[GEM] THE GEM MESSENGER, Volume 26, Number 38

Tue Sep 20 19:00:05 PDT 2016

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     THE GEM MESSENGER
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Volume 26, Number 38
Sep.20,2016

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Table of Contents

1. 2016 GEM-CEDAR Workshop Report: The Magnetic Reconnection in the Magnetosphere Focus Group

2. Postdoc Positions Related to Space and Solar Physics

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1. 2016 GEM-CEDAR Workshop Report: The Magnetic Reconnection in the Magnetosphere Focus Group
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From: Paul Cassak, Andrei Runov, Brian Walsh and Yi-Hsin Liu (paul.cassak at mail.wvu.edu)

In year four for the focus group on Magnetic Reconnection in the Magnetosphere, four sessions were convened at the summer workshop.  Two sessions were individual (with approximately 70 and 34 attendees, respectively), one was joint with “Testing Proposed Links between Mesoscale Auroral and Polar Cap Dynamics and Substorms” (81 attendees) and one was joint with the “Dayside Kinetic Processes in Global Solar Wind-Magnetosphere Interaction” and “Transient Phenomena at the Magnetopause and Bow Shock and Their Ground Signatures” focus groups (73 attendees).  The sessions were driven by talks but led to lively discussion.  Summaries of each session follow, followed by a brief discussion of future plans.

Session 1 – Individual session - Monday, June 20

This session began with scene-setting talks on dayside reconnection, highlighting recent observations from the Magnetospheric Multiscale (MMS) mission. Allison Jaynes showed that FEEPS high-energy electron measurements on MMS reveal the importance of these energies in reconnection, and are beginning to shed light on the relationship between reconnection processes and acceleration of 30-100's keV electrons. New features observed include: energetic electron acceleration up to 100 keV at the magnetosheath boundary layer, microinjections of energetic electrons in the dusk/midnight sector, and inverse energy dispersion of energetic ions in the magnetosheath.  John Dorelli summarized early results from the first dayside MMS season and discussed implications for global magnetosphere modelers.  Two general topics were discussed: (1) MMS has seen electron demagnetization consistent with signatures (e.g., “crescent distributions”) seen in full PIC simulations of asymmetric magnetic reconnection, and (2) MMS has seen large intermittent parallel electric fields (much larger than those predicted by steady collisionless reconnection theory).

In other talks on dayside reconnection, Meng Zhou discussed high frequency electrostatic waves in the vicinity of ion diffusion region on the Earth's magnetopause detected by MMS. They found that energy dissipation contributed by these high-frequency waves is negligible compared to that contributed by the lower-frequency process.  Joo Hwang discussed ongoing magnetic reconnection along the boundaries of large-scale nonlinear Kelvin-Helmholtz waves detected by MMS.  The observed field and particle features, in particular electron distribution functions, indicate that MMS traversed the outer region of the electron diffusion region where the bulk kinetic energy is transferred to field and internal energy.  Jan Egedal argued that MMS measurements at the dayside magnetopause show that electrons from the high density inflow penetrate some distance into the low density inflow, and are characterized by crescent-shaped distributions. A theoretical model was presented which relates the salient details of these observations to electron dynamics in the inner reconnection region.

Slava Merkin gave a scene setting talk on magnetotail reconnection, presenting analytical results on kinetic and MHD stability of the magnetotail, including tearing and ballooning/interchange, for new classes of magnetotail equilibria allowing spontaneous onset of magnetic reconnection. He then showed Katie Garcia’s results on how the stability parameters can be calculated in global MHD simulations revealing the formation of reconnection-prone tail configurations as a result of solar wind driving. Tony Lui emphasized that magnetic reconnection and current disruption are not mutually exclusive. 3D particle-in-cell (PIC) simulation results published by Sitnov et al. [2014] demonstrate that magnetic reconnection can be a consequence of current disruption and vice versa. Misha Sitnov, using 3D PIC simulations of spontaneous formation of dipolarization fronts from 2D tail like current sheet equilibria, showed that ion and electron temperature variations across the front (in the X-direction) are consistent with THEMIS observations (Runov et al., 2011, 2015; Sergeev et al., 2015), while their variations along the front (in the Y-direction) are out of phase, weakly correlated with flapping and strongly correlate with buoyancy-driven structuring of the front. Moderate ion and electron temperature anisotropy and agyrotropy at and right behind the front are strongly enhanced further downstream near the newly formed X-line.  Finally, Liang Wang discussed comparative multi-fluid moment/PIC simulations of asymmetric magnetic reconnection. The 10-moment model evolves pressure tensors for both electrons and ions, and the results agree well with PIC with either local or non-local approximations to the heat flux.

