FG8. Near Earth Magnetosphere: plasma, fields, and coupling

Co-chairs:

• Sorin Zaharia (szaharia [at] lanl.gov)
• Stan Sazykin (sazykin [at] rice.edu) and
• Benoit Lavraud (Benoit.Lavraud [at] cesr.fr)

Group Overview

This focus group aims to improve physical knowledge and modeling of the near- Earth (< 10 RE) magnetosphere and its coupling with the outer magnetosphere. It broadens our understanding of inner magnetosphere plasma transport and includes the self-consistent coupling between plasma and electric and magnetic fields. It also focuses on quantifying the effect of plasma sheet source populations on the evolution of the inner magnetosphere.

Scientific Motivation

Currently there are gaps, in both modeling and observations, in our knowledge of both the fields and the plasma sheet boundary dependence. From a modeling point of view, a gap exists between self-consistent but physically oversimplified models and models that treat plasma correctly but not the fields. Existing global MHD models include self-consistent fields, but the MHD formalism cannot adequately describe the inner magnetosphere (closer than 10 RE), because it does not include gradient and curvature drifts. On the other hand, existing kinetic models (e.g. RAM, RCM, CRCM) treat plasma transport, acceleration and losses more or less realistically but do not properly account for the effect of the plasma on the fields. Observationally, the fields are also rather poorly described. While empirical models have been constructed that statistically describe B-fields and convective E-fields, they hardly do so for specific events; moreover, no model exists for the inductive E-fields. Finally, the dynamics of the inner magnetosphere depends both on the physics mechanisms involved, but also on the plasma sheet inputs. No clear study of the relative importance of the two exists. In summary, to further our knowledge of the inner magnetosphere we need better specification of the electric and magnetic fields, as well as of the driving plasma sheet properties. From a modeling point of view, it is desirable to have a kinetic approach that includes all relevant species (ions and electrons), self-consistent three-dimensional magnetic, convective and induced electric fields, as well as loss mechanisms.

Goals

This focus group will include both modeling and observational components that will improve the knowledge and specification of the inner magnetosphere electric and magnetic fields, their interaction with the plasma, as well as their dependence on the plasma sheet populations; a main deliverable will be the development of a realistic inner magnetosphere GGCM module, consistent with the main goal of the GEM program.

Potential Research Topics

1. Effect of the 3D self-consistent feedback between plasma and magnetic field on the inner magnetosphere particle transport and acceleration during various activity such as storms and substorms.
2. Specification (observational and modeling) of the convective E-field during storms, Region-2 field aligned currents, coupling to ionosphere and shielding.
3. Magnitude and location of the inductive E-fields arising from time-varying B-fields, through both modeling and observations (e.g. conjugate measurements – in situ plus ionospheric).
4. Effect of plasma sheet density, temperature and local time distribution on the large-scale morphology of the ring current ions and electrons in the inner magnetosphere.
5. Parameterization and relative importance of various loss processes during active times, including extreme disturbances.
6. Influence of inner magnetosphere fields on radiation belt particles; adiabatic effect; radial diffusion - what part, if any, of ULF wave diffusion is captured by time changing model fields?
7. Coupling of inner magnetosphere models with outer MHD models; which is driving which.

Original proposal to the GEM steering committee

Full text of the proposal to the GEM steering committee that led to creation of the focus group can be found here: PDF proposal

GEM Workshop meeting reports

June 2007 GEM meeting report

The Near Earth Magnetosphere Focus Group held three breakout sessions at the 2007 GEM, on Wednesday, June 20.

Session 1. The topic of this session was the influence of plasma sheet properties on the ring current.

Benoit Lavraud showed that a cold, dense plasma sheet leads to enhanced ring current. Comparing RAM simulation results for the proton ring current with idealized boundary conditions of cold vs. hot plasma sheet (with the same energy density), he found that cold plasma sheet can penetrate much closer to Earth (due to its reduced gradient-B drift). He also presented observations of the cold dense plasma sheet (CDPS), which show 2 distinct populations at midnight and dawn. The source and degree of participation of the dawn population to the ring current are questions that need to be answered in the future.

