Reconstructing Mercury's magnetic field in magnetosphere using radial basis functions

Abstract Based on the Magnetometer observations of the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft in orbit around Mercury, we construct a global magnetic field model of Mercury's magnetosphere using radial basis functions (RBFs). This model is parameterized by magnetic disturbance level and the fields are a sum of internal and external sources in the magnetosphere, including magnetopause and magnetospheric currents. The RBF-based model does not impose preconceived assumptions on the fields and constructs the system of tail currents and field-aligned currents (FACs) simultaneously. Compared with the previous models, the residuals between the observed and modeled magnetic field are significantly reduced at different magnetic activity levels and this indicates that our model is reliable and robust. Some features in Mercury's magnetosphere are also constructed based on the RBF model. The magnetic field is compressed in the boundary layer inside the dayside magnetosphere and stretched at the nightside due to the strong dawn-dusk cross-tail currents beyond 1.5 R M ( R M is Mercury's radius). The X-line location at the nightside is reduced from 4.6 RM in the magnetic quiet period to 2.9 RM in the magnetic active period and fits the magnetic disturbance indices in linear form. The FACs are downward (upward) in the dawn (dusk) sector and are increased with magnetic disturbance levels. In summary, the RBF-based model could reveal all principal features in the magnetosphere and their changes associated with magnetic disturbance levels.