[GEM] THE GEM MESSENGER, Volume 26, Number 44

[Newsletter Editor]

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     THE GEM MESSENGER
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Volume 26, Number 44
Oct.27,2016

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Table of Contents

1. 2016 GEM-CEDAR Workshop Report: Testing Proposed Links between Mesoscale Auroral and Polar Cap Dynamics and Substorms Focus Group

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1. 2016 GEM-CEDAR Workshop Report: Testing Proposed Links between Mesoscale Auroral and Polar Cap Dynamics and Substorms Focus Group
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From: Kyle Murphy, Toshi Nishimura, Emma Spanswick, and Jian Yang (kyle.r.murphy at nasa.gov)

The Testing Proposed Links between Mesoscale Auroral and Polar Cap Dynamics and Substorms Focus group (FG) intends to elucidate connections between auroral structures and their magnetospheric counterparts, and to bring closure to the question of substorm triggering. This report covers the three stand-alone sessions we had, and the report from the Magnetic Reconnection FG will cover a joint session we had together. Sessions 1 and 2 were devoted to event discussions and general contributed talks, and Session 3 focused on auroral streamers.

1. Event discussion

Prior to the workshop, the FG co-chairs selected three isolated substorm events based on availability of colored all-sky imager data and satellite conjunctions and invited three substorm experts (Larry Lyons, Larry Kepko and Tony Lui) to analyze those events from their viewpoints. In this session, they presented their interpretations of the events and opened lively discussions with the well-attended audience. We for the first time saw an agreement of substorm precursor sequence among three substorm experts in one of the three events. This is a substantial progress in the long-lasting arguments of substorm pre-onset sequence in the substorm community. However, while they all recognized existence of poleward auroral activity prior to onset in the other two events, their interpretations were considerably different. The differences arose from limited viewing conditions by imagers and current limited understandings of the role of poleward auroral activity prior to substorm onset. These issues will be addressed at future workshops by selecting different events and by soliciting a broader range of contributions including from modelers.

Event #1: Larry Lyons presented auroral images, suggesting PBI formation and equatorward propagation of a streamer minutes before onset. He also suggested a streamer made close contact to a growth phase arc. However, comments were raised about whether the near-Earth plasma sheet between ~8 to 18 Re could be mapped less than 1 degree in latitude. Larry Kepko’s analysis showed that the poleward expansion of onset arc did not seem to disturb an existing arc poleward of the expanding one. He suggested that viewing angle might mislead our perception of aurora motion. Tony Lui mentioned that a streamer was present before onset but there was a considerable separation from the thin onset arc.

Event #2: Larry Lyons pointed out two streamers propagated equatorward and one of them made close contact with the growth phase arc before onset. He showed radar data, which suggested equatorward flows associated with streamers. He also showed THEMIS plasma sheet observations, suggesting weakly enhanced earthward flows. Larry Kepko and Tony Lui agreed with the interpretation of the optical sequence by Larry Lyons. Andrei Runov pointed out that the electric field data were not reliable for this event, due to shadow effects.

Event #3: Larry Kepko pointed out the onset expansion exhibited something like omega band. He suggested that maybe there were streamers beyond the view of an ASI. Larry Lyons showed SuperDARN data, suggesting the existence of a Harang Reversal. Tony Lui thought this was possibly a streamer-triggering-substorm case.

2. Contributed talks

Liz MacDonald showed a beautiful auroral image taken by a professional photographer. The aurora exhibited spatially quasi-periodic beads, each accompanied with vertical rays. It happened during a storm main phase. Eric Donovan and Jun Liang showed results comparing time series of >30 keV electron flux and ground riometer data. One application is to improve the magnetic field mapping accuracy. Shin Ohtani modeled the PBI orientation and width in the ionosphere. Dick Wolf presented criteria of Kelvin-Helmholtz instability and interchange stability in the near-Earth plasma sheet high pressure region that corresponds to a growth-phase arc. Misha Sitnov used system science approach to investigate the substorm triggers and drivers. Larry Kepko presented auroral images, suggesting beading as a consequence of a flow braking.

3. Streamer session

The purpose of this session was to address the broad science questions “How commonly do substorm precurosrs occur?” and “What are the similarities and differences of PBIs/streamers/plasma sheet flows during isolated substorms, active-time substorms and non-substorm times?” outlined in the Focus Group Proposal. To this end the session discussed the role of streamers in substorms onset and ionospheric dynamics, the relation between substorm onset and fast flows, and the penetration of flows into the inner magnetosphere. Katie Garcia-Sage, Bashi Ferdousi, Bob Lysak and Jian Yang presented simulation of substorms and plasmasheet flows discussing (a) the differences between convective and substorm initiated flows (b) mapping of plasma sheet flows to the ionosphere and the resulting auroral/streamer signatures (c) substorms onset and (d) the relation between growth phase bubbles and streamers. Xianging Chu and Bob McPherron presented a statistical analysis of fast flows and substorm onset using Point Processes to determine whether the two phenomena where statistically linked. Nadine Kalmoni presented statistics of the azimuthal structuring of the onset arc demonstrating that all are structured and that auroral beads observed at onset are a special case when the structuring is very clear. Jiang Lui presented a statistical analysis of field aligned currents from THEMIS. Toshi Nishimura discussed the similarities and differences between streamers during different geomagnetic activity and Drew Turner presented observations from the Van Allen Probes and MMS discussing how injections can make it deep into the inner magnetosphere.


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