*************************** ** THE GEM MESSENGER ** *************************** Volume 20, Number 28 October 5, 2010 ---------------------------------------------------------------------- 1. 2010 Summer Workshop Report: Tail Research Area ---------------------------------------------------------------------- From: Larry Kepko and Mike Henderson The following report summarizes the discussions held by the Tail Research Area Focus Groups at the most recent GEM Workshop in Snowmass, Colorado. *** Plasma Entry and Transport Focus Group From: Antonius Otto , Jay R. Johnson , and Simon Wing PET had three breakout sessions on Monday Jun 21, 2010. Overall, the sessions were well attended and two of the breakout sessions were oversubscribed. There was a good balance of observational and theoretical/modeling presentations. Session 1: Ion outflow effects in the plasma sheet Three Cluster O+ studies were presented. Observations of O+ outflow during storm and substorm in the magnetotail suggest that cusp was the source and that the southern hemisphere has higher frequency of O+ outflow, although the reason is not clear (Lynn Kistler). Evidence of O+ heating was presented and attributed to pressure (Jichun Zhang). The solar EUV radiation conrols H+ and O+ densities and consequently their density ratio (Chris Mouikis). Three Multi-fluid LFM (MFLFM) O+ outflow studies were presented. MLFLM with three combinations of Strangeway et al. [2005] and [2009] relationships show that O+ outflow moves tail X-line, which is attributed to increased pressure due to O+ (Oliver Brambles). In MFLFM, higher O+ decreases polar cap potential, increases tail Vx, and higher tail width (Katherine Garcia). Moreover, O+ outflow leads to more unstable KH on the flanks and reduces the magnetic activity (Slava Merkin). KH simulations in Saturn's magnetosphere suggest that mass increase leads to lower growth rate (Peter Delamere). Reconnection due to heavy ions may lead to dawn- dusk asymmetry as observed in Wing et al. result (Jay Johnson). Due to the oversubscription of the session, Simon Wing's presentation on field-aligned current was voluntarily withdrawn. Session 2: Constraints on the plasma sheet entry and transport An MHD simulation on bubble transport in the magnetotail was presented and how the transport is affected by the shape and size of the bubble. (Joachim Birn). Apparently Te/Ti ratio is conserved during magnetosheath entry into the plasma sheet, despite the fact that the entropy is not conserved (non adiabatic process) (Joe Borovsky). LASK simulation examined the storm time the H+ density, H+ energy density, O+ density, and O+ energy density (Vahe Peroomian). The same simulation shows that IMF field line can get intertwined with closed field line in the magnetotail. LFM simulations show flows channels in the magnetotail, which are manifested as BBFs during southward IMF and "fingers" during northward IMF (John Lyon). The same study shows that an entropy profile that is similar to the empirical profile (Joe Borovsky) after southward IMF turning. An event of bubble propagation in the magnetotail and its signatures in the ionosphere were observed. Cooling of the ion hot component and dawn-dusk temperature asymmetry were modeled and compared with Wing et al. observations (Colby Lemon). PBI's flow in the polar cap and Harang reversal are linked to the plasma sheet plasma bubbles (Larry Lyons). Perpendicular flow fluctuations are observed to be larger than the average values; the tail transport is determined to be competition between convection and diffusion (Chih-Ping Wang). Large entropy increases associated with slow shocks were examined with energy conserving MHD simulations (Antonius Otto). Session 3: GEM challenge John Lyon presented successes and difficulties with RCM – MHD coupling. For example, coupling MHD with RCM can provide R2 current, but the convection pattern is unusual. MHD-RCM field aligned currents show small pearl structures. One of the difficulties is that slow flow is violated at the MHD – RCM boundary. Challenges were introduced – (1) How much entropy can increase in reconnection and the role of slow shocks; (2) Why the Ti/Te ratio seems to be conserved; and (3) Entropy changes associated with the collective behavior of bursty bulk flows. *** Near-Earth Magnetosphere: Plasma, Fields and Coupling Focus Group From: Sorin Zaharia (szaharia at lanl.gov), Stan Sazykin (sazykin at rice.edu) and Benoit Lavraud (Benoit.Lavraud at cesr.fr), Focus Group co-chairs: The Near-Earth Magnetosphere focus group held 3 breakout sessions at the 2010 GEM Summer Workshop in Snowmass, CO. The main goal of the focus group is to improve our physical knowledge and modeling of the near-Earth magnetosphere and its coupling with the outer magnetosphere. The focus group is coordinated by Sorin Zaharia, Stan Sazykin