FG: Storm-Time Inner Magnetosphere-Ionosphere Convection

Focus Group Co-Chairs

• Joseph Baker, Virginia Tech (jo.baker [at] vt.edu)
• J. Michael Ruohoniemi, Virginia Tech (mikeruo [at] vt.edu)
• Stanislav Sazykin, Rice University (sazykin [at] rice.edu)
• Peter Chi, University of California Los Angeles (pchi [at] igpp.ucla.edu)
• Mark Engebretson, Augsburg College (engebret [at] augsburg.edu)

Term of Effort

5 years (2013 – 2017)

Abstract

A new GEM Focus Group (FG) is proposed to study Storm-Time Inner Magnetosphere – Ionosphere Convection (SIMIC). This FG will bring together experimentalists, modelers, and theorists to synthesize a new understanding of how plasma distributions, convection electric fields, and current systems emerge and evolve in the inner magnetosphere and conjugate ionosphere during geomagnetic storms. The new SIMIC FG is motivated by: (1) improvements in self-consistent physics-based modeling of the coupled inner magnetosphere-ionosphere system which require ongoing validation and improvement, (2) several recent augmentations to ground- and space-based instrumentation which collectively provide new datasets with unprecedented spatiotemporal coverage and resolution, and, (3) recent ramping up of solar activity leading to increased geomagnetic activity. Two specific scientific themes related to inner magnetosphere - ionosphere convection that will be explored in detail are the Sub-Auroral Polarization Stream (SAPS) and penetration electric fields. The new SIMIC FG will build upon the achievements of two existing FGs which are just now coming to completion in 2012-2013, namely, the Near-Earth Magnetosphere: Plasma, Fields and Coupling FG and the Plasmasphere-Magnetosphere Interactions FG. The new SIMIC FG will also be complementary to several ongoing FGs, such as Scientific Magnetic Mapping and Techniques (SMMT) and Tail-Inner Magnetosphere Interactions (TIMI). The specific goals of the SIMIC FG are: (1) develop an improved canonical description of convection in the coupled inner magnetosphere - ionosphere during storms, (2) validate and improve the performance of coupled inner magnetosphere-ionosphere models, and, (3) make steps toward developing a new module for active ionospheric feedback during storms. A particular emphasis of the SIMIC FG will be to encourage the use of spatially distributed ionospheric measurements and network magnetic observations for validating and improving geospace models. Finally, there will be ample opportunity to involve the CEDAR community which has similar interests in examining geomagnetic storm phenomena and has several useful datasets that can be brought to bear on this problem.

Topic Description

To be able to understand and model the dynamics of the Geospace environment, the GEM community has always sought to analyze how large-scale magnetospheric current systems and plasma flows are generated, and how mass, energy, and momentum flow throughout the coupled magnetosphere-ionosphere-thermosphere system. The large-scale global electric and magnetic fields play a major role in magnetospheric convection. For example, it is now known that plasma convection in the inner magnetosphere - ionosphere: (1) can be highly structured by forming subauroral polarization stream (SAPS) channels, (2) may be transient at times (i.e. prompt penetration ionospheric electric fields), (3) is important for controlling plasmasphere dynamics, and, (4) includes magnetospheric dipolarization fronts associated with entropy “bubbles” and auroral phenomena that have meso-scale transient convection signatures. Yet our understanding of these dynamical processes in the inner magnetosphere during active periods is quite limited due to the paucity of spacecraft measurements in the region of interest. As a result, existing empirical models of the inner magnetosphere are static and statistical in nature, with most of them being based on single-point spacecraft measurements accumulated over extended periods of time. Therefore, further progress in geospace modeling requires an improved understanding of the coupling of convection features between the inner magnetosphere and ionosphere during geomagnetic storms. The new SIMIC FG will bring together globally distributed space- and ground-based datasets to characterize storm-related convection dynamical processes in the inner magnetosphere-ionosphere region, and fully coupled magnetosphere-ionosphere models to examine large-scale features of inner magnetosphere-ionosphere coupling during geomagnetic storms (e.g. SAPS, penetration electric fields, and substorm-related signatures). The assembled data sets will also be used to assess the accuracy of the modeling results.

Timeliness of the Focus Group

This FG is timely for the following reasons:

• In recent years there have been substantial augmentations to mid-latitude ground-based instrumentation. These include: (1) new mid-latitude SuperDARN radars, (2) expanded networks of auroral instruments and ground-based magnetometers (e.g. THEMIS GBOs), and, (3) improved coverage of GPS receivers for producing regional maps of Total Electron Content (GPS-TEC).
• Likewise, there is increased coverage of spacecraft datasets which together provide extensive in-situ measurements of the inner magnetosphere (e.g. Cluster, THEMIS, Van Allen Probes) and the subauroral ionosphere (e.g. AMPERE, DMSP, POES).
• Solar activity is rising toward solar maximum and so an emphasis on storm-time phenomena is particularly timely. The past 2-3 years has already provided several exciting events which have showcased the new capabilities provided by expanded instrument coverage. Over the next 3-5 years we can expect continued increases in activity which will provide ample more storm events for study.

