2019 Summer Workshop, Santa Fe, NM

GEM Summer Workshop 2019: session summaries

The 2019 GEM summer workshop was held between June 24-28, 2018 at the Eldorado Hotel in Santa Fe, NM. We held four sessions in the Summer 2019 Workshop.

- 2019 Summer Workshop : Session schedule

UMEA/Dayside Kinetics/IHMIC joint session

The theme of the session was to consider the ULF wave response to dayside transients with different temporal/spatial scales and asymmetries. The guest convener Tom Elsden first introduced the session and the questions posed to the participants:

• How are ULF wave properties affected by asymmetries in the upstream driver? What modelling/observational work is required to answer this?
• Further, how then do the resulting ULF wave asymmetries impact the M-I system?
• How does the 3D structure of dayside kinetic phenomena (e.g., spatial scale of magnetopause disturbance, location relative to magnetic equator) affect the ULF response in different hemispheres/LT sectors?
• Can we use magnetospheric observations to determine the size (localized vs global) of a dayside transient? Is the response well-enough understood?

Ferdinand Plaschke gave an invited overview of dayside transients generating ULF waves inside the magnetosphere: solar wind variations, foreshock phenomena (e.g., hot flow anomalies, foreshock bubbles, foreshock waves), magnetosheath jets and mirror modes, as well as magnetopause processes (e.g., flux transfer events and the Kelvin-Helmholtz-instability). Magnetosheath jets have recently become the focus of scientific interest as they occur often, have significant impact, and act as long-range link between the bow shock and the magnetopause, ultimately connecting foreshock processes with effect observable on ground.

Tom Elsden discussed recent results from a newly developed 3D MHD code looking at ULF wave excitation in the outer magnetosphere. He showed the importance of understanding the normal waveguide modes of the system in order to predict 3D FLR structure/location, as well as commenting on future uses of the code to study ULF waves driven by local magnetopause disturbances.

Boyi Wang presented recent observations of the role of foreshock/magnetosheath disturbances in triggering magnetospheric Pc5 ULF waves. Significant magnetosheath disturbance was observed with a foreshock transient in the pre-noon sector. The disturbance further triggers a series of Pc5 ULF wave and the wave can propagate from dayside all the way to midnight.

Bob Lysak and collaborators have investigated quarter-wave field line resonances, which are observed when one footpoint of the field line is in sunlight and the other is in darkness, using a numerical simulation of ULF waves in the inner magnetosphere. They have found that such quarter-wave emissions excited by a shock-like impulse at the magnetopause, can occur on field lines within the plasmasphere near the terminator, consistent with the observations of Obana et al. (2015) that showed the resonant frequency nearly doubling when the magnetometer observing the wave passed from darkness into sunlight.

Xueling Shi presented Conjugate Observations of ULF Waves during an Extended Period of Radial IMF. The ULF waves were observed over a wide range of dayside local times and outer magnetospheric L shells. The upstream ion foreshock during an extended period of radial IMF probably plays an important role in providing a seed perturbation for the growth of the KH instability which generates the dayside ULF waves.

Finally, UMEA Focus Group co-chair Michael Hartinger reviewed discussions from previous GEM Workshops related to the session theme. While numerous past GEM presentations indicate a relationship between dayside kinetic phenomena and magnetospheric ULF waves, there are unresolved questions concerning the effectiveness of different transients in driving waves. Statistical studies and modeling efforts are needed to determine how transients related to different spatial distributions and speeds on the magnetopause affect wave activity.

Dayside Kinetics/Bow Shock joint session

The theme of the session was to discuss new studies of key kinetic processes which are important to both the bow shock and dayside region. The main topics included transmission of transients/waves through the shock, impact of shock processes on the downstream region, and the formation of shock-like structures in different dayside regions.

Ian Cohen presented MMS data from 8 Jan 2018, when it encountered its only interplanetary shock to-date, observing electron heating, near-specularly reflected ions, and apparent significant non-linear electric field structures. The high-resolution particle and field measurements enabled multiple approaches to calculate the cross-shock potential for this marginally supercritical shock.

Xin An used particle-in-cell simulations to reveal the formation process of foreshock transients and to provide clear evidence on the critical role of electric fields in shaping the magnetic field structures, as well as in coupling the energy of hot ions to that of the secondary shock, which is subsequently dissipated through the excitation of magnetosonic waves. They further demonstrated that higher Mach number of the parent shocks favors the formation of the secondary shocks, which will be appealing to consider in particle acceleration of high Mach number astrophysical shocks.

Yann Pfau-Kempf presented Vlasiator simulation results on the transmission of foreshock ULF waves to the magnetosheath.

