A new magnetic observatory in La Réunion Island

Abstract. A new magnetic observatory has been set on La Réunion island in the Indian Ocean through a collaboration between the "Institut de physique du globe de Paris" (IPGP) local volcano observatory (OVPF) and its magnetic observatory service. This observatory is isolated and serves for monitoring the evolution of the magnetic field in that region. It is also particularly useful for large scale modelling of the core field and other contributions to the geomagnetic field. Three-component vector magnetic field data are continuously collected at 1 Hz using a fluxgate, while scalar data are collected at 0.2 Hz with a proton magnetometer. The data are transmitted every 5 minutes to IPGP main site and made immediately available to the scientific community (see www.bcmt.fr). Due to the strong magnetic field generated by the surrounding volcanic rocks, the differences between the magnetic field strengths as recorded by the proton magnetometer and the strengths calculated from the recorded vector field values vary during a day. To circumvent this difficulty, constant offset values of -2400 nT, 280 nT and -20 nT are systematically added to the X, Y and Z magnetic field components prior to the data distribution. We show that this efficiently reduces the differences between measured and calculated magnetic field strengths inside a day. Definitive observatory data have been calculated over the year 2023 and, although the baseline values present strong variations throughout that year, the derived data meet the quality required for an INTERMAGNET observatory. A Fourier analysis of the data shows that these are not contaminated by a significant noise even if peaks at 0.2 Hz indicate a small cross-talk between vector and scalar instruments.