2016 Summer Workshop, Santa-Fe, NM

GEM Summer Workshop 2016

The 2016 GEM summer workshop was held between 19-24 June at the Santa Fe Convention Centre. This was the first of five years of the new Dayside Kinetics FG. We participated in 4 joint sessions on Tuesday, Wednesday, Thursday and Friday. Please see below for a summary of each session. For more details please contact one of the FG chairs, or the presenter.

Session Summaries

Tuesday: Dayside magnetopause processes and transport

The “Magnetic Reconnection in the Magnetosphere” focus group jointed with the “Transient phenomena at the Magnetopause and Bow Shock and their Ground Signatures” and “Dayside Kinetic Processes in Global Solar Wind-Magnetosphere Interactions” FGs in the afternoon of Tuesday (06/21/2016). This joint session encouraged cross-focus group interaction and open ended discussion on the topics of magnetopause reconnection, flux-transfer events, Kelvin-Helmholtz instability, magnetopause waves, and other boundary layer processes. In the end, as we wished, we had plenty of talks on observation and modeling with the emphasis on global magnetospheric aspects of reconnection.

Sanni Hoilijoki showed that reconnection rate at the dayside magnetopause in a global hybrid-Vlasov simulation correlates well with the analytical model by Cassak and Shay [2007]. In addition, their results indicate that the magnetosheath waves affect the reconnection rate.

Sun-Hee Lee showed that (1) The inverse dispersions of the 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. (2) Using combined ground radar and MMS/EIS observations they estimated a longitudinal extent of 1.5 RE for the reconnection line.

Xuanye Ma showed that magnetic reconnection with a super-critical perpendicular sheared flow forms an expanding out flow 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 KH substantially increases the loss rates for both ion species at the dusk as well as the dawn magnetopause flanks. They also showed that after the magnetopause crossing and prior to the escape into the interplanetary space, energetic oxygen remains in the magnetosheet much longer than hydrogen, which is consistent with recent MMS observations.

Andrey Samsonov et al. 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.

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.

Chih-Ping Wang showed that during a prolonged northward IMF interval (~5 hr) with very steady SW/IMF conditions, ARTEMIS at X = 60 Re near the dusk magnetopause boundary layer observed quasi-periodic (7-10 min) perturbations in plasma and magnetic field. Simultaneous observations from the two ARTEMIS probes indicate that the perturbations were propagating tailward with a spatial scale of ~8 Re 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. The resulting perturbations can qualitatively explain the observed perturbations.

In OpenGGCM, Kris Maynard showed evidence that reconnection happens at two simultaneous x-lines during FTE formation. They are able to quantify the reconnection rate using the quasi potential.

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 proves that the magnetopause is in force balance and reveals multiple sub-layers exist in the magnetopause.

Using the magnetic and particle data, Richard Denton and collaborators found the motion of the MMS spacecraft through the reconnection structure described in the Burch et al. Science paper.

Maimaitirebike Maimaiti showed a case study focused on the time interval of 18:00 - 20:00 UT On September 2014, when RISR-N was located in the noon sector, and directly measured reverse convection in the dayside throat region while IMF was transitioning from strong positive By to strong positive Bz. Time-lagged correlation analysis reveals that the IMF By influence acted on a lag time which was 10 minutes faster than that of the Bz component. They attribute this difference in lag time to the occurrence of magnetic merging at two different magnetopause sites as determined by favored merging geometries for the two components of the IMF.

Wednesday GEM, PM1: Magnetospheric signatures of dayside transients

This session was joint with the “Dayside Kinetic Processes in Global Solar Wind-Magnetosphere Interactions” and “Transient Phenomena at the Magnetopause and Bow Shock and their Ground Signatures” FGs. There were 8 presentations, and throughout the session discussion topics included (1) preferred driving conditions/magnetopause perturbations for triggering different magnetospheric signatures and (2) modeling the ULF response to localized magnetopause indentations.

