*************************** ** THE GEM MESSENGER ** *************************** Volume 24, Number 32 October 11, 2014 ---------------------------------------------------------------------- 1. 2014 WORKSHOP REPORT: Tail-Inner Magnetosphere Interactions Focus Group ---------------------------------------------------------------------- From: Vassilis Angelopoulos (UCLA), Pontus Brandt (APL), John Lyon (Dartmouth) and Frank Toffoletto (Rice) The focus group had 3 breakout sessions on Tuesday, June 17 on a variety of topics related to the specific questions related to dipolarization fronts. Specifically speakers we asked to address 2 questions: (1) How is the formation of the substorm current wedge related to BBFs/dipolarization fronts? (2) What is the physics of the oscillations in the field and plasma seen ahead of the front? In addition to the 3 sessions reported here there was also a joint session with the reconnection focus group, the report for which can be found in the reconnection focus group report. Xiangning Chu looked at the poleward expansion of the aurora and its relation to the substorm current wedge in order to discriminate between two models for the poleward motion. One is a tail ward retreat of the flux pileup near the Earth; the other the change in mapping due to magnetospheric dipolarization. He studied in detail an event in Feb. of 2013 where there was THEMIS all sky data and the P3 and P4 satellites mapped to near the auroral arc. Each time the THEMIS satellites saw a flow burst, the arc on the ground brightened and made a small retreat Northward. The mapped arc position using a T96 model went from 10 RE to 60 RE in 20 minutes, requiring a speed in the tail much faster than the typical 50 km/s seen. By adding a substorm current wedge magnetic field model to T96, he was able to show good agreement with the mapped P3 and P4 positions and arc position on the ground. Thus, the magnetic dipolarization model is favored from this event. Joachim Birn discussed the field-aligned currents associated with BBF’s and the substorm current wedge. He broke down the currents in the large-scale wedge into a number of components: one associated with By on the sides of the BBF, another around the reduction of Bz at the head of the flow, another to dipolarization, and another from pressure buildup. He showed his simulation of a single entropy depleted flux tube to illustrate this picture. He noted, however, that his simulations show the simple picture with a single flux tube breaking up into multiple flow channels. In this case the single substorm current wedge is broken up into a number of “wedgelets”. The net effect of this collection of wedgelets is to somewhat broaden the overall substorm current wedge. Yan Song discussed the generation of field aligned currents and electric fields. She showed that their generation flowed naturally out of a formalism which directly concerned E and j, rather than the usual MHD approach which just really considers force balance. Bob Lysak discussed a simulation model he developed with coworkers at Minnesota and Univ. of Newcastle to study ULF waves in the inner magnetosphere, particularly to study how waves can mode convert. The simulation uses a dipole grid going from L = 1.5 -10 and follows both compressional and Alfven waves. The model has a height resolved ionosphere as the inner boundary condition. Bob showed preliminary results driving the code with a 50 sec period compressional wave located mainly in the equatorial plane. The wave was able to excite a plasmaspheric resonance mode, showing the global effects of an external driver on the inner magnetosphere and the mode conversion coming from the interplay of compressional between Alfven waves. Testuo Motoba studied the correlation between auroral beading and the activity in the plasma sheet. The beading has been shown to be conjugate in the two hemispheres, so it is logical to look for a drive in the plasma sheet. It is very difficult to find good satellite conjunctions because of the small spatial scale of the beads. He did find a sub-interval during a prolonged storm where he was able to identify pre-breakup signals in the satellite data in the inner magnetosphere that correlated with the auroral beading. Toshi Nishimura showed a connection between auroral streamers and sub- auroral proton aurora. For the event he studied THEMIS A was in the plasmasphere and showed ring current ions. THEMIS D was in the plasma sheet and observed fast flows and enhanced ion fluxes. THEMIS A showed a bursty build up of the ring current during this time. Auroral streamers mapped to the magnetosphere connected the phenomena seen at both spacecraft. During the storm there were continuous PBI’s and streamers only some of which made it to the equator-ward edge of the aurora. Those that did reach the edge were correlated with proton aurora that propagated into the sub-auroral region. Ying Zou showed the temporal linkage of localized polar cap structures that propagate to the open-closed boundary at typical speeds of 600 km/s. The linkage of the polar cap structures to PBI’s to streamers to, eventually, substorm onset seems to follow consistently from the data. Doug Cramer discussed his work in modeling the flux into the inner magnetosphere during CME and CIR driven storms. He has extended the work he did using the CRCM and Tsyganenko models by using the OpenGGCM simulation model to look at the how continuous or bursty the energy flux into the inner magnetosphere is. He ran OpenGGCM without a coupled ring current model and looked at the nature of the flux across a L = 10 boundary. He found that the flux is bursty for both CME and CIR storms with both