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GEM Focus Group Proposal 2013
Analysis and Synthesis of Geospace Current Systems (Currents in Geospace)
1) Topic
Electric currents flowing through the geospace can highly distort the magnetic field configuration,
changing particle drift paths and therefore having a nonlinear feedback on the currents themselves. A
number of current systems exist in the magnetosphere, most notably: (1) the dayside magnetopause
Chapman-Ferraro currents, (2) high latitude “region 1” field-aligned Birkeland currents (closed on or
near the magnetopause), (3) mid-latitude “region 2” field-aligned currents connected to the partial ring
current, (4) magnetotail currents closing on the nightside magnetopause, and (5) the symmetric ring
current. In geospace, however, some of these currents systems flow in close proximity to each other
and it is very difficult to identify a local measurement as belonging to a specific system. This is important, however, because how the current closes and how these loops change in space and time governs the magnetic topology of the magnetosphere and therefore controls the physical processes of
geospace. There is confusion among magnetospheric physicists about how to even define these currents, let alone which one dominates at what time during geomagnetic activity. The interpretation of
currents in the magnetosphere is challenging. The problem is that it is difficult to create a physically
realistic description of the current systems and simultaneously ensure the uniqueness of the resulting
current system. The other issue is terminology, and that sometimes studies are ambiguous about the
current systems in geospace. Yet, this is vitally important for understanding the physics governing particle flow because these currents distort the magnetosphere from its typical quiet-time configuration.
Moreover, different current systems form a global current system in geospace and their synergy is crucial for magnetospheric physics at system science level.
2) Timeliness
To understand the whole system of currents in geospace, it is not enough to simply understand each
component separately. Significant progress has been made on the global modeling of the Earth’s magnetosphere with MHD approach such as LFM, BATS-R-US, and GUMICS codes as well as on the
modeling of local regions such as, for example, ring current models (RCM, CRCM, HEIDI, IMPTAM
codes). Empirical models such as Tsyganenko-type models and event-oriented models for the
magnetospheric magnetic field are in great demand. At present, they are at such a level of sophistication that the details of the configuration and dynamics of current systems represented in them define a
lot of the model output. At the same time, several missions at different altitudes and in different regions
such as CLUSTER, THEMIS, Van Allen Probes, GOES satellites, and LEO spacecraft provide in-situ
information about the currents flowing in these regions. Most notably, AMPERE, which provides magnetic disturbances measured by the Iridium constellation, allows for the first time to investigate the
evolution of global FAC distributions. Thus we have in situ measurements of currents in geospace at an
unprecedented level of spatial coverage, with which we should be able to address individual current
systems in the context of global energy and momentum transport. However, without a consensus
agreement on how to even define the different current systems, our community is at risk of continuing
our present mode of multiple, sometimes contradictory definitions and confusing comparisons. We will
not reach our full potential and productivity as a research community unless we actively and intentionally forge such an agreement.
Magnetic storms differ from one another during different phases of a solar cycle but they occur during entire solar cycle. In its highly disturbed state during a storm, the magnetosphere is subject to
emergent phenomena and nonlinear behavior. However, electric current must close and the laws of par-
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ticle dynamics and electromagnetics must be obeyed. Therefore, a useful way of distilling the complicated interplay of the geospace system components during storms is to understand how currents flow
through it and how this relates to particle populations and field configurations.
A synoptic approach, as well as an analytical approach, is vital for understanding electric current
systems in the geospace. This is so because magnetospheric current systems transport energy and momentum from one region to another, and measurements of local currents in one region are usually not
sufficient for comprehending the entire current system. An example for such an issue for the day side is
the issue of the saturation of the cross polar-cap potential. One possible explanation is that the intensity
of the dayside R1 current has an upper limit as its closure current at the magnetopause cannot exceed
that of the Chapman-Ferraro cur-rent (Siscoe-Hill formulation), which sets a limit to the cross polarcap potential. Another explanation is concerned with the effects of R1 current on the shape of the dayside magnetopause, which affects the solar-wind magnetic flux that interacts with the magnetosphere.
Testing those ideas requires addressing the entire closure of the R1 current and its impact on the solar
wind-magnetosphere interaction.
The collaboration between modeling and observational efforts is most vital. Whereas global MHD
models, especially if coupled with a ring current module, are most suitable for studying the closure of
magnetospheric currents, their results need to be critically tested by observations. On the other hand,
experimental studies of any such subject need some guidance or prediction from modeling studies that
can be tested with existing data.
3) Fit: How the FG would relate to existing FGs?
Because of its emphasis on a specific issue of global importance, the “Currents in Geospace”FG will
have direct synergies with nearly all of the existing FGs:
The Magnetosheath: The magnetopause currents define the boundary between the magnetosphere and
magnetosheath, and in fact some of the "magnetopause" currents actually close within the
magnetosheath or on the bow shock surface. The proposed FG would leverage the activities of the
Magnetosheath FG to quantify current closure pathways in this region of geospace and their relationship to particle populations.
Metrics and Validation: The plan for this proposed FG includes conducting 2 GEM Currents Challenges, in Years 2 and 4. The Metrics and Validation FG will be asked to help coordinate these challenges
and ensure broad participation and rigorous data-model comparisons.
The Ionospheric Source of Magnetospheric Plasma--Measuring, Modeling and Merging into the GEM
GGCM: The proposed FG seeks to relate current systems to the charged particles carrying the current,
and the existence of heavy ions within the magnetosphere has the potential to significantly alter current
flow. This is especially true in weakly magnetized regions such as thin plasma sheets.
