FG: Self-Consistent Inner Magnetospheric Modeling

Co-chairs

Cristian Ferradas (cristian.ferradasalva at nasa.gov), NASA Goddard

Qianli Ma (qma at bu.edu), Boston University

Chao Yue (yuechao at pku.edu.cn), Peking University

Sam Bingham (sam.bingham at jhuapl.edu), JHU/APL

Jacob Bortnik (jbortnik at atmos.ucla.edu), UCLA

Research Area

Inner Magnetosphere, M-I coupling

Overview

The terrestrial ring current is comprised primarily of protons, oxygen, and electrons from a few keV to several hundred keV and plays an important role in regulating the energy density and field configuration of the magnetosphere. The storm time ring current is formed by particles, originally from the solar wind and the ionosphere, that are injected into the inner magnetosphere due to changes in the electric and magnetic fields and the associated enhanced magnetospheric convection. The instability of the particles in the ring current provides the free energy of various waves, (e.g., EMIC, magnetosonic, and chorus waves) which play important roles in the dynamic evolution of the inner magnetosphere through wave-particle interactions. For example, the temperature anisotropy of tens of keV electrons generates whistler-mode chorus waves, which can drive pitch angle scattering and precipitation. The subsequent precipitation to the ionosphere modifies the ionospheric conductance, which in turn has feedback effects in the inner magnetosphere through changes to the electric potential pattern. Despite recent advances in ring current modeling, current models are not able to fully capture the dynamics of the ring current and the broader inner magnetosphere during disturbed times in a self-consistent manner. Understanding the coupling processes between the ring current and other plasma populations in the inner magnetosphere is crucial to self-consistent modeling. Our focus group aims to improve the physical understanding and modeling of the ring current interactions with and feedback from other populations (e.g., plasmasphere, radiation belts, and ionosphere), through theoretical studies, numerical modeling, and observations from satellite and ground-based missions.

Topic Description

This focus group aims to improve the understanding of the development and decay of the storm-time ring current and its broader impact on the inner magnetosphere and magnetosphere-ionosphere (MI) system in order to further the capabilities of self-consistent modeling. To achieve the goal of our focus group, we will engage the GEM community to put-forth and answer science questions related to gaps in our current ability to:

(1) represent the electric and magnetic fields self-consistently

We plan to assess how well are current inner magnetosphere models accounting for the observed fields, particularly, how well are the effects of the plasma on the fields accounted for. For example, it is known that precipitating electrons modify the ionospheric conductivity, which is crucial in self-consistent calculations of the fields.

(2) quantify the relative roles of different loss mechanisms to the ring current

Current models are unable to adequately predict the rapid decay of the ring current during the early recovery phase of storms. This indicates that there is a gap in our current understanding of losses. The main loss processes include magnetopause shadowing, charge-exchange, and particle precipitation to the atmosphere. While the rapidly changing fields determine the depth of penetration of the ring current and how it is impacted by magnetopause shadowing, the ion composition and neutral densities impact charge-exchange losses. The relative impact of each loss process has not been fully quantified.

(3) derive wave growth rates self-consistently

A key element in the interaction between the inner magnetosphere plasma populations relates to wave-particle diffusion processes in the magnetosphere. Current models usually account for wave-particle interactions using empirical models of the wave parameters. As such, they cannot sufficiently predict the important plasma waves driven by and interacting with the thermal, suprathermal, and ring current populations. A more self-consistent approach should be employed, in which the wave growth rates are calculated from the anisotropic particle pitch angle distributions, and in turn the generated waves drive the diffusion coefficients of the particles to cause pitch angle diffusion or acceleration.

(4) understand wave-particle interactions involving thermal, suprathermal, and ring current populations

There is limited understanding about the relation between the plasma waves generated by ring current particles and the other particle populations. For example, observational evidence shows the correlation between EMIC waves (generated by protons in the ring current) and suprathermal helium and oxygen ions, but the efficiency of such heavy ion heating at several hundred eV energies is not yet quantified through resonant interaction modeling.

(5) evaluate the non-linear effects of waves on particles

A remaining challenge regards the inclusion of nonlinear particle scattering and acceleration effects due to large wave amplitudes in addition to quasilinear theory. Satellite observations indicate that EMIC waves frequently have large amplitudes (> 1 nT). Quasilinear theory, which is commonly used to study particle scattering effects, has an assumption that wave amplitudes are small. Therefore, the validity of quasilinear modeling results needs to be confirmed and non-linear effects need to be taken into account to model wave-particle interactions.

(6) assess the relative importance of different mechanisms leading to the development and decay of the electron ring current

Electrons in the ring current have been largely overlooked and there is a compelling need to better quantify them as they play an important role in the dynamics of the inner magnetosphere. Electrons represent the source population for whistler-mode chorus waves and the seed population for the radiation belts, and precipitating electrons modify the ionospheric conductivity, which is crucial in self-consistent calculations of the fields. Currently, models do not capture their ring current dynamics well and fail to predict electron fluxes accurately. We need to assess how the model deficiencies are related to the assumed fields, sources, and losses.

Full focus group proposal

2020 Activities

2020 VGEM Summer Workshop

Session 1: Ring Current Dynamics

In this session we will assess the transport, energization, loss, and composition of the ring current ions and electrons, and the associated variations in electric and magnetic fields. We welcome research talks related to the ring current dynamics through numerical modeling and satellite observations.

Date: Wednesday, July 22nd, 1:00 pm - 2:30 pm EDT

Session 2: Wave-Particle Interactions

In this session we will asses wave-particle interactions in the ring current, which drive the excitation of plasma waves, and the scattering or heating of thermal, suprathermal and energetic ions and electrons. We solicit both modeling and observational efforts.

Date: Wednesday, July 22nd, 3:00 pm - 4:30 pm EDT