Session 2 – Joint with “Testing Proposed Links between Mesoscale Auroral and Polar Cap Dynamics and Substorms” - Monday, June 20

John Foster presented a scene setting talk on ground-based observations with radars and global positioning system (GPS) total electron current (TEC) that reveal the circulation of ionospheric F-region plasma related to dayside reconnection. The temporal and spatial variations of enhanced-TEC SED plumes and polar patches at ionospheric altitudes map to similar features and dynamics at the dayside magnetopause.  Bill Lotko presented a scene setting talk about how global simulations show that the ionosphere influences dayside and nightside reconnection in several ways: 1) via outflows of ionospheric O+ which can reduce the Alfven speed in the reconnection inflow region and thus the reconnection rate; 2) via meridional gradients in the ionospheric Hall conductance, which cause a dawn-dusk asymmetry in ionospheric convection and the reconnection rate that supports it; and 3) via the effective resistance of the ionosphere to field-aligned currents flowing from reconnection dynamos (principally nightside), which regulates the location of the magnetotail x-line.

Observational presentations included Vasillis Angelopolous, who discussed the Heliophysics/Geospace System Observatory, which goes beyond the International Solar-Terrestrial Physics program (which employed isolated single probes to establish global connections on longer time-scales) to build upon an emerging paradigm of global coupling through transient, regional flows and to seek a fuller understanding of how kinetic plasma processes lead to regional activations, and how these are affected by / drive global connections. Several nice system conjunctions explore the cross-scale coupling of dayside-nightside reconnection in 2015-2016; the THEMIS orbit maneuver execution is on track for numerous conjunctions in the next few years. Ying Zou argued that as polar cap arcs reach the nightside auroral poleward boundary, they lead to poleward boundary intensifications (PBIs) and thin-oval intensifications ~85% of the time. These oval intensifications happen <~10 min and at almost the same longitude of the contact, consistent with MHD simulations where reconnection is triggered by lobe inflows. Stefan Kiehas showed a five-year statistical ARTEMIS study around -60 Earth radii downtail, finding that ~ 30% (v_perp) to ~ 50% (v_x) of all flows are directed earthward (v > 300 km/s). A dawn-dusk asymmetry with preference to the dusk sector is also found, which is more pronounced for tailward flows and increases with flow speed.  

On the theoretical side, Misha Sitnov discussed the results of 3D PIC simulations of 2D magnetotail equilibria, including spontaneous formation of dipolarization fronts and reconnection onset. He showed that field-aligned currents caused by fronts may be due to Hall effects and with mixed hemispheric parity due to the tail current sheet flapping motions.  Haoming Liang showed that the Hall electric field accelerates lobe oxygen but not protons because the Hall electric field is smaller than the oxygen gyroradius.  He plotted distribution functions of oxygen near the dipolarization front and showed that the dipolarization front thickness is related to the oxygen concentration in the plasma sheet.

Session 3 – Joint with “Dayside Kinetic Processes in Global Solar Wind-Magnetosphere Interaction” and “Transient Phenomena at the Magnetopause and Bow Shock and Their Ground Signatures” - Tuesday, June 21

This joint session had talks on observation and modeling with an emphasis on global magnetospheric aspects of reconnection.  Sun-Hee Lee showed that (1) the inverse dispersions of energetic ions were observed by MMS/EIS in the magnetosheath just outside the magnetopause and the observed ion structure can be explained as the effect of a transient solar wind dynamic pressure pulse, and (2) using combined ground radar and MMS/EIS observations, they estimated a longitudinal extent of 1.5 R_E for the reconnection line. Naritoshi Kitamura reported that the extension of the Geotail mission until March 2019 was approved for the coordinated observations with the MMS spacecraft. A conjunction event between Geotail and MMS on 18 November 2015 showed that the magnetopause reconnection line shifts toward the winter hemisphere for southward IMF.  Richard Denton used magnetic and particle data from MMS to find the motion of the MMS spacecraft through the reconnection structure described in the Burch et al. Science paper. 