Michael Balikhin showed the first direct observations of quasi-perpendicular bow shock nonstationarity, which was achieved during a Cluster close separation campaign. The main result was that nonstationarity is initiated by electron scale structures within the ramp, agreeing with the gradient catastrophe model, but not those proposed by some numerical PIC simulations.

Heli Hietala presented global 3D hybrid simulations of magnetosheath jets. The jets identified from the simulation using similar criteria as in spacecraft observations extend from the bow shock into the subsolar magnetosheath and have very irregular shapes.

Terry Liu’s statistical study using THEMIS shows that high solar wind dynamic pressure, large solar wind plasma beta, and high bow shock Alfven Mach number favor the formation of magnetosheath jet-driven bow waves. Jets with a bow wave have higher probability to have larger particle energies than jets without a bow wave.

Reconnection/Dayside Kinetics joint session

Magnetic reconnection itself is a key dayside kinetic process and it is closely related to other kinetic processes, including waves and turbulence. The goal of this session was to understand fundamentals of dayside reconnection. The main topics included:

• What are the characteristics of magnetic reconnection on the dayside?
• What role does reconnection play in forming various dayside transients?
• What are the new approaches/opportunities of studying magnetic reconnection?

Katariina Nykyri presented MMS observational and global simulation results on the generation mechanism of a new kind of magnetic bottle structure with energetic particles of both solar wind and ionospheric origin at the southern dayside magnetospheric boundary layer formed by low latitude reconnection. The center bottle, characterized by weak magnetic field, was filled with high fluxes of 90 degree pitch angle energetic electrons and ions.

Andrew Dimmock gave an overview of the SMILE Soft X-ray Imager (SXI) which will observe the dayside-magnetosphere interaction in soft X-rays resulting from solar wind charge exchange. The novel new dataset can be used to track the motion of the magnetopause and cusps, making it possible to investigate the fundamental modes of solar wind-magnetosphere interactions.

Brian Walsh presented an update on the development of the CuPID Cubsat Observatory. The 6U cubesat will image ion dispersions in the cusps to study meso- and macro-scale properties of magnetic reconnection.

Xuanye Ma compared the Kelvin-Helmholtz (KH) instability in a fluid simulation with test particles with a hybrid simulation. The Hall MHD with test particle and hybrid simulation give almost identical particle mixing rate in the KH instability. Test particle shows the KH instability can form an anisotropic velocity distribution.

Karlheinz Trattner considered the dynamics of elongated dayside X-lines using MMS observations and the maximum shear model. Marcos Silveira and collaborators surveyed flux transfer events observed by the MMS mission in the vicinity of the Earth’s magnetopause from Y = -12 to 12RE with a large range of characteristic time and cross-section length. One case of a small-scale flux transfer event with an electron scale structure was presented.

Dayside Kinetics/MMV joint session

This session focused on the Dayside Kinetics Southward IMF Challenge. We discussed the progress in comparing observations and modelling results for the event on 2015-11-18 01:50-03:00 UT, featuring an MMS-Geotail magnetopause conjunction with SuperDARN radar observations. Heli Hietala first presented a summary of the Challenge progress so far. We then moved on to new observation-modelling comparisons, in particular of the magnetopause transients (are they due to simple boundary layer motion or more FTE-like).

Sarah Vines presented an overview of the MMS observations from the Challenge event that were provided for the data-model comparisons (magnetic field and plasma moments in the published LMN system and dB power spectra), and the results of an initial run of the maximum magnetic shear model. Additionally, they discussed low-energy ion composition for this event, particularly the heavy magnetospheric ions (He+, O+) reaching the outer magnetosphere and magnetopause that are energized in the current layer and reconnection exhaust.

Karlheinz Trattner presented new maximum shear model results for the event and comparison with MMS. According to their analysis, MMS observed a single clean magnetopause crossing bracketed by several boundary layer encounters before and after the crossing. Each boundary layer encounter showed southward accelerated ion beams indicating the presence of an X-line north of the satellites, with no FTE signatures on the southern side of the X-line.

Zhifang Guo used a three-dimensional global-scale hybrid simulation to study the MMS observations during the event. The location of the magnetopause reconnection, the global distribution of the X-lines, the spatial and temporal variation in reconnection, the electromagnetic power spectra, and the ion velocity distributions were compared with the observations.

Marcos Silveira compared the MMS observations with Yuxi Chen’s MHD-EPIC results for the challenge event, where the model observed some of the structures in the similar location of MMS3. The simulation reproduces qualitatively the MMS observations of magnetopause transients, suggesting the probes observed edges of possible flux transfer events in the magnetosphere.

We finished with a discussion on the wrapping up of the Challenge, including JGR-Earth and Space Science Special Issue manuscript coordination.