Fluxgate Magnetometer Offset Vector Determination Using Current Sheets in the Solar Wind

The zero offset of the fluxgate magnetometer (FGM) on board the spacecraft varies slowly with time, therefore the FGM needs regular in-flight calibration. There are abundant physical phenomena in the solar wind, such as waves, mirror mode structures, and current sheets. Several in-flight calibration methods have been developed based on the properties of Alfvén waves or mirror mode structures instead of current sheets. Here, we develop a method to determine the zero offset O using current sheets in the solar wind, which is based on an assumption that the magnetic field in the normal direction of the current sheet is zero. The nonzero magnetic field in the normal direction is the projection of O , therefore we can obtain the component of O in the normal direction. In the offset cube, the zero offset is expected to be in a plane, which is referred to as the optimal offset plane (OOP). Each current sheet can obtain an OOP in the offset cube. At least three nonparallel OOPs must be used to determine the zero offset. We test our method by using data from the Magnetospheric Multiscale mission and find that our method is able to determine the zero offset. Our method can simultaneously use Alfvén waves, mirror mode structures, and current sheets to determine the zero offset, thus it might be a useful tool to perform the in-flight calibration of the FGM for solar wind monitors.