Chih-Ping Wang showed that during a prolonged (~5 hr) northward IMF interval with very steady SW/IMF conditions, ARTEMIS at X = 60 R_E near the dusk magnetopause boundary layer observed quasi-periodic (7-10 min) perturbations in the plasma and magnetic field propagating tailward with a spatial scale of ~8 R_E in the X direction. Simulation of this event with LFM model shows that K-H waves are formed in the near-Earth flanks and propagate to the mid-tail, which qualitatively explain the observed perturbations. Cong Zhao used magnetometer and fast plasma instrument measurement from four MMS spacecraft to calculate the gradient of magnetic and plasma pressure as well as the curvature force. The force analysis shows that the magnetopause is in force balance and reveals multiple sub-layers exist in the magnetopause.  Maimaitirebike Maimaiti showed a case study when RISR-N was located in the noon sector and directly measured reverse convection in the dayside throat region while the IMF was transitioning from strong positive B_y to strong positive B_z. Time-lagged correlation analysis reveals that the IMF B_y influence acted on a lag time which was 10 minutes faster than that of the B_z component, and this was attributed to the occurrence of magnetic merging at two different magnetopause sites as determined by favored merging geometries for the two components of the IMF.

On the theoretical side, Sanni Hoilijoki showed that reconnection rates at the dayside magnetopause in a global hybrid-Vlasov simulation correlate well with the analytical model by Cassak and Shay [2007]. In addition, their results indicate that magnetosheath waves affect the reconnection rate.  Xuanye Ma showed that magnetic reconnection with a super-critical perpendicular sheared flow forms an expanding outflow region to maintain the total pressure balance, and violates the Walen relation. Plausible observational signatures in the outflow region include decreased density and pressure and increased magnetic field strength. Sasha Ukhorskiy showed that, for the first time, the high-resolution LFM global MHD model was coupled with a symplectic test-particle code and used to investigate the role of the Kelvin-Helmholtz (KH) instability in the magnetopause losses of energetic hydrogen and oxygen ions. They showed that the KH substantially increases the loss rates for both ion species at the dusk as well as the dawn magnetopause flanks and that after the magnetopause crossing and prior to the escape into the interplanetary space, energetic oxygen remains in the magnetosheath much longer than hydrogen, which is consistent with recent MMS observations.  Andrey Samsonov calculated magnetopause positions for stationary cases with northward and southward IMF orientations using a set of empirical and global MHD models. The differences in positions of selected reference points between northward and southward cases characterize the strength of MI currents, but their exact meaning is still not understood.  Kris Maynard used OpenGGCM to show evidence that reconnection happens at two simultaneous X-lines during FTE formation. They quantified the reconnection rate using the quasi-potential.  

Session 4 – Individual session - Friday, June 24

The final session included observational and modeling discussions of both dayside and magnetotail reconnection. Brian Walsh discussed different models for the macroscopic properties of reconnection and presented initial observational work to separate between them.  Rishi Mistry presented exhausts formed from symmetric guide field reconnection, as observed by MMS in the magnetosheath. These extremely high resolution measurements are compared to 2D PIC simulations, showing good agreement. Yongliang Zhang presented an improved method to self consistently estimate the deep tail reconnection location using energy-latitude dispersion of polar rain electrons observed by LEO satellites.  Heli Hietala showed ARTEMIS two-spacecraft observations of reconnection in the lunar distance magnetotail near the dusk flank during a period when the north lobe had high density mantle/boundary layer plasma and the south lobe had a much lower density. The Hall magnetic field and jet profiles were shifted in accordance to this density asymmetry, which was also clearly visible in the ion distribution functions measured within the jet.

Jean Berchem presented the results of a large-scale iPic3D simulation of the dayside magnetopause, which uses the initial and boundary conditions from a high-resolution global MHD simulation and resolves the electron diffusion region (EDR). The results indicate that crescent-shaped electron distributions can be present relatively far away from the EDR; hence, the observation of crescent-like distributions is a necessary but not sufficient condition to identify the encounter of an EDR.  Yi-Hsin Liu discussed comparisons of reconnection with a guide field with a pressure gradient caused by density or temperature.  The asymmetric nature of the X-line is essential in understanding the diamagnetic suppression of magnetic reconnection.

