://www.irf.se/sv/) for the Swedish data, and the DTU Space (Danish Institute of Space Physics, https://www.space.dtu.dk/) for the Danish data. Additionally, we thank the British Geological Survey (BGS) for providing us with Lerwick (LER) and Sable Island (SBL) real time observatory data, as well as geomagnetic coordinate data (please visit https://geomag.bgs.ac.uk/). Finally, we want to extend our special thanks to the UAF (Alaska, Fairbanks), the USGC (USA) and Carisma (Canada) for providing us with the North American data.

It is of utmost importance for norlys users to be aware of the following disclaimers.

[1] It is a citizen-science initiative: the present model is merely experimental. It means that although it bases its theory and data on science literature and scientific observations, the model itself has not been peer-reviewed and is not associated with any scientific / governmental institution. It is to be used at the user’s sole discretion.

[2] Very good but never 100% accurate: strong ionospheric currents like the Auroral Electrojet and the magnetic field variations they create are often associated with auroral activity. However, there is still a gap between ionospheric currents data and real-life auroral activity. When current-generated field variations are intense, the model becomes more accurate but quiet times may introduce some bias. Thus, although our model has been tested to present a thorough estimate of the auroral oval and its activity, there may be some inaccuracy and discrepancies in the intensity and location of the auroral activity at times.

[3] Aurora ‘outside of the oval’: To follow up on the last point, you may experience some auroral probability ‘blobs’, which are far from the oval. Please note that although we have implemented a code that limits errors, the raw magnetometer data are provided by different institutions around the world and there are often significant differences in the instrumentation used. Therefore, although we recalibrate all data following an advanced baseline calculation, there may still be data errors and discrepancies from time to time, showing you zones of aurora probability that seem out of place. They are easily identified by their ‘blobby’ look and by their distant location to the auroral oval. These often disappear quickly in the course of several minutes.

[4] Delays: the model is updated every minute by retrieving magnetometer data. The latter already presents a form of delay compared to the real-time local magnetic activity. In the field, most auroral activity is evolving slowly, over dozens of minutes, if not hours. This makes the use of magnetograms rather easy and timely. However, you may regularly experience a brightening of the aurora, which only last for seconds or minutes. These quick intensifications tend to appear with a delay in a magnetogram array and might consequently be finished before they can be read in our model. However, there is a triple silver lining to this. A) A lot of these brightenings are still slow to develop, enabling our model to catch up and show you an increase in auroral brightness in time. B) By following our model and the time bar regularly for the nightside oval where these intensifications happen frequently, users can put themselves in the best position to catch the brightenings by identifying the build-up process (growth), which is characterized by a thinner, dimmer oval slowly migrating equatorward. This is when using webcams together with the model becomes crucial. C) Our model sometimes shows a ‘dynamic’ area before the model registers an aurora strength change. This can help get ready more quickly to not miss the show.

[5] Spatial Interpolation within our model calculation area: The oval representation may be spatially inconsistent at times because some countries and land masses are simply not covered by magnetometer data, or because we haven’t been able to gain access to magnetometer data for such areas. Therefore, a stronger interpolation had to be implemented in such zones, leading to more spatial inaccuracy. For example, we have much fewer magnetometers at lower latitudes, so the representation of the oval will become much more uncertain when the oval really expands equatorward during extreme geomagnetic storms. In such cases, it shouldn't be too much of an issue as other features of our app would notify you of the very intense geomagnetic conditions at mid-latitudes. By clicking on a location, you can reveal the confidence level according to the distance to the closest magnetometer station.

[6] Strong spatial Interpolation outside of our model calculation area: In a new update, we have implemented an algorithm that extrapolates strongly between magnetometer-rich and magnetometer-poor zones, so that the oval appears more complete. This is especially the case in the zone outside our calculation area, i.e. mostly Russia. Please note that interpolated values are much less accurate in time, in place and in intensity in these zones.

[7] Southern hemisphere oval: It has long been demonstrated that the northern auroral oval and its southern counterpart are mirrored. We call this property auroral oval conjugacy. In Layman’s terms, it means that the aurora borealis and the aurora australis should theoretically produce the same activity at the same time and at the same place. Many of our early users wished to get access to the southern hemisphere oval and this very property enables us to do just that despite the lack of regular magnetometer stations to draw the southern oval correctly. We pasted and fitted a mirrored image of the northern oval calculated by our model in the southern hemisphere centered around the southern geomagnetic pole. Users in the southern hemisphere can now have an estimation of the oval according to their location. However, a word of caution. Despite oval conjugacy, many recent studies have also pointed out differences arising between the two ovals, some of which are thought to come from solar wind properties, the magnetic configuration of the IMF (By, Bx), magnetospheric properties and even sunlight (conductivity in the ionosphere)! Therefore, we advise our southern hemisphere users to take this representation of the southern oval with a grain of salt. We recommend that you follow the oval in its entirety, its global intensity and its latitude, and that you give less attention to longitudinal accuracy. Following this simple rule should limit the number of errors. We are still working to implement magnetometer and webcam data into this model to render it more accurate in the future.

[8] Lack of data: some users get surprised or frustrated to see very weak or no auroral activity on our model at times. However that’s how the aurora works! Most of the time, the aurora oval is quiet and gets enhanced only on sporadic occasions, except during prolonged geomagnetic storming featuring sustained, strong and negative IMF Bz. Our model is not a forecast like the OVATION model, which always shows some ‘green’ no matter the regime in the solar wind or in the magnetosphere. Our model is a nowcast of the real-life auroral activity, so it is completely normal that it appears weak or near empty. For example, a background solar wind with sustained positive IMF Bz will often generate an extremely weak and closed down oval. Although it is near impossible for the oval never to contain any form of aurora, there are many times where the auroral activity along the oval is very weak or almost absent. Such instances occur often under generally quiet solar wind conditions, and/or in the evening oval, and/or in the polar cap, and/or during the growth phase of weaker substorms. In such situations, auroras may still occur in the oval in weaker forms whereas our model does not display much visually. That’s why our intensity scale is based on strong auroral activity. When you don’t see anything on the model, it is important that you A) click around on the map to detect very weak values that are hard to detect visually (typically values between 0 and 1, showing a very weak green), B) monitor the model continuously over several minutes to spot the reappearance of the oval, C) check webcams regularly to verify the evolution of the oval when the model fails to show it. As soon as the magnetometer activity gets stronger again, the oval should reappear. Working with magnetometers has its advantages but it also has its drawbacks, and this is one of them. We are only interpreting what magnetometers register, nothing else!