inflow and outflow in the equatorial plane with about a 2 hour periodicity. The CIR storms showed a greater variance in the flux across the boundary. Xiaojia Zhang studied the relation of ECH waves to the diffuse aurora. ECH are one mechanism for the scattering into the loss cone. He used the Ovation model for a pattern of the ionospheric precipitation that was then mapped to the magnetosphere. He found that ECH is the dominant mechanism from the dawn side to near midnight. Frank Toffoletto presented two studies from Jian Yang. In the first, the effects on a thin arc from a N-S aligned streamer were studied using a narrow depleted channel in the RCM-E. The model was first preconditioned through a growth phase. Then a channel had a reduced PV? for 10 minutes over a 1/2 hour LT width was introduced. The resulting simulation predicts both east and west moving arcs with a higher speed to the W (~2 km/s) than to the E (~0.5 km/s). In the second presentation, the effects of field-line slippage were studied. The idea is that if plasma moves relative to its original position it changes the PV? distribution creating a bubble/blob pair. In the case studied, slippage was introduced near an auroral arc. The results were an enhancement of the arc. Shin Ohtani discussed the O+/H+ ratio in the plasma sheet. The ratio depends on position in the plasma sheet. It is not clear whether there is energy dependent energization or whether there might be a velocity filter effect in action. Christine Gabrielse gave two presentations. In the first, she looked at the statistics for ion and electron injections. She found a correlation between the injections and Al increases, Bz increases, flux pile-up, velocity flow bursts, and increased Ey. For a series of dispersionless electron injections the injections progress closer to the Earth and more dawnward. In the second presentation she modeled the injection process. In her earlier work she used a narrow channel with a constant, enhanced E and found acceleration and injection. In the current study she used overlapping Gaussians rather than a step function to get a rapid rise in E with a slower decay. Once again she got energization and injection, but now was able to explain the observed depletion of particles below the highest energies injected. Jacob Bortnik gave a progress report on his work to develop a self- consistent global model for the precipitating flux in the KeV range. His group is building a case-specific global, time-dependent chorus wave model, which will be linked to RAM-SCB, and the BATS’R’US MHD model. It will also include contributions from hiss. Estimates of the wave power will be obtained from inversion of the POES local precipitation measurements; these can then be mapped to RAM-SCB for a global picture. Slava Merkin discussed his work on studying resistive reconnection using a Cartesian version of the LFM code, LFMBOX. He studied 2-D equilibria relevant to tail configurations, one from Lembege and Pellat (LP) and another from Sitnov and Schindler (SS). The LP configuration should be stable to collisionless tearing while the SS - because of its enhanced Bz going tailward may be unstable. With zero resistivity, the SS configuration appears to be unstable to an ideal MHD instability, which may affect its stability to collisionless processes. Mike Wiltberger showed his current work with simulating flow channels using the LFM code. He simulated a range in solar wind magnetic field strength and clock angle, as well as using different ionospheric conductance models. He found that the BBF/flow channels appear in almost all cases although the do seem to be quantitative differences between cases. He also showed preliminary work on creating a statistical picture of the BBF’s using a superposed epoch analysis. Janet Green discussed her work to get clean data sets that can be used to study the development of the ring current and radiation belts. In order to be able study this effectively, the satellite data must be converted to phase space density. She discussed the issues with both the GOES and POES data in terms of proton contamination and general errors. The actual satellite data are now available in NETCDF format rather than the idiosyncratic original form. Jenny Kissinger showed data from the Van Allen Probes during the SMC phase of a storm. Chorus was seen all during the SMC phase. The RBSP data show that there was an injection before the SMC, During the SMC the flux level remained relatively high but was variable. After the SMC, the flux levels were much smoother. There was a general discussion of where the focus group should concentrate its efforts. Two areas came to the fore. Vassilis Angelopoulos suggested that the question of the linkage of the dayside to the nightside BBF’s and flow channels shown by the propagation of polar cap structures from the dayside giving rise to auroral streamers should be given high priority. There is no current explanation for how these structures form and how they ultimately produce BBF’s. There was an agreement to try to coordinate the dayside-nightside linkage with the dayside focus topic. Andrei Runov brought up the issue that most dipolarization fronts/ flow bursts never get close to the inner magnetosphere. Yet, the presence of these midtail phenomena seem to be strongly correlate with, for example, the build-up of the ring current. There was general agreement that more work needs to be done to study how the energy is transferred across this gap region. +-------------------------------------------------------------------+ | 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 | +-------------------------------------------------------------------+