2018 Summer Workshop, Santa Fe, NM
GEM Summer Workshop 2018
The 2018 GEM summer workshop was held between June 17-23, 2018 at the Eldorado Hotel in Santa Fe, NM
Session Summaries
Monday 10:30 AM - 12:00 PM - Open Questions
We discussed dayside open questions and unresolved problems, facilitated by short “discussion starter” presentations. The emphasis was on MMS observations and kinetic scale processes. Drew Turner begun the discussion on foreshock transients, followed by Mike Shay with magnetosheath turbulence and electron-only reconnection. The session had about 50 participants.
Drew Turner talked about particle acceleration associated with hot flow anomalies and foreshock bubbles. He presented observations where ions are accelerated to ~1 MeV and electrons to 100s keV. During Turner's presentation, there were two mini-debates: 1) Whether the accelerated ions have a solar wind or a magnetosphere origin. Sun Lee believes the ions may originate from the magnetosphere, while Drew Turner and Terry Liu attributed the acceleration to multiple fermi-acceleration as the particles bounce between the bow shock and the discontinuity in the solar wind. 2) Whether kinetic physics is necessary for explaining the formation of foreshock transients. David Sibeck pointed to interesting MHD simulations by Antonious Otto.
Mike Shay noted that magnetosheath turbulence is different from solar wind turbulence in that the sheath turbulence has a more limited cascade in k space and much faster cascade rate. Because of these reasons, the sheath turbulence might have its unique properties that cannot be applied to turbulence in other systems. He presented Tai Phan’s recent observations of a thin current sheet where only electrons exhibit jets while ions don't. The electron jets exhibit a reversal in direction, indicating that reconnection has occurred. During Shay's talk, there was discussion about whether electron-only reconnection can be identified via Walen relation.
Towards the end of the session we discussed future plans and activities for the Focus Group. One of the future directions proposed for the FG would be to understand thin current sheets: solar wind, foreshock, magnetosheath, as well as in the laboratory. It would be interesting to statistically characterize the current sheet properties, categorize into reconnection & non-reconnecting conditions, and compare the thin current sheets in different regions. Another proposed future direction would be to understand magnetopause reconnection extent. Potential efforts include spacecraft conjunctions (MMS, THEMIS, Cluster, Geotail), space-ground coordination, and modeling.
Tuesday 1:30 PM - 3:00 PM & 3:30 PM - 5:00 PM - Dayside Challenges (w/ MMV FG)
Part I: Southward IMF Challenge: simulation-observation comparisons
Heli Hietala first introduced the background of the southward IMF challenge event (2015-11-18) and reviewed the current understanding based on solar wind, MMS-Geotail, and radar observations. To proceed with the analysis, two participating modeling teams (Yuxi Chen with MHD-EPIC and Yu Lin with a global 3D hybrid) had joined forces with observers (Sarah Vines and Sun Lee, respectively).
We first heard each collaboration present their simulation-observation comparisons on five prescribed topics: magnetic field and plasma signatures, waves, magnetopause location, and X-line dynamics. The MHD-EPIC simulated magnetic field and ion density and temperature agreed well with observations inside the magnetosheath, but showed some inconsistencies in the magnetosphere. The simulated ion reconnection jets were a factor of two smaller. The simulation well reproduced the magnetopause location and X-line extent. Sun Lee presented their preliminary hybrid simulation results. The simulated magnetic field and particle moments are qualitatively consistent with observations, but there were clear differences as well. The simulated X-line extent seemed broader than MHD-IPIC or observations. More careful analysis will be performed for the hybrid simulation.
Yuxi Chen, Sarah Vines, and Sun Lee then presented their additional findings of the challenge event. Sarah Vines discussed the magnetopause thickness (>1 ion inertia length), presence of warm oxygen cloak, impact of plume (assumed to be small), and the location of the spacecraft observations relative to the X-line location predicted by maximum shear angle. Yuxi Chen discussed electron dynamics in the MHD-EPIC simulation including electron jet and electron heating. Sun Lee showed D-shaped ion distributions away from the reconnection X-line in observations and the hybrid simulation.
