2013 Workshop Lyons GEM-CEDAR Workshop Summary

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GEM-CEDA: Ideas for the future

We believe that this was an excellent workshop and that substantial progress was made towards the main goals of educating the full MIT community on the very many areas where coupling phenomena are crucial, and of motivating future research where coordinated study by the Aeronomy and Magnetospheric communities can potentially lead to substantial progress beyond that which can be achieved by each community individually. Many areas for future study where identified, and those identified by the session chairs include:

A. The Dayside MIT response to transient solar wind, bow shock, and magnetopause phenomena session addressed transients in regions ranging from the foreshock to the ionosphere, and the processes that connect them. Issues that were called out as needing attention in the near future are:

1. Including proper inner boundary/ionosphere conditions in global hybrid and MHD simulations.
2. Conducting integrated science studies that employ multipoint measurements to identify the sequence of phenomena that link upstream (foreshock and solar wind) phenomena to downstream (ionospheric) responses.
3. Performing detailed comparisons of the results from global simulations with in situ observations that can help distinguish between and improve models, and provide guidance for interpreting observations of flow vortices in the magnetosphere that form in response to solar wind dynamic pressure variations.
4. While in situ measurements are needed to understand microphysical processes, only global measurements can provide the information on dimensions and occurrence rates that are needed to determine the significance of various proposed solar wind-magnetosphere interaction processes, such as steady and bursty reconnection, waves driven by pressure variations, and the Kelvin-Helmholtz instability. The global observations might come from nearly developed ENA or soft x-ray imaging techniques.
5. There is much still to be learned about ionospheric upflow/outflow, plasmasphere and TEC variations, the behavior of the F-region, SAPS, thermosphere winds, and mesospheric phenomena in response to the heliospheric current sheet.
6. Evaluating the magnetosphere-ionosphere-thermosphere system response to solar wind dynamic pressure fronts, in terms of FACs, Joule heating, and their relation to thermospheric density and winds, including quantitative correlation studies between thermospheric parameters and FACs/Joule heating. Evaluation of the relative contribution of Poynting flux and particle precipitation to the thermospheric response to pressure fronts is also needed.

B. The session on structure and dynamics of polar cap ionospheric convection and plasma was concerned with the morphology of high-latitude flows from the polar cap to the auroral zones, leading up to and continuing through substorms and the associated impacts on ground-based ionospheric diagnostics.

1. A scenario involving streamers emerging from PBIs, extending to lower latitudes, and making contact with SAPS flows in the vicinity of the Harang region just prior to substorm onset provided an important framework. An overarching GEM/CEDAR takeaway message was the importance of ground based/satellite conjunctions in identifying this scenario and other prominent morphological features (such as flow and auroral structures within the polar cap) and facilitating their interpretation and correspondence to magnetospheric phenomena. Effects on the full MIT system will need to be considered going forward.
2. Radio scintillations, which are produced predominantly by polar cap patches and also within the SAPS zone. While scintillations are understood phenomenologically, important details, including the precise role of gradient drift and other plasma instabilities in producing the Fresnel-scale irregularities involved and the appropriate choice of pierce-point altitudes, require further study. Aggregating information from diverse sources of data emerges here again as an important CEDAR/GEM theme.
3. One of the most critical and fruitful areas of joint CEDAR/GEM research is in the area of ion outflows which accompany auroral intensifications and FAC. Outflow produces the O+ population that carries a large part of the ring current during storms, affects the growth rate of EMIC waves, reduces the nightside reconnection rate through its influence on the Alfven speed, reduces the cross-polar cap potential, and may play a role in sawtooth events, and so is a central component of MI coupling.
4. O+ outflow is thought to be due to some combination of the effects of 1) suprathermal electrons, 2) centrifugal acceleration, 3) transverse heating by wave-particle interactions and the subsequent effect of the mirror force, and 4) the pondermotive force associated with Alfven waves. Determining the relative contributions of these mechanisms necessitates the collaboration of theory, observation, and models and represents an ideal joint focus area for GEM/CEDAR.

C. The nightside meso-scale convection session considered the coupling between plasma sheet flow structures and the aurora.

