*************************** ** THE GEM MESSENGER ** *************************** Volume 20, Number 26 September 26, 2010 ---------------------------------------------------------------------- 1. 2010 Summer Workshop Report: GGCM Research Area ---------------------------------------------------------------------- From: Slava Merkin and Stan Sazykin *** GGCM Metrics and Validation Focus Group Report. co-chairs: Masha Kuznetsova and Aaron Ridley The group met for 1.5 hours on Tuesday at 1:30 pm to discuss the status of the GEM Modeling Challenge. The goal of the Challenge is to help to evaluate the current state of GGCM models, to track model improvements over time, to demonstrate effects of model coupling and grid resolution and to facilitate interaction between research and operation communities in developing metrics for space weather model evaluations. Events and physical parameters for the Modeling Challenge were selected at the GEM 2008 Workshop. Event 1: Oct 29, 2003 06:00 UT - Oct 30, 06:00 UT Event 2: Dec 14, 2006 12:00 UT - Dec 16, 00:00 UT Event 3: Aug 31, 2001 00:00 UT - Sep 01, 00:00 UT Event 4: Aug 31, 2005 10:00 UT - Sep 01, 12:00 UT * Status of on-going Metrics Studies (MSs). MS 4: Ground magnetic perturbations. First report is submitted to Space Weather J. (Pulkkinen et al, 2010). Howard Singer made a presentation on NOAA SWPC metrics and validation needs. The MS on ground magnetic perturbations is of primary interest and will be used by NOAA SWPC as a base for validation of geospace prediction models to determine which model or models should begin transition to operations in 2012. Suggestions on further refinement of ground magnetic perturbation MS: focus on regional dB/dt and Kp (noon, dusk, midnight, dawn, high-latitude, low-latitude, ...). MS 1: Magnetic field at geosynchronous orbit. First report is submitted to Space Weather J. (Rastaetter et al, 2010). MS 1 and 4 will be repeated next year with updated models to show progress over time. MS 3. Plasma parameters at geosynchronous orbit - on hold. SOPA ion corrections for MPA are needed for pressure comparison. J. Borovsky and R. Friedel are working on removal of electron contamination from the low-energy ion channels of SOPA. MS 2: Magnetopause crossings by geosynchronous satellites. Comparison with LANL magnetopause in/out time series demonstrated wide variety of model results. In-depth comparative study of magnetopause positions was addressed at the "Baseline model comparison" session (Tuesday 3:30). MS 5: Dst index study (added at GEM 2009 Summer Workshop) in collaboration with Inner Magnetosphere FG. CCMC staff demonstrated updated Metrics Tool Suite that now include Dst Index study. Dan Welling showed the results of early RAM_SCB validation. Lutz Rastaetter presented report on first round of DST submissions (two events only). The results are quite different for weak and strong storms. We agreed to add more events and more empirical models. Metrics to be used: RMS prediction efficiency and Maximum ratio. Different methods for Dst calculations will be analyzed. A draft report will be discussed at GEM mini-workshop in December. The Deadline for timeline submission for all models/events: October 15, 2010. * Ideas for new Events and Metrics Studies. NOAA SWPC recommendations (Howard Singer): - First priority: Regional dB/dt, Kp. - Second priority: Auroral boundary position. This study is also a priority for AFWA. Plans: Analyze ground magnetic perturbation dependence on local time using the same events and model outputs (short-term). Analyze latitude dependence (long-term). Continue discussion on settings for auroral boundary position study at GEM mini-workshop. Dayside FAC and Energy Deposition FC recommendations (Delores Knipp) – Ionosphere Joule heating. Delores will provide DMSP Poynting flux timelines. – CCMC will add Joule heating to on-line plotting tool, provide information on model output format for model output submissions. - Additional events recommended for ionosphere Joule heating metrics study (MS 6): Event 5: May 15, 2005 00:00 – May 16, 2005 00:00. Event 6: July 9, 2005 00:00 – July 12, 2005 00:00. Continue discussion on settings for Ionosphere Joule heating study at GEM mini-workshop. Ideas for Joint GEM-CEDAR project: –Ionosphere Joule heating + hemisphere power. –Coupled magnetosphere/ionosphere runs. Compare with stand-alone models. For the GEM Baseline Model Comparison session, there were four presentations that compared the location of the magnetopause at different IMF strengths. CCMC, GUMICS, BATSRUS and LFM all participated in the comparison. It was determined that the OpenGGCM and LFM typically had magnetopauses that were 1-2 Re inside of BATSRUS and GUMICS. The modelers were unsure as to why this may occur. The group also discussed the strength and morphology of magnetospheric currents, particularly the magnetopause and bow shock currents, during weak, moderate and