Editor's Note: This issue contains two Focus Group reports from the Summer Workshop. More reports will appear in upcoming issues. Table of Contents ====================================================================== 1. Workshop Report: Workshop Report: Modes of Magnetospheric Response 2. Workshop Report: Substorm Expansion Onset: The First 10 Minutes ====================================================================== *************************** ** THE GEM MESSENGER ** *************************** Volume 21, Number 23 October 2, 2011 ---------------------------------------------------------------------- 1. Workshop Report: Modes of Magnetospheric Response ---------------------------------------------------------------------- Conveners: Robert McPherron and Larry Kepko The goal of the Modes of Magnetospheric Response Focus Group is the improvement of knowledge of the physical mechanisms that provide different dynamical modes of response of the magnetosphere to the solar wind. These include substorms, steady magnetospheric convection, sawtooth injection events, pseudo breakups, and poleward boundary intensifications. Due to the increased number of concurrent sessions driven by the joint workshop with CEDAR, the Modes FG held only one breakout session. It was well-attended, with good audience participation. Of the nine speakers, 5 were women, and the overwhelming majority of speakers were either students or young scientists. As usual for this focus group, there were a number of talks on SMCs and sawtooth events. Anna DeJong described a method to identify SMCs, using the AE indices. Her new algorithm identified 45 of 51 events found with satellite images, and identified a total of 2314 SMCs from 1997-2008. Jenni Kissinger presented statistical results of fast flows and flux transport during SMCs. Flows very rarely penetrate inside 15 Re during SMC. The results showed a diversion of fast flows during SMCs instead of the impact and pile-up at midnight as seen during substorms. Xia Cai reported on the relationship between sawtooth events and magnetic storms. She finds that most sawtooth events occur in a magnetic storm primarily in the main phase or at its peak development. She did identify a few events that seem to occur during very weak and steady Dst depression. Jian Yang described RCM-E simulations of SMC events. He reminded us of the pressure inconsistency problem and how it is necessary for a flux tube to have low entropy to penetrate to the inner magnetosphere after reconnection. He found that the best simulation of SMC had Bz in the tail larger than during substorms and the plasma sheet was thicker. Oliver Brambles described the effects of ion outflow on the magnetosphere convection mode using the MFLFM model, incorporating the Strangeway outflow formula. In general MHD simulations quickly converge on the SMC state when driven by steady solar wind. However, if oxygen outflow during the simulation exceeds some critical value the solution becomes periodic substorms. Delores Knipp compared the Poynting flux response during Steady Magnetospheric Convection and Sawtooth Oscillation Events, and identified significant (and unexpected) differences. The data appeared to agree with the Brambles result. Leila Mays described the geomagnetic response to solar wind structures during the recent solar minimum. She used Dst to define different strength storms and then related these to solar wind structures that caused them. She found that CMES are highly variable and that different parts of the CME may be responsible for the largest response in different CMES. Frederick Wilder suggested that in the electrojets there is a maximum current that can be carried, which can lead to a current driven (Farley-Buneman) instability. This could then be an ionospheric mechanism for polar cap saturation. Lasse Clausen described how changes in open magnetic flux can be tracked using the AMPERE constellation of Iridium satellites. Magnetic perturbations seen by the spacecraft define the location of region 1 and 2 field- aligned currents. Circles are fit to these and the magnetic flux within the circle calculated as a function of time. Loading and unloading of flux associated with substorms is extremely obvious. Additional work is required to establish precisely the location of the open-closed field line boundary relative to the Region 1 circle, but this technique promises to be a valuable resource in the future. ---------------------------------------------------------------------- 2. Workshop Report: Substorm Expansion Onset: The First 10 Minutes ---------------------------------------------------------------------- Conveners: V. Angelopoulos, A. Runov, S.-I. Ohtani and K. Shiokawa Overall FG objectives: Observations during recent and coming years are redefining the questions related to substorm phenomena allowing us to revisit the timing, location, onset mechanism and effects of the global substorm instability. The primary work of the focus group is observational. It relies on the abundance of new data from THEMIS, Cluster, ground based radars and other concurrent satellite platforms to study the details of the first few minutes before and after substorm onset, with the goal of identifying the physical process responsible for the avalanche of energy release during substorms and the roles and physical connections between the relevant processes at different parts of the magnetosphere. For example, is throttling of the magnetotail reconnection rate at the distant magnetotail related to pulsations or periodic injections in the inner magnetosphere? Detailed event studies, using the unprecedented spatial coverage in the magnetotail and magnetosphere along with high temporal resolution from ground measurements of aurora and magnetic field constitute the primary means of addressing such questions. Granted, however, that global MHD and localized simulations are rapidly increasing their ability to realistically model expansion phase