*************************** ** THE GEM MESSENGER ** *************************** Volume 23, Number 27 September 5, 2013 ---------------------------------------------------------------------- 1. 2013 Workshop Report from The Magnetic Reconnection in the Magnetosphere Focus Group ---------------------------------------------------------------------- From: Paul Cassak (WVU), Andrei Runov (UCLA), and Homa Karimabadi (UCSD) 2013 marked the first year for the focus group (FG) on Magnetic Reconnection in the Magnetosphere. Four sessions were convened, including one joint session with the Transient Phenomena at the Magnetopause and Bow Shock and Their Ground Signatures FG, one joint session with the Substorm Expansion Onset: The First 10 Minutes FG, and two independent sessions. Each session had a number of short contributed presentations to guide discussion, including presentations both on observations and on simulations and theory. Summaries of each session follow, with a discussion of future plans at the end. Session 1 - Tuesday, June 18, 1:30-3:00pm (Joint Transient Phenomena/Reconnection session) The broad topics of the joint Transient Phenomena/Reconnection session were (1) the production, evolution, and consequences of flux transfer events (FTEs), (2) plasma transport into the magnetosphere due to Kelvin-Helmholtz instabilities (KHI) and magnetic reconnection, and (3) the effect on reconnection rate and particle acceleration due to strong asymmetries such as those habitually at the polar cusps and transiently from plasmaspheric drainage plumes impacting the magnetopause. There were two presentations on observational aspects of FTEs. Karlheinz Trattner (Lockheed Martin) showed observational evidence for a hemisphere effect for FTEs. Yaireska Collado-Vega (GSFC) presented Cluster observations showing FTE motion is strongly dependent on conditions in interplanetary space. Some FTEs move with a sunward component; most of these events had a strong By, which is consistent with predictions from Sibeck and Lin. There were four presentations broadly on plasma transport through KHI and reconnection. Binzheng Zhang (Dartmouth) showed LFM simulations that included a non-zero By. He discussed the entry of electrons into the cusp due to dayside reconnection, and that there are two different populations. There was a discussion on the relative importance of reconnection and KHI. Takuma Nakamura (Los Alamos) showed results of 3D particle-in-cell simulations of secondary reconnection occurring during KHI, emphasizing the necessity of 3D. The reconnection can disturb the vortex and generate turbulence, which enhances mixing and transport. Xuanye Ma (University of Alaska) discussed the interaction of KHI and reconnection for large magnetic shear. In particular, each affect strongly impacts the other, with KHI limiting the reconnected flux and modifying the dissipation region structure. A guide field decreases the growth of KHI. Finally, Shiva Kavosi (University of New Hampshire) showed global magnetohydrodynamic simulations with Open GGCM of the KHI using parameters obtained from observations by THEMIS. She showed that results from Open GGCM simulations and THEMIS observations are consistent. She also showed that the frequency and amplitude of the KH waves depend on the solar wind driving velocity-larger driving velocities generating KH waves with higher frequencies and larger amplitude. There were two presentations on reconnection affected by asymmetries in the cusp and due to plasmaspheric plumes. Rick Wilder (CU-LASP) showed Cluster observations of reconnection at the polar cusp, which is strongly asymmetric and has a significant shear flow. He observed the exhaust is predominantly on the magnetospheric side of the magnetopause, consistent with theoretical predictions of asymmetric reconnection. He also compared the observed outflow speed to theoretical predictions. Sun-Hee Lee (University of Alaska) presented observations of cold ions in magnetopause reconnection, which likely come from plasmaspheric plumes. The particles accelerate near the flow boundary, being picked up by the electric field and have a mass dependent energization. These particles are not seen on the magnetosheath side, indicating that they may play a very limited role in the reconnection process. The results presented in this session are important for the role of reconnection in solar wind-magnetospheric coupling, magnetospheric convection, particle acceleration, and for plasma transport into the magnetosphere. Session 2 - Wednesday, June 19, 10:30am-12:15pm (Joint Substorm Expansion Onset/Reconnection session) In