strong solar wind driving, and significant differences between the different models were found. The modelers are going to work to try to ensure that the models' boundary conditions and other parameters are as close as possible in further comparisons. It was also suggested that the leaders of the working group collect data files from each of the modeling group, so the exact locations and current structures could be directly compared, instead of just images. *** GGCM Methods and Modules Focus Group Report co-chairs: Brian Sullivan, Michael Shay The overarching goal of this focus group is to understand the physics of collisionless magnetic reconnection on magnetospheric length scales (100-1000 ion inertial lengths). This was the final year for this focus group. The two sessions included 9 speakers this year: Ray Fermo, Dmitri Uzdensky, Joachim Birn, Kittipat Malakit, John Meyer, Michael Shay, John Lyon, Brian Sullivan, Kai Germaschewski Primary areas of focus this year included: o Asymmetric reconnection: corrections and additions to Cassak-Shay formula & asymmetric reconnection in turbulence, and o The role of plasmoids in magnetic reconnection * Asymmetric Reconnection Reconnection is generally asymmetric in nature, and asymmetric reconnection has been a major focus over the lifetime of this focus group. Joachim Birn presented corrections to the Cassak-Shay formula for asymmetric reconnection. These corrections include compressibility effects, and proper treatment of Poynting flux and enthalpy flux through the reconnection region. New effects include a plasma-b dependence for the reconnection rate, and an even split of the Poynting flux between enthalpy flux and bulk kinetic energy flux. This even split occurs independent of b, and independent of the ratio of upstream densities and field strengths on the two sides of the reconnection layer. One context in which asymmetric reconnection occurs is in the reconnection of plasmoids in turbulent plasma. Intermittent turbulence with reconnection has been observed just downstream of the bowshock, within the magnetosheath (Retino et al. Nature Physics 3, 235 - 238 2007). Michael Shay presented simulations of reconnection in turbulence. The results indicated that understanding current sheet formation and reconnection in turbulent regions is likely key to understanding the dissipative physics in MHD turbulence. * Role of Plasmoids in Reconnection Reconnection research currently finds itself in a paradigm shift due to the realization that in large systems such as the magnetosphere, Sweet-Parker current sheets at high Lundquist number are unstable to a super-Alfvénic, secondary tearing, or "plasmoid" instability. This instability has been seen in resistive MHD, Hall MHD, and PIC simulations. In two-dimensional simulations of reconnection, this leads to reconnection regions containing many x-points separated by plasmoids. Flux-ropes are the three-dimensional analog of these plasmoids. This plasmoid instability leads to reconnection rates much higher than those predicted by Sweet-Parker theory, although not as high as the rates previously reported in Hall MHD, for example, in the GEM reconnection challenge papers, which focused on a relatively small system. Plasmoids speed up the reconnection process within resistive MHD, but they also rapidly generate kinetic scale current sheets, which may make Hall physics important at lower Lundquist numbers than previously thought. Plasmoid dominated reconnection is inherently dynamic, and potentially bursty. Consequently Sweet-Parker theory, which assumed quasi-steady behavior does not apply well in this regime. Understanding such inherently dynamic reconnection requires a statistical treatment. Dmitri Uzdensky et al. and Raymond Fermo et al. have presented statistical models of plasmoid distrubution (size, lifetime, etc.) Fermo's model has been found to compare favorably with data from ~1000 Cluster crossings of FTEs at the dayside magnetopause. Understanding plasmoid-dominated reconnection in large-scale systems will likely be a major part of global scale reconnection research for the next several years. Outstanding questions include: How do plasmoids impact the onset of fast reconnection in collisionless systems? Are they merely a transient phase, or do they play a key role in generating sub-d_i scale current sheets? Can global models achieve realistic reconnection rates and current sheet geometries with plasmoids simply by simulating high Lundquist number resistive MHD reconnection, or is the Hall term vital to fast reconnection even in a plasmoid-dominated regime? What might be the role of plasmoids in generating enhanced localized resistivity around the many x-lines that separate plasmoid. +-------------------------------------------------------------------+ | 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 | +-------------------------------------------------------------------+