*************************** ** THE GEM MESSENGER ** *************************** Volume 22, Number 22 August 30, 2012 ---------------------------------------------------------------------- 2012 WORKSHOP REPORT: Transient Phenomena at the Magnetopause and Bow Shock and Their Ground Signatures Focus Group ---------------------------------------------------------------------- From: Focus Group Leaders Hui Zhang , Q.-G. Zong, Michael Ruohoniemi, and David Murr The "Transient Phenomena at the Magnetopause and Bow Shock and Their Ground Signatures" focus group held four sessions with 25 presentations. The sessions were organized as follows: 1. Foreshock Phenomena 2. Magnetopause Phenomena 3. Ground Signatures 4. Planning session Various foreshock phenomena including hot flow anomaly (HFA), foreshock compressional boundary (FCB), and foreshock bubbles were investigated by this focus group using both in-situ observations and global hybrid simulations. Turner et al. gave an overview of these foreshock phenomena. Speakers presented results illustrating that HFA is a universal phenomenon. HFA has been observed at the bow shock of the Earth, Mars, Saturn, and Venus. Wang et al. (presented by Zong) investigated 87 HFAs with large flow deflection (with the magnitude of Vy or Vz in GSE coordinates greater than 200 km/s) from Cluster-C1 observations from 2003 to 2009 and found that the large flow deflections in HFAs are location dependent and that the ions are near-specularly reflected at the bow shock. In addition, both in-situ observations by NASA THEMIS spacecraft and global hybrid simulations demonstrate that HFAs can be generated spontaneously (in the absence of any current sheets) at quasi-parallel bow shocks where the interplanetary magnetic field lies nearly parallel to the shock normal. Omidi et al. showed that the simulated SHFAs form as a result of the interaction of foreshock cavitons with the bow shock. Simulations show the formation of large numbers of SHFAs and demonstrate that they are an inherent part of quasi-parallel shock dissipation processes. Cluster observations show that magnetic flux rope can form within a magnetosheath HFA. Multiple THEMIS spacecraft observations have been used to investigate the propagation and expansion speed of an HFA. Omidi et al. demonstrated the dynamic nature of the foreshock compressional boundary and its relation to foreshock cavities. Using global hybrid simulations with steady and time varying IMF conditions, they showed that even during steady IMF conditions, the FCB is highly dynamic and in practice will likely not reach an equilibrium state. Simulations also show that FCBs are part of foreshock cavities and should be detected at their edges regardless of which mechanism is responsible for the formation of foreshock cavities. Rojas-Castillo et al. presented Cluster observations of FCBs and showed that they form either downstream of the ion foreshock boundary or coincide with it. Observations show the presence of FCBs during steady or time varying IMF. They also show the presence of FCBs under a wide range of solar wind speeds and IMF cone angles. The foreshock phenomena may have significant impacts on the Earth's Magnetosphere-Ionosphere System. Presentations in the second and third sessions used a variety of space- and ground-based measurements to examine the response of the magnetosphere to solar wind transients and various foreshock phenomena. Turner et al. showed that 23 transient foreshock events (including HFAs, FCBs, and foreshock bubbles) were identified from one day's THEMIS C data (July 14, 2008) when the solar wind is steady (~700 km/s). These foreshock events resulted in significant magnetopause disturbances observed by THD and THE just inside of the magnetopause. They also showed that foreshock activity correlates with enhanced ionospheric convection, based on equivalent ionospheric currents (EICs) derived from GMAGs and SuperDARN radar signatures. Global PC3-5 wave activity observed by Cluster, THEMIS, and GOES is also correlated with foreshock transient activity. Korotova et al. presented THEMIS observations of an unusual bow shock motion attending a magnetospheric transient event. Ferdinand Plaschke used MHD theory to show that THEMIS observations of a magnetopause surface wave were inconsistent with the Kelvin-Helmholtz instability. Yari Collado-Vega gave two presentations. In the first, the motion of FTEs observed by the Cluster spacecraft were found to be consistent with both component and anti-parallel merging, depending on the IMF conditions. In the second, the rotation axis of magnetopause vortices in MHD simulations during dynamic solar wind conditions was found to be mainly aligned with the z-direction, whereas for fixed solar wind conditions it was in the x-y directions. Wenhui Li showed OpenGGCM-CTIM simulations of magnetic reconnection at the dayside cusp region when IMF Bz ~ 0. The simulations reproduce both Poynting flux and neutral density "hot spots" which are consistent with observations. Xuanye Ma presented 3D local MHD simulation results of anti-parallel magnetic reconnection with a perpendicular shear flow. The simulation results showed that the development of reconnection changes the onset conditions for KH modes, allowing waves of different wavelength to develop in different regions of the reconnection geometry. Subsequently, the magnetic diffusion regions are twisted and strongly modified by KH modes. Rick Wilder showed DMSP observations of fast sunward flow channels on open field lines under northward and By-dominant IMF conditions. Sunhee-Lee presented Cluster observations of asymmetric reconnection at the dayside magnetopause. Lee et al. identified the separatries, flow boundaries, and central current sheet on the magnetospheric side and magnetosheath side by sharp boundaries in wave spectrogram, particle differential energy flux, flow, field, and density gradient. Then they deduced the geometry of the asymmetric reconnection based on the different separatrix angles. Shi et al. presented Cluster observations of a transition layer equatorward of the cusp, which contains both magnetosheath and magnetospheric populations, during northward IMF conditions. This transition layer is possibly formed by dual-lobe reconnection when the IMF is northward. Michael Hartinger presented a case study of global Pc5 ULF waves and argued their characteristics were more consistent with a transient foreshock driver rather than upstream wave activity. Nathaniel Frissell presented a new analysis technique for extracting ULF wave signatures from high time resolution SuperDARN "camping beam" data and David Murr showed how transient features can be extracted from GPS/TEC measurements. Mark Engebretson presented Svalbard observations of a post-noon EMIC wave burst associated with an outward motion of the bowshock measured by the Cluster spacecraft. Bob Clauer talked about an unusual class of event in which a solar wind pressure increase produces a decrease in the low latitude magnetic field, rather than an increase. Finally, Juan Rodriguez presented an overview of "crewcuts" which are quiet-time auroral features extending equatorward from the dayside oval during negative Bx and By-dominated conditions. During the planning session, we discussed outstanding questions to be answered by this focus group and post summer workshop plan. We revised the outstanding questions proposed in the original proposal such that we shortened the list of outstanding questions, more clearly identified the regions that should be studied in response to transient solar wind and foreshock phenomena, and broadened the types of phenomena that could be studied. We also set up tasks immediately following GEM. The focus group wants to have a list of events that can be analyzed by the entire community from different perspectives. These events are initially going to be provided by Drew Turner and Hui, and then posted on the wiki. We plan on compiling a list of phenomena known to cause different types of disturbances, post them on the wiki, and link them to the events that we have posted. The focus group will also be joining the GSFC Monday Dayside science teleconference (supported by THEMIS) at noon as a mechanism for continued communication and presentation of science topics. +-------------------------------------------------------------------+ | 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 | +-------------------------------------------------------------------+