phenomena, results of the detailed data analysis at multiple critical locations within the magnetosphere provide important testable constraints against which the models can be judged. The inner magnetospheric observations also constrain models and simulations of inner magnetospheric instabilities (such as ballooning mode, current disruption). The accurate timing and spatial information about auroral arcs and currents would constrain models of M-I coupling. Finally, the combination of accurate timing of onset phenomena (flows, dipolarization, arc brightening, injection, etc.), multipoint measurements, and excellent knowledge of ionospheric currents and aurora would enable challenges to the global MHD groups. Thus naturally the Substorm Expansion Onset Focus Group interacts closely with a number of existing focus groups (GGCM Modules and Methods, Metrics and Validation; Near Earth Magnetosphere: Plasma, Fields, and Coupling; Diffuse Aurora, Inner magnetosphere). Status: The FG has been operational since 2008 and has had three Summer GEM (and 3 pre-AGU mini-GEM) sessions. There are two more years remaining. A number of significant accomplishments can be recounted: A substorm database has been assembled and studied from various observational perspectives. These have resulted in a revised picture of the substorm onset process, whereby the phenomena at 20-40Re are closely linked to the inner magnetosphere and can, in many cases (perhaps all) trigger the avalanche of substorm energy, via the arrival of flow bursts. Notably, two aspects of the mid- to distant-tail phenomena have received new (perhaps renewed) attention: First, in the magnetotail dipolarization fronts have been measured to propagate Earthward before they collapse into the inner magnetosphere. Second, north-south arcs have been observed to emanate from (or close to) the polar cap boundary and propagate equatorward just prior to substorm onset. The two phenomena are likely manifestations of the same global process. Current research is focusing on the question of whether the phenomena observed in the near-Earth (at the dipole-like) region and near the equatorward-most arc at onset is the result of energy from the magnetotail or the manifestation of a new, local instability of an unstable pre-onset equilibrium. Organization: The FG has traditionally divided its observational reports into four general questions. These provide artificial boundaries but help organize the talks and manage our forums efficiently. They are: 1. Onset timing: observations/theory/simulations pertaining to where/when onset starts 2. Propagation: How do mid-tail onset signatures propagate to near Earth and to the ground? 3. Mapping: How do physical processes map, can we improve our understanding of coupling? 4. Transition region between stretched and dipole field lines: processes and evolution. This organization was successful over the first 2 years as the questions related to onset-timing, propagation direction and mapping were naturally addressed by the unique configuration of THEMIS tail- alignments. In 2011, thanks to a shift in community interests towards questions related to the interaction of fast flows with the inner magnetosphere and the nature of the inner magnetospheric instability, the following seemed a more natural organization of the questions at hand: 1. Pre-onset signatures/conditions/PBIs: Observations of free energy and instability drivers 2. Relative timing/mapping/propagation: High-resolution observations of onset phenomena 3. Transport mechanisms and relations to ionosphere: Drivers of transport and coupling Deliberations in 2011: 1. Pre-onset signatures/conditions/PBIs: Observations of free energy and instability drivers * Larry Lyons reported on observations (RISR-N, RANK polarDARN radar, and THEMIS ASI) of the poleward boundary intensifications being triggered by polar cap enhanced ionospheric flow phenomena in grouind radars. It is unclear what drives the flows to begin with – but prior reports of these phenomena by Moen and Lorentzen do exist. Lyons things that these polar cap flows are evidence of driven reconnection. * Ping Zhu reported on resistive 2D (X-Z) MHD/OpenGGCM simulations of a ky=0 mode. This is an axial mode, no structure in y-direction, and can cause initial loss of equilibrium on closed field lines at onset in the near-Earth tail, leading to subsequent tearing/reconnection. MHD modeling of PBI and N-S arc (Feb. 29, 2008 event) equatorward and westward motion are reproduced. But the onset is well equatorward of the open-closed boundary. A local minimum of PV^gamma is developed and observed to cause interchange instability. * Nishimura/Lyons presented new Champ-THEMIS array observations of the R1 and R2 current systems. They showed that the pre- existing arc is at the poleward edge of the R2 system, but inside the R2 system – arguing that this is evidence that the pre-existing arc is driven by the pressure gradient at the inner magnetosphere, and thus this is evidence of destabilization of the pressure system by a new substorm instability. * Kazuo Shiokawa (for Ryuho Kataoka) presented evidence that the pre-onset arc shows fine structures ranging from about 3- 4 km (3-min before breakup) to more than 10 km scale (1-min before breakup). This is again interpreted as evidence of possible destabilization of the arc by local pressure gradient or other local instability in the near-Earth plasma sheet. 