and Benoit Lavraud. The three focus group sessions, held on Wednesday and Thursday (06/23- 24) featured short presentations and discussions related to the following scientific research topics: Session 1: Inner-outer magnetosphere coupling: - Effect of depleted entropy bubbles on the inner magnetosphere as obtained from a 3D MHD simulation (J. Birn) - Coupling of Rice Convection Model (RCM) with a global MHD code: interchange-related dynamic flows and oscillations; plans to modify RCM to include inertial terms (F. Toffoletto) - Effect of ion outflow on ring current (through plasma sheet density/temperature, cross polar cap potential drop and ion composition) (D. Welling) - 1-way coupling of the BATS-R-US global MHD code with the Comprehensive Ring Current Model (CRCM) and Radiation Belt Environment (RBE) codes; importance of electric field self-consistency (Q. Zheng) - Specification and effect of plasma properties at geosynchronous orbit in RCM; ring current dependence on ionospheric conductivity (M. Gkioulidou) Session 2: Observational studies and empirical models: - Empirical magnetic field modeling – modification of the T96 model by adding a substorm current wedge; importance of magnetic field model for M-I coupling (G. Lu) - Results from the TWINS mission; stereoscopic ion inversion providing pitch angle information; validation vs. THEMIS data; presentation of available TWINS data products (J. Goldstein) - Exploring plasmaspheric subcorotation through radar observations (Blackstone –mid-latitude) of westward flows on field lines mapping into the plasmasphere (L. Claussen) Session 3: Interaction between plasma and fields in the near-Earth magnetosphere - coupling between different elements in numerical models (plasma, electric and magnetic fields): - Two presentations accompanied by spirited discussions on comparisons of different formalisms for studying plasmas: MHD, guiding center and Vlasov theory (R. Strangeway); differences between single-fluid MHD and kinetic formalisms, and what one needs to add to MHD in order to reproduce inner magnetosphere physics (S. Zaharia) - Effect of self-consistency/stretched magnetic fields on ring current morphology and dynamics (V. Jordanova; R. Ilie) - Importance of self-consistent treatment of particles and fields in the storm-time inner magnetosphere, explored through comparison of simulated and observed magnetic intensities and ion plasma parameters from GOES, Polar, LANL (M. Chen) - Simulation of Steady Magnetospheric Convection (SMC) event with RCM- E needs to be driven with depleted flux tubes in order to reproduce THEMIS observations (F. Toffoletto) The second half of the 3rd breakout session was devoted to a community discussion on future plans for Focus Group activities. A list of tentative topics emerged regarding breakout sessions at the 2011 GEM Summer Workshop: 1). Simulate events in the GGCM Modeling Challenge/calculate observable metrics; 2). Obtain fields/plasma conditions with applications to radiation belts/inner magnetosphere waves; 3). Obtain electric field maps with applications to plasmasphere physics; and 4). Conclude Phase 1 of the Near-Earth Magnetosphere Challenge, involving the simulation of an idealized geomagnetic storm. The above topics will be further refined at a Mini-workshop session that the focus group intends to organize before the 2010 AGU Fall Meeting in San Francisco. Some of the sessions above could be organized as joint sessions with other relevant focus groups. Finally, the discussion steered toward ideas for wrapping up the focus group activities in 2012. Starting from the focus group proposal approved by the GEM Steering Committee, several possible deliverables as the outcome of the focus group were discussed, to be conveyed through various media: a final report or a review paper (with individual papers attached), as well as publication on the Web; these deliverables would include: - A description of progress in inner magnetosphere physics undergone under the focus group - A list of inner magnetosphere models, improved physics features and couplings developed - Physics results from the Near-Earth Magnetosphere Challenge; a comparison of different models and a discussion of the effects of different physics features through simulating both an idealized (Phase 1) and real (Phase 2) geomagnetic storm. *** Modes of Magnetospheric Response Focus Group 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. The Modes of Magnetospheric Response held three breakout sessions this past meeting, loosely organized around themes of non-linear coupling, sawtooth events, and the magnetospheric mode response to the extreme solar minimum. In the first breakout, non-linear coupling, we were interesting in exploring how aspects of non-linear coupling affected or determined the response mode. Speakers and