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:
- 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?
- 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?
- Why do some storms produce major subauroral ion and electron
precipitation events and associated intense low latitude auroral
emissions?
- 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:
- 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?
- 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:
- How does the modification of the electric field structure in the
inner magnetosphere by ring current shielding effects impact coupling
to the underlying ionosphere?
- 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:
- 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?
- 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?
- 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:
- 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?
- Why are some storms more effective for radiation belt injection?
Here the effects of storm sudden commencements (SSCs) appear to be
important.
- 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:
- 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?
- 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?
- 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:
- 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.
- What is different about storms that produce large relativistic
electron enhancements compared to those that do not?
- Is there a particular pattern of magnetospheric activity that
preceds relativistic electron enhancements? (e. g., size history of
plasmasphere?)
- Are elevated plasma sheet densities related to subsequent electron
enhancements?
- Is elevated substorm activity needed to pre-heat new source
material?
- What is the temporal evolution of the radial flux profile?
- Are there signatures of the acceleration process in the pitch angle
distributions?
- What is the temporal evolution of the spectrum?
- Is the phase space density of energetic electrons in the
interplanetary medium sufficient to account for observed enhancements
in the magnetosphere?
- Does the phase space density profile indicate any preferred local
acceleration region?
- If local acceleration is indicated, could this be provided by
wave-particle scattering and if so which waves are involved?
- What are the major mechanisms for electron loss from the radiation
belts following stormtime injection or acceleration?
- What are the principal mechanisms that control the quasi-steady
state radial distribution of energetic electrons in the absence of
major storms?
- What is the relative role of local acceleration and radial
diffusion as a source for inner zone electrons?
- 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.
Implementation
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.
References
- GEM Geospace Environment Modelling, A Program of Solar-Terrestrial
Research in Global Geosciences, GEM Steering Committee, NSF, 1988.
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