*************************** ** THE GEM MESSENGER ** *************************** Volume 23, Number 26 September 3, 2013 ---------------------------------------------------------------------- 1. 2013 Workshop Report from the Plasmasphere-Magnetosphere Interactions (PMI) Focus Group: Final Report. ---------------------------------------------------------------------- From: Jerry Goldstein, Joe Borovsky, and Maria Spasojevic This is a report of activities of the Plasmasphere-Magnetosphere Interactions (PMI) Focus Group (FG) at the 2013 Geospace Environment Modeling (GEM) Workshop. PMI Breakout Sessions This was the final year of sessions of the PMI Focus Group. To close out the FG and address the central question, "How Are Magnetospheric Processes Regulated By Plasmaspheric Dynamics (and Vice Versa)?" we hosted two (2) Breakout sessions at the 2013 GEM Summer Workshop: A. Scientific Progress Since 2012: The first session (and of course part of the second) consisted of people giving talks about progress made since the previous GEM Summer Workshop. B. Does the Plasmasphere Have a Future? The second session contained a discussion about the future of plasmaspheric research at GEM, and whether or not a new plasmaspheric-oriented Focus Group was needed. Session A: In the first (plus) session, the following speakers/topics were included: 1. Wen Li -- An unusual enhancement of low-frequency plasmaspheric hiss associated with substorm injected electrons. 2. Brian Walsh -- plumes at the magnetopause. 3. Joe Borovsky -- estimates of plumes and dayside reconnection. 4. Dan Welling -- long lived plumes. 5. Vania Jordanova -- simulation results. 6. Richard Denton (for Jonathan Krall) -- simulations with SAMI3. 7. Richard Denton -- simulation of EMIC waves for the June 9-10 2001 event. 8. Konstantin Gamayunov -- model results for EMIC waves. 9. Kyungguk Min -- quiet time equatorial mass distribution. 10. Jichun Zhang -- on the "trunk-like" ion spectral feature at the inner edge of the plasma sheet. Taken as a whole, the presentations showed that there was solid progress on ongoing plasmaspheric research topics and there were new findings. Many of the talks were not primarily concerned with the plasmasphere, but rather with another particle population which is influenced by the plasmasphere (or vice versa). This breadth of topic illustrated how intimately coupled the plasmasphere is with the rest of the magnetosphere and ionosphere. Session B: In the second session, a good discussion was had about what plasmaspheric research efforts were ongoing, what people wanted to do in the future, and whether or not a new umbrella Focus Group is needed at GEM which would deal primarily with the plasmasphere. The overwhelming consensus was that there was no need for a new Focus Group. There are a lot of ongoing and evolving plasmaspheric research topics, but each one of them is synergistic with another ongoing Focus Group at GEM. Hence, the plasmaspheric research will continue, and it will still fit in well with the GEM program of research. Specific matchups that were talked about: Plasmaspheric waves --- Radiation Belts and Wave Modeling (ending soon) Plasmasphere effect on radiation belt -- Radiation Belts and Wave Modeling Plasmaspheric refilling -- The Ionospheric Source of Magnetospheric Plasma Plasmaspheric drainage -- Magnetic Reconnection in the Magnetosphere Plasmaspheric convection -- Storm-Time Inner Magnetosphere-Ionosphere Convection Plasmaspheric composition -- The Ionospheric Source of Magnetospheric Plasma Adding the plasmasphere to codes -- Metrics and Validation After 5+ years of the PMI focus group, we quit 10 minutes early. Science and Programmatic Imperatives for the Community The PMI Focus Group has identified several science and programmatic recommendations for continued progress on the science that the Focus Group has supported in the last several years. • Ion Composition: More observations and models of inner magnetospheric ion composition are urgently needed to close the loop on several PMI science topics, including wave growth and wave-particle interactions, global MHD, and the possible role of oxygen enrichment in modulating dayside reconnection and substorms. • Plume Structure: Modelers need to get more meso- to fine-scale structure into their simulated plumes, in order to match the observed cross-scale structure. • UT and Longitudinal Effect: For several years various case studies have hinted that there may be a longitudinal (and/or UT) modulation of the strength of storms and the density of plumes. This effect must be quantified and understood. • Wave Growth, Propagation, and Resonance: Simulations need to use 3D, realistic density for their plasmaspheres (e.g., cross-scale spatial structure both in and out