[GEM] THE GEM MESSENGER, Volume 27, Number 50

Mon Oct 30 07:19:28 PDT 2017

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     THE GEM MESSENGER
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Volume 27, Number 50
Oct.30,2017

Announcement submission website: http://aten.igpp.ucla.edu/gem/messenger_form/

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Table of Contents

1. 2017 GEM Workshop Report: Dayside Kinetic Processes in Global Solar Wind-Magnetosphere Interaction Focus Group

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1. 2017 GEM Workshop Report: Dayside Kinetic Processes in Global Solar Wind-Magnetosphere Interaction Focus Group
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From: Heli Hietala, Xochitl Blanco-Cano, Gabor Toth, and Andrew Dimmock (heli at igpp.ucla.edu)

The Dayside Kinetics FG held four sessions during the Summer 2017 GEM Workshop. The Tuesday (06/20) session on “Magnetosphere-ionosphere coupling processes associated with localized disturbances caused by dayside kinetic phenomena” held with the ULF FG and the Proposed Links FG is summarized in the ULF FG’s report, and the Thursday (06/22) session on “Magnetopause phenomena” held together with Magnetic Reconnection FG is summarized in the Magnetic Reconnection FG’s report.

Tuesday 06/20:
Dayside Kinetics Challenge session
joint with Modeling Methods and Validation FG

The southward IMF event on 2015-11-18 01:50-03:00 UT, featuring an MMS-Geotail magnetopause conjunction with SuperDARN radar observations has been set as the challenge event. During this challenge we analyze the various dayside phenomena (magnetic reconnection, FTEs, magnetosheath waves, etc.). We aim to conduct comparisons between (i) observations and models with different levels of kinetic physics; (ii) different models; (iii) in situ and remote observations. So far, we have over a dozen observers who have signed up to analyze the measurements, and three different simulation models: particle-assisted MHD (Ilja Honkonen), MHD with embedded PIC (Yuxi Chen), and global hybrid-PIC (Yu Lin).

In this session, attended by over 40 observers and modelers, we had presentations of the observations made throughout the magnetosphere during the event, as well as on the preliminary simulations. The session chairs (Heli Hietala and Lutz Rastaetter) presented the slides and results of those challenge team members who were unable to attend this year’s workshop.

Starting from global scale observations, Rishi Mistry and Heli Hietala reviewed the analysis of ACE, Wind, and ARTEMIS solar wind measurements that led to the chosen input values for the models. The details of the analysis are available on the CCMC website. Andrew Dimmock compiled OMNI and THEMIS statistics of solar wind and magnetosheath observations under similar conditions to the challenge event. While purely southward IMF conditions are a staple for simulations, they are rarely observed. Toshi Nishimura presented radar observations during the 2015-11-18 campaign event. He described a 2-d perspective of the bursty magnetopause reconnection during the event, and presented the azimuthal size and propagation speed of the reconnection jets. Christine Gabrielse reviewed the nightside observations: Three THEMIS spacecraft were located in the tail near midnight around -8 to -9 RE XGSM during the Dayside Challenge event (01:50-03:00UT). They observed plasma sheet thinning during the event, followed by a small dipolarization, particle injection, fast earthward flow ~24 minutes after the event, and a large dipolarization, particle injection, and fast earthward flow ~40 minutes after the Challenge Event. 

Moving to smaller scale observations, Xochitl Blanco-Cano studied waves observed by MMS near and inside the magnetosheath jet structure associated with the northward turning of the IMF at the end of the Challenge interval. They find that the fluctuations near the jet have the properties of mirror mode waves and are associated with temperature anisotropy Tperp > Tpar. In contrast, off angle propagating waves are observed inside the magnetosheath jet, probably transmitted from the upstream (no temperature anisotropy is associated with these waves). Rick Wilder showed MMS wave and electric field data from the event, with a special focus on the parallel electric fields associated with whistlers on the separatrix. The presence of a beam as well as potential anisotropy was observed, as well as trapped energetic electrons that may be accelerated by a combination of the whistlers and the non-linear parallel electric fields. Steve Petrinec showed the densities of the minor ion species as observed by MMS/HPCA during the dynamic magnetosheath intervals (possibly FTEs) associated with the Challenge interval. Enhancements in the He+ and O+ ions above 1 keV were observed at these times.

With respect to preliminary simulation results, Ilja Honkonen contributed a reference MHD simulation to the challenge. He found that the X-line location was similar to the estimates based on MMS and Geotail observations. The model is available at CCMC and the code at github.com/iljah/pamhd for anyone to download, use, study, modify and redistribute. Yuxi Chen performed a three-dimensional one hour-long global simulation using the MHD with embedded PIC (MHD-EPIC) model to study the dayside magnetopause reconnection. They studied both the global and kinetic scale phenomena that are related to the reconnection, and the simulation results agree with the observations.

The next steps of the challenge are to (i) continue the simulations (we encourage more models to join), (ii) perform more comprehensive analyses of both the observations and the simulations, and (iii) make quantitative comparisons.

You can find more information of the challenge at: https://ccmc.gsfc.nasa.gov/support/GEM/Dayside_Kinetic_Processes/Dayside_Kinetic_Challenge/Introduction.php 

Thursday 06/22:
Dayside Kinetics Contributed Science session

We solicited short presentations on dayside kinetic phenomena and their role in global magnetospheric dynamics. We had so many requests that unfortunately we could not fulfill all of them due to time constraints. We also briefly reviewed the goals of the FG and plans for future activities. The session had over 30 participants.

Sun Hee Lee presented a "Comprehensive Case Study of Magnetosheath Pressure Pulses and Rapid MP/BS Motion": A series of density/pressure pulses in the magnetosheath and a rapid transition from the magnetosphere to solar wind were observed by MMS during intervals with solar wind discontinuities and/or radial IMF intervals. The magnetospheric responses to these transient pressure pulses are observed in the magnetic field perturbations in the inner magnetosphere from the Cluster data and ground magnetometer data. Boyi Wang presented 2-D optical observations of dayside diffuse aurora brightening associated with magnetosheath high-speed jets. The observations by south-pole station all sky imager in conjunction with THEMIS satellites shows that magnetosheath high-speed jets are associated with both diffuse and discrete aurora brightening. The average size of the diffuse aurora pattern is ~4 Re after being mapped to the equatorial plane. Katariina Nykyri presented the work of her student, Miles Bengtson, on “Global Perspective on Substorm Onset and Trigger”: they investigated ARTEMIS, THEMIS, MMS and Geotail observations and also ground based signatures, and based on timing analysis they concluded that the magnetosheath activity on the dayside (observed by MMS) triggered the substorm. They think that these magnetosheath/partial magnetopause observations and auroral imaging require more collaborative analysis, and therefore the event could be interesting for this FG in the future. Daniel Graham gave an overview of the proposed ESA mission THOR (Turbulence Heating ObserveR) to investigate turbulence in the near-Earth plasma environment, with unprecedented fields and particle measurements. THOR is designed to investigate how turbulence heats plasmas, how energy is partitioned between different particle species, and how dissipation operates in different regimes of turbulence. David Mackler presented a single MMS burst case study of a magnetosheath current sheet crossing where he identified plasma turbulence. He did this by using the Partial Variance of Increments method on fast survey flux gate magnetometer data in addition to identifying the slope and break of the power spectral density. Seth Dorfman presented the first satellite measurement of the ULF wave growth rate in the ion foreshock (Dorfman, et. al., GRL 2017). The measured growth rate is found to fall within dispersion solver predictions during the initial growth time.

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