Abstract
Magnetic fields in the inner magnetosphere can be obtained as vector sums of the Earth’s own internal magnetic field and magnetic fields stemming from currents flowing in the space plasma. While the Earth’s internal magnetic field is accurately described by the International Geomagnetic Reference Field (IGRF) model, the characterization of the external magnetic fields is significantly more complicated, as they are highly variable and dependent on the actual level of the geomagnetic activity. Tsyganenko family magnetic field models (T89, T96, T01, TA15B, TA15N), parameterized by the geomagnetic activity level and solar wind parameters, are often used by the involved community to describe these fields. In the present paper, we use a large dataset (2001–2018) of magnetospheric magnetic field measurements obtained by the four Cluster spacecraft to assess the accuracy of these models. We show that, while the newer models (T01, TA15B, TA15N) perform significantly better than the old ones (T89, T96), there remain some systematic deviations, in particular at larger latitudes. Moreover, we compare the locations of the min-B equator determined using the four-point Cluster spacecraft measurements with the locations determined using the magnetic field models. We demonstrate that, despite the newer models being comparatively slightly more accurate, an uncertainty of about one degree in the latitude of the min-B equator remains.
Highlights
Quantitative models of magnetic fields in the Earth’s inner magnetosphere are crucial for various scientific purposes
All the analyses were performed in geocentric solar magnetic (GSM) coordinates
We further assume that the situation was symmetric with respect to the GSM X − Y plane, that is, that there were no systematic differences between the results obtained for positive and negative Z values
Summary
Quantitative models of magnetic fields in the Earth’s inner magnetosphere are crucial for various scientific purposes. These include the magnetic field line mapping, the evaluation of energetic particle motions and radiation belt modeling in general, as well as electromagnetic wave generation and their tracing between the observation points and source regions. The main reasons are its large temporal variability and complicated current systems contributing to the magnetic field. Both the location and magnitude of the individual currents need to be predicted by the respective models [2]. These are typically parameterized by geomagnetic activity indices and solar wind parameters [3]
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