1. While waves are important for E|| formation and geomagnetic pulsations, wave physics is not normally included in global M-I simulations, and efforts should be made to do this. It was suggested that self-consistent simulations by considering dynamically changing conductance, precipitation, convection and neutral wind will affect large-scale dynamics and should thus be considered in the future, and that there should be efforts towards realistic models of these.
2. High-resolution, dynamic observations or statistical models that consider specific disturbance phenomena, rather than being just a function of a geomagnetic index such as Kp, are desired.
3. High-resolution observations have now started, using combinations of radar and optical and imaging. They showed fast, structured flows associated with auroral streamers and substorm onset, and detailed evolution of the ionospheric trough. It is important to continue high-resolution observations for detecting meso-scale structures. Possibilities include SuperDARN measurements in higher cadence, a plan for deploying GPS receivers for monitoring small-scale ionospheric density structures, using imagers for obtaining precipitating particle flux in 2-d. Continuing and integrating such observations are needed for understanding of meso-scale structures in M-I coupling and for quantitative modeling.

D. MIT coupling from the auroral oval to sub-auroral, low, and equatorial regions

1. There is a continued need for global scale observations and models.
2. A significant puzzle: plasmasphere refilling, what determines the time scale? Models are seemingly "unphysical" in this area. RBSP might provide useful information.
3. An interesting research direction: what accounts for rapid variability of high latitude convection? What causes sudden changes in the scales of irregularities that are observed at high latitude? To what degree is this driven by magnetospheric processes? What processes are responsible? (Note that large-scale observations can catch rapid variations).
4. To what extent is a simple mapping satisfactory for relating storm time inner magnetosphere and ionospheric convection. We need to understand the wave coupling.
5. New observations/direction: Optical aurora and coherent radar backscatter have revealed a 3D image and origin of backscatter; this requires a very high rate date (< 1 sec!).
6. Models of H+ precipitation and how the beams spread with decreasing altitude should be considered and evaluated more thoroughly than has been done in the past.
7. Auroral region system interactions are not well understood, and need to be captured observationally. Ideas for this are,
   1. (a) 30-100 satellites flying through auroral structure, and
   2. (b) Combining radar data and other observations.
   3. Questions include
      1. (a) what organizes auroral arcs?
      2. (b) what is role of neutral wind?, and
      3. (c) what is the full MIT coupling, including the role of winds.
8. The role of By in large-scale MI coupling needs further consideration, as do interaction variations with local time and season.
9. The physics of polar-equatorial coupling still needs to be understood.
10. We need to learn how to properly account for past history of the thermosphere-ionosphere and magnetosphere.
11. Lower atmosphere tidal effects cannot be ignored in unraveling the role of the magnetosphere.

E. The were numerous ideas for the future presented in the session on coordinated use of space-based RBSP/THEMIS and ground-based observations to address geomagnetic storm phenomena, including ring current and radiation belt formation, and plasmasphere evolution.