topics included: Bob Weigel, who expressed the idea that a quantitative understanding of solar wind coupling should begin with linear prediction to obtain a basic understanding of how much can be explained without more complex models; Delores Knipp showed unexpectedly large increases in ionospheric mass density that have been found in the declining phase of cycle 23; Jennifer Kissinger presented an overview of SMC; Larry Lyons presented evidence that IMF fluctuations during high-speed streams appear to be an independent driver of convection as measured by radars; Jennifer Kissinger suggested that SMC and stream I/F are highly correlated in the declining phase with SMC occurring after the stream interface; Bob McPherron estimated the viscous interaction impulse response function and showed that it explains about 5% of AL variance. The second breakout sought primarily to establish the observational features of sawtooth events. Mike Henderson presented an overview of sawtooth injection events developing the thesis that they are simply very large substorms during steady strong driving, and do not represent a fundamentally different mode of magnetospheric response. One of the defining characteristics of sawtooth events are injection signatures that appear sunward of the terminator. During the spirited discussion, it was suggested that rather than representing a fundamentally different mode of reconfiguration, the sawtooth injection region was a 'standard' injection that was rotated towards the dusk terminator. Joe Borovsky took the counter position and argued that these are a distinctively different state of the magnetosphere. He suggests that there is a problem in the definition and selection of events. The final breakout session encouraged presentations covering the magnetospheric response, state of the magnetosphere, and solar wind energy transfer during the extreme solar minimum. Dan Baker showed SAMPEX data indicating that relativistic electrons vanished from the magnetosphere during the end of this last solar cycle. He tied this to the solar wind velocity dropping below 500 km/s for an extended interval. Howard Singer summarized the Galaxy 15 failure that occurred during an extremely large substorm produced by a weak CME and magnetic storm. Suzie Imber determined the probability of earthward and tailward TCR motion from Themis data as a function of distance down the tail, and concluded that these are equal at 30 Re much further than previous estimates of the location of X-line. Tung-Shin Hsu (presented by Bob McPherron) showed that the recurrence rates and intensity of substorms in rising and declining phase of solar cycle differ substantially. *** Substorm Expansion Onset: The First 10 Minutes Focus Group From: Vassilis Angelopoulos (Vassilis at ucla.edu) Kazuo Shiokawa (Shiokawa at stelab.nagoya-u.ac.jp) Andrei Runov (arunov at igpp.ucla.edu) Shin Ohtani (Ohtani at jhuapl.edu) The group had four separate sessions to discuss the following topics Topic 1: Onset timing: observations/theory/simulations Topic 2: How do midtail onset signatures propagate to near Earth and to the ground? Topic 3: Ground-Space Mapping of Physical Processes Topic 4: Substorm processes near transition between stretched and dipole field lines All presentations in this focus group were summarized into a matrix showing correspondence of each observation/model result to various substorm-onset physical models whether it gives positive or negative supports of the models. The matrix is available at the GEM Wiki page (http://www- ssc.igpp.ucla.edu/gemwiki/index.php/FG12._Substorm_Expansion_Onset:_Th e_First_10_Minutes). 1. Onset timing: observations/theory/simulations This session addressed the following problems: 1. The substorm onset timing as determined from multiple satellites, 2. Determination of the location of the first energization in the magnetotail, 3. Determination of the propagation time delays of the signal from the tail to the ground. Pre-onset and onset auroral forms, visible in THEMIS all-sky images, obtained during a set of isolated substorms were discussed. The sequence, including pre-onset polar boundary intensification (PBI) was reported for a large number of isolated substorms (Y. Nishimura). The time delay between the PBIs and substorm onset was reported to be up to 5 - 10 minutes. It was noted, that PBIs are not necessarily associated with the near-Earth reconnection, but may be caused by distant tail reconnection. New analysis of THEMIS observations during Jan 29, 2008 and Feb 2, 2008 substorms, reported earlier by A.T.Y. Lui and S.B. Mende, respectively, showed that in the coordinate system, rotated with respect to Y GSM in order to account the solar wind Vz, variations in magnetic field and plasma velocity, contrary to previous conclusions, indicate signatures of reconnection prior