Slava Merkin presented results from the effort coupling the high-resolution version of the LFM global magnetosphere with Sasha Ukhorskiy’s test particle simulation. The work was done primarily by Kareem Sorathia at JHU/APL and showed that losses of magnetospheric energetic particles (100 keV protons and O+ ions) at the magnetospheric flanks were enhanced by the well-developed Kelvin-Hemholtz instability. De-sheng Han discussed throat aurora, using statistical analysis to show that auroral features relate to scales of ~3RE in the equatorial plane and are the ionospheric signatures of the interaction of cold magnetospheric ions with dayside magnetopause reconnection. This implies that throat aurora may provide important information on studying the interaction of cold magnetospheric plasma with magnetopause reconnection. Boyi Wang discussed the driving mechanisms of poleward moving auroral forms (PMAFs) with coordinated all sky imager and satellite observations, showing a strong statistical relationship with southward turnings of the IMF (72%), with a response time of ~8 minutes. Boyi Wang also discussed the dayside auroral response on closed field lines to an IMF discontinuity, using multiple satellites in the dayside magnetosphere, magnetosheath, and solar wind. They associated the IMF discontinuity with a localized, propagating magnetopause compression, brightening/azimuthal propagation of dayside diffuse aurora, and localized magnetospheric ULF waves with large amplitudes. Michael Hartinger discussed how the high-latitude ground magnetic response to an interplanetary shock depends strongly on the local ionospheric conductivity; inter-hemispheric comparisons from recently deployed Antarctic AAL-PIP magnetometers, Greenland magnetometers, and global MHD simulations show the response varies rapidly with location relative to the auroral oval. Hui Zhang presented HFA generated Pc3 ULF waves observed by multiple spacecraft and ground magnetometers. The ULF waves are standing Alfvén waves. The wave power of poloidal mode is stronger than that of toroidal mode. The Pc3 ULF waves were observed at dawn, noon and dusk sectors, indicating the magnetospheric response to the HFA is global. The goal of the work presented by Heli Hietala is to determine impact rates of magnetosheath high speed jets and their properties at the magnetopause, which can then be used as input to global magentospheric models. The high speed jets are related to kinetic foreshock processes, and drive significant local increases in dynamic pressure and ULF fluctuations at the magnetopause. The jets occur preferentially in radial IMF conditions, happening at rates as large as 9/hour with typical perpendicular scales of 1.34 RE. Alexa Halford spoke about BARREL observations of a solar energetic electron event. There were ULF oscillations observed with precipitation and it is yet unclear if this is due to the movement of the open closed boundary or processes within the magnetosheath as these same oscillations were not observed in the solar wind.

Thursday: Kick-off session of the first dayside modelling challenge

Heli Hietala introduced the new Dayside Kinetics focus group, co-chairs, and overview of the challenge. We wish to start this new focus group on "Dayside Kinetics" with a modeling challenge where, after agreeing on a short interval of steady solar wind input conditions from the first MMS dayside season, we will conduct comparisons of the various dayside phenomena. The aims of the challenge are to (i) Collect coordinated in situ and remote observations to assess the dynamics of the magnetospheric system and for model validation; (ii) Quantify agreement/disagreement between datasets and models; (iii) Determine reasons for data/model, model/model, and data/data differences; (iv) Advance our understanding of multi-scale plasma processes and their role in SW-magnetosphere interaction.

First, we had three presentations on different approaches to including kinetic effects in global simulations. Sanni Hoilijoki presented the global hybrid-Vlasov simulation model Vlasiator that describes ions as six dimensional velocity distribution functions and electrons as charge-neutralizing fluid. Global 5 dimensional (2D-3V) show that Vlasiator can generate important features of solar wind-magnetosphere interaction, for example, oblique 30s foreshock waves, magnetosheath mirror mode waves and multiple X-line and FTE formation at the dayside magnetopause. Yuxi Chen presented MHD-EPIC - an MHD simulation with an embedded particle-in-cell (PIC) model - and its 2D and 3D applications for Earth's dayside reconnection. Crescent phase space distribution was found near the reconnection site, and they also demonstrated that the global structure of dayside reconnection does not change much with ion mass. Amitava Bhattacharjee presented integration of kinetic effects in multi-fluid global simulations, discussing different closure schemes and the 5-moment and 10-moment models.