of plumes, nonmonotonic density profiles, and profiles constrained by measurements). We need to know the conditions that drive waves, and we need to know the effects of both those conditions and of the waves. We also must gauge how well measured plasma conditions agree with the linear theory that is widely used. • Epoch Time Analysis: For anything linked to plume dynamics (density, waves, etc.), a superposed epoch analysis is recommended because standard (purely indicial) statistical analysis may obscure physical processes that are initiated or terminated at particular storm phases. Plasmasphere-Magnetosphere Interactions (PMI): What Has Been Learned? Since 2008 when the PMI FG was first convened, four main topics have been addressed, I through IV below. As described below, during the tenure of the PMI Focus Group, much scientific progress has been made in all three topics. (I) Wave Particle Interactions: This topic has focused on: (A) How the evolving global distribution of cold plasma governs the growth and propagation of waves, especially those that control energetic particles; and (B) How ambient plasma properties such as temperature, density, and composition influence wave particle interactions. The theoretical quantitative effect of background plasma upon wave development and propagation has been quantified and elucidated. Ray tracing simulations indicate that VLF whistler waves spend more time in the plasmasphere than in regions with more tenuous plasma, and the whistler wave growth rate is heavily dependent upon the background density. The wave normal angle clearly influences the scattering rate. Ducting of whistlers is most effective for density irregularities satisfying particular relationships to the wave properties. Non- linear (or quasi-linear) theory may very well be required, in fact, given some very large wave amplitudes (e.g., 2-100 mV/m chorus) found in recent observations. Ray tracing modeling of hiss and chorus has shown good agreement with observed wave dynamic spectra, suggesting the conclusion that cold plasma can exert significant control on wave power, and on the resonance condition with energetic particles. A key development has been the application of regression analysis to produce a THEMIS-based empirical model of chorus emissions. Very relevant to PMI, cold plasma plumes must be considered in mature models: a broad plume may stop chorus from getting in, while the normal narrowing (with time) of the plume can gradually "open the gate". The current consensus is that 3D simulations with nonmonotonic density are a high priority for future progress. ULF waves are also severely attenuated inside the plasmasphere. Simulation results have demonstrated a significant effect of the plasmasphere upon the ULF wave mode structure: the frequency of FLRs is lowered, and spectral power is shifted inward in L-shell by the presence of the inner cavity. Very recent results have shown the importance of proper characterization of these ULF waves that can modulate the loss cone angle of energetic electrons. Multiple simulation results indicate that knowledge of cold plasma (composition and density) is crucial to properly constrain and understand EMIC wave propagation and growth. Observational evidence also indicates that background density is a crucial influence upon wave growth and propagation. Simulation of EMIC waves indicates that structure within plumes (on spatial scales from meso- to fine-scale) can strongly modulate wave growth, and therefore this internal structure must be considered/included in future models. But cold plasma must be considered self-consistently with other particles and fields to get the whole picture. There is certainly a correlation between plumes and electromagnetic ion cyclotron (EMIC) waves, as revealed both by direct in situ cross-comparison and in situ plasma proxies for EMIC growth. However, it has become clear that the plume-EMIC correlation must be considered carefully and separately from EMIC growth from magnetic compression by solar wind pressure pulses. While cold plasma properties make a big difference in simulations of EMIC wave growth and propagation, statistical analysis of ground-based Pc1 observations reveals at best a weak correlation with the simultaneous occurrence at geostationary orbit of plasmaspheric plumes. On the other hand, EMIC wave occurrence does correlate well with solar wind pressure pulses. This systematic organization (by physical process) of EMIC wave growth has emerged from all observations: in situ, ground-based, and global imaging. Because EMIC waves are believed to scatter ions effectively, two imaging tools have emerged as possible proxies for EMIC waves: proton aurora seen by IMAGE FUV and low altitude ENAs observed by the two TWINS