This magnetometer gives you the values of the magnetometer stationed at The Swedish Institute of Space Physics in Kiruna, Sweden. It is often used in Europe to see if there are aurora chances. In other places then Europe, like North America, other magnetometers should be used like the Canopus oval or another magnetometer close to your location.
But how do we read this plot? The plot displays the X, Y and Z values that are being observed at the magnetometer in Kiruna. The line of interest is the black line. It represents the X-component which shows us how far south the auroral oval reaches. When the Earth's magnetic field isn't being disturbed and geomagnetic conditions are at very quiet levels we will see values of about 10685 nanoTesla (nT) for the X-component. However, when the magnetic field is being disturbed we will see that the values on the graph will start to fluctuate and those values are important for us to determine if there is a chance to see auroras.
During geomagnetic storming when Kiruna is on the day light side of the Earth, the Kiruna magnetometer could deflect in an opposite way because the auroral oval is always pointed away from the Sun and the magnetometer will deflect less. This is also why it's important to look at magnetometers closer to your location.
For the middle latitudes, in particular the European region, you can capture photographic aurora when there is a deflection of at least 700nT and visual aurora can be expected when the deflection is 1300nT or more. We understand that this might be complicated so let's work with two examples.
In middle latitudes locations, like Belgium and The Netherlands, the most common form of aurora that occurs, are weak auroras low on the northern horizon which might be hard to see with the naked eye. A good example of how the Kiruna magnetogram would look like in such a situation can be seen on the picture below. The deflection was about 1200nT and the predicted Kp-index at that moment was 7. We can conclude that weak visual aurora was possible for northern parts of The Netherlands and Germany.
A second (rather extreme) example is this magnetogram from 30 October 2003. Two Coronal Mass Ejections from a X17 and X11 solar flare arrived at Earth and caused extremely severe geomagnetic storming with auroras which could be seen all the way in Portugal, Europe and Florida in the United States! At all middle latitude locations, auroras could be seen directly overhead! These storms will always be remembered as the "Halloween Storms of 2003" and were the strongest geomagnetic storms of SolarCycle 23 with a Kp-index of 9.
But how do we determine this deflection? When in Earth's magnetic field get's disturbed, the magnetometers will react to it and thus the Kiruna magnetogram will show us minor deflections from the normal quiet level of 10650nT. This deflection is also expressed in nanoTesla units (nT). The start of the deflection helpful is in the beginning of the storm before the measured values drop. It's difficult to explain this in words so in the graph below you'll see a good example of a deflection, measured at the Kiruna station. The deflection is shown as a yellow area in the graph; it starts shortly after the arrival of the Coronal Mass Ejection before it gradually degrades in value till it reaches it's lowest measured point. This deflection, expressed in nanoTesla, is the value we have to look at if we want to see or photograph the aurora. In this example the deflection is around 500nT and that is associated with a local Kiruna K-indice of 6 and thus was this not enough for aurorae on the lower middle latitudes.
De K-index is just like the Kp-index, a geomagnetic storm index with a logarithmic scale from 1 to 9 but as measured by a single station and not from multiple stations combined. Based on the deflection from the Kiruna magnetometer we can try to determine the K-indice for that specific station. For the station at Kiruna, we do this with the help of the table below. Be aware that, due to it's location, this magnetometer is only be helpful for observers from Europe.
|K-index||Deflection in nanoTesla||Storm type|
|0||0 - 15||No storm, quiet conditions|
|1||15 - 30||No storm, quiet conditions|
|2||30 - 60||No storm, quiet conditions|
|3||60 - 120||No storm, quiet conditions|
|4||120 - 210||Active geomagnetic conditions|
|5||210 - 360||G1 - Minor geomagnetic storm|
|6||360 - 600||G2 - Moderate geomagnetic storm|
|7||600 - 990||G3 - Strong geomagnetic storm|
|8||990 - 1500||G4 - Severe geomagnetic storm|
|9||1500 and more||G5 - Extreme geomagnetic storm|
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