[P-EM13] Dynamics of the Inner Magnetospheric System

[PEM13-01] Vlasiator simulation of Earth’s magnetosphere: application to radial diffusion

★Invited Papers

*Harriet George¹、Adnane Osmane²、Emilia Kilpua²、Solene Lejosne³、Lucile Turc²、Maxime Grandin²、Milla Kalliokoski⁵、Sanni Hoilijoki²、Urs Ganse²、Markku Alho²、Markus Battarbee²、Marja Bussov²、Maxime Dubart²、Andreas Johlander、Talgat Manglayev、Kostis Papadakis²、Yann Pfau-Kempf²、Jonas Suni²、Vertti Tarvus²、Hongyang Zhou²、Minna Palmroth^2,4 (1.Laboratory for Atmospheric and Space Physics, University of Colorado Boulder, Boulder, CO、2.Department of Physics, University of Helsinki, Helsinki, Finland、3.Space Sciences Laboratory, University of California, Berkeley, Berkeley, CA, United States、4.Space and Earth Observation Center, Finnish Meteorological Institute, Helsinki, Finland、5.Japan Aerospace Exploration Agency, Tokyo, Japan)

Vlasiator is a hybrid-Vlasov model that is designed for global simulations of Earth’s magnetosphere. With the hybrid-Vlasov approach, ions are described as velocity distribution functions and electrons are treated as a charge neutralizing fluid, providing a self-consistent description of ion dynamics in the Earth’s magnetosphere. This provides noiseless representations of magnetospheric physics that can be directly compared to spacecraft observations. Vlasiator has been applied to study many features of near-Earth space, including foreshock wave activity, ionosphere-magnetosphere coupling and magnetotail reconnection.


Recently, Vlasiator was also applied to the Earth’s radiation belts for the first time in order to study radial diffusion. Radial diffusion is a key process that acts to non-adiabatically transport radiation belt particles across drift shells due to the violation of the third adiabatic invariant, the L* coordinate. We apply the global electric and magnetic field data provided by Vlasiator to develop a methodology to evaluate radial diffusion directly from the driving wave activity. We use a Hamiltonian formalism for particles confined to closed drift shells with conserved first and second adiabatic invariants to compute changes in the guiding center drift paths from background electric and magnetic field fluctuations. Performing this calculation for different energies allows the rate of change of L* to be evaluated for different populations traveling along the same guiding center drift path without the need to inject and trace test particles. We investigate the feasibility of this methodology by computing the time evolution of L* for an equatorial ultrarelativistic electron population traveling along four guiding center drift paths in the outer radiation belt of a five minute portion of a Vlasiator simulation. Due to the short time scale and geometry of the test run, low amplitude Pc3 fluctuations are the primary driver of radial diffusion, which results in preliminary estimates for the radial diffusion coefficients that are two to six orders of magnitude below those corresponding to more active magnetospheric conditions with Pc5 fluctuations as the primary driver. However, our results show that an alternative methodology to compute detailed radial diffusion transport is now available and could form the basis for comparison studies between numerical and observational measurements of radial transport in the Earth’s radiation belts.