Table of Contents ====================================================================== 1. IAGA Division III Report Reviews Available at GemWiki 2. Workshop Report: The Magnetosheath Focus Group 3. Workshop Report: Dayside Field Aligned Currents and Energy Deposition (FED) ====================================================================== *************************** ** THE GEM MESSENGER ** *************************** Volume 21, Number 19 August 22, 2011 ---------------------------------------------------------------------- 1. IAGA Division III Report Reviews Available at GemWiki ---------------------------------------------------------------------- From: Larry Kepko Chair, IAGA Division III We are pleased to report that the IAGA Division III reporter reviews can be found at http://aten.igpp.ucla.edu/gemwiki/index.php/IAGA_Div_III_Reviews Reporter reviews are created by our scientific colleagues and presented at the biennial IAGA meetings. They succinctly summarize the last two year's of research for each scientific area, and therefore represent a valuable resource for the scientific community. If you have a reporter review presentation from a previous year that you would like to share, please contact me directly and we will place it online. The presenters expend considerable time and energy putting together these presentations. Should you find them useful, please consider letting them know, as I'm certain they would appreciate it. ---------------------------------------------------------------------- 2. Workshop Report: The Magnetosheath Focus Group ---------------------------------------------------------------------- From: Katariina Nykyri and Steve Petrinec, Focus Group Co-Chairs The Magnetosheath Focus Group held two sessions at the 2011 Joint CEDAR-GEM Workshop. Eleven presentations were given, covering all three main topics of the Focus Group: 1) Large Scale Structure of the Magnetosheath, 2) In situ Magnetosheath Physics and 3) Magnetosheath Impact on the Magnetosphere. In addition, a Magnetosheath Challenge has been devised, and will soon be officially issued. Summary of presentations: The first presentations of the focus group used the THEMIS data sets to explore a variety of foreshock and magnetosheath phenomena, and compared these observations with recent numerical models. Hui Zhang presented THEMIS observations of a structure which starts as a foreshock cavity and finally evolves into a hot flow anomaly (HFA). Foreshock cavities may be the early stages of HFAs. Examples of two types of structures at the foreshock were also shown. Some are foreshock cavities consistent with Schwartz et al. [2006], and some are Foreshock Compressional Boundaries (FCB) consistent with Omidi et al. [2009]. Global hybrid simulations [Omidi et al., JGR 2010] have also predicted a new type of event (foreshock bubbles) that forms in Earth's foreshock and can affect the magnetosheath and magnetosphere. It forms as IMF discontinuities sweep up the ion foreshock region upstream of the bow shock, convect with the solar wind, and efficiently accelerate energetic particles. Drew Turner presented the first clear evidence of these events using THEMIS data. The distinguishing features between foreshock bubbles and HFAs and their effects on the magnetosheath were discussed, including global expansion of the bow shock and magnetopause followed by a sudden compression and the introduction of very energetic ions and electrons to the system. Chih-Ping Wang showed statistical magnetosheath ion and electron temperature profiles from 3 years of THEMIS observations. Ion and electron temperature, as well as ion to electron temperature ratios, are directly correlated with solar wind speed. While ion and electron temperature decreases with downtail distance, the temperature ratio remains almost constant. Katariina Nykyri also showed used this data set to show there is no clear dawn-dusk asymmetry of magetosheath temperatures for Parker-spiral or ortho-Parker-spiral orientation. More heating at the dayside magnetosheath is observed for plasma b < 1 than for b < 0.1. The magnetosheath is hotter for larger solar wind speeds and Alfvén Mach number. It has been shown that the total pressure at the subsolar magnetopause differs from the solar wind dynamic pressure and these changes depend on IMF orientation. Andrey Samsonov stressed that for a radial IMF orientation, the magnetosheath thermal pressure is anisotropic and the parallel pressure may exceed the perpendicular pressure in the subsolar region. This anisotropy may explain the unusual magnetopause shape observed during such times. Ted Fritz showed ISEE energetic ion observations for a magnetosheath interval, indicating that such ions do not travel sunward. Nick Omidi demonstrated that despite the presence of ULF waves and kinetic processes in hybrid simulations, reasonable comparisons between hybrid and MHD simulations are possible during southward IMF. Jean Berchem showed that simulation results compare fairly well with gas-dynamic predictions (Spreiter et al., 1966), but significant differences are found near the shock and the magnetopause; are worse in the noon-midnight meridian plane. As expected, cusps and FTEs significantly affect the magnetosheath flow around the magnetopause. Yongli Wang showed the results of 3D modeling efforts of the magnetopause using spacecraft crossings from multiple missions, and employing the Support Vector Regression technique. Mike Schulz described a new coordinate system that shows promise for constructing analytical streamline (Euler-potential) models of the