Corrections for anomalous crustal magnetic field determined from magnetic observatory data

Abstract

The magnetic field of the Earth’s crust provides essential information about the geological features of a region, its origin, and the spatial and temporal characteristics of the total magnetic field.Numerical estimation and consideration of the contribution of the crustal field are a necessary step in constructing accurate models of the secular variation of the main magnetic field of the Earth based on observatory data. To accurately determine the corrections for the crustal field at the locations of magnetic observatories, we apply an algorithm to process the original observatory data, which allows us to define all three orthogonal components of the crustal magnetic field vector. To assess the reliability of the obtained values, a modified standard deviation 𝜎′ is proposed, which depends on the data series length and involves statistical indicators from long‑term observation series of the benchmark observatories. As a result, updated corrections were obtained for 118 observatories using data over 1998‑2025. For 65 observatories, such data are published for the first time. For the remaining observatories, the results were compared with previously acquired values. For some components and observatories, the deviations exceed 3𝜎′, which confirms the need for regular updating the contribution of the Earth’s crustal field at magnetic observatories. The results obtained also made it possible to assess the accuracy of existing models of the crustal field.