Second, we had three presentations on available observations. Naritoshi Kitamura gave an overview of two good conjunction events between Geotail and MMS on 2 October 2015 (decay of mesoscale FTE during quasi-continuous spatially extended reconnection at the magnetopause [Hasegawa et al., GRL, 2016]) and 18 November 2015 (the magnetopause reconnection line shifts toward the winter hemisphere for southward IMF [Kitamura et al., GRL, 2016]). Heli Hietala presented a list of THEMIS-Cluster-Geotail dayside conjunctions that offer a possibility to observe foreshock/bow shock, magnetosheath, and magnetopause simultaneously. She also noted that ground-based observatories can offer support in resolving/validating the global picture. Andrew Dimmock gave a summary of a data analysis tool [Dimmock et al, 2013], which compiles large datasets of in-situ measurements used for either statistical mapping or analysis. He discussed how these large databases could be generated for upstream criteria comparable to model input conditions facilitating new model-data comparison studies.

Third, we had a vibrant discussion among the 30-40 session participants (approx. 50/50 observers and modelers) on the science priorities, specs and metrics of the challenge. Another important subject of discussion was determining the most optimal and feasible approach to comparing experimental and simulated datasets. We discussed the possible merits of three, 30-45 minute runs with different geometries: a southward IMF polar plane run, a northward IMF polar plane run, and an equatorial plane run. We discussed the pros and cons of metrics including FTEs, magnetosheath waves and turbulence (power spectra, thin current sheets, heating), foreshock and bow shock generated transient structures, magnetospheric effects (excited magnetospheric waves and energetic particles) and the properties of the magnetopause reconnection diffusion region.

Friday: Kinetic and transient processes in the foreshock, bow shock, and magnetosheath

Joint session with Transient Phenomena at the Magnetopause and Bow Shock and Their Ground Signatures FG

Kinetic effects throughout the dayside magnetosphere are driven to a large extent by an array of local and external transient phenomena. The purpose of this joint session was to determine how results from these focus groups could be combined to understand these effects on the dayside system from a global perspective.

Terry Liu showed THEMIS observations of a new ion and electron foreshock upstream of a foreshock bubble's shock. Foreshock bubble's shock could be an additional accelerator and a particle source for the parent shock acceleration. Sanni Hoilijoki and Heli Hietala presented, on behalf of Yann Pfau-Kempf, recent results obtained with the hybrid-Vlasov model Vlasiator. Magnetosheath perturbations are found to deform the bow shock so that transient foreshock-like field-aligned ion beams form, a scenario supported by Geotail observations. Heli Hietala presented ARTEMIS observations of ULF wave growth in the foreshock at lunar distances. The growth rate obtained from the two spacecraft measurements, as well as the other properties of the waves, match well the results of a dispersion solver that uses the observed ion beam distribution as an input. Andrey Samsonov presented a method for incorporating kinetic foreshock effects into a global MHD model. They simulated four events with very distant subsolar magnetopause crossings that occurred during nearly radial IMF intervals lasting from one to several hours. They changed the solar wind boundary conditions for a global model assuming that the density and velocity in the foreshock cavity decrease to ~60 % and ~94 % of the respective ambient solar wind values during intervals with small IMF cone angles. Christina Chu presented a hot flow anomaly (HFA) analog simulated in BATS-R-US and observations of how it affected the magnetosphere. This work will be used to analyze ground signatures observed with HFAs. Hui Zhang presented a statistical study to determine what kinds of discontinuities are more efficient to generate HFAs. Their results show that magnetic field on at least one side of the interplanetary discontinuities has to be connected to the bow shock in order to form HFAs. Discontinuities with large magnetic shear angles are more efficient to form HFAs. Current sheets with thickness from 1000 km to about 3162 km are more efficient to form HFAs. HFAs are more likely to form when the reflected flow from the bow shock is along the discontinuity.