Updated Plan for GEM Inner Magnetosphere and Storms Campaign

To: GEM Community
From: Mary Hudson (maryk@comet.dartmouth.edu)

The following updated Plan for GEM Inner Magnetosphere and Storms Campaign will serve as a guideline for campaign activities in the coming year, as well as a report from our planning working group sessions which met at the 1996 and 1997 GEM Snowmass meetings. Further comments or suggestions can be addressed to:

Dick Wolf, GEM Steering Committee chair (wolf@alfven.rice.edu) or

Mary Hudson, IM/Storms campaign convenor (maryk@comet.dartmouth.edu).

Plan for GEM Inner Magnetosphere and Storms Campaign

The 1988 document [1] defining the GEM project (Geospace Environment Modelling) specified a sequential series of theory campaigns coupled with support for observations, measurement, data analysis and information systems. These campaigns were roughly organized into studies of geospace regions extending from the outer regions of the magnetosphere inward, with the long term goal of attaining quantitative global modelling predictions, with specification of ``weather in space'' appearing in the Executive Summary.

Much has happened during the intervening years, including five years of support for the Magnetopause and Boundary Layer Campaign and three years for the Tail and Substorm Campaign, which have been run in parallel with considerable gain for addressing the long term goal. In particular, researchers in one campaign have appeared in the next, in addition to bringing new investigators into the program, and the GEM endeavor has benefited from the sharing of expertise and discoveries between campaigns. It quickly became apparent that success in achieving predictive modelling capability as an end goal required a parallel working group, recently given campaign status, which focuses specificly on the development of a modular Geospace General Circulation Model (GGCM). This latter campaign has just been initiated in the Fall of 1996 and will focus on tying together modelling efforts from preceding and follow-on campaigns in a unified, quantitative and testable format.

A concurrent major development with support from and impact on the GEM community is the National Space Weather Program, an interagency program which is an outgrowth of the need expressed in the original GEM Executive Summary to be able to predict in a timely, quantitative and reliable way, variations in both the satellite space environment and effects on the ground due to those variations. It is timely both for GEM and the NSWP that the next campaign will focus on the Inner Magnetosphere and Storms. The coupling of the inner and outer magnetosphere is most dynamic during storm periods, and the new campaign will both benefit from the knowledge and tools acquired in the preceding campaigns and contribute important inner boundary constraints to the GGCM development. From a space weather point of view, understanding the dynamics of the inner magnetosphere is arguably the most critical from a space-weather point of view, since that is where most operational spacecraft reside.

In order to define goals for the Inner Magnetosphere and Storms campaign, three working groups have met at the annual GEM Snowmass Meeting in June 1996 and 1997. These working groups and and their 1997 co-chairs were:

Working Group 1: Plasmasphere and ring current coupling, Jim Horwitz and Janet Kozyra, co-chairs

Working Group 2: Storm injection and recovery mechanisms --- ring current and radiation belts, Dan Baker and Mary Hudson, co-chairs

Working Group 3: Energetic electron variability, Richard Thorne and Geoff Reeves, co-chairs

Each working group has posed a set of questions which constitute a starting point for the new campaign, to be augmented by further community input. It was further decided at the June 1997 GEM meeting to reduce the number of working groups from three to two, incorporating ring current questions into the activities of Working Group 1, and radiation belt issues into Working Group 3, thereby eliminating Working Group 2, and overlapping sessions of common interest at future GEM Workshops. We have, however, formulated a set of questions within each of the three preliminary working groups which stand as a report from the planning activities, and form a basis for proceeding with the new campaign. It is expected that the structure of the Inner Magnetosphere and Storms campaign will continue to evolve in support of the overall goals of the GEM program.

Plasmasphere and Ring Current Coupling

The major outstanding questions posed by Working Group 1 were concerned with ring current decay, large-scale plasmasphere dynamics and flux tube refilling, the role of wave particle interactions in storm time ring current recovery and outer plasmasphere development, and the magnetic field structure of the inner magnetosphere.

Specific questions related to ring current decay include the following:

  1. Are the ring current and magnetopause currents the major contributors to the Dst index (a widely used tool for monitoring ring current growth and decay during geomagnetic storms)? How important are magnetotail current systems to the time-variation of this index?

  2. What processes produce short time-scale (t < 6 hrs) losses from the ring current that are reflected in the Dst index? How important to the ring current global energy balance are adiabatic drifts to the dayside magnetopause, variations in the plasmasheet source population, overshielding dusk-dawn electric fields and subauroral ion and electron precipitation losses? Are the relative importance of these processes a function of the severity of the storm?

  3. Why do some storms produce major subauroral ion and electron precipitation events and associated intense low latitude auroral emissions?

  4. What role do plasma waves (Pc5, ion cyclotron, lower hybrid, etc.) play in producing precipitation loss from the ring current, redistributing energy between ring current ion species and channeling ring current energy into the thermal populations of the inner magnetosphere?

