[GEM] THE GEM MESSENGER, Volume 28, Number 37

Thu Aug 9 20:32:46 PDT 2018

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     THE GEM MESSENGER
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Volume 28, Number 37
Aug.09,2018

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

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Table of Contents

1. GEM Tail Environment and Dynamics at Lunar Distances Focus Group: 2018 Workshop Report

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1. GEM Tail Environment and Dynamics at Lunar Distances Focus Group: 2018 Workshop Report
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From: Chih-Ping Wang, Andrei Runov, David Sibeck, Viacheslav Merkin, and Yu Lin (cat at atmos.ucla.edu)

The Tail Environment and Dynamics at Lunar Distances FG held two sessions at the 2018 GEM summer workshop. There were a total of 12 presentations.

1. Robert Allen presented observations from the Cassini Earth fly-by of keV ions in the distant magnetosheath. These observations suggest both a high variability in the width of the distant magnetosheath, as well as indications of a distinct magnetosheath population as far down-tail as 6000 RE. 

2. Jay Johnson (presented for Yu Lin) presented the generation, structure, and propagation of kinetic Alfvén waves in the magnetotail associated with fast flows based on 3D global hybrid simulations using ANGEL3D. The results show (1) Alfvénic waves are generated in reconnection, propagating earthward and tailward near the plasma sheet boundary layer. (2) Alfvénic waves propagate to the north (along the direction of B) in the Northern Hemisphere and to the south (against B) in the Southern Hemisphere in the dipole-like field region. Kinetic Alfvén waves associated with bursty flows in the plasma sheet observed by THEMIS and in the ionosphere by DMSP were also shown.  

3. Shin Ohtani described the statistical study of dipolarizations observed by the Van Allen Probes in the inner magnetosphere (Ohtani et al., 2018). The statistics showed that dipolarizations (i) take place more frequently closer to the Van Allen Probes apogee distance and (ii) propagate earthward.  He suggested that these results can be explained by assuming two wedge current systems, one with the R1 sense staying outside of geosynchronous orbit and another with the R2 sense moving earthward along with injections. He discussed this idea in the context of the flow braking and the plasma bubble penetration.

4. Joachim Birn presented results from further analysis of an MHD simulation of the current diversion in the substorm current wedge (SCW) (applicable also to individual flow bursts), showing, from lower to higher latitude, field-aligned currents of region 2, region 1, and region 0 sense. While R1 and R2 FACs were associated with pressure gradients, and thus persisting for longer times after the generating flows subside, the R0 current, recently observed in the tail by Rumi Nakamura, were " inertia-driven", and thus likely short-lived and less likely to map to Earth. He also showed the energy flow and conversion from magnetic to flow energy, which suggests enthalpy flux as the ultimate energy source feeding the SCW. 

5. Jiang Liu presented coordinated observations of flows measured by Swarm and omega band aurora from all sky imagers. The observations show: (1) An ionospheric flow shear exists near the poleward boundary of the omega band arc and leads to an eastward flow peak poleward of the arc. (2) The flow shear is located near the boundary separating region 1 and region 2 currents and maps to a nightside L shell of 6-11. (3) The flow shear may drive the omega band via Kelvin-Helmholtz instabilities.

6. Xiaochen Shen presented Kelvin-Helmholtz waves (KHWs) observed simultaneously in the near-Earth space by Geotail (X ~ -5 RE, dawn side) and mid-tail region by ARTEMIS (X ~ -50 RE, dusk side). Results suggest that both the phase velocity and spatial scale of KHWs may increase as they propagate along the magnetopause. Further observations of KHWs in the same side of the magnetosphere is needed to confirm the time evolution of KHWs along the Earth's magnetopause. 

7. San Lu presented three-dimensional PIC simulation results showing a dawn-dusk asymmetry of the magnetotail thin current sheet. This asymmetry is formed through ExB drift in the Hall electric field on a small spatial scale and a short time scale. The asymmetry of magnetotail current sheet properties can explain why there are more magnetotail reconnection occurrences, transients, and substorm onsets observed on the duskside as compared to the dawnside. 

8. Anton Artemyev presented a local 3D structure of the thinning current sheet with a dataset collected by three THEMIS spacecraft and GOES 15. He demonstrated that the near-Earth current sheet thinning is accompanied by the formation of the equatorial plasma gradients directed toward midnight. Formation of these gradients is accompanied by an intensification of the dawn-dusk current (current sheet thinning) and field-aligned currents with opposite polarities at the dawn and dusk flanks. An increase of the equatorial plasma pressure (and lobe magnetic field) is provided by a cold plasma density increase in the near-Earth tail.

9. Stefan Kiehas presented modeling results of a bent magnetotail current sheet built by means of a generalization of the Harris–Fadeev–Kan–Manankova family of symmetric solutions of the Vlasov–Maxwell equations. He showed and discussed the conditions that a bent current sheet can destabilize the magnetotail.

10. Andrei Runov presented tail current sheet structure at lunar distances observed by ARTEMIS. The results show: (1) Magnetic eld shear makes a signicant contribution to the pressure balance for 50% of observed current sheets. (2) Intense eld-aligned currents 1–10 nA/m2) exist at the lunar distance magnetotail.

11. Chih-Ping Wang presented a candidate event for the next modeling challenge. From ~06-12 UT on 9 July 2017, 8 satellites were approximately aligned along the noon-midnight meridian (|Y| < 10 RE). Cluster and Van Allen Probes were on the dayside, GOES 13 and 15 were on the nightside, Geotail was at X ~ –12 RE, MMS at X ~ –22 RE, and ARTEMIS P1 and P2 were at X ~ –62 RE. IMF was northward from 0600 to 0830 UT with the solar wind dynamic pressure gradually increased from 2 to 5 nPa. IMF turned sharply southward at 0830 UT and stayed southward until 10 UT. AE jumped sharply at ~09 UT. SYM-H was > 0 during the entire event. 

12. Jiang Liu presented field-aligned currents (FACs) computed from the 4 MMS satellites. The results show: (1) In the magnetotail, localized, intense field-aligned currents are often observed by MMS. (2) The collective effect of many such intense FACs is the Region 1 and Region 2 currents.

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