spacecraft. During the PMI FG's tenure, in situ (at geostationary orbit) proxies for EMIC growth have been advanced to a mature state as well. EMIC linear wave growth proxies are in agreement with actual EMIC wave observations (and with detached proton arcs seen in FUV imaging), and can be useful where actual wave measurements are not available. Epoch time analysis is recommended for any processes linked to plume dynamics, such as the possible link between EMIC wave growth and plume density. (II) Plume Dynamics and Recirculation: This topic has examined how eroded plasmaspheric plasma is transported throughout the magnetosphere, how it evolves, and how plumes may influence reconnection and solar-wind-magnetosphere coupling. The global structure of plumes is reasonably well understood and quantified: plasmaspheric models do a good job of predicting where and when plumes will occur, and what density they will have. During storms and substorms plume plasma convects sunward inside a "drainage corridor" whose shape, size, and location vary with epoch time and disturbance level. This "drainage corridor" is a region where plumes are most likely to be found (based on global convection characteristics found from a simple superposition of cross-tail and corotational E-fields); the plasmaspheric drainage corridor is the global pathway for cold plasma to make its way to the dayside reconnection site. Even after several years of effort, the structure inside plumes is not yet so well captured. Numerous observations have illustrated that plume plasma is highly structured, both in flow field and in density, with indications of fine structure on scale sizes below what instruments have ever measured. The creation of this fine structure is still an outstanding question: does it arise from turbulent electric/magnetic fields, or does ExB-drifting plume plasma spontaneously shred itself as it convects? The high degree of plasmaspheric and plume density structure (and sub-structure) has been a major component of this topic. Plume structure can arise from either rapid temporal variation of the solar-wind-driven E-field, or local inhomogeneity of the convection field; it is the latter effect in particular that is not yet well characterized enough for models to reproduce interior density structure. Statistical analysis of ion density data has, however, produced the first reported observation of a possible minimum scale size of under 250 km (0.04 RE) for the fine- scale structure within plasmaspheric plumes, hinting at the mechanism responsible for the structure. Interhemispheric asymmetries (linked to north-south asymmetry in the field-aligned flows), composition of the ionosphere, and kinetic processes add yet more complication to the density structure of the plasmasphere. Penetration electric fields have been shown time and time again to be a strong influence on both the plasmasphere and the lower-energy range of the ring current, and these fields are observed in SuperDARN radar to closely correlate with the IMF north-south conponent, with a 15-20 minute delay, consistent with older IMAGE-EUV-based estimates for the "penetration delay time" for the inner magnetospheric E-field. The sub-global convection field is still being characterized: observations of strong spatial and temporal E-field gradients and variability in the subauroral ionosphere within SAPS channels are seen in both low-altitude orbiting spacecraft and ground-based radar. During the PMI FG's tenure, increasing evidence has emerged in support of the effect of plumes on reconnection. Some observations have shown a measurable control of plume plasma upon the reconnection rate. Theoretical analysis has quantified how asymmetric reconnection (i.e., reconnection in which inflow and outflow regions have different properties) is applicable to the plume influence on dayside magnetopause reconnection. Observations also show that the super dense plasmasheet (possibly enriched by plumes) may influence the stormtime level of relativistic electrons. From simulation results, it may be that plumes affect the dayside reconnection rate most strongly for the strongest storms, which feature severe magnetopause contractions. (III) Plasma Density Structure and Evolution: This topic has been concerned with how density structures of various spatial and temporal scales form and evolve, and how plasmaspheric filling varies spatially and on time scales from hourly to solar cycle. An early thread of this topic was how cold plasma density features can be used to diagnose inner magnetospheric (IM) electrodynamical effects such as erosion, shielding, and subcorotation. For example, modeling of undulatory ripples that travel across the duskside plasmapause has revealed a new type of region-2 current