    Unresolved issues associated with the coupling between the inner magnetosphere and the magnetotail region are:

  5. How do substorm induction electric fields associated with dipolarization events affect ring current dynamics? Do stretched magnetic field lines, resulting from intense substorm current sheets, lead to nonadiabatic motions of high energy ions within the inner magnetosphere? What are the consequences?

  6. How does the thermal plasma respond to storm and substorm electric fields? Is substorm dipolarization a viable process for creating warm trapped ions in the inner magnetosphere? Are there near-midnight outward plasmasphere extrusions caused by penetrating eastward electric fields induced during substorm growth phase? Can the dayside outer plasmasphere be circulated into the plasmasheet, and possibly explain so-called ``superdense'' plasma sheet regions?

    Questions regarding the coupling between the inner magnetosphere and underlying ionosphere are:

  7. How does the modification of the electric field structure in the inner magnetosphere by ring current shielding effects impact coupling to the underlying ionosphere?

  8. How do depleted outer plasmaspheric flux tubes refill and what are the roles of wave-particle interactions, suprathermal electrons and electrostatic potential barriers in this process? What is the ionospheric connection of heavy ion density enhancements in the mid-latitude outer plasmasphere and also how are these heavy ion density enhancements related to equatorially-trapped light ion populations(possibly on these same field lines). Why does the He+/H+ density ratio appear to be relatively constant through the plasmasphere, even during considerable total density variation? Is there a plasmaspheric signature for the nighttime ionospheric electron temperature enhancements seen near L=4?

    Questions related to thermal plasma energetics (including coupling between energetic and thermal plasmas), density structures and dynamics, include:

  9. How do cold plasma enhancements in the dusk bulge region affect ring current decay? Do density plateaus in the dusk sector overlap with the ring current? Are they coupled to the ring current in some way? How do stormtime modifications to the electric field structure in the inner magnetosphere (e. g., SAID events) affect plasmaspheric dynamics and structure the outer plasmaspheric density? Is there a minimum in the plasma density at the equator in the outer plasmasphere? What controls the incidence or disappearance of dayside plasmapauses?

  10. What is the relative importance of wave heating and collisional energy transfer from the ring current and suprathermal ion populations in heating the thermal plasmas of the inner magnetosphere during storms and substorms? How do these heat sources vary with local time and L value and with storm and substorm phases? Is there a systematic relationship between warm and hot proton characteristics near synchronous orbit that is consistent with marginal stability of electromagnetic ion cyclotron(EMIC) waves? What are the meso- and global-scale effects of MHD~wave ``breaking'' in the other plasmasphere?

  11. What are the major sources and sinks of suprathermal (sub-keV) ion populations in the inner magnetosphere during geomagnetic storms? How are these populations distributed in L value and local time? How do they affect the temperature structure of the thermal ions and the variation of this temperature structure throughout and following the storm interval?
Answering some of these questions will require the use of new, higher time resolution data sets from satellites which either traverse the inner magnetosphere (e. g. Polar, Equator S, DE--1, ISEE--1, geosynchronous, Akebono) or measure particle precipitation at lower altitudes (e. g. Fast, Sampex). While awaiting global neutral atom, EUV, and radio sounding imaging satellite studies, novel coordinated groundbased techniques will play an important role. For example, ``Magnetoseismology'' or use of ground magnetometer arrays to sense remote properties of the inner magnetosphere, has been proposed. These, along with the increasing sophistication of modelling efforts, will provide new tools for tackling the preceding partial list of problems in ring current-plasmapshere coupling to be addressed during the Inner Magnetosphere and Storms campaign.

Storm Injection and Recovery Mechanisms: Ring Current and Radiation Belts

While Working Group 1 has focused on questions of ring current- plasmasphere interaction, ring current recovery and plasmasphere refilling, Working Group 2 will address mechanisms for radiation belt injection and buildup of the storm time ring current; also radiation belt loss mechanisms which are distinct from ring current recovery, which is closely coupled to interaction with the plasmasphere. The relationship between storms and substorms is addressed here, where we see the important connection between this and the preceding GEM campaigns. A partial list of questions posed for study include:
  1. Why are some storms more effective for ring current buildup and slow recovery? What is their relationship to substorms, solar wind dynamic pressure and IMF Bz? Are variations in the density and/or temperature of the inner plasmasheet (a major ring current source population) an important prerequisite for a large ring current buildup and how are these variations related to upstream solar wind conditions?

  2. Why are some storms more effective for radiation belt injection? Here the effects of storm sudden commencements (SSCs) appear to be important.

  3. Why are some storms more notable for drop in geosynchronous particle flux? Relationship to ring current buildup may be important.

