*************************** ** THE GEM MESSENGER ** *************************** Volume 22, Number 25 September 10, 2012 ---------------------------------------------------------------------- 1. 2012 WORKSHOP REPORT: The Ionospheric Source of Magnetospheric Plasma: Measuring, Modeling, and Merging into the GGCM Focus Group ---------------------------------------------------------------------- From: Dan Welling , Robert Schunk, and Richard Chappell The Ionospheric Source of Magnetospheric Plasma: Measuring, Modeling, and Merging into the GGCM (or, simply, OutflowMMM) Focus Group held four sessions at this year's GEM Summer Workshop: one for each of the "M"s in the title and a planning session to organize future tasks. The key concluding points from these sessions are as follows: 1) It remains unclear what the most important energization mechanisms are under different circumstances. 2) There remains a great deal of contention on what modeling approach best captures outflow dynamics. 3) The merging community is slowly shifting from examining the immediate and basic effects of adding outflow to global systems to investigating potential improvements of merging techniques to enhance simulation accuracy. 4) Future activities will work to homogenize the three sub-groups and audiences with focus-group-wide projects. Session Summaries: The Measuring session had 5 speakers with an audience of approximately 50. Dr. Tom Moore began the session by reviewing what is known and what remains unanswered. Unknowns included the core ion velocity distributions, ion-neutral relative velocities, and the distinct roles of heat and electromagnetic flux on outflows. Dr. Andrew Yau followed with a presentation on the importance of quiet time O+ outflow. He noted that these fluxes can take 5 hours to reach the plasma sheet, but the source remains a point of uncertainty: is this population the result of the classical polar wind, or are other energization mechanisms playing lead roles? Dr. Naritoshi Kitamura then presented work on field aligned potential drops and their role in outflowing populations. He noted that such drops could accelerate hydrogen and oxygen to 20eV. Rob Redmond presented an investigation on the apparent dawnward bias of escaping O+, which reduces with activity. His current conclusion is photoheating at sunrise causes this bias. Finally, Dr. Anatoly Streltsov presented simulation work on ionospheric electron density voids. He found that these could be driven by small-scale waves produced by downward flowing field-aligned currents. The discussion for this session was lively and involved. It is clear that there are very limited observational data on the ion outflow that have been taken from spacecraft with potential control and by instruments that have large enough geometric factors to successfully characterize both the ionospheric source and the fate of these upward flowing particles in the magnetosphere. Measurements such as these will be required as the magnetosphere-ionosphere community works toward the merged models that include the coupling of these two regions. Dr. Bob Schunk was the first of five speakers at the Modeling session, which was attended by approximately 30 people. He reviewed the important physical processes that must be accounted for in numerical models, and then showed results from his modeling team. He emphasized the importance of capturing the full velocity distribution of each species, the polar rain contact potential at high altitudes, and energization mechanisms not captured by simpler fluid-based models. Dr. Alex Glocer presented comparisons of his Polar Wind Outflow Model (PWOM) results to various observational and empirical databases and found good agreement for various solar zenith angles. Next, Paul Song introduced a new model for ionospheric electrodynamics that receives electromagnetic waves as input rather than an assumed imposed electric field or field-aligned currents. He emphasized that this methodology takes much longer to reach equilibrium than conventional ionospheric electrodynamics models. Dr. Uri Omelchenko presented arguments for the use of full 3D hybrid magnetosphere models. He discussed the physics of the model, the technology required to perform the resource- intensive simulations, and the increased detail that can only be captured using this approach. Finally, Vahé Peroomian used results from his Large Scale Kinetic model to introduce two key questions: how do global modelers constrain outflow during storms, and how do modelers benchmark results when there are no observations of composition? Again, the discussion of this session was lively with an emphasis placed on understanding the differences between the different modeling approaches and determining which approach best captures outflow dynamics. The third session, Merging, saw a similar audience to the previous session but had an additional speaker (6 total). Dr. Daniel Welling began by reviewing the various effects outflow has on the magnetosphere ionosphere system; from changes to the cross polar cap potential to the interdependent relationship outflow has with the ring current. This presentation was followed by Dr. Raluca Ilie, who showed comparisons of TWINS satellite measurements with multifluid MHD simulations that included outflow (via the PWOM). TWINS has observed substorm-driven O+ enhancements; Dr. Ilie showed similar behavior in her MHD model. Dr. Yiqun Yu, using the same model, but with a constant and prescribed outflow, showed how outflow can effect the formation of Kelvin-Helmholtz (KH) vortices by expanding the region along the flanks that is KH unstable. Dr. Alex Glocer then presented a potential coupling mechanism that would include high altitude wave- particle interaction (WPI) acceleration. His concept was to use an empirical WPI acceleration term in a non-anisotropic MHD model to continue parallel outflow acceleration deeper into the magnetophere. Yanhua Liu moved the discussion from acceleration to reconnection by presenting data from the Cluster constellation that showed how outflow of heavy ions affects the tail. He found that the ratio of O+ to H+ correlates negatively with tail flare angle size, implying that as O+ increases, reconnection and tail stability also increase. Finally, Dr. Bill Lotko reviewed the extensive work by the CISM team to tackle the issue of coupling outflows to their global model. The use of the Strangeway relationship was discussed, as was outflow's role in producing sawtooth oscillations in the magnetosphere. The approach of the CISM team was contrasted against the use of PWOM and the additional methodology proposed by Dr. Glocer. The final session opened discussion to all in order to plan the future of the OutflowMMM focus group. It was quickly decided that upcoming activities should aim to homogenize the measuring, modeling, and merging sub-communities in order to cross pollinate ideas and further fold observations rapidly advancing modeling and merging efforts. Next, many ideas for group-wide research activities were raised and discussed, ranging from the specification of WPI acceleration rates and their potential application to outflow and global models to creating a set of idealized magnetospheric simulations that capture the various “modes” of outflow activity. After much discussion, it was decided that the simplest and most productive path forward would be to challenge both outflow and global modelers to simulate situations without any ionosphere contribution, then turn on outflow and compare and contrast the two magnetospheres. These activities will be organized through the upcoming OutflowMMM email list. The first simulations will be presented at the upcoming Fall AGU Mini-GEM. All interested researchers should contact Dr. Daniel Welling (dwelling@umich.edu) to sign up for the OutflowMMM email list. +-------------------------------------------------------------------+ | To subscribe GEM Messengers, send an e-mail to | | | | with the following command in the body of your e-mail message: | | subscribe gem | | To remove yourself from the mailing list, the command is: | | unsubscribe gem | | | | To broadcast a message to the GEM community, please contact | | Peter Chi at | | | | Please use plain text as the format of your submission. | | | | GEM Messenger is also posted online via newsfeed at | | http://heliophysics.blogspot.com and | | http://www.facebook.com/heliophysics | | | | Back issues are available at ftp://igpp.ucla.edu/scratch/gem/ | | | | URL of GEM Home Page: http://aten.igpp.ucla.edu/gemwiki | | Workshop Information: http://www.cpe.vt.edu/gem/index.html | +-------------------------------------------------------------------+