*************************** ** THE GEM MESSENGER ** *************************** Volume 24, Number 31 October 9, 2014 ---------------------------------------------------------------------- 1. 2014 WORKSHOP REPORT: The Magnetosheath Focus Group ---------------------------------------------------------------------- From: Katariina Nykyri and Steve Petrinec The Magnetosheath Focus Group convened three sessions during the 2014 GEM workshop: two on Thursday and one on Friday. One session was combined with the Geospace System Science Focus Group; one was a joint session with the Magnetic Reconnection in the Magnetosphere Focus Group, and the final, Friday morning session was independent. Together, these three sessions represented the last of the five-year Magnetosheath Focus Group. 1. Magnetosheath joint session with GSS: “Origin of non-adiabatic heating from magnetosheath (MSH) into the magnetosphere (MSP)”: Joe Borovsky delivered opening words for this session: Specific entropy (non-adiabatic heating) increases by ~two orders of magnitude from the MSH into the MSP. Antonius Otto showed that significant non- adiabatic heating observed in MHD simulations associated with magnetic reconnection occurred only when MSH beta is very low ~0.01. Simon Wing showed that cold component ions are 30-40 percent hotter on the dawn- side plasma sheet compared to the dusk-side; however, because the dawn plasma sheet is also denser, no clear dawn-dusk asymmetry is observed in plasma sheet specific entropy. Ion to electron temperature ratio is pretty constant, although both species are heated in the MSP. Jay Johnson discussed how compressional waves such as Kelvin-Helmholtz waves can create kinetic Alfven waves (KAW) at the magnetopause boundary. KAW can heat ions effectively. More KAW are observed along the dawn-flank. Need to determine from observations the full k-vector of the KAWs. ERAU Ph.D student Thomas W. Moore identified (using multi-point Cluster observations) a high-frequency left handed polarized (in the plasma frame) wave packet inside a Kelvin-Helmholtz vortex during Parker-Spiral IMF at the dawn flank. This wave packet was observed during interval of plasma heating and mixing. An observational dispersion relation is currently being compared with theoretical dispersion relation of KAW and other plasma waves. Andrew Dimmock discussed development of statistical data analysis software for Solar Wind-Magnetosheath-Magnetosphere System Science that organizes data with respect to physical boundaries (bow shock and magnetopause). Katariina Nykyri discussed results of a statistical study of specific entropy using 7 years of THEMIS data: Regions of low ?i around the magnetopause correlate with enhanced ion entropy, Si. Entropy is larger downstream quasi-parallel shock compared to dusk. MSH velocity fluctuations correlate with enhanced MSH entropy. 2. Magnetosheath joint session with Magnetic reconnection: Xuanye Ma discussed 3D simulation results of the Kelvin-Helmholtz Instability showing that the 3D growth of KHI is similar for northward/southward IMF and that patchy reconnection in KH vortices does not contribute to the majority of the open flux. Joachim Birn discussed the energy budget during magnetic reconnection: how much goes into heating and does compression give irreversible heating? Andrii Lynnuk discussed how FTE motion over the dayside doesn't agree with anti-parallel or component reconnection model predictions. However, he did not consider shear flow. Katariina Nykyri showed results of her recently developed macro-scale MHD simulations of the KHI including magnetosheath velocity fluctuations at different frequencies and amplitudes. The frequency, amplitude and number of modes affect the growth of the KHI and when secondary reconnection in KHI vortices starts. Homa Karimabadi’s new 2D and 3D global hybrid simulations showed for the first time the generation of magnetic flux ropes and turbulence downstream of the quasi-parallel shock. Yonglijang Zhang showed (using FUV and particle observations) that under a long (~4 hours) and strong northward IMF Bz (> 20 nT), the polar cap was filled with discrete arcs (including proton precipitations a few to ~10 keV). Possibly double lobe reconnection created new closed field lines on the dayside and extended to the night-side causing the polar cap (open field lines) to disappear. Rick Wilder showed (using MHD Simulations with DMSP and SuperDARN observations) that faster lobe circulation in the summer hemisphere occurs during northward IMF. Results suggest that reconnection between the IMF and the lobe field be more common in the summer hemisphere, while winter hemisphere lobe flux remains largely stagnant. This leads to hemispheric asymmetries in the ionospheric potential that are not dependent on ionospheric conductivity. 3. Magnetosheath session: During the Friday session, a 6+year statistical study of THEMIS magnetosheath ion temperature observations was presented by Andrew Dimmock. Although a slight dawn/dusk asymmetry in temperatures was found (slightly higher temperatures along the dawn flank as compared to dusk), no significant change in asymmetry was observed when the large data set was filtered by solar wind speed or by IMF Bz. An observations-based study of magnetic field fluctuations in the magnetosheath was also presented. In this case, dawn/dusk asymmetry were more pronounced for slow solar wind as compared to fast solar wind. Filtering by IMF Bz resulted in much less dawn/dusk asymmetry of field fluctuations. Plasmaspheric plumes and their influence on physical processes at the magnetopause (the occurrence and rate of magnetic reconnection and the growth of Kelvin-Helmholtz instabilities) was also a major topic of this session. Studies of this phenomenon were presented by Hwang Kyoung-Joo and Brian Walsh. Lastly, a brief summary of observed high- speed jets in the magnetosheath and their influence on the magnetosphere was presented by Heli Hietala. These jets could be formed due to ripple-like bow-shock structures. The magnetosheath 5-year focus group final report will be delivered later. +-------------------------------------------------------------------+ | To broadcast announcements to the GEM community, please contact | | Peter Chi, GEM Communications Coordinator, at: | | | | | | Please submit your announcements in plain text or Word document. | | | | To subscribe the GEM Messenger, send an e-mail to | | | | with the following command in the body of your e-mail message: | | subscribe gem | | To remove yourself from the mailing list, the command is: | | unsubscribe gem | | | | GEM Messenger is also posted online via newsfeed at | | http://heliophysics.blogspot.com and | | http://www.facebook.com/heliophysics | | | | Back issues are available at: | | http://www-ssc.igpp.ucla.edu/gemwiki/messenger/ | | | | URL of GEM Home Page: http://aten.igpp.ucla.edu/gemwiki | | Workshop Information: http://www.cpe.vt.edu/gem/index.html | +-------------------------------------------------------------------+