Potential future modeling efforts include performing a baseline MHD simulation and comparing it with the MHD-EPIC and the hybrid simulation, as well as comparing particle distributions in MHD-EPIC and the hybrid.
You can find more information of the Southward IMF challenge at: https://ccmc.gsfc.nasa.gov/support/GEM/Dayside_Kinetic_Processes/Dayside_Kinetic_Challenge/Introduction.php
Part II: Day-Night Connection Challenge: a substorm triggered by magnetosheath jets?
Ying Zou introduced the second challenge event – day-night connection challenge. The event from 2015-12-25 was reported by Katariina Nykyri at the last Summer GEM and it was found to imply a potentially important role of dayside kinetic processes in a triggering nightside substorm. The event was therefore selected as the challenge event to call for community joint efforts to achieve collaborative analysis and understanding.
First Chih-Ping Wang provided an introduction to the theme by reporting observations of a different event where a foreshock transient continuously propagated from upstream to ~60 Re downstream of the Earth in ~1-2 hr.
Katariina Nykyri then presented the current progress of the challenge event. In the event, the IMF turned from southward to northward and stayed northward for ~40 min. Yet interestingly, the IMF also had a large Bx component, and MMS in the quasi-parallel magnetosheath observed several jets with southward magnetic field. These jets are expected to trigger dayside low latitude reconnection when impinging on the magnetopause, likely further triggering the substorm disturbance in the nightside magnetotail. With respect to whether dayside magnetopause was active, Simon Wing presented DMSP observations. He found that the dayside auroral oval stayed at significantly lower latitudes than typical northward IMF condition, indicating that dayside reconnection was active, likely due to the magnetosheath jets. Xueling Shi presented SuperDARN observations, where she found anti-sunward cusp convection following the detection of magnetosheath jets, again implying active magnetopause reconnection. She further observed radar signatures of substorm disturbances in the nightside including flow channels and Pi2 pulsations. Future follow-up of this challenge event includes modeling/simulations.
The sessions had 40-50 participants.
Wednesday 3:30 PM - 5:00 PM - Joint session with the Reconnection FG
This was a joint session between the Dayside Kinetics and Reconnection focus groups, and revolved around magnetic reconnection at the Earth’s magnetopause and in the Earth’s magnetosheath. Brian Walsh used global MHD simulations to discuss reconnection spreading at the dayside magnetopause, and showed that a typical MHD front moving through the magnetosheath and draping along the magnetopause is sufficiently fast and would likely not limit the spreading speed of reconnection. Mike Shay presented results from MMS that have shown reconnection occurring in the turbulent magnetosheath. The reconnection events found, however, are “electron-only” reconnection, where the ions do not participate in the reconnection process. Sarah Vines showed comparisons between the expected reconnection electric field derived from AMPERE and the LFM-MIX model and observations by MMS, and found the rates are on the order of 0.5 and 1 mV/m and were generally consistent. Allison Jaynes showed election enhancements up to over 100 keV in concert with elevated power in the whistler mode wave band during many crossings by MMS of the low latitude boundary layer. There are often intense parallel electric fields observed along with these signatures, indicating a non-linear component to the whistler mode waves and pointing towards the potential acceleration mechanism. Jason Shuster demonstrated the ability of the MMS Fast Plasma Instrument to compute terms in the Vlasov equation. Techniques for determining spatial and velocity-space gradients of the distribution function from the skymaps provided by FPI were presented and applied to thin current sheet observations in the magnetosheath. In support of the upcoming Solar wind - Magnetosphere - Ionosphere Link Explorer (SMILE), Hyunju Connor suggested an equation that represents magnetopause motion as a function of magnetopause reconnection rate and solar wind dynamic plasma pressure. This equation will help the SMILE team to extract the reconnection rate from the observable magnetopause motion. Ari Le presented a set of 3D fully kinetic simulations matching plasma parameters of three different MMS magnetopause diffusion region encounters with varying guide fields. Lower hybrid drift fluctuations contributed to electron transport and heating, while the anomalous dissipation in Ohm's law was very weak.