For the observational part of a three-pronged observation/simulation/theory study, Andrei Runov presented results of event studies of ion velocity distribution function observations within and around dipolarizing flux bundles (DFBs) in the near-Earth plasma sheet. The results indicate that the ion distributions within DFBs often exhibit a perpendicular anisotropy, which may provide free energy for EMIC wave excitation. Joachim Birn demonstrated characteristic ion velocity distributions at dipolarization fronts (DFs) obtained by test particle orbit integration in the MHD fields of near-tail reconnection and flow bursts. After a brief field-aligned anisotropy right at the DF, the distributions consisted of two, parallel and antiparallel, field-aligned beams combined with a ring-like perpendicular population. Phil Pritchett presented results from 3D PIC simulations of the formation of reconnection exhaust jets with finite cross-tail extent that evolve to form the characteristic dipolarization front structures.  In the near-Earth region, the ion velocity distributions at 5-10 d_i in back of the front show evidence for a depletion in the parallel phase space density in the velocity range of 1-2 V_Ti.

In discussions of numerical efforts, Kai Germaschewski presented the status of the next generation OpenGGCM, a global magnetosphere model that incorporates extended-MHD and now multi-fluid effects, using 5- and 10-moment models that for each species include a scalar and pressure tensor, respectively. These models have shown promise in reconnection test cases like the Harris sheet and island coalescence problem, and have now been applied to global simulations of Jupiter's moon Ganymede, where they show consistent results on the global structure of Ganymede's magnetosphere, as well as expected significant departures from a simple resistive- MHD model due to Ganymede's large ion inertial scales.  Yi-Hsin Liu discussed efforts to design PIC simulation services at NASA’s CCMC, and ideas for joint projects in support of MMS mission. In particular, CCMC plans to launch services that help MMS scientists analyze particle distributions and determine the reconnection plane using local kinetic simulations. Masha Kuznetsova introduced the CCMC implementation of post-processing and visualization tools (based on the RECONX algorithm by Alex Grocer, John Dorelli and Colin Komar) that calculates and displays separator surfaces, separatrices, and magnetic null locations. They suggested to initiate a Separatrix Location Challenge based on the proximity of MMS during reconnection crossing events with the separatrix calculated from global magnetosphere models using the RECONX tool.

Future Directions

Next year will be the final session for the Magnetic Reconnection in the Magnetosphere focus group.  We expect MMS observations and analysis with related theoretical and numerical efforts will be a strong component of the session, which will follow the second dayside phase.  We plan to be an outlet for magnetospheric studies of reconnection both at the kinetic and global scales, and expect conjunctions with other satellite and ground-based measurements will continue to be a crucial aspect of group discussions.  

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2. Postdoc Positions Related to Space and Solar Physics
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From: Fan Guo (guofan at lanl.gov)

Outstanding candidates are invited for immediate postdoc openings, with one postdoc each in the areas of computational plasma physics, plasma astrophysics including space and solar physics, and protoplanetary disks. For the computational plasma physics and plasma astrophysics positions, background in computational fluid physics and/or plasma kinetic physics is highly desirable. For the protoplanetary disk position, background in computational planet-disk interaction studies is highly desirable. The positions are offered by the Nuclear and Particle Physics, Astrophysics and Cosmology group within the Theoretical Division at Los Alamos National Laboratory (http://t2.lanl.gov/ and http://t2.lanl.gov/astrophysics/). The successful candidates are encouraged to collaborate with the current group members on on-going projects, and will also be able to develop his/her own research programs. The initial appointment is for two years, with a possible third-year extension.

Candidates should send their applications electronically, including a CV, publication list, and a concise research statement (within 2 pages) describing past achievements and future plans. Applicants should arrange three reference letters to be sent electronically as well. All material and further inquiries can be sent to Hui Li, Shengtai Li and/or Fan Guo at t2astropostdoc at lanl.gov .

Candidates may be considered for a Director's Fellowship and outstanding candidates may be considered for the prestigious Marie Curie, Richard P. Feynman, J. Robert Oppenheimer, or Frederick Reines Fellowships. Applicants with US citizenship will also be considered for the Metropolis Postdoctoral Fellowship in Computational Physics. Applications must be received before Nov. 7, 2016 for full consideration. The review of applications will be on-going until offers are accepted.

Please go to http://www.lanl.gov/careers/career-options/jobs/all-jobs.php and search for job # IRC52416 for the full description. For general information to the Postdoc Program go to http://www.lanl.gov/careers/career-options/postdoctoral-research/index.php.

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