We now have the capability to simultaneously monitor the following parameters with unprecedented spatiotemporal coverage and resolution:

• Subauroral ionospheric convection (e.g. mid-latitude SuperDARN)
• Flux-tube plasma content (e.g. GPS-TEC, magnetometer FLR measurements)
• Field-aligned currents (e.g. AMPERE, ground magnetometers)
• Auroral precipitation signatures and boundaries (e.g. THEMIS GBOs, DMSP).

Collectively, these datasets provide exciting new possibilities to examine the interrelationship between convection, currents, and plasma structuring; as well as test the predictions of the latest generation of coupled inner magnetosphere – ionosphere models.

Relation to existing GEM Focus Groups

The SIMIC FG will have direct synergies with the following existing FGs:

• Radiation Belts and Wave Modeling (2010-2014): Improved understanding of inner magnetosphere-ionosphere convection on global scales during geomagnetic storms will provide valuable constraints for the theoretical studies of energization and loss of radiation belt electrons carried out by the Radiation Belts and Wave Modeling (RBWM) FG.
• Metrics and Validation (2011-2015): The SIMIC FG will have a primary emphasis on carrying out detailed model-data comparisons to verify the performance of the latest generation of coupled inner magnetosphere-ionosphere models. The new FG thus has direct relevance to the Metrics and Validation FG.
• Tail-Inner Magnetosphere Interactions (2012-2016): Inner magnetosphere-ionosphere electrodynamics is driven by convection from the tail, with a large fraction of energy and mass transport controlled by so-called “entropy bubbles” which is of primary interest to the Tail-Inner Magnetosphere Interactions (TIMI) focus group. The results of the TIMI FG will thus have a direct bearing on the SIMIC FG.
• Scientific Magnetic Mapping and Techniques (2011-2015): Improved understanding of inner magnetosphere-ionosphere convection will provide new constraints for the Scientific Magnetic Mapping and Techniques (SMMT) FG. By the same token, new improved mapping techniques will undoubtedly help in the interpretation of event periods selected for study by the SIMIC FG.

Specific Goals and Deliverables

The specific goals and deliverables for the SIMIC FG are:

• Develop an improved canonical description of the storm-time evolution of plasma distributions, convection, and field-aligned currents in the coupled inner magnetosphere and ionosphere.
• Improve inner magnetospheric models (e.g., RCM, RAM-SCM, HEIDI, CRCM) to better predict dynamical phenomena during storms. These improvements will be guided by observations and exploring model parameters known to have large uncertainties (e.g., conductivities).
• Improve existing GGCMs such as SWMF, LFM, and OpenGGCM that are based on global MHD models but include coupling to other physics-based models. These improvements will come through identifying which physical processes and numerical aspects (e.g., grid resolution, time stepping) require modification to reproduce observed features.
• Make steps toward developing a new module to incorporate active ionospheric feedback on subauroral magnetic flux tubes during geomagnetic storms.
• Compile collections of linked papers exploring the dynamics of the coupled inner magnetosphere - ionosphere based on first principles modeling and detailed model-data comparisons.
• Encourage and expand the usage of distributed ionospheric datasets and magnetometer observations for validating and improving geospace models.
• Forge closer ties with the CEDAR scientific community in the study of geomagnetic storm phenomena.

GEM Research Areas

The SIMIC FG will primarily be associated with the following two GEM Research Areas:

• Inner Magnetosphere and Storms (IMS)
• Magnetosphere-Ionosphere Coupling (MIC)

It is also of secondary relevance to Geospace General Circulation Model (GGCM)

Science Questions, Activities, and Challenges

Some of the science questions addressed by the SIMIC FG include:

• How accurate are present empirical models of the inner magnetosphere electric and magnetic fields in capturing the latitude and longitude of dynamic ionospheric convection features during storms (e.g. SAPS)?
• Does self-consistent modeling of inner magnetosphere-ionosphere electric and magnetic fields accurately capture storm-time ionospheric features (e.g. time-scale of penetration electric fields and location/intensity of SAPS)?
• Is the standard model of SAPS formation and evolution accurate? To what extent does active ionosphere-thermosphere feedback play a role?
• Is the standard model of inner magnetosphere shielding by the region-2 field-aligned currents accurate? What are the time-scales on which penetration electric fields operate? What parameters modulate the amount of shielding?
• To what extent is it accurate to treat inner magnetosphere magnetic flux tubes as electrostatic equipotentials?
• What are the ionospheric convection signatures of “entropy bubbles” and to what extent are numerical models able to reproduce the observations?
• To what extent is the ionosphere a source of plasmaspheric depletion during storms? How is plasmaspheric depletion connected with other features of storm-time magnetosphere – ionosphere coupling?
• How are recent observations of post-noon enhancement in plasmaspheric mass density and annual variations related to similar ionosphere-thermosphere asymmetries?

Some of the activities and challenges that will be conducted include:

• Compilation of multi-instrument datasets for selected event periods to develop an improved canonical understanding of how inner magnetosphere – ionosphere convection evolves during geomagnetic storms in relation to field-aligned currents and large-scale plasma structures.
• Issuance of challenges for modelers to reproduce actual events (e.g. SAPS and penetration electric fields) with the aim of validating model performance and producing improvements.
• Compilation of collections of linked papers for a special issue of JGR or other relevant journal.