magnetosheath surrounding a magnetopause of rather general prescribed shape. By specifying distance from the magnetopause along an outward normal of calculable direction, the new system also shows promise for organizing in situ magnetosheath data obtained from spacecraft. Steve Petrinec showed that the dayside magnetosheath can be remotely imaged with energetic neutral atoms (IBEX). Although the time integrations are long, during steady conditions these observations could be used to place constraints on plasma properties (e.g., the polytropic index). This technique could be exploited in future missions to provide global, dynamic images of the magnetosheath region. Magnetosheath Challenge The devised Magnetosheath Challenge is comprised two main tasks: 1) To run global hybrid and MHD models for a set of fixed, steady solar wind conditions, and 2) To identify similar 'steady' intervals from in situ observations within specified, constrained parameter ranges. Magnetosheath parameter comparisons between models and observations include: Plasma moments; temperature and pressure anisotropies; electron/ion temperature ratios; wave power and wave mode spectra in B, v, density, and pressure fluctuations; specific entropy; and others. This challenge will be officially issued once appropriate, rigorous metrics have been determined. ---------------------------------------------------------------------- 3. Workshop Report: Dayside Field Aligned Currents and Energy Deposition (FED) ---------------------------------------------------------------------- From: Delores Knipp, Stephan Eriksson, and Herb Carlson Focus Group Co-Chairs The Dayside Field Aligned Currents and Energy Deposition Focus Group held two 2-hr sessions. Fifteen presentations and one student demo were given; the attendance for the first session was about 50 and for the second session about 25. Summary of presentations: Stefan Eriksson described Alfvén Mach number and IMF clock angle dependencies of sunward directed E x B flow channels and their embedded Joule heating rates in the ionosphere. He showed a BATSRUS run from CCMC for May 15, 2005, highlighting field aligned currents and flow channels. He suggested further model runs and statistics check of the dependencies in the DMSP F-15 data. Wenhui Li described results from a JGR paper entitled: The Relation between Dayside Local Poynting Flux Enhancement and Cusp Reconnection. The paper reports OPENGCM simulations for several events in late 2004 and in 2005. The paper concludes that flank merging is a source of field-aligned currents, E x B flow channels and intense Poynting flux to the cusp. Aaron Ridley investigated Effects of concentrated dayside energy deposition on the global and regional thermosphere using a BATSRUS Idealized simulation for May 15, 2005. He found neutral density enhancements associated with IMF By and appropriately placed particle deposition. Yue Deng showed the significance of difference heating mechanisms to the cusp neutral density enhancement using the GITM non-hydrostatic model. She compared effectiveness of Poynting flux and soft particle precipitation in producing neutral density enhancements near the cusp. Soft particle deposition into the upper F regions is a very efficient heat source. She concluded that the altitudinal distribution of energy input is important to neutral upwelling and TEC distribution. Comment by Bob Strangeway: From FAST observations, you always get high soft electron precipitation when there is large Poynting flux. How do you separate the two? Delores Knipp discussed a GRL manuscript entitled: Extreme Poynting Flux in the Dayside Thermosphere: Examples and Statistics. The paper reports results of sorting DMSP F-15 Poynting flux by IMF and solar wind type. During intervals of large IMF By the Poynting flux deposition peaks in dayside with the Pre/Post noon maximum in Poynting flux depending on IMF By sign. During some events the Poynting flux exceeds 100mW/m2. The locations of these extreme events are consistent with the dayside flows channels discussed in Li et al. (2011). She also reported a 9-day periodicity in the 2005 DMSP orbit integrated Poynting flux. Comment by Aaron Ridley: Use Robinson formula to get Pedersen conductance from electron JE flux and number flux. Then compare Poynting versus Sigma P*E2. Chin Lin showed polar cap neutral density enhancements observed by the CHAMP accelerometer. He surveyed CHAMP neutral density data and searched for density perturbations that were two sigma or more above the previous 24-hour orbit average. He found a tendency for long lasting perturbations on dayside and near dawn. The tendency appears to have strong IMF By modulation. Further the high-latitude density peaks occur in summer hemisphere in 2001-2005 Lasse Clausen showed global Poynting flux derived from SuperDARN and AMPERE measurements. He used SuperDARN and AMPERE to get 2-min average Poynting flux. He showed example from December 20, 2010. The AMPERE coverage may miss confined reverse convection at high latitude. Comment by Shin Ohtani: AMPERE needs 10 min to replace one satellite with another one along the same orbit plane. Questioning the 2 min resolution approach. Slava Merkin used AMPERE, SuperDARN, and LFM to deduce ionospheric electrodynamics. He reconstructed the potential distribution from AMPERE and compared this with SuperDARN. AMPERE and SuperDARN can help confirm conductances by rotations of flow vectors. The AMPERE data show NBZ system during August 3-4, 2010 in the sunlit hemisphere. Using LFM, he mapped a Poynting flux patch in northern hemisphere