 |
|
|
|
| Magnetometer measurements and the northern lights |
|
|
The northern lights are formed when electrically charged particles collide with the atoms in the atmosphere so that these start shining. Where the electrically charged particles drop down, electrical currents are also formed high up in the atmosphere. These currents may be measured by measuring alterations of the magnetic field down here on the ground.
|
|
Click here in order to get a larger version.
|
|
Read about the magnetic field and study the illustrations in the article "The magnetic field of the Earth".
There are many measuring stations for magnetic fields all over the world. In Norway we have magnetometers from New-Ålesund in the North to Karmøy in the South. By comparing data from several stations it is possible to find out where the currents exist.
Magnetometers measure the magnetic field in three directions, H, D and Z.
H is the magnet field component along the ground (horizontal)
Z (or V) is the vertical component
D, also called the declination or magnetic declination, is the direction (angle) that the horizontal component has in relation to the geographical north.
A compass will always point in the D-direction. To be able to find the true north it is necessary to know the declination where you are.
An electrical current will always create a magnetic field around itself. The direction of the magnetic field may be determined by using the so-called right hand rule. If you let your right hand thumb point in the same direction as that of the current, and bend the other fingers, they will point in the direction in which the magnetic field runs. |
| |
In the figure below we may see in the bottom image a current coming towards us (the small circle with a dot in the middle). Around this current the magnetic field runs in circles. Where it hits the ground we can see the magnetic field running down into the ground on one side of the current, and up from the ground on the other side of the current.
We may use this in order to find out where the current is situated. If a magnetometer station measures that the alteration of the Z runs one way, while another station near the first one measures that the alteration runs in the other direction, then the current must lie somewhere between the two stations. |
| | |
|
| |
The figure below shows measurements of the Z-component of the magnetic field from the Norwegian stations (Click on the image in order to get a larger version). Just after 6 pm a great change of the magnetic field at all stations may be observed. The change is greatest in the North, so it is probably there where the current lies. If we compare the curves for the Longyear town (LYB) and the Bjørnøya (BJO) we see that they each run their own way. We may then assume that the current and thus also the northern lights lie somewhere between the Longyear town and the Bjørnøya.
The magnetometer data from Norway are available from The Northern Lights Observatory The Northern Lights Observatory in Tromsø.
By entering “Stacked D, “V” or “H” one may see plots from all the stations simultaneously. Under “Equivalent currents” we may see an attempt to determine currents based on the magnetometer data. These pages show real time data and may therefore be used in order to check whether the northern lights are on their way. |
| | |
|
|
|
|
|
| |
|
|
| |
|
|
|
|
|
|