Scientific Magnetic Mapping & Techniques: A key element of mapping magnetic field lines from the
ionosphere to the equatorial magnetosphere is the nondipolar distortion from magnetospheric current
systems. The proposed FG will work towards a common definition of all current systems in geospace
and a better understanding of how these current systems vary with geomagnetic activity.
Tail-Inner Magnetosphere Interactions: The flow of plasma from the tail to the inner magnetosphere is
often quite localized within the magnetotail, altering the closure of current within the plasma sheet and
sometimes leading to new current closure pathways (such as the substorm current wedge). The proposed FG will work with the TIMI FG on the definition of tail current and return currents to quantify
this relationship between plasma flow and magnetic structure.
Transient Phenomena at the Magnetopause and Bow Shock and Their Ground Signatures: The ground
signatures of transient phenomena are related to the magnetopause and bow shock by currents. There-
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fore, this proposed FG will converse with the leaders of the Transient Phenomena FG to better define
the closure of magnetopause current and their relationship to particle populations.
Storm-Time Inner Magnetosphere-Ionosphere Convection: The modification of the nightside
ionospheric electric potential pattern is related to magnetospheric particle dynamics through the closure
of the partial ring current. Furthermore, the inner magnetospheric electric field is modulated by the
high-latitude convection pattern (e.g., prompt penetration E-fields), and knowledge of the R1 currents
is needed to fully understand the changes to the midlatitude potential pattern. The proposed FG will
coordinate with the SIMIC FG on the definition of ring current, partial ring current with field-aligned
currents closure to the ionosphere, R1 and R2 field-aligned currents, to better relate the magnetospheric
plasma populations with changes in the electric potential.
4) Goals & Deliverables
The main objective of this proposed FG is to understand how currents flow as a whole system and as
certain currents through geospace during disturbed times. Five specific questions will be addressed:
 What are the definitions for current systems in geospace? How should we physically and
phenomenologically define current systems in geospace?
 What are the locations and intensities of currents for various driving conditions?
 What are the transitions from one current system configuration to another?
 How can we diagnose magnetospheric processes from the temporal development and global distributions of current systems?
 What is the synergy of different current systems, such as for example, R1 FACs and magnetopause currents, the ring current and tail current?
The main deliverables include:
- definitions of current systems in geospace, as viewed from a variety of observational and computational analysis techniques;
- application of the agreed set of definitions for the various current systems to a few case study intervals;
- to develop an initial formulation for the locations and intensities of currents as a function of solar
wind driving and geomagnetic conditions;
- to request two journal special issues, with synthesis papers summarizing the main findings about
current systems in geospace, especially regarding the selected interval analyses.
5) Co-chairs
Natalia Ganushkina (ganuna@umich.edu), University of Michigan, USA/Finnish Meteorological Institute, Finland
Shin-Ichi Ohtani (Shin.Ohtani@jhuapl.edu), APL, USA
6) Research Area
The ”Currents in Geospace” FG will address one of the main goals of the whole GEM program: ”Develop an integrated physical understanding of the geospace dynamical system.” It will be associated to
all GEM Research Areas, since currents flow in all regions of the magnetosphere, with the main relevance to GGCM and MI-Coupling. It is proposed to place the "Currents in Geospace" FG administratively under the coordination of the GGCM Research Area.
7) Term
The proposed FG duration is 5 years starting from summer 2014.
8) Expected activities
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For Year 1:
We will announce the main discussion question on definitions for geospace current systems. Participants will be encouraged to present and discuss the options for defining current systems in geospace
and compare their pros and cons in a rational and objective deliberation. The goal is to reach consensus
on definitional sets for the various current systems. We will also discuss and decide on the specifics for
the First GEM Currents Challenge (event list and data-model comparison strategy).
For Year 2:
We will announce the First GEM Currents Challenge concerning the locations and intensities of currents for various driving conditions. Participants will be encouraged to bring the latest data sets and
numerical tools for a few pre-selected events. For this Challenge, we will study the dynamics of the
current systems, focusing on how they change in location and intensity through the selected events. The
goal is to reach consensus on the temporal and spatial dynamics and evolution of these currents within
geospace for these intervals.
For Year 3:
We will present and discuss the analyses of the events selected at the First GEM Currents Challenges
and thoroughly examine the reached consensus on the temporal and spatial dynamics and evolution of
these currents within geospace for these intervals. We will also continue to discuss the definitions for
geospace current systems. A journal special issue will be requested for papers summarizing the main
conclusions about definitions of current systems in geospace and their temporal and spatial dynamics.
We will also discuss and decide on the specifics for the Second GEM Currents Challenge.
For Year 4:
We will announce the second GEM Currents Challenge on the events with transitions from one current system configuration to another. The Challenge will include the examination of the solar wind and
geospace data to select several intervals that include these transitions from one current system configuration to another. These events will be individually analyzed over the next few months for detailed
study. We will select 3 or 4 intervals that cover a wide range of possible current system scenarios and
geomagnetic activity levels. We will also encourage participants to conduct large statistical surveys of
magnetospheric current systems based on our consensus definitions. This will augment the individual
event case studies and dramatically increase the robustness of the Challenge’s findings. The goal is to
develop an understanding of how geospace makes these transitions, and look for identifiable processes
that signify the transition.
For Year 5:
We will, based on all previous efforts, compile a methodology for determining the current system configuration. This system will use whatever data is best suited for predicting the state of the geospace current system, and therefore could be based on upstream solar wind conditions, in situ geospace observations, or ground-based measurements. The goal is to develop a parameterization that is generally applicable for defining current systems within the magnetosphere. As a completion of all the efforts, a second journal special issue will be requested for papers summarizing the main conclusions about current
systems in geospace. Submission to this special issue will be made open to all others in the research
community who might also be studying this problem.