*************************** ** THE GEM MESSENGER ** *************************** Volume 20, Number 25 September 22, 2010 ---------------------------------------------------------------------- 1. Summer Workshop Report: Dayside Research Area ---------------------------------------------------------------------- From: Jean Berchem and Karlheinz Trattner The following report summarizes the dayside science discussions held during the 2010 GEM meeting in Snowmass, Colorado. This meeting marked the beginning of two new focus groups: the Magnetosheath and Dayside Field-Aligned Currents and Energy Deposition (also part of the Magnetosphere-Ionosphere Coupling research area) and the conclusion of the Cusp Physics focus group. The final report of the Cusp Physics will appear in another GEMstone issue. *** DAYSIDE-1. Cusp Physics FG6 Chairs: Karlheinz Trattner , Nick Omidi and David Sibeck The GEM Focus Group on "The Cusp" has come to an end this year. With 12 confirmed speakers distributed over two sessions this Focus Group showed a continued strong interest throughout the community with many interesting topics. It was the ultimate goal of the workshop to enhance our understanding of the cusp physics, its coupling to other parts of the system such as the bow shock, magnetopause and the ionosphere and the important role it plays in dayside particle transport and energization. The Cusp session covered the following subjects: Interactions of FTE's with the cusp David Sibeck reported on an ongoing project about FTE motion towards the cusp. Hybrid simulations are used to determine if events generate density variations in front of an FTE and subsequently cause fast or slow shocks as discussed by Sonnerup. Only fast moving events exhibit wakes (slow mode density enhancement), which should be visible on Cluster in front of fast moving FTE's as the satellites cross the magnetopause. Early in life an FTE starts out below Mach 1. It subsequently speeds up to a sonic Mach number of ~4. However, the FTE never gets into the fast (or slow) shock regime, by staying below Alfven Mach number 1. Nick Omidi presented 3D hybrid simulations of FTE interaction with the cusp and showed that as in the 2.5-D simulations, when an FTE enters the cusp, a secondary magnetic reconnection takes place. The resulting reconnection jets inject plasma into the magnetosheath and the cusp with the latter leading to density enhancements in the cusp. Plasma transport into the cusp Pat Newell reported on DMSP merging cusp bursts, and showed auroral observations from the Polar UVI instrument including data from two DMSP satellite crossings at local noon during that event. The event is driven by southward IMF conditions. The DMSP satellites detected two large Alfvenic electron bursts, one located at the poleward edge of the old cusp location and one at the equatorward edge of the new cusp location. Associated flow bursts contributed a significant fraction of the typical cross polar potential. Ion observations which showed low energy cutoffs revealed details of the timing sequence. Steve Petrinec presented a study addressing energetic particle transport into the cusp in energetic ions near the magnetopause reconnection site. Steve started his presentation with observations from the IBEX satellite. The IBEX satellite was launched to image the edge of our solar system, the termination shock, in neutral atoms. However, IBEX can also be used to image charge exchange with the geocorona in the cusps and at the subsolar point where the strongest fluxes of neutrals have been observed. To investigate energetic ion transport into the cusp, Steve used THEMIS observations near the reconnection site at the magnetopause and discussed an event to determine if shock accelerated energetic ions can make it into the magnetosphere, and subsequently into the cusp. The quasi-parallel bow shock during this event was located in the northern hemisphere and THEMIS showed energetic ions streaming in from the bow shock when the satellite was located north of the reconnection site. No energetic ions are detected at THEMIS when the satellite is located south of the reconnection site since the reconnection site cuts off the access to the northern hemisphere quasi-parallel bow shock region. Hyun Conner used MHD codes to reconstruct cusp ion structures observed by satellites and presented simulations results on cusp structure during southward and northward IMF. She found that the observed model MHD cusp structures depend strongly on the chosen virtual satellite orbit. Tom Guild presented high-altitude ion dispersion signatures observed with TWINS. The plasma instruments onboard the TWINS satellites in a highly elliptical orbit show isolated ion energy dispersions in the high altitude cusp on lobe field lines. Tom wants to determine if flank processes can account for the observations (e.g., Kelvin- Helmholtz) and if the dispersions are consistent with cusp injections. Energization of ions in diamagnetic cavities Katariina Nykyri's presentation on cusp diamagnetic cavity (CDC) structure fluctuations and origin of high-energy particles covered several research topics within the Cusp Focus Group, also addressing the origin of waves observed in the cusp and the source region of cusp energetic particles. Katariina investigated a Cluster cusp crossing which showed an extended CDC and energetic ions and electrons by using Cluster data and MHD simulations. The Cluster data are used to place the satellite within the MHD simulation frame. Katariina found that electrons in the CDC are trapped within the CDC which favors local acceleration. Most of the wave power is at low frequencies. However, most of the waves observed in the CDC are encounters with the boundary of the cavity. Katariina suggested a couple of observational features to be answered in future studies by various groups interpreting energetic particle data in the cusp. These questions include (a) Ion flux drops off as a function from distance to the cavity boundary, (b) High energy ions with ~180 degree