1. We need to combine ground and in-situ observations with modeling to understand dynamics of the radiation belt. For example, we need to know where the plasmapause is to determine where electron energization will occur. Furthermore, MI coupling, including flow bursts is necessary for this, as well as for seed electrons and wave generation. Penetration and shielding E are also critical. For losses, we can use riometers, which are very sensitive to 50-60 keV precipitation, and LEO satellites to tell which of particles are actually precipitating. Additionally, it is necessary to determine the relative effects of wave driven losses and outward radial diffusion, which can propagate losses down to low L shells.
2. A Canadian proposal is in for a 9 element imaging riometer array covering L= 4 to 7 within the THEMIS ASI field of view, that will be cross-calibrated and with fields-of-view stitched together. This could be a critically useful tool for looking at wide field diagnostics of precipitation and energetic particle access to the ionosphere.
3. For modeling ring current development, multi-spices, self-consistency, dynamic plasma wave models, and the role of ion and electron precipitation are all important areas for the future. Additionally, modeling of electron loss is important not only for electrons, but also for conductivity which feeds back onto inner magnetospheric electric field.
4. We need to evaluate how deep can auroral streamer related flow channels go, and do they have an effect on the ring current particle injection and pressure enhancement. Understanding of this will require relating region 2 currents and streamer related flow channels.
5. Space weather events are now viewed extremely seriously by the U.S government, and ensemble modeling may be valuable for improving forecasting.
6. Self-consistent MIT coupling is very important, and should be considered much more thoroughly, including important neutral wind flywheel effects. Effects of flywheel driven electric fields on the magnetosphere should be identified and evaluated.
7. GEM must move beyond treating the ionosphere as just a boundary condition, and the thermosphere as just responding to forcing, and CEDAR must move treating disturbances based on Kp and on empirical convection models.
8. Modelers need good ideas about simulation physical parameters that are most useful for specific application and for use with good observational data. Challenges include which metrics to us, how to quantify a physical phenomenon, how to address uncertainties in model settings, how to prepare observational data for validation, and how to target real physical parameters. This will require bringing modelers and data providers together across both the CEDAR and GEM communities.
9. We need detailed mapping of sub-auroral electric fields from RBSP down to DMSP altitudes (~840 km), and to ground radar observations, and we need to consider the variation of SAPS events as well as connections to Region 2 current and to the full convection loop. We should also evaluate relations to other features of the plasmasphere and plasmasphere boundary layer as a function of altitude.

F. Ideas for coordinated model-data studies to support new and innovative CEDAR/GEM science include:

1. Completing the coupling processes among magnetosphere, ionosphere, and thermosphere models. Currently, some weak areas for coupling are auroral acceleration, plasma outflow, plasmasphere processes, and realistic magnetic-field mapping.
2. MHD models, as well as observations, indicate strong energy transfer in the cusp region. The associated plasma processes need to be more thoroughly understood.
3. What are the critical boundaries for MI electromagnetic coupling, such as between open and closed field filed lines, within the convection pattern, of precipitation region, and associated with Region 1 and 2 currents. How do we map these from the magnetosphere to the ionosphere and how do we validate the mappings?
4. Auroral models are needed for applications, research, and even for tourism. Validation is now important.
5. Observations show, for average (~steady-state) conditions, that Pedersen-weighted winds are ~40% of the ion convection velocity, and that the relation between field-aligned currents and ionospheric potential corresponds to a mean Pedersen conductance of ~3-8 S for moderate IMF Bz south conditions. These quantities are quite important for MIT coupling. How do these quantities vary for dynamic conditions?
6. First-principles models currently have a low prediction efficiency for Poynting flux, particularly for smaller scales. How can this be improved and validated?
7. How can we best construct IT model-validation metrics in a way that corresponds to the relevant physical processes? Some possibilities are:
   1. (a) magnetospheric energy input,
   2. (b) expansion of convection to lower latitudes,
   3. (c) build-up of plasma and structure at mid-latitudes,
   4. (d) gravity-wave propagation from high to low latitudes, as measure of impulsive energy input,
   5. (e) onset/timing/evolution of the global circulation,
   6. (f) Evolution of composition change,
   7. (g) ionospheric negative storm phase at midlatitude, and
   8. (h) disturbance dynamo.
8. Using field-aligned currents from AMPERE shows promise for driving magnetospheric electrodynamic inputs for IT models. Improvements may come from better models of ionospheric conductivities, and from an electric-potential solver that can account for hemispheric asymmetries between the polar regions.
9. Combining the theory of the ionospheric feedback instability with the theory of the ionospheric Alfven resonator shows great promise for explaining observations of structured aurora. The question arises as to how can we best evaluate these processes? Also, ion outflows in downward current regions, where the electric field is very structured, and lifting of the ionosphere could be important
10. Many scientific questions related to MI coupling could be well addressed with a grand ground-based observatory consisting of multiple instruments spread over North America. This would enable studies of the relation between small- and large-scale processes. How can an optimal observing system be designed and funded to support the entire community?

Submitted by sessions chairs: Hui Zhang David Sibeck, Dave Hysell, Jo Baker Josh Semeter, Toshi Nishimura, Tony Mannucci, Naomi Maruyama, Liz MacDonald, Phil Erickson, Art Richmond, Eric Donovan, and Larry Lyons (submitted 10 July 2013)