system, i.e., traveling pairs of filamentary region-2 currents that arise from interchange unstable ring current plasma and modulate the cold background density. In support of this capability, new observational capabilities have been explored, such as plasmaspheric tomography using GPS signals and analysis of ultra-low-frequency (ULF) waves observed by ground magnetometer stations. Tomography is now allowing us to obtain a global snapshot of the entire (or the majority of the) dayside cold density distribution. These newer and still developing observational techniques can augment the already extensive cold plasma measurement database used by the GEM community. Significant progress has been made in characterizing the average composition (H+ versus O+) of the plasmasphere, using statistical analysis of geostationary observations (both plasma and waves), and the average refilling rates during recovery, using radio-sounding of field-aligned density. It is clear that the next generation of models must incorporate sub- global structure, and account for dynamics on longer time scales, especially during and after the recovery phase. Refilling is a major example of long-time-scale density. Numerous studies, both observational and theoretical, have honed our understanding of time- dependent and time-averaged refilling rates. Plume shredding is a major example of sub-global structure, motivating the conclusion that modelers need to think about how to put more structure into the plume. Significant discussion in this topic has dealt with possible formative mechanisms of particular meso-scale features such as the plasmaspheric "armpit", i.e., global density depletion inside and west of the base of an afternoon-sector plume, with a likely candidate being a combination of the natural corotation of plasma plus a sub-global duskside eddy flow whose existence is merely postulated. These results have added new emphasis to the understanding that our knowledge of the meso-scale convection field must be increased by an order of magnitude, if our models are to provide truly improved predictions for the plasmaspheric density distribution. (IV) System-Level Plasmasphere-Magnetosphere Interactions: This topic has focused on the role of the plasmasphere in the overall magnetosphere-ionosphere-thermosphere system response. To address this topic, sessions were typically held jointly with scientists from the CEDAR community. The goal was to develop our understanding of the interaction among components of the larger system. Numerous results have shown how various subsystems (e.g., ionosphere, ring current, neutral winds, etc.) fit together into the larger magnetospheric system, and how these various components interact as part of the overall system response during stormtime. Significant discussion in the PMI FG has focused upon what concrete progress has been made in understanding specific subsystems or their interrelationship. For example, the relationship between plasmaspheric plumes and ionospheric storm-enhanced density (SED) tongues has been explored at length, with the conclusion that the dynamics of SED tongues and plumes are clearly linked during stormtime, indicating strong M-I coupling along the entire flux tube. The role of oxygen ions in SAR arc formation also points to the urgent need for better understanding and modeling of composition. The inner magnetospheric electric field, including variability in the PBL, and general electrodynamics initiated by region-2 M-I coupling, is a major topic still requiring more exploration. A major accomplishment presented at PMI Sessions is the development of newer, improved statistical analysis of the inner magnetospheric electric fields: a superposed epoch analysis of Cluster electric fields was shown to produce dynamic features of the inner magnetospheric fied, keyed to storm phase, and statistical characterization of SAPS was presented. Inclusion of ionospheric-thermospheric coupling has also been shown to have a measurable and significant impact on the generation of SAPS. All in all, concrete progress has been made, and future work along these lines should yield continued progress in the coming years. +-------------------------------------------------------------------+ | The GEM Messenger is the electronic newsletter for the | | NSF GEM Program and Workshops. | | | | Editor: Peter Chi, GEM Communications Coordinator | | E-mail: | | | | To subscribe GEM Messengers, send an e-mail message to: | | | | with the following command in the body of your e-mail: | | subscribe gem | | To remove your e-mail address from the list, the command is: | | unsubscribe gem | | | | 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 | +-------------------------------------------------------------------+