When energetic solar particles impact our magnetic field, their energy can be transferred into our atmosphere. One of the affects of this are displays of the Northern Lights or Aurora Boreallis. Using a magnetometer we can measure changes in the Earths magnetic field which may indicate auroral displays.
Above is a live stream from my magnetometer. Under normal conditions it flows along showing a very grdual rise and fall. Should there be solar activity however, large displacements will occur.