Chih-Ping Wang analyzed the dependence of plasma sheet properties, during northward IMF, on solar wind (SW) density, velocity and IMF Bz, using Geotail, ACE and Wind data. The data was separated into 8 bins, corresponding to low/high value combinations of the 3 driving parameters. The parameter combination of high SW density, high IMF Bz and low velocity was found to lead to a cold plasma sheet with highest density and lowest temperature. On the other hand, a low SW density, low Bz and high velocity result in a hot and tenuous plasma sheet (lowest density, but highest temperature).

Margaret Chen used Wang’s two extreme plasma sheet conditions (cold/dense and hot/tenuous) from Geotail data as boundary conditions for her magnetically self-consistent ring current model. First, she traced ions with the Magnetospheric Specification Model (MSM) from Geotail orbit to geosynchronous, and then used the values there as boundary conditions. She found that the cold/dense plasma sheet leads to much stronger ring current. She concluded that accurate ring current modeling requires realistic modeling of pre-storm plasma sheet.

Colby Lemon addressed the question of how the fast initial recovery of a storm may be affected by plasma sheet density and convection strength. He showed 6 simulations performed with the RCM-E model, with different plasma sheet densities and polar cap potential drops. The results show that lower plasma sheet densities lead to faster recovery, with the fastest recovery resulting when plasma sheet density is lowest while convection is still strong.

Vahe Peroomian looked at ion access and energization by tracing particles in the fields of a global MHD storm simulation. Oxygen ions were launched from the ionosphere, with protons launched in the solar wind. While direct entry (through the plasma sheet) into the ring current was found to occur, Vahe found that ion transport from the distant tail to inner magnetosphere can be also indirect, with particles moving along dynamic field lines and ending up much closer to Earth after mirroring, thus bypassing the plasma sheet.

Liz MacDonald studied the influence of ion composition at geo. orbit on the ring current. By performing RAM simulations with various H+/O+ boundary composition ratios, she obtained very different ring current pressure, showing that ion composition plays a very significant role in the ring current. She then described the upcoming oxygen monitoring capability at geosynchronous that will be on LANL satellites, through the Advanced Miniaturized Plasma Spectrometer (AMPS), which will measure H+, O+, He++ and e-.

Jichun Zhang presented an RCM study of depleted entropy channels (bubbles) injected into the inner magnetosphere. The bubbles are imposed by reducing the PV^gamma content. He found that bubbles lead to higher plasma energy density. In particular, the electric field is increased inside depleted channels, which injects fresh particles more effectively. The violation of adiabaticity (which presumably causes the bubbles) pushes the ring current farther inward and seems to be a key element in storm physics.

Yongliang Zhang discussed the ring current aurora (RCA) – a new terminology for aurora emissions due to precipitating particles from the ring current. He showed that global FUV imagers provide insight into the RCA because they image proton precipitation. As observations of RCA provide information on loss processes in the RC, he concluded that global auroras should be used in validating magnetospheric models.

Pontus Brandt showed a study performed with Shin Ohtani on global circulation of oxygen ions. ENA observations show strong energization of RC O+ ions during substorms, with protons less energized. CRCM simulations of a substorm coupled with test particle ions successfully reproduce the oxygen ion energization, with the take-home message being that oxygen ions make the ring current stronger.

Session 2: The topic of the second session was the self-consistent interaction between plasma and electric and magnetic fields in the inner magnetosphere.

Sorin Zaharia described the inner magnetosphere model that is developed at LANL based on his 3D magnetic field solver and Vania Jordanova’s RAM code. Recently, the code has been extended to ~10 Re in the tail, with the outer plasma boundary condition there taken from observational profiles. Sorin showed that taking into account the effect of plasma on the B-field leads to very different results than if a dipole field is used. When the self-consistent simulation of a moderate storm is compared with the one using a dipole B-field, it was found that there are significant deviations of the field from dipolar even at L=4-5, lower plasma pressure, and noticeable variability in radial profiles.

Mike Liemohn addressed the question of small scale E-field structuring in the inner magnetosphere that he finds in his ring current simulations. Mike showed a simulation of the April 22, 2001 storm, in which plasma pressure becomes structured – at the same time, small structuring is seen in the computed E-field. According to Mike’s analysis, ENA images in the tens of keV energy range would not be sufficient for the IMAGE HENA instrument to resolve the structuring. Mike challenged the audience to identify data that could be used to prove or disprove his model results.