2. Relative timing/mapping/propagation: High-resolution observations of onset phenomena * Jim LaBelle presented evidence that Z-mode converted waves are a tell-tale signature of onset. The waves arise from precipitation of 0.1-5keV electrons. This is proposed as a good T=0 observable of onset from afar (from poleward of the active aurora). * Michael Shay presented strong evidence that the energy release during reconnection in kinetic simulations is able to provide sufficient kinetic Alfven wave Poynting flux to power auroral acceleration via electron acceleration along the field lines. * Joachim Birn presented evidence that driven reconnection can result in bubble penetration to the inner magnetosphere. Through 3D MHD simulation of mid tail reconnection. He presented initial onset of reconnection followed within several min by onset of fast reconnection and entropy loss, which in turn was followed after ~2min by onset of SCW and penetration of low entropy to near tail, braking and diversion of flow. * Larry Lyons presented evidence that dipolarization fronts and associated flow bursts are associated with auroral streamers for 5 events in total of 6 events. Azimuthal separation of spacecraft may create apparent time difference of timing. * Russell Cosgrove showed a global correlation analysis among data of 24 magnetometers. The first disturbance has a broadband correlation signature, but later the pulsations coalesce to a few discrete frequencies. Correlation steeply increases and ceases, while power slowly grows, suggesting transition from linear to non-linear global instability as a whole magnetosphere-ionosphere system. 3. Transport mechanisms and relations to ionosphere: Drivers of transport and coupling * Xing, Xiaoyan showed THEMIS ion spectra which indicates that the ion injection at the dipolarization front causes enhancement of azimuthal pressure gradient a few min before the onset, and causes enhanced upward FAC and intensification of thin onset arc. * Hwang, Joo showed evidence of particle energization associated with dipolarization front (DF/BBFs). Fermi- acceleration makes bi-directional electrons. Then the electron beam causes whistler mode waves that energize particles at and around the DF. * Jiang Yang modelled the substorm injection boundary and related bubbles using 3D simulation. He showed that there is a two step flux enhancement: 1) high PV5/3 plasma ahead of bubble, and then 2) inside the bubble. * Yasong Ge discussed ion and electron features at the dipolarization front. In one case the ESA shows earthward flow, while the SST does not. In another case, both ESA/SST see the earthward flow. The dipolarization front can energize and reflect plasma sheet ions in field-aligned direction and cause proton aurora in the ionosphere. This is being simulated by Xuzhi Zhou. * Michael Shay (for Penny Wu) investigated how do the reconnection properties change by lobe density. Dipolarization front amplitude and reconnetion rate increase linearly with increasing Nps/Nlobe. Reconnection occurs faster for lower lobe density. * Feifei Jiang presented observations of the preexisting arc by THEMIS, FAST, and ground ASIs. She showed that the preexisting arc just before onset is located at the boundary between the dusk Region 1 and 2 current region, at the poleward part of the energetic ion precipitation and corresponding to the inverted-V region. * James Weygand showed reconstruction of equivalent ionospheric currents and of vertical current systems (in/out) from ground magnetometer arrays. The current systems were compared with Harang and pre-onset aurora locations for several events. They showed that the pre-onset aurora is equatorward of the Harang reversal and poleward of the peak in the R2 current system. This is consistent with the Nishimura results. * Vassilis Angelopoulos showed Artemis data that indicate tailward moving plasmoids correlating well with the onset of substorms. New information on timing can be obtained from the tail at lunar distances. Specifically the plasmoids seem localized in Y and their release is very closely related to the first few minutes of substorm expansion. They seem to be a critical part of the expansion onset process, not just its aftermath. * Stefan Kiehas showed Artemis plasmoid observations during substorms. By modeling individual flux-ropes/plasmoids/TCRs as observed by two spacecraft, and timing their propagation speed in comparison with the measured flow speed, they showed that the plasmoids are twisted, possibly by magnetic forces acting upon them during/after the release process. Summary, 2011: The Substorm FG questions have evolved considerably over the last year. Rather than asking where things start, the group is addressing now more the coupling of mid-tail reconnection (or high latitude/polar cap boundary activations) to possible precursors of these activations (in the solar wind and/or polar cap) and to possible consequences near- Earth. In the inner magnetosphere questions are related to the destabilization of an already marginally unstable (perhaps preconditioned by growth phase currents or pre-onset flow bursts) inner magnetosphere. In the magnetotail questions are related to what determines the generation of low entropy flux tubes that are most geoeffective (since they propagate closest to Earth): is it a driven or a spontaneous process. Finally Artemis data being so close to the mid-tail region where these phenomena originate (albeit mostly on the tailward side) may be able to provide critical constraints on these questions, especially since the ejecta (plasmoids, flows) are not modified by Earth's strong field and pressure forces. Studies such as that by Yasong Ge (UNH), Jun Liang (U Calgary), Jiang Yang (Rice) and Xuzhi Zhou (UCLA) who are looking at the proton aurora intensification at onset from ground, space, MHD and particle kinetic modeling, have arisen through GEM and epitomize GEM’s spirit. The rapid pace of discovery in many aspects of the substorm problem bespeak of a very dynamic field of study with an expectation of many more successes in the remaining 2 years. +-------------------------------------------------------------------+ | To subscribe GEM Messengers, 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 | | | | To broadcast a message to the GEM community, please contact | | Peter Chi at | | | | Please use plain text as the format of your submission. | | | | 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 | +-------------------------------------------------------------------+