[GEM] THE GEM MESSENGER, Volume 25, Number 41

Tue Sep 29 18:53:17 PDT 2015

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     THE GEM MESSENGER
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Volume 25, Number 41
September 29, 2015

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Table of Contents

1. 2015 Summer Workshop Report: Tail Environment and Dynamics at Lunar Distances Focus Group
2. GemWiki User Feedback Solicited

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1. 2015 Summer Workshop Report: Tail Environment and Dynamics at Lunar Distances Focus Group
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From: Chih-Ping Wang (cat at atmos.ucla.edu), Andrei Runov, David Sibeck, Viacheslav Merkin, and Yu Lin

The Tail Environment and Dynamics at Lunar Distances FG held its first and only session at the 2015 GEM summer workshop on Monday (June 15th) morning. This session was devoted to open discussion on mid-tail science questions and how they can be answered. The objective is to establish specific scientific questions to be addressed in the following years. There were nine speakers, including leaders from three other FGs. For achieving the two goals of this FG (to establish fundamental understanding the mid-tail and to develop model to evaluate the underlying physical processes), the speakers pointed out many fundamental but critical questions, including: (1) How do solar wind conditions (IMF discontinuities, interplanetary shocks, IMF change from northward to southward) change the mid-tail magnetosheath and magnetosphere and what are the resulting dynamics? (2) What do we know about the various boundary processes? (3) How is the mid-tail environment affected by the Moon? (4) What are characteristics of the current sheet structure and dynamics? (5) What are the connection of the mid-tail to the ionosphere and near-Earth tail? (6) What are the time scale and time lag of the connection to the solar wind and other regions?

The presentations are available at http://people.atmos.ucla.edu/cat/FG/2015-GEM-talks/

Hui Zhang discussed transient phenomena at the tail bow shock and magnetopause. She showed that a Hot Flow Anomaly (HFA) can deform the magnetopause, such as by creating a magnetopause bulge. The bulge can convect tailward with magnetosheath flow. For a lifetime of ~18 min estimated from the ionosphere signatures (traveling convection vortices) and convection speed of 100-500 km/s, a HFA is expected to travel to 17-85 RE down the tail. She pointed out two main questions for this FG: What do HFAs look like in the mid-tail?  What is the tail response to HFA?

Sheng-Hsien Chen presented observations of waves in the mid-tail LLBL and  lunar wake. He found that there is a lack of periodicity in ULF (~1– 60 min) surface waves in the LLBL. However, there is a presence of kinetic waves in the LLBL and lunar wake. He pointed out two main questions for this FG: (1) How is the interaction of LLBL plasma with the Moon in the mid-tail subjected to kinetic Kelvin-Helmholtz instability, lower-hybrid instabilities, kinetic ballooning/interchange instability, and reconnection? (2) What are the typical values for plasma scale lengths (L), anomalous resistivity due to lower-hybrid drift waves (η), associated diffusion coefficients (Dαα), and Lundqvist number (μ0 L VA / η) across the interfaces?

Denny Oliveria presented Open GGCM MHD simulations of a shocked magnetotail due to an interplanetary shock on 2012-03-08 and compared with the ARTEMIS observations at 60 RE . He found that enhanced current density in the current sheet due to shock compression and the center of the magnetotail shifted to Y = ¬–20 RE due to the strong Vy shear, which are consistent with the observations. MHD predicts interesting features of R-1 FACs that need to be compared with ground magnetometers. He suggested that more event simulation-observation comparisons with ARTEMIS observations are needed to understand the mid-tail response to sharp solar wind/IMF changes.

Rob Fear discussed magnetotail structure associated with transpolar arcs. He showed an event with Cluster in the lobe at X ~ –8 RE and Z ~ -12 RE, which saw perpendicular electron fluxes indicating closed field lines at very high latitudes, and IMAGE saw a transpolar arc, which supports that magnetotail reconnection during northward IMF can be a candidate for transpolar arcs. Newly reconnected field lines map sequentially deeper into the polar cap. Thus when a transpolar arc extends across fully to the dayside, this closed field line structure will extend a long way downtail. He suggested to use ARTEMIS data to investigate the connection between mid-tail structures and transpolar arcs.

Peter Chi presented ion cyclotron waves at the Moon and their connection to the plasma sheet and the lunar exosphere. He showed that the tail environment at lunar distances can be influenced by the presence of the Moon. The Moon can be a dominant particle source in the tenuous magnetotail.  He suggested to identify the generation mechanism(s) of ion cyclotron waves at the Moon (through studying the morphology of ICW and the wave/particle data). Also if the pickup ions are the source of ICW, the amount of exospheric particles (and their escape) can be estimated by the measurements of ICW. 

Ivan Vasko presented current sheet observations by Geotail in the mid and distant tail. He found quite often thin and intense current sheet in the 30-50 and 80-100 RE regions; more intense near midnight. Intense current is found to be associated with fast ion flow and electrons likely the main current carrier. He suggested that ARTEMIS separated in space can provide better understanding of the formation of thin current sheet and electron dynamics.

Andrei Runov pointed out that lunar orbit in the magnetotail is in-between the statistically most probable Near Earth Neutral Line (NENL) and Distant Neutral Line (DNL) locations. Thus, in the framework of magnetotail reconnection and related phenomena, including BBFs, dipolarization/jet fronts, particle energization and transport, observations there are greatly important. He suggested to propose a joint session with the Reconnection in the Magnetosphere FG.

John Lyon showed LFM simulations at lunar distances for growth phase and sawtooth event.  He found that for growth phase conditions (IMF changes from northward to southward), bubble initiates at lunar distance. For the sawtooth event driven by O+ outflow, the X-line is seen to move between the near-Earth neutral line and lunar distance. He suggested to increase resolution in the mid-tail region and compare simulations with statistical observational results.

Joe Borovsky discussed mid-tail and systems science in terms of what affects the mid-tail, what the mid-tail affects, and whether there are ‘complex-systems behaviors’ in the mid-tail. He suggested a potential joint session with the Geospace Systems Science FG to access the mid-tail and to figure out time scale and time lags for those connections.

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2. GemWiki User Feedback Solicited
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From: Peter Chi (gemeditor at igpp.ucla.edu)

With the help by NSF, we have learned that a visitor of the GemWiki website saw a warning issued by his antivirus/antimalware software that the GemWiki site was a known threat. While we have used several web tools and confirmed that the GemWiki site is safe to visit, we hope to know if other members of the GEM community have experienced the same problem.

If your computer tells you that GemWiki is a malicious website, please e-mail gemeditor at igpp.ucla.edu what antivirus/antimalware software your computer uses. The GemWiki website can be accessed at:

http://aten.igpp.ucla.edu/gemwiki/index.php/Main_Page

Your feedback can help us understand more about these false warnings and possibly correct them. Comments on other aspects of the GemWiki site are also welcome.

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