pitch angle on magnetosheath field lines (c) Observed pitch angles for energetic electrons and (d) High energy particle fluxes drop sharply at the magnetosphere boundary. Brian Walsh investigated Cluster data for his study on energetic pitch angle distributions in the exterior cusp. Pitch angles of energetic electrons observed by Cluster in the cusp peak at 90 degrees. These observations are used to model pitch angle scattering in the cusp by assuming random polarization, random direction of propagation, a set spectral length and a set correlation length. His model also shows that the energetic electrons in the cusp behaved adiabatically and peak at 90 degrees. Future studies will expand this model to use ions. Ted Fritz presented the work of an extensive statistical study by John Niehof on CDC and CEP correlation study. The study is based on Polar data in the cusp. Out of 2117 satellite passes, 1192 cusp crossings were observed. In this cusp survey 734 CDC and 970 CEP events were recorded. Of those 681 cusp crossings showed CDC and CEP events. John concluded that CDC and CEP are directly related. Other source regions for CEP ions discussed in the literature are the quasi-parallel bow shock and magnetosphere which were also discussed in the survey but showed no significant correlation. Julia Pilchowski reported on particle acceleration in CDC for southward IMF. Julie uses test particles in an MHD simulation to model CDC and their characteristics. The simulation model was set for southward IMF and uses electric and magnetic fields from local cusp simulations. Test particles are launched within the cavity and remain trapped for 50 minutes. The maximum energy gain reached by the ions is 70 keV while the maximum energy gain reached by electrons is 40 keV. The particle movement within the CDC is an oscillation between the boundaries (gyration and drift). *** DAYSIDE-2. The Magnetosheath FG Chairs: K. Nykyri and S. Petrinec The Magnetosheath FG had its first session at the GEM meeting on 23rd of June 2010. The session held five oral presentations, a planning session and one poster presentation on Thursday 24th. The organizers had asked the participants to focus their presentations around three main categories: 1) Large Scale Structure of the Magnetosheath, 2) In- situ Magnetosheath Physics and 3) Magnetosheath Impact on the Magnetosphere. Large-scale structure of the magnetosheath and surrounding regions Merka et al. used a 'machine learning technique' (SVRM) to model the outer boundary of the magnetosheath. Model inputs include solar wind parameters and dipole tilt angle of the magnetosphere. Model is trained on a large subset of observations, and tested against a separate subset of observations. This method is to be used to aid in the empirical understanding of the large-scale configuration of the outer magnetosheath boundary. Yongli Wang used the same 'machine learning technique' described in the previous presentation to model the magnetosheath. Similar model inputs as for the bow shock. This method is to be used to empirically model of the large-scale configuration of the magnetosheath region. Michael Schulz developed an orthogonal coordinate system for the magnetosheath. The motivation for developing this coordinate system is to create analytic streamline models for a general class of magnetopause shapes. This is to aid in the analytic understanding of the large-scale configuration of the magnetosheath. Magnetosheath processes and impact on the magnetosphere Nick Omidi presented some observations in the magnetosheath that show there are regions of depressed magnetic field associated with increased fluxes of energetic particles. Nick's 2D global hybrid simulations were able to capture these phenomena. Observations and simulations indicate that these regions are more likely during small IMF cone angles, when the Q-|| region of the bow shock is close to the subsolar location. These regions could alter the plasma entry into the magnetosphere. Jan Soucek reported that Soucek et al. (2008) have found that the mirror mode instability changes character (or, evolves) with distance from the bow shock. Near the bow shock, there are many instances of quasi-sinusoidal compressional magnetic waves. Further from the bow shock, there are more 'peaks' (i.e., occasional large compressions superposed on a background level). Closest to the magnetopause, there are almost no quasi-sinusoidal compressional magnetic waves; only 'peaks' and 'dips'. The results of this study have important implications for the heating and anisotropy of the magnetosheath plasma; and how the mirror mode instability can potentially affect plasma entry into the magnetosphere e.g. change reconnection rate at the magnetopause. Alexander Sjogren presented initial results of the statistical study of magnetosheath temperatures (measured by THEMIS spacecraft) vs. solar wind conditions. The goal is to study whether the dawn-side magnetosheath is statistically hotter than the dusk-side flank for the Parker-Spiral IMF and vice versa because the location of the quasi- parallel bow shock changes. These initial results did not show any clear trend. The work is continuing on this in order to address if the plasma sheet temperature asymmetry could partly be generated by initial asymmetry present already in the magnetosheath. Future activities Planning was undertaken for next year's joint meeting with CEDAR, and for the future efforts of this focus group. In particular it was discussed how it would be beneficial for the magnetospheric physics and CEDAR community if the magnetosheath focus group activities would results in a statistical spatial map of magnetosheath properties for different IMF and solar wind conditions such as turbulent properties of the magnetosheath. Seed turbulence in the magnetosheath has impact on transport across the magnetopause by affecting growth rates of various instabilities such as Kelvin-Helmholtz and tearing-mode. Correlation studies between different geomagnetic indices and spatial distribution of