    Clearly different timescales are involved in what we characterize as a geomagnetic storm: SSC timescale of minutes, the ring current buildup, enhanced convection and substorm timescale of hours, and the ring current recovery timescale of days. We can currently model different parts of a storm on separate timescales, but cannot yet model a whole storm, with or without an SSC, all the way through to ring current recovery at all relevant particle energies. Because the various populations are coupled, we cannot address the total picture of storm dynamics pertaining to space weather without combining temporal scales.

    Other questions which tie into Working Groups 1 and 3 are:

  4. What is the ionospheric contribution to the ring current? What contribution do solar protons make to the more energetic component? Is the production of very energetic ring current ions related to recurrent substorm activity?

  5. Storm injection of electrons is not well understood. Some storms cause loss, possibly adiabatic, to the magnetopause, followed by a 1--2 day delay in buildup of fluxes to greater than pre-storm values. Others, such as the March 24, 1991, event and another on August 18, 1991, provide inward transport of outer zone electrons on the SSC timescale as a main feature. What is the net effect of storms, or different types of storms, on electrons?

  6. Electron contribution to the ring current has been largely neglected.

    This partial list captures the flavor of outstanding questions pertaining to storm dynamics. A last question which opens many and ties into the GEM Tail Substorm Campaign, is:

  7. What is the relationship between storms and substorms? Clearly substorms occur within storms and affect ring current buildup and outer zone electron recovery and buildup. What distinguishes a storm from a series of substorms which can have many similar effects?

Energetic electron variability

A predictive quantitative understanding of energetic electron variability should be a major focus of the Inner Magnetosphere and Storms Campaign. Flux buildup, known to be hazardous to spacecraft due to charging effects, has a degree of predictability based on the known correlation with recurring high speed solar wind streams. However, actual flux levels are not quantitatively predictable at present due to our lack of understanding of the coupling and energization mechanisms within the magnetosphere. A number of focused questions have emerged regarding the relationship of electron radiation belt flux variability to storms and substorms, as well as to recurring solar wind high speed streams.
  1. What is different about storms that produce large relativistic electron enhancements compared to those that do not?

  2. Is there a particular pattern of magnetospheric activity that preceds relativistic electron enhancements? (e. g., size history of plasmasphere?)

  3. Are elevated plasma sheet densities related to subsequent electron enhancements?

  4. Is elevated substorm activity needed to pre-heat new source material?

  5. What is the temporal evolution of the radial flux profile?

  6. Are there signatures of the acceleration process in the pitch angle distributions?

  7. What is the temporal evolution of the spectrum?

  8. Is the phase space density of energetic electrons in the interplanetary medium sufficient to account for observed enhancements in the magnetosphere?

  9. Does the phase space density profile indicate any preferred local acceleration region?

  10. If local acceleration is indicated, could this be provided by wave-particle scattering and if so which waves are involved?

  11. What are the major mechanisms for electron loss from the radiation belts following stormtime injection or acceleration?

  12. What are the principal mechanisms that control the quasi-steady state radial distribution of energetic electrons in the absence of major storms?

  13. What is the relative role of local acceleration and radial diffusion as a source for inner zone electrons?

  14. What is the importance of energetic electron precipitation on middle atmospheric and ionospheric chemistry?

The preceding questions focus on the relativistic electron signatures directly, while a number of clues regarding both acceleration and loss may be contained in the wave properties of the magnetosphere which are dramatically altered during storms and substorms. For example, enhanced wave activity may produce energization of relativistic electrons as well as pitch angle diffusion. The solar wind does not appear to be an adequate adiabatic source of relativistic electrons without further energization above that due to radial diffusion and conservation of first and second adiabatic invariants.


It is expected that the Inner Magnetosphere and Storms Campaign will be implemented along lines analogous to the Boundary Layer and Tail-Substorm campaigns, with an accelerated startup which capitalizes on our experience from preceding campaigns and responds to the urgency of the National Space Weather Program goal of achieving improved prediction capability by the next solar maximum. The next GEM proposal opportunity should include a call for theoretical and observational research proposals which develop new tools and coordinate resources from both the satellite and groundbased communities to address the problem areas and questions outlined above. The goal is to obtain a predictive model or set of models quantifying inner magnetosphere dynamics which then can be coupled into the concurrent GGCM campaign effort. The GEM Steering Committee has allocated two days (one day and two half-days) of the June 1998 Snowmass Meeting for Inner Magnetosphere and Storms Campaign workshop activities. We anticipate a continued high level of community interest and participation, as was demonstrated in the two years of planning workshops for the Inner Magnetosphere and Storms Campaign. Its timeliness for synergism with the International Solar Terrestrial Physics (ISTP) program, the National Space Weather Program and development of the GGCM within GEM is expected to attract an enthusiastic proposal response from the community to the Fall 1997 GEM solicitation.


  1. GEM Geospace Environment Modelling, A Program of Solar-Terrestrial Research in Global Geosciences, GEM Steering Committee, NSF, 1988.

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