to auroral onset (V. Angelopoulos for J. Lui). The timing was found to be consistent with fast magnetosonic wave propagation time. Results of statistical timing analysis of cumulative magnetic flux transfer in the plasma sheet with respect to auroral and Pi2 onsets were reported (V. Angelopoulos for J. Lui). The results show an increase of flux transport in the tail ~1 min prior to the Pi2 onset. Onset signatures on MF radio waves coming from poleward arc were reported (J. LaBelle). These signatures can be an indicator of PBI. Their spectra show patchy structure and group delay with a time scale of 0.1s, giving F-region density profile. SuperDARN (7s resolution) show Pi2 oscillation (4.5-6mHz, amplitude=~50m/s) at subauroral latitudes (J. Baker). Recent progress and problems in construction of substorm timing database were reported (C. Gabrielse). Error bars for Pi2, AE, Bz, Vx, flux, and Ey are now added. Data need to be binned with respect to MLT distance from the substorm meridian. Theoretical considerations of momentum transfer via Alfvenic interaction from magnetopause into the magnetosphere were discussed (Y. Song). It was suggested that during the growth phase the tailward force in the plasma sheet balances with earthward JxB force. Sudden change of solar wind condition may terminate the tailward force and then the earthward force excess initiates substorm. Multiple onset corresponds to multiple localized Alfveninc interaction at the plasma sheet and breakdown of the frozen-in condition. 2. How do midtail onset signatures propagate to near Earth and to the ground? The session discussed 1. Physical mechanisms of energy release in mid-tail and near-Earth plasma sheet and their possible relationships; 2. The role of magnetotail transients (BBFs, dipolarization fronts, flux ropes, PVgamma-depleted tubes, transient FACs, etc…) in energy and mass transport during substorms; 3. Mechanisms of particles energization and injection; 4. Physical constrains for the plasma sheet-ionosphere communication. THEMIS observations during the March 1, 0155 UT substorm suggested that mid-tail reconnection triggered an instability in the near-Earth plasma sheet (A. Runov). The time delay between the very first signatures of reconnection and first signatures of the near-Earth plasma sheet instability was reported to be 5 min. The multi-point observations of dipolarization fronts showed that they are thin boundaries separating ambient plasma sheet and energetic plasma, intruded into the near-Earth plasma sheet (A. Runov). Formation and earthward propagation of dipolarization fronts in the course of a substorm was shown in the event-oriented global MHD simulations (Y. Ge). This indicates that although the thickness and structure of the fronts are dictated by kinetic processes, their origin may be described using the MHD-approach. THEMIS observations demonstrate an increase in 30 – 500 keV particle fluxes (both ion and electron) at the fronts. Thus, the dipolarization fronts are important agents in context of energy transport and particle energization during substorms. Role of PBIs as precursors for substorms was discussed based on THEMIS ASI observations (S. Mende) and MHD simulations (P. Zhu). The THEMIS ASI observations suggest that PBIs are indeed often observed ahead of auroral substorm onset, however, they are not necessary for substorm development. The event-oriented MHD modeling reproduced PBIs and their equatorward motion. The model PBI, however, was located equatorward of open-closed field lines boundary. An origin of the PBI in the plasma sheet is to be established. The particle-in-cell simulations of reconnection showed generation of kinetic Alfven waves (KAWs) which may carry 0.001- 0.09 erg/sm2/s energy at a distance of 20 RE downtail (M. Shay). In the ionosphere, it corresponds to 1-10 erg/cm2/s, which is sufficient to create visible aurora. A scale of this structure, mapped onto the ionosphere, is of a few hundreds up to a thousand kilometers. Propagating at a velocity of 1000 km/s or more, the KAWs may establish a connection between plasma sheet and ionosphere in time scale of a few tens of seconds. This may explain the 70 – 90 s-time lag between reconnection signatures in space and aurora, reported recently (e.g., Angelopoulos et al., 2008, Gabrielse et al., 2009). 