to reconnection site in opposite hemisphere. Jiannan Tu discussed the time scales of dynamic Magnetosphere- Ionosphere-Thermosphere coupling. He characterized: * Short time scale= Alfven wave travel time * Intermediate time scale = 10-20 min for quasi steady state * Long time scale > 1 hr for steady state of entire MIT system And found most energy deposition is during intermediate time scales. The implication is that transient stages are prolonged periods with the time scales longer or comparable to those of many important ionospheric-thermospheric processes. The inductive-dynamic (inductive electric field and non-zero time derivatives of momentum equations) approach is required to properly describe the ionosphere/thermosphere during the transient periods. Gang Lu showed distributions of FACs and Poynting Flux under northward and southward IMF. She compared the individual satellite measurements with the global maps of Poynting flux derived from AMIE for Nov 2004 storm, and showed that even with 2 concurrent DMSP satellites (DMSP F- 15 and F-16), they are not adequate to describe the global energy deposition. She also showed dayside energy deposition during northward IMF and large East-West IMF. Art Richmond discussed statistical Poynting flux patterns from DE -2 derived from 18 months of data. The derived patterns show net Earth- directed Poynting flux. He showed that dayside energy deposition dominates for all IMF clock angles Rick Wilder discussed the effect of Magnetospheric field Line topology on dayside FACs and Energy Deposition for a December 5, 2004 event. He showed a case where strong northward IMF drives reverse convection in both hemispheres; stronger in summer hemisphere; Theta aurora in summer hemisphere and concluded that the winter hemisphere supported reverse convection on closed field lines. He also discussed an August 24, 2005 event with an expanded polar cap and Joule heating on open field lines. That event showed evidence of > 10 keV ions. Juan Rodriguez discussed auroral forms that extend equatorward from the persistent midday aurora during geomagnetically quiet periods. He showed data from a 630 nm all sky imager near the cusp. The auroral forms appeared equatorward of cusp near noon with east-west extent of 1000 km. These are possible flux transfer events. He also showed additional events called "crew cuts" events with no known physical association. Herb Carlson discussed dates/times seeking satellite over flights to compare ground based with satellite signatures of: magnetic reconnection, down going energy, and ion outflows. He showed data from EISCAT 2 min resolution since 2000, that should contain FTEs. The FTE’s should pull solar-produced plasma into polar cap and create patches that give rise to polar cap scintillation. He suggested that polarward moving forms with signatures of particle flash are indicators of FTEs and asked what other signatures are associated with FTEs? He is looking for high altitude data above DMSP. Eric Lund showed sounding rocket measurements of electron heating in association with field-aligned currents and soft precipitation from the SCIFER rocket launch on 18 Jan 2008 over Svalbard. The rocket had an apogee of 1468 km. He noted a series of poleward moving auroral forms. He showed measured electron temperature. He argued that energy to transfer to electrons required about 100 sec. Liam Kilcommons demonstrated the DMSP Poynting flux database. General discussion: Local versus global density enhancements needs to be defined (Strangeway). Soft electron precipitation dependent on FAC sense, thus dependent on IMF By and side of noon. Asymmetry expected (Strangeway). Importance of IMF By to Poynting flux now demonstrated. Hardy formula only good for summer; how was this data set generated? (Lotko) Plasma connectivity (M-I coupling) missing from all MHD codes (Lotko, Ridley agrees). Does Hardy model have two particles populations, including a narrow 1 keV population poleward of current sheet from prior reconnection? Overarching questions for FED to consider For the currents and current loops essential to linking the M-I system, to what extent and under what conditions it is most useful to view the magnetosphere as: mostly capacitive and/or inductive given a current and a voltage source? What is the source population for the major current carriers for the key current loops in the key regions? For the EM energy flow ultimately tracing back to being driven by the solar wind, relatively directly near the cusp and indirectly on the night side: how significant is reconnection driven Poynting flux on the dayside and on the nightside? What parameters modulate the impact of this energy deposition on the thermosphere? How do we best characterize the "sea-saw" imbalance between dayside and nightside reconnection rates, as that imbalance modulates polar boundary locations, area, potential drop, and energy deposition? How do we model and validate theory for the time-dependent current loops where discrete changes (and shears) in plasma flow must self- consistently lead to corresponding interdependent changes in currents, precipitating particles, conductivity, and a nonlinear energy deposition response? Given importance of the "cusp location" to the question of Poynting flux dependence on IMF, to what extent can we improve our understanding of current system variability around the cusp? +-------------------------------------------------------------------+ | 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 | +-------------------------------------------------------------------+