Vania Jordanova showed RAM simulations with different B-fields (dipole, empirical Tsyganenko, and self-consistent computed with the Zaharia solver) also for the 22 April 2001 storm. Vania found that results differ significantly for the different field models. In general, the empirical T04S field yields the largest gradient/curvature drift velocities. In the storm main phase, proton fluxes are smallest with T04S and total ring current density is reduced compared to the dipole case. The self-consistent B-field yields intermediate results. With non-dipolar B-fields, localized pressure peaks appear. Also, with the self-consistent B-field, strong EMIC waves are predicted at larger L.

Mark Engebretson presented EMIC wave observations, bringing up the question of why ground-based signatures of EMIC waves are not observed in the plasmapause region during the main/early recovery phase, but are in the late recovery phase. Mark showed conjunction ground based/spacecraft data (with two spacecraft, one at 4500 km altitude and the other one at geo) at L=4.5 for one storm. In the main phase, the data shows EMIC wave activity out in the magnetosphere but waves are not observed on the ground or at 4500 km. This might suggest that the waves are absorbed well above the ionosphere or are not emitted in the direction of the ground.

Frank Toffoletto showed RCM-E simulations of an idealized substorm growth phase. After running the model for ~4 hrs, the pressure and magnetic fields consistently display oscillatory structure, which could be physical instabilities. An eigenmode analysis of the RCM-E configuration with Chris Crabtree’s code finds a tail region between 10 and 15 Re to be ballooning unstable when the field is very stretched. While RCM-E cannot model the instability evolution, this result may indicate that adiabaticity is violated in the unstable region. Reducing the adiabatic invariant in an ad-hoc manner on the RCM-E boundary leads to B-field dipolarization and injection of a noticeable ring current.

Hiroshi Matsui presented an empirical model of the convection E-field in the inner magnetosphere based on Cluster E-field measurements and DE-2/radar data. The model convection patterns were organized by the interplanetary E-field. Qualitatively, the empirical patterns are similar to those computed with models such as RCM. However, standard deviations are comparable to E-field absolute values, indicating significant variability of the field; this could be due to mesoscale structuring or induction E-fields.

Pamela Puhl-Quinn described her recent work on analyzing simultaneous electric field observations of sub-auroral ion drift (SAID) events using magnetospheric (Cluster) and ionospheric (DMSP) E-field data. She showed one case study that showed quite good agreement of Cluster and DMSP observations.

Session 3: The final session started as a continuation of the self-consistent interaction discussion.

Mike Schulz gave some theoretical remarks on self-consistent interaction between plasma, electric and magnetic fields. He remarked that analytical formulations (e.g. the Dungey model) are useful for simulating realistic features. He warned against looking for causality in Maxwell’s equations, i.e. what is driving what. One can only say with regard to Maxwell’s equations that the right hand side equals the left hand side.

Jerry Goldstein presented an electric field model constructed from an externally driven electric field model (Volland-Stern) plus an internal SAPS model. By tracing particles in this combined model, with either observations or a plasmapause model for initialization, he obtained remarkably good correlation with MPA data of plume location.

Tim Guild showed the effects of self-consistency in electric and magnetic fields on the plasma sheet control of ring current. For the study he used RCM, which has self-consistent electric fields, but did not include the charge exchange. He analyzed a moderate storm and found that adding magnetic self-consistency lowers the effect of plasma sheet density on the ring current energy (the self-consistency in the E-field alone was already lowering it from a linear to a square root dependence on the PS density).

Yukitoshi Nishimura presented storm-time large scale electric fields obtained from 7 years of Akebono observations. The largest fields are found at dawn and dusk. He also used the field to calculate empirical convection potentials. A twocell convection pattern is clearly observed. He further traced ions in the obtained empirical fields and found significant energization.

Jo Baker discussed SuperDARN measurements and implications for convection. He also performed a test of equipotentiality of the magnetic field lines, by analyzing conjugate SuperDARN and Cluster EDI measurements. While he found a fairly good correlation, there was also large variance, which points out to nonequipotentiality (possible reasons for it being induced electric fields and field-aligned potential drops).