magnetosheath properties would be useful in this effort. The focus group plans to utilize the NASA web-meeting interface offered by David Sibeck to coordinate activities for next summer's joint GEM-CEDAR workshop. *** DAYSIDE-3. Dayside Field-aligned currents and Energy Deposition FG Chairs: D. Knipp , G. Crowley , S. Eriksson , and R. Lopez The goals of the Dayside Field-aligned currents and Energy Deposition (FED) Focus Group goals are: Discover/Explain the relation between enhanced dayside field-aligned currents, their sources in the solar wind and the impacts in the ionosphere-thermosphere system. FED activity status As of the summer 2010 GEM meeting, the FED Focus Group had been functioning for 6 months. The FG was established to address the occurrence of anomalous thermospheric density signatures that seem to be associated with interplanetary shocks and large in-the-ecliptic interplanetary magnetic field (IMF) values. These often, but not exclusively, occur while the IMF BZ is positive. New Poynting flux data from the DMSP F-15 satellite suggest extreme localized field aligned currents are playing a role in the intense energy input. During the remaining 2.5 years of the Focus Group there will be a sustained effort to incorporate AMPERE data into the mix of observations and include available data from polar cap observatories. Two of the storm events (15 May 2005 and 9-11 July 2005) have been adopted by the Metrics Study Focus Group in order to bring a multiple model perspective to the events. The FED FG will likely be the subject of a joint session at the 2011 combined GEM-CEDAR meeting. FED session highlights Delores Knipp presented an overview of the FED effort and showed DMSP Poynting flux from select events. The data reveal localized Poynting flux enhancement during intervals of strong BY (DMSP) and neutral/northward IMF. Stefan Eriksson reviewed Poynting flux observations for the 15 May 2005 storm: He showed the relation between high-latitude reconnection driven convection and NBZ currents. His presentation illustrated FACs adjacent to well-defined flow channels. Geoff Crowley presented an overview of thermospheric response from select events. He presented conclusive evidence of large thermospheric density effects associated with localized Poynting flux deposition based on CHAMP satellite data and TIMEGCM simulations. Bob Strangeway related cusp-region FACs, IMF By control and ion outflows. His report focused on FAST data. Mike Wiltberger showed preliminary results from the Major Storm of August 24, 2005. He will be doing further analysis of the LFM Run. Dan Weimer reviewed measurements and predictions of thermospheric temperature changes based on work he has done with drag data provided by US Space Command. He reported good global agreement from the empirical model. Simon Wing discussed source regions of dayside field-aligned currents based on statistical analysis of many years of DMSP data. Wenhui Li showed results from an OPEN GGCM study of dayside energy deposition during northward IMF during the January 21, 2005 storm event. He has been able to trace the field lines from the flank merging region to the location of strong Poynting flux deposition shown by Delores Knipp. Bob Strangeway led an additional discussion on determining the open- closed field line boundary from low altitude spacecraft. Betsy Mitchell showed evidence from her PhD. dissertation work that IMF By decouples energy input into the ionosphere from energy input into the inner magnetosphere. Gang Lu showed ionospheric convection, field-aligned current, and Poynting flux under strongly northward IMF conditions during the November 08, 2004 storm onset. She showed evidence of reverse convection in both hemispheres. Ramon Lopez suggested that some of the field aligned current associated with the large dayside energy deposition events originate at the bow shock. There was additional discussion of the relation between ion upwelling and ion outflows and possible association of these with polar cap scintillation. Paul Song offered additional perspective and discussion about the magnetic field configuration during northward IMF. *** DAYSIDE-4. Dayside Research Area Planning Because the activity of the Cusp Focus Group was coming to an end a Dayside Research Area planning session was convened. The goal of that session was to identify areas of interest and foster collaborations that will lead to proposals of new dayside focus groups at the GEM meeting during Fall AGU. About 25 people met and discussed the status of our comprehension of physical processes occurring in the dayside magnetosphere. The consensus was that one of the main issues is the lack of quantitative models that predict where, and the form that energy, momentum, and mass enter the magnetosphere. In particular, the group identified areas that could be of interest for future dayside focus groups: - Connecting cusp and auroral structures: e.g. use dayside wave phenomena and energetic particles entering/leaving the cusp (Cluster, DMSP, ground-based observatories) - Dynamic processes at the magnetopause: e.g., effects of FTEs, dayside transients, pressure pulses, KH waves (THEMIS, Cluster) - Interhemispheric coupling: e.g., summer/winter hemispheres and North/South high latitudes; effects on polar cap potential saturation; results could be used to modify global models (DMSP, ground-based observatories, IRIDIUM, SWARM, CHAMP) - Mapping magnetopause structure to the ionosphere and vice versa: e.g., open/closed field line delineation; polar cap morphology (THEMIS, ground-based observatories, IRIDIUM, SWARM, CHAMP) - External causes of internal waves in the outer magnetosphere (THEMIS, Cluster, ground-based observatories, satellite imaging) - Interaction of dense cold plasma plumes with the magnetopause (THEMIS, IMAGE, ground-based observatories) +-------------------------------------------------------------------+ | 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 | +-------------------------------------------------------------------+