Empirical Modeling of Dayside Magnetic Structures Associated With Polar Cusps

Abstract

The magnetic structure of dayside polar cusps is intimately related to the high-latitude field-aligned currents (FACs) and the cross-B diamagnetic currents due to the penetrated plasma of magnetosheath origin. The dayside FAC configuration is sensitive to the azimuthal component of the interplanetary magnetic field, manifested in the latitudinal splitting and longitudinal overlapping of the Region 1 FAC zone around noon. The diamagnetism of the polar cusp plasma results in deep cleft-shaped depressions of the ambient magnetic field. Neither of the above factors have yet been properly addressed in the existing empirical models of the distant magnetosphere. To fill this gap, an advanced data-based model has been developed, including the spiral structure of the dayside FACs and their splitting/overlapping in response to the orientation and magnitude of the azimuthal interplanetary magnetic field component By. The cusp diamagnetic field depressions are modeled using a new approach, based on a 3-D system of magnetic “bubbles” (Tsyganenko & Andreeva, 2018, https://doi.org/10.1029/2018GL078714). The magnetic effects associated with FACs and diamagnetic currents are represented within the framework of a single hybrid model, fitted to large subsets of spacecraft data. The obtained results are analyzed in the context of the dayside magnetic field response to interplanetary conditions and the geodipole tilt angle.