Latitudinal Profiles of Nightside Isotropy Boundaries: Comparison of Observations and Predictions of Adaptive Magnetospheric Model

There is significant interest in monitoring the instantaneous magnetic configurations and dynamic states of the magnetotail and understanding what controls them. A unique and attractive opportunity is provided by remote sensing of the radial profile of the equatorial magnetic field curvature based on low-latitude energetic particle measurements of isotropy boundaries (IBs), providing that you can determine the origin of isotropic precipitation. To validate the magnetic field line curvature scattering (FLCS) as the main mechanism of the isotropy boundary formation, we compare coarse energy versus latitude IB profiles (in 3 + 3 energy channels) measured during a few dozen passes of POES and ELFIN spacecraft with the theoretical predictions of the adapted (AM03) magnetospheric model. Two studied intervals in August 2022 include substorm events of various intensities for which good spacecraft coverage in the near magnetotail helps reconstruct the adaptive model in the areas where the IBs are formed. We find a general agreement between the predicted and observed coarse IB profiles' shape and latitude, validating the FLCS hypothesis. Deviations are also observed, and we discuss the factors that can influence identification of the true FLCS profiles in observations and predictions, including limitations of adaptive modeling, non-monotonic radial structure of the tail magnetic field, and interference of FLCS with other precipitation mechanisms related to wave-particle interactions. Most can be avoided by improving the sensitivity, energy coverage, and resolution in future instruments.