the joint session with the Substorm group, Andrei Runov (UCLA) began with a discussion of what observers want to know from theorists: Is reconnection in the magnetotail inherently bursty (in reference to flow channels and dipolarization fronts) and what determines the duration of magnetotail reconnection? Why is reconnection mostly duskward (0 < Y < 8 R_E)? What is the relative role of reconnection and interchange? Joachim Birn (Space Science Institute) presented work on two related studies. The first addressed reconnection onset and energy conversion in a 2D magnetotail configuration in particle- in-cell (PIC) and magnetohydrodynamic (MHD) simulations. In each, external forcing produces two distinct current sheets which come together at onset, and the current in the y direction stretches to the earthward boundary and may be important for aurora. Entropy in the MHD sense is conserved well in PIC simulations during the growth phase and pressure is anisotropic in the PIC simulations. The second study studied energy fluxes in same simulations. MHD over-predicts the energy fluxes and the dominant flux out of the reconnection site is enthalpy. Reconnection in the distant tail was studied both observationally and numerically. Stefan Kiehas (Austrian Academy of Sciences) discussed observations of reconnection signatures near lunar orbit using ARTEMIS spacecraft. Beams were observed going Earthward, bidirectionally, and tailward, suggestive that reconnection occurs tailward of ARTEMIS while a near Earth X-line also was reconnecting. Yasong Ge (University of New Hampshire) showed plasmoids in the distant tail in global simulations. The plasmoids kick the far reconnection site out of the magnetotail. The structure of magnetotail transients was also addressed. Jim Drake (University of Maryland) argued that a pressure anisotropy disallows Petschek slow shocks in kinetic systems such as the magnetotail. Also, a model for the observed dip in B_z in dipolarization fronts as caused by the finite size of the front in the cross-tail direction was presented. Numerical tests using 2D PIC were presented, but 3D is necessary. Misha Sitnov (Johns Hopkins University) presented new 3D PIC simulations in a magnetotail configuration. These simulations produced flapping, reconnection, interchange, and the lower hybrid drift instability. These results underscore the importance of 3D in magnetotail dynamics. In a second presentation, it was shown that PIC simulations revealed slippage, which gives rise to a quadrupolar Hall field (unlike results from MHD). Session 3 and 4 - Wednesday, June 19, 1:30-3:00pm and 3:30-5:00pm The two general reconnection sessions were far-reaching. The first session focussed on dayside reconnection, with important physical questions related to its impact on solar wind-magnetospheric coupling and its observational signatures in the runup to the Magnetospheric MultiScale (MMS) mission. John Dorelli (NASA-GSFC) discussed global magnetospheric simulations including the Hall effect. It is prohibitive at this time to use realistic parameters for Earth, so the simulation parameters were appropriate to Ganymede. He found that the Hall effect has profound effects on magnetospheric convection, field aligned currents, and magnetopause structure when compared to MHD simulations. He also showed flux ropes near the cusp can have significant effects on dayside reconnection. Joe Borovsky (Space Science Institute) called for a better understanding of the local physics of reconnection for potential implementation into solar wind- magnetospheric coupling models. There was an interesting discussion on how to incorporate both local and global effects into such coupling functions. Colin Komar (West Virginia University), the CCMC Student Research Contest winner for magnetospheric research, discussed how to locate dayside reconnection sites by finding magnetic separators and determining which, if any, of many existing models explains where reconnection occurs. Interesting results were reported on how reconnection is changed in the presence of asymmetries that are common on the dayside. Michael Hesse (NASA-GSFC) presented results on changes to the dissipation region during reconnection including a surprising increase in the reconnection rate in the presence of a guide field. He also presented initial studies on the dissipation region physics in asymmetric reconnection where the electron pressure gradient is small, which differs from symmetric reconnection. Kittipat Malakit (Mahidol University) discussed the presence of a new electric field that only appears in asymmetric reconnection and may be