Yihua Zheng looked at the influence of electric fields on the coupling between the magnetosphere and ionosphere. She showed simulations with the CRCM model, with and without trough (low density plasma region) conditions. With trough conditions, the applied low Pedersen conductance in the trough leads to large amplitude flows (subauroral polarization streams, or SAPS) that resemble observations. She concluded that ionospheric changes affect the ring current through electromagnetic coupling.

Sasha Ukhorskyi looked at radiation belt radial transport due to magnetopause compression from solar wind dynamic pressure variations. He used empirical B-field models and calculated the induced E-fields that are consistent with the Bfield time dependence. He then analyzed the ULF waves from solar wind pressure spectral fluctuations.

Jimmy Raeder presented work done with W. Li on the formation of super-dense plasma sheet. In an OpenGGCM simulation, he showed that after northward IMF, southward IMF turning compresses the cold dense plasma on high latitude field lines, which is subsequently pushed toward the Earth by near-tail reconnection and forms the super dense plasma sheet near geo. orbit (MHD results compatible with MPA observations).

The second half of the session was a community discussion about the future direction of the focus group. Several people mentioned the familiar GEM concept of “Community Challenge” – it would be interesting to have in the near future (1-2 years) a challenge study whereby the models would all run an idealized event, so as to compare the results. For the next GEM, two possible breakout session topics emerged: 1). Study the effect of the added model features on model output, in order to find out which are crucial for inner magnetosphere physics modeling; quantify the relative effect of plasma sheet boundary properties, B and E self-consistency, anisotropy, losses in models; how are the new physics features verified by / improve consistency with observations? 2). Continuous improvement in empirical specification: better empirical plasma sheet models (including activity binning and ion composition), empirical E-field and plasmasphere models. These would also be the topics of a Mini-GEM session the focus group will be organizing in San Francisco the Sunday before the 2007 Fall AGU.

June 2008 GEM meeting report

The Near Earth Magnetosphere focus group held 3 breakout sessions in its 2nd year of activity at the 2008 GEM Summer Workshop in Zermatt, UT. The main goal of the focus group is to improve physical knowledge and modeling of near-Earth magnetosphere and its coupling with outer magnetosphere. The focus group is coordinated by Sorin Zaharia, Stan Sazykin and Benoit Lavraud.

The three focus group sessions, held on Tuesday and Wednesday (06/24-25) were well attended and featured short presentations and discussions of progress on the two main research fronts the focus group has concentrated to achieve its goals:

1. Data-based/empirical models - short presentations described both continuing progress on empirical modeling (such as the UNH IMEF E-field model), as well as a significant number of new research efforts on this front, from new magnetic field to plasma pressure models; below is a synopsis of the main topics discussed:

• Empirical plasma sheet specification – either for use in models (C. Lemon, a plasma sheet property database for geosynchronous orbit) or validating model results, e.g. observational verification of ring current injection from the plasma sheet (C.-P. Wang, Themis observations)
• Empirical E-field specification: overview of improvements in the UNH IMEF model based on Cluster data - the model is now publicly available (H. Matsui, P. Puhl-Quinn); its first use in a physics-based ring current model (V. Jordanova, RAM); dichotomy between convective electric field dependence on IMF southward turning in the plasma sheet vs. earthward of it (Y. Nishimura)
• Empirical B-field: M. Sitnov, new dynamical model (with a dramatic increase in spatial resolution); J. Zhang, T89GS - model constrained by spacecraft observations that satisfies force balance near spacecraft; R. Denton – adjusting TS05 model to better fit GOES observations; N. Ganushkina - event-oriented B-field model – modification of Tsyganenko model (good for studying detailed magnetic field variations for a specific event, time period, or magnetospheric region)
• Empirical plasma pressure model of the inner magnetosphere (P. Brandt – obtained by combining in-situ with global ENA observations)
• Radar observations of ionospheric convection (L. Lyons, Poker Flats AMISR; J. Baker, mid-latitude SuperDARN); qualitatively similar features observed in model results (Lyons, RCM)

2. The second research area, physics-based modeling, tackled mostly the coupling between different elements in the models (plasma, electric and magnetic fields); highlights from the presentations include:

