ALOMAR Observatory - Fluxgate magnetometer

The earths magnetic field:

Both the sun and the earth have magnetic fields, generated by electrical currents flowing inside the respective bodies. In addition to electromagnetic radiation (e.g.,
light, radiowaves, x-rays), the sun emits an electrically-charged gas (solar wind plasma) which carries the 'frozen-in' solar magnetic field along with it as it streams away from the sun. The plasma is composed almost entirely of electrons and protons. Perturbations in the plasma density/magnetic field propagate as Alfven waves. At 1-AU (astronomical unit - the mean distance of the earth from the sun = 150 mill. km) the solar wind plasma density is about ten particles per cubic centimeter, the solar wind speed is about 400 km/s, and the magnitude of the interplanetary magnetic field (IMF) is about 10 nT.

If there were no solar wind, the earth's magnetic field would be dipolar, but the pressure of the solar wind causes the simultaneous distortion of the earth's magnetic field, and deflection of the solar wind around the earth.

Perturbations of about 1000 nT are common during disturbed times, sometimes lasting for several days, but usually with time scales of only minutes or hours.

The USOC fluxgate magnetometer measures the slow variations of the terrestrial magnetic field (H, D and Z component). Variations down to approx. 1 nT (nano Tessla) can be logged with max perturbation readout of approx. 1000 nT.