A comprehensive model of Earth’s magnetic field determined from 4 years of Swarm satellite observations Terence J. Sabaka1*  , Lars Tøffner‑Clausen2, Nils Olsen2 and Christopher C. Finlay2

The European Space Agency’s three-satellite constellation Swarm, launched in November 2013, has provided unprec‑ edented monitoring of Earth’s magnetic field via a unique set of gradiometric and multi-satellite measurements from low Earth orbit. In order to exploit these measurements, an advanced “comprehensive inversion” (CI) algorithm has been developed to optimally separate the various major magnetic field sources in the near-Earth regime. The CI algo‑ rithm is used to determine Swarm Level-2 (L2) magnetic field data products that include the core, lithospheric, iono‑ spheric, magnetospheric, and associated induced sources. In addition, it has become apparent that the CI is capable of extracting the magnetic signal associated with the oceanic principal lunar semidiurnal tidal constituent M2 to such an extent that it has been added to the L2 data product line. This paper presents the parent model of the Swarm L2 CI products derived with measurements from the first 4 years of the Swarm mission and from ground observatories, denoted as “CIY4,” including the new product describing the magnetic signal of the M2 oceanic tide.