The annual variations shown in Fig. 2 are already corrected using tiltmeters installed in the sensors of the magnetometers, and are out of phase with the temperature variation of the magnetometers.
The remaining variation can then be more directly interpreted in terms of conductivity variations, magnetometer distribution, and other effects, which could lead to variations with UT.
FGE 3-axial fluxgate magnetometer (DTU, Denmark) for recording the variations of the EMF components; GSM-19 scalar magnetometer (Gem Systems, Canada) for recording the modulus of the EMF vector.
The continuous data recording at the observatory are provided by the following instruments: FGE 3-axial fluxgate magnetometer (DTU, Denmark) for recording the variations of the EMF components; GSM-19 scalar magnetometer (Gem Systems, Canada) for recording the modulus of the EMF vector.
The DMI Greenland magnetometers recorded variations of the ionospheric Hall currents while Ørsted, a Danish low-altitude Earth-orbiting satellite, measured the magnetic effect of field-aligned currents (FAC).
We calculated the PLV values for all possible combinations of magnetometer sensors and averaged them for each subject.
Studies using magnetometer arrays to map lateral variations of conductivity in the crust and upper mantle have shown that large conducting anomalies induce anomalous magnetic fields that typically amplify the amplitude of the geomagnetic variations by some tens of percent (see, for example, discussion in Egbert 2002b, and references therein).
To ensure the precision needed for contemporary researches, a periodic calibration of the variation magnetometer should be carried out at every observatory.
A second hut houses a variometer of the type δD/δI vector magnetometer (Riddick et al., 1995), which automatically measures the variations of the magnetic field vector once per minute.
Apart from the direct measurement of the magnetic field on Earth or in space, these magnetometers prove to be useful whenever a phenomenon is linked with variations of magnetic field in space or in time, such as anomalies arising from submarines, skiers buried under snow, archaeological remains, and mineral deposits.