3D MHD model of substorm suggests the combination of fast reconnection and ballooning instability in the course of substorm development (J. Birn). The simulation shows that the ballooning instability may increase a speed of reconnection outflow and plays an important role in penetration of reconnected flux tubes into the near-Earth plasma sheet. Results of MHD comprehensive MHD modeling also suggest that equatorward-moving aurora may be caused not only by earthward fast flow, but also by Alfven wave propagation and total pressure fluctuations (B. Lysak). Analysis of simultaneous measurements of the waves in PiB range on gound and in space indicates a clear relation between them: PiB observed on the ground, GOES, and THEMIS corresponds well (M. Lessard). Time delay from THC, THD, THE, GOES12, and South Pole is within 2 minutes, from THC first to South Pole last. Earthward fast flow caused compressionl PiB that is transferred field-aligned Alfven waves to cause Alfvenic aurora at the onset. (both reconnection and near-eath instability can make Alfven waves). 3. Ground-Space Mapping of Physical Processes In this session we discussed the mapping of substorm-related ionospheric signatures/structures to the night-side equatorial plane. It was reiterated that the field-line mapping requires extreme caution. The improvement of the adaptive time-dependent field-line model was reported, which shows, for an example event, that the auroral onset can be mapped to 22-26 RE down the tail instead of 15 RE (Kubyshkina/Angelopoulos). It was also discussed that because of the stretched configuration of tail magnetic field, large-scale FAC sheets on the night side can be mapped to completely different parts of the magnetotail. Whereas the R1 current is mapped to the flanks, R2 is mapped to the midnight sector of the near-Earth plasma sheet, and accordingly, the Harang discontinuity mapped to the equator extends in the radial, rather than the azimuthal, direction (Lu). A few different approaches were reported, which addressed mapping by comparing ionospheric signatures with in situ measurements in the plasma sheet. One approach is to map the front of the auroral streamer to the satellite location when the satellite observed a fast plasma flow in the plasma sheet (Nishimura & Xing). In one example event one THEMIS probe observed a fast flow at x = -11 RE when an auroral streamer was heading to the Harang discontinuity, which was followed by a breakup (Nishimura). The result suggests that the onset location as well as the Harang discontinuity was inside the field line on which the satellite was located. However, caution needs to be exercised in discussing the radial distance since the satellite is often located off the equator. A similar approach was also reported for particle precipitation. The precipitation energy spectrum measured by DMSP and the energy spectrum of the plasma-sheet plasma measured by THEMIS agree best for electrons when the equatorial footpoint of DMSP is close to the THEMIS probe location in MLT, but such a tendency was not clear for ions (Gabrielse). Another approach was to use the (empirical) relationship between proton aurora intensity and proton precipitation for locating the satellite footpoint in the 2D proton aurora image based on the satellite observation of proton flux in the loss cone in the plasma sheet (Spanswick). The general morphological mapping of onset arc was also discussed. The onset arc tends to be located at the poleward edge of the proton aurora (Donovan). This is consistent with the fact that the precipitating proton flux in the downward R2 current is smaller than that in the upward R1 current by almost an order of magnitude (the b2i boundary can be found in the middle of R2 currents) and that the most equatorward auroral acceleration very often takes place at the equatorward edge of the upward R1 current (Ohtani). 4. Substorm processes near transition between stretched and dipole field lines This session is focused on the temporal and spatial transition from stretched to dipole field lines at substorm onset. THEMIS P3/P4/P5 (apogee of 10-12 Re) have surveyed this region since 2007 and will make more focused multi-satellite measurements with separations of 100-3000 km in 2010-2012 together with the conjugate ionospheric measurements by optical instruments, SuperDARN radars, magnetometers, and riometers. During this session, Xiaoyan Xing showed that the azimuthal pressure gradient at the substorm growth phase estimated by two THEMIS satellites shows development of sharp gradient a few min before onset corresponding to upward field-aligned current. Ping Zhu showed using the Open CCGM model for a spatially-periodic black auroral event on February 22, 2009, that the plasma sheet become (interchange) unstable at highly-stretched transition region at pre-onset phase. Vadim Utritsky (presented by Eric Donovan) showed that east-west wave- like structure on the multiple onset arc show different propagation at three neighboring arcs, suggesting distant reconnection (poleward arc) initiate ballooning instability (wave structure in the equatorward arc) in the inner magnetosphere. +-------------------------------------------------------------------+ | 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 | +-------------------------------------------------------------------+