Storm-time ring current: model-dependent results

Abstract

Abstract. The main point of the paper is to investigate how much the modeled ring current depends on the representations of magnetic and electric fields and boundary conditions used in simulations. Two storm events, one moderate (SymH minimum of −120 nT) on 6-7 November 1997 and one intense (SymH minimum of −230 nT) on 21-22 October 1999, are modeled. A rather simple ring current model is employed, namely, the Inner Magnetosphere Particle Transport and Acceleration model (IMPTAM), in order to make the results most evident. Four different magnetic field and two electric field representations and four boundary conditions are used. We find that different combinations of the magnetic and electric field configurations and boundary conditions result in very different modeled ring current, and, therefore, the physical conclusions based on simulation results can differ significantly. A time-dependent boundary outside of 6.6 R E gives a possibility to take into account the particles in the transition region (between dipole and stretched field lines) forming partial ring current and near-Earth tail current in that region. Calculating the model SymH* by Biot-Savart's law instead of the widely used Dessler-Parker-Sckopke (DPS) relation gives larger and more realistic values, since the currents are calculated in the regions with nondipolar magnetic field. Therefore, the boundary location and the method of SymH* calculation are of key importance for ring current data-model comparisons to be correctly interpreted.

Magnetosphere dynamics during the 14 November 2012 storm inferred from TWINS, AMPERE, Van Allen Probes, and BATS-R-US–CRCM

“…A ring current model can be considered as a bounce-averaged kinetic code and normally operates with a large number (from hundreds to thousands) of "species", i.e., distributed in energy, pitch angle, or first and second adiabatic invariants. Currently, there are several major ring current models used by the community: the standard Rice Convection Model (RCM) (Harel et al, 1981;Toffoletto et al, 2003) or the RCM-E, a version that includes frictional dissipation (Lemon et al, 2003;Chen et al, 2015); the Magnetospheric Specification Model (MSM) (Wang et al, 2003(Wang et al, , 2004; the Comprehensive Ring Current Model (CRCM) (Fok et al, 1993(Fok et al, , 1995(Fok et al, , 2001(Fok et al, , 2014 and its successor, the Comprehensive Inner Magnetosphere-Ionosphere model (CIMI) (Fok et al, 2014); the Ring current-Atmosphere interactions Model (RAM) (Jordanova et al, 1994(Jordanova et al, , 2001 and its extended version with magnetic equilibrium solver Zaharia, 2008); the Hot Electron and Ion Drift Integrator (HEIDI) code (Liemohn et al, 1999); and the Inner Magnetosphere Particle Transport and Acceleration model (IMPTAM) (Ganushkina et al, 2012).…”

Van Allen Probes investigation of the large‐scale duskward electric field and its role in ring current formation and plasmasphere erosion in the 1 June 2013 storm

“…[, ], Ganushkina et al . [, , ], and Gkioulidou et al . [] have shown that injection events make a significant contribution to the ring current.…”

“…The large‐scale (≳ R E and ≳ 1 h duration) duskward convection electric field and smaller‐scale (~5 min) injection electric fields, associated with the injection of ions and electrons, play an important role in the energization of ring current particles as they drive an E × B flow of plasma sheet plasma into the inner magnetosphere [e.g., Axford , ; Fok et al ., ; Ebihara and Ejiri , ; Fok et al ., ; Ganushkina et al ., , , ]. As ions and electrons E × B drift from the weaker magnetic field in the plasma sheet to the stronger field of the inner magnetosphere, they gain energy consistent with conservation of their first adiabatic invariant, μ = W ⊥ / B , where W ⊥ is the perpendicular energy of the particle and B is the magnetic field strength.…”

Modeling of ion dynamics in the inner geospace during enhanced magnetospheric activity

“…In this frame, a comparison of our results with other available models (e.g., Fok et al, 2001;Jordanova et al, 2010), as well as with data from observations, may act as further validation. In a relevant work by Ganushkina et al (2012), a benchmark of models was conducted, and the results showed that the computed ring current, for moderate and intense disturbances, depends on the field models. In our work, the benchmark of the T89 model has shown few differences within the simulated region in comparison to the later models, the facilitation of which may, however, increase the accuracy in the magnetic field.…”