• Modeling many events with simple setup (model works better for one storm type, i.e. sheath-driven storms, suggesting different storm drivers lead to more or less complex inner magnetosphere physics) (M. Liemohn, HEIDI - Michigan RAM)
• Ballooning instability in RCM-E; continued driving, simulating a growth phase, pushes the magnetosphere toward both MHD and fast MHD unstable states (F. Toffoletto)
• Substorm simulations: with RCM-E (J. Yang, using Geotail data to set up boundary; results consistent with observations); with a “bubble” imposed (RCM with new T89GS force-balanced model - J. Zhang; injection of bubble leads to higher pressure in the near-Earth magnetosphere)
• Wave studies: analytical pitch-angle diffusion - three lowest eigenvalues for the pitch-angle diffusion coefficient (M. Schulz; results could be used in ring current models); connection theory/observations - whistler modes (derived from LANL plasma observations + linear theory; enhanced growth rates found in the recovery phase; E. MacDonald)
• Effect of plasma boundary on RC injection (cold dense plasma more geoeffective; local time boundary distribution also very important - B. Lavraud, RAM; in simulations with self-consistent E-field, higher plasma sheet pressure causes quicker shielding of the penetration E-field - M. Gkioulidou, RCM)
• 1-way coupling of RAM with self-consistent B-field with SWMF (using SWMF pressure on RAM boundary) reconfirms previous results that cold, dense plasma sheet –a common feature in MHD models – is more “geoeffective,” i.e. leads to higher inner magnetosphere plasma pressure) (S. Zaharia)

The second half of the 3rd breakout session was devoted to a community discussion in which a future modeling challenge relevant to Focus Group goals emerged. The challenge will entail several near-Earth/inner magnetosphere models simulating, with same (or equivalent) input, both an idealized and a real event (geomagnetic storm). The challenge will bring together researchers from all major near-Earth magnetosphere modeling groups : RAM-SC B (LANL); HEIDI (Michigan RAM), RCM, RCM-E, CRCM, M. Chen’s model. The challenge will involve 3 stages: 1). Idealized event, with simple inputs/physics (with the goal of setting a baseline for all models). The second and third stage will involve full-physics modeling of an idealized and real event, respectively (thus the 3rd stage will involve both modelers and data analysts). More details about the challenge/model setup will be communicated to the community via e-mail and the new Focus Group Wiki. It is expected that the first stage be completed by and results presented at the 2008 GEM Mini-workshop (Sunday before AGU Meeting) in December, where the focus group plans to have a session. The 2009 Summer Workshop will then see initial results from the simulation of an idealized event with full model capabilities, with the goal of finding out the relative role of different physics features (e.g. plasma/fields self-consistency) present in the models.

June 2009 GEM meeting report

The Near Earth Magnetosphere focus group held 3 breakout sessions at the 2009 GEM Summer Workshop in Snowmass, CO. The main goal of the focus group is to improve physical knowledge and modeling of the near-Earth magnetosphere and its coupling with the outer magnetosphere. The focus group is coordinated by Sorin Zaharia, Stan Sazykin and Benoit Lavraud.

The sessions, held on Wednesday, June 24, featured short presentations and discussions of progress on the two main research fronts selected for the present phase of the focus group, as well as results from the recently initiated Near-Earth Magnetosphere Challenge.

1. Observations/empirical models

Short presentations addressed the following topics:

• Empirical electric field specification: overview of improvements in the UNH Inner Magnetosphere Electric Field (IMEF) model based on Cluster data (P. Puhl-Quinn), now being extended to include extreme periods; CLUSTER study of Poynting flux associated with the convection E-field (Y. Nishimura); induced E-fields were shown to be very important for inner magnetosphere particle transport (Gang Lu).
• Empirical magnetic field model TS07D (M. Sitnov); dramatic increase in spatial and temporal resolutions; model is now available on APL website; model shows that in some events the storm-time magnetosphere can be dominated by the tail current).
• During storms with low Mach number solar wind, the dayside B-field can be reduced instead of compressed (due to external Region-1 type currents near the open-closed boundary; Joe Borovsky)
• Empirical plasma pressure model of the inner magnetosphere (P. Brandt, presentation by M. Sitnov – obtained by combining in-situ with global ENA observations)
• First results from the TWINS mission (J. Goldstein, M.-C. Fok); stereo ion inversion leads to improved accuracy; validation vs. THEMIS data.
• Radar observations of ionospheric convection (J. Baker, mid-latitude SuperDARN; 8 new mid-latitude radars coming online in the next 4 years, providing more spatial coverage for model-data comparisons.)
• Pc4, Pc5 wave observations (THEMIS data); correlation with solar wind (Liu et al.)