measurable at the dayside. The electric field is due to finite Larmor radius effects when the dissipation region substructure is smaller than the Larmor radius. Stefan Eriksson (CU-LASP) discussed observations of a reconnection event in the solar wind that displayed a tripolar Hall magnetic field structure instead of the standard bipolar structure. This may be the result of having multiple nearby X-lines, and could presumably happen at the dayside. Brian Walsh (NASA-GSFC) discussed the effect on dayside reconnection of plasmaspheric drainage plumes, showing slower outflow when plume material is present. These studies are important for understanding observational signatures of reconnection expected to be measured when the MMS satellites are on the dayside. The overarching theme of the second session was kinetic scale physics, especially at the electron scale (in anticipation of MMS), though a number of other topics were discussed. A very interesting and important discussion arose on the subject of how electrons are heated in reconnection sites. Tai Phan (University of California- Berkeley) showed observations that electron heating in magnetopause reconnection events is proportional to the asymmetric outflow speed squared. This could explain why little heating occurs in the solar wind and why a lot of heating appears in the tail. In a collaborative study, Mike Shay (University of Delaware) showed simulations are consistent with the observations, with the cause being electrons that are accelerated by magnetic field lines slinging out of the exhaust. An alternate model of electron heating due to pressure anisotropy was presented by Jan Egedal (MIT). In this model, electrons are accelerated by a trapping potential. The scaling of the predicted heating is different in these two models, so whether or when either mechanism is dominant remains a topic of future study. On other topics, Joachim Birn (Space Science Institute) discussed magnetotail transients, including a study of how particles get accelerated in dipolarization fronts. Particles do not have to be right at the reconnection site to be accelerated. Amitava Bhattacharjee (Princeton) discussed the production of plasmoids during magnetotail reconnection, specifically the distribution of their sizes and their relation to plasmoids in other settings. Lars Daldorff (University of Michigan) discussed an effort to couple particle-in- cell (PIC) simulations with global magnetospheric simulations with BATS-R-US. A lively discussion on the challenges of accomplishing this goal ensued. Gabor Facsko (Finnish Meteorological Institute) discussed how disturbances in the solar wind can force magnetotail reconnection and can generate plasmoids. Finally, Yanhua Liu (University of New Hampshire) discussed how oxygen affects magnetotail reconnection, including the observations of counter streaming heavy ion distributions in PIC simulations and Cluster observations. Oxygen is accelerated by the out of plane electric field. Future Directions As can be seen from the breadth of topics discussed in the Reconnection FG sessions in 2013, both fundamental reconnection physics and applications continue to make strong contributions to the GEM community. In the second year of the Magnetic Reconnection in the Magnetosphere focus group coming up in 2014, two topics will be emphasized. One is dayside reconnection and solar wind-magnetospheric coupling. In particular, observational results and quantitative theoretical/numerical assessments of the impact of dayside reconnection on solar wind-magnetospheric coupling are encouraged. The second topic is kinetic signatures of reconnection in the runup to MMS, which is expected to take place not long after the 2014 GEM meeting. Electron scale physics, including heating and particle acceleration will be a topic of great import, as well as furthering knowledge on the observational signatures expect to be seen by MMS. +-------------------------------------------------------------------+ | The GEM Messenger is the electronic newsletter for the | | NSF GEM Program and Workshops. | | | | Editor: Peter Chi, GEM Communications Coordinator | | E-mail: | | | | To subscribe GEM Messengers, send an e-mail message to: | | | | with the following command in the body of your e-mail: | | subscribe gem | | To remove your e-mail address from the 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 ftp://igpp.ucla.edu/scratch/gem/ | | | | URL of GEM Home Page: http://aten.igpp.ucla.edu/gemwiki | | Workshop Information: http://www.cpe.vt.edu/gem/index.html | +-------------------------------------------------------------------+