Rice Convection Model simulation of the substorm‐associated injection of an observed bubble into the inner magnetosphere: 1. Magnetic field and other inputs

Abstract

[1] The objective of this work is a realistic Rice Convection Model (RCM) simulation of a modest substorm that occurred on 22 July 1998 and was observed by the Geotail spacecraft in the inner plasma sheet. It represents the first time the RCM has been used for detailed modeling of an inner magnetospheric event using data from a spacecraft in the inner plasma sheet beyond geosynchronous orbit to drive the model's time-dependent boundary conditions. Since this represents a substantial departure from past practice, we present, in this paper, a detailed account of how model inputs are determined. An accompanying paper presents results and interpretations. Model inputs are adjusted to achieve approximate consistency between RCM-computed values and measurements by Geotail, which was within the RCM modeling region near X GSM = À9 R E , Y GSM = 0. To represent the magnetic field in the growth phase, we utilize a Tsyganenko (1989) statistical magnetic field model, adjusted to agree with Geotail-measured pressure and magnetic field in a new way using analytic solutions to the linear Grad-Shafranov equation. The magnetic field during the expansion phase is represented by adding a substorm current wedge using formulas developed by Tsyganenko. Induction electric fields play a central role in these simulations, because they are large in the vicinity of the substorm injection region. We provide a detailed description of how induction electric fields are included in the RCM as well as a prescription of the electromagnetic gauge condition used in the code.

Rice Convection Model simulation of the substorm‐associated injection of an observed plasma bubble into the inner magnetosphere: 2. Simulation results

“…(Here the potential electric field is computed by mapping potentials to the magnetic equatorial plane from the ionosphere. For more details about our definition of “induction” and “potential,” see section 3 of Paper 1. )…”

“…The potential electric field near midnight, though more structured because it was computed self‐consistently, is also predominantly westward for X > −12. The induction electric field was computed from our time varying magnetic field model, as described in section 3.3 of Paper 1. For X > −12, the induction and potential electric fields tend to be of roughly comparable size during the dipolarization.…”

“…Although the potential electric field is calculated carefully and self‐consistently within the RCM, the induction field depends on an input model of the substorm current wedge. As discussed in Paper 1, parameters of the substorm current wedge were chosen to fit measurements at one point (Geotail), at X ≈ −9, Y ≈ 0. Thus, calculated induction electric fields far from that point lack substantial observational or theoretical support.…”

“…Our objective is to understand how the bubble evolves as it moves toward the inner magnetosphere and how it affects magnetospheric and ionospheric electric fields and other parameters. An accompanying paper [ Zhang et al , 2009] (hereafter referred to as Paper 1), describes details of how Geotail data were used to set boundary conditions and specify the inputted magnetic field. This paper concentrates on run results and their interpretation.…”

On the contribution of plasma sheet bubbles to the storm time ring current

“…In recent years, the Rice Convection Model (RCM) and the Rice Convection Model-Equilibrium (RCM-E) have been extensively used to investigate how the plasma inside depleted flux tubes is transported in the nearEarth region [Lemon et al, 2004;Zhang et al, 2008;Zhang et al, 2009aZhang et al, , 2009bYang et al, 2008Yang et al, , 2011Yang et al, , 2012Yang et al, , 2014aYang et al, , 2014b. The model uses the slow-flow approximation and assumes an isotropic pressure distribution along magnetic field lines.…”