2. Physics-based numerical Models

Presentations discussed the following issues:

• The recent extension of the magnetofriction code to anisotropic equilibria (for future use e.g. in CRCM); the issue of mirror/firehose instabilities - F. Toffoletto
• CRCM model runs vs. TWINS observations (M.-C. Fok); while ENA (and 12 keV fluxes) peak at post-midnight, the ion pressure peak is still at pre-midnight local times
• The correlation between plasma sheet local time peak density and ring current pressure peak location vanishes when a self-consistent E-field formulation is used (Yihua Zheng, CRCM).
• Effect of models used to drive ring current formation (Vania Jordanova, RAM/RAM-SCB); the self-consistent B-field moves anisotropic regions farther from Earth; N. Ganushkina/M. Liemohn: Dst calculation with the DPS formula vs. Biot-Savart for non-dipole field leads to different results
• 1-way coupling of RAM-SCB with the Space Weather Modeling Framework (SWMF) shows strong ring current and Region-2 currents in RAM-SCB, and good agreement w/ Iridium observations (S. Zaharia)
• Inner magnetosphere physics – Hall MHD not sufficient to produce ring current (Dan Welling, BATS-R-US Hall MHD vs. vanilla MHD)

3. Near-Earth Magnetosphere Challenge

One session was devoted to presentation of results from the recently initiated Near Earth Magnetosphere Modeling Challenge. The challenge has brought together researchers from all major inner magnetosphere modeling groups: RAM-SCB (V. Jordanova, S. Zaharia, LANL), HEIDI (M. Liemohn, Michigan), RCM (S. Sazykin, Rice), RCM-E (S. Sazykin, Rice; C. Lemon, Aerospace), CRCM (N. Buzulukova, GSFC; Y. Zheng, JHU/APL), M. Chen’s model (Aerospace), IMPTAM (N. Ganushkina, FMI). The first step in the Challenge, Phase 0, involved an idealized event, with simple inputs/physics (with the goal of setting a baseline for all models). Phase 0 results were discussed; the total energy (or, equivalently, Dst) values from the different models were found to be close enough (within max. 10% of one another) considering the model differences (e.g. anisotropic vs. isotropic), so Phase 0 is about to be concluded. The results have been posted on a dedicated Challenge website: http://spacibm.rice.edu/~gem_challenge/ A mailing list for the Challenge has been established as well.

The remainder of the session involved a community discussion ironing out details about the next stage in the Challenge (Phase 1). Phase 1 will involve full-physics modeling of an idealized storm, with the goal of finding out the relative role of different physics features in the models. An updated table with the idealized storm parameters will soon be published on the Challenge website.

Some preliminary results from Phase 1 were shown by M. Liemohn (work of N. Ganushkina, IMPTAM) and S. Zaharia (RAM-SCB). The focus group plans to have a session at Mini GEM 2009 where more extended Phase 1 results will be discussed; then, Phase 1 will be wrapped up at Summer GEM Workshop 2010.

The last stage of the Challenge will be Phase 2 (one or a suite of real event simulations), in which both modelers and data analysts will be involved. The focus group is investigating the possibility of a joint effort with GGCM Metrics Modeling Challenge at this stage.

GEM Near-Earth Magnetosphere Challenge

Starting in 2008, the focus group will have a "challenge" project that is aimed at cross-validating multiple ring current and convection numerical inner magnetospheric models, arriving at a common GGCM-style inner magnetospheric module that will employ both first-principle models and empirical data-based components, and eventually applying the models to the science questions listed in the focus group description.

Based on comments and discussions, the organizers of the focus group drafted a plan for the challenge. The most current version of the document can be found here

The Challenge Web page has been set up for collecting results of the challenge. There is also a dedicated mailing list for exchanging information (Mailing List Web page, which also holds mailing list archives).

More details to be added following the mini-GEM workshop session in December 2008.