Magnetospheric `penetration' of IMF By viewed through the lens of an empirical RBF modeling

N. A. Tsyganenko and V. A. Andreeva


The spiral structure of the interplanetary magnetic field (IMF) is known to induce intra-magnetospheric azimuthal magnetic field By which strongly correlates with the IMF By. We reconstruct this effect for the first time in 3D, using a large set of data taken in the near/inner magnetosphere and a flexible magnetic field model based on expansions in radial basis functions (RBF). The RBF model serves here as a magnifying glass with tunable resolution, focused on the specific region of interest. In this study, we used it to explore the IMF-induced By both on a global scale (i.e., for the entire range of local times) and in the night sector only, to better visualize details in the region with the strongest `penetration' magnitude. The induced By was found to maximize on the nightside at distances R~10-12Re, where it concentrates around the solar magnetic equator and bifurcates into a pair of peaks located in pre-dawn and post-dusk sectors. The By penetration is associated with the IMF-induced asymmetry of field-aligned currents at the plasma sheet boundary. Even on a statistical level, the peak values of the induced By can substantially exceed the external IMF By. The effect is significantly stronger under southward IMF Bz conditions and grows with increasing geodipole tilt angle.
JGRA, published Dec 27, 2019:

This work was supported by the Russian Foundation for Basic Research (RFBR) grant 17-05-00415.