Table of Contents ====================================================================== 1. Workshop Report: Diffuse Auroral Precipitation Focus Group 2. Workshop Report: Scientific Magnetic Mapping and Techniques ====================================================================== *************************** ** THE GEM MESSENGER ** *************************** Volume 21, Number 27 October 17, 2011 ---------------------------------------------------------------------- 1. Workshop Report: Diffuse Auroral Precipitation Focus Group ---------------------------------------------------------------------- Focus Group Leaders: Richard Thorne and Joe Borovsky At the 2011 GEM Summer workshop, there were two separate breakout sessions dealing with new observation and theoretical modeling of the diffuse aurora, followed by a wrap up session chaired by Eric Donovan and Richard Thorne, which summarized the major new results during the five-year focus group. It has been show that the most intense diffuse auroral precipitation is mainly caused by scattering of plasma sheet electrons by whistler mode chorus [Thorne et al., Nature, 467, 943, 2010], although electrostatic electron cyclotron harmonic waves can be important for the precipitation from L > 10. The diffuse aurora has interesting spatial structure and can pulsate over intervals of 5-20 sec. While the relationship between diffuse and pulsating aurora is not entirely resolved, many reports have been published stating that pulsating aurora appears to emerge from within regions of diffuse aurora (although not every region of diffuse aurora necessarily leads to pulsating aurora). New results are contributing to significant progress in understanding pulsating aurora. Nishimura et al. [Science, 330, 6000, 81-84, 2010] show conclusively that pulsating aurora can be driven by lower band chorus waves, answering a question that was asked decades ago. Jones et al. [JGR, 116, A3, 2011] show that the spatial extent of pulsating aurora events averages 7.3 in MLT and that the most probable duration of events observed by a single camera is roughly 1.5 hours (although there are examples where events last several hours, up to 8 or more). They also note that the source region of pulsating aurora drifts or expands eastward, away from magnetic midnight. Below is a summary of the 2011 summer workshop activities. Session 1: Observations and Origin of Pulsating Aurora, Chaired by Wen Li and Sarah Jones At the GEM 2011 meeting, presentations were made that addressed a wide range of pulsating aurora topics: Marc Lessard presented an overview of pulsating auroral observations and then showed two new observations. The first of these is the presence of "worms" of black aurora, embedded within pulsating patches. These features are typically aligned in the east-west direction, having an average width of 3 km and length of more than 50 km. Their durations range from 8 seconds to 2.5 minutes (based on a study of 26 events). He also showed a movie (using cameras from the THEMIS array) showing pulsating simultaneously over Canada and Alaska for nearly 8 hours and persisting through the occurrence of 2 or 3 substorms. The implication is that the substorms may provide the seed population for pulsating aurora. Sarah Jones and Allison Jaynes showed images from a field study that was conducted from March 12-16, 2002 (courtesy of Dave Knudsen). The images were taken using Trond Trondsen's narrow-field intensified CCD camera that was installed at Churchill, Manitoba. The camera was oriented along the local magnetic zenith where small-scale black auroral forms are often visible within a region of pulsating aurora. The observations show black forms with irregular shape and non-uniform drift with respect to the relatively stationary pulsating patches. The pulsating patches occur within a diffuse auroral background as a modulation of the auroral brightness in a localized region. The images show a decrease in the brightness of the diffuse background in the region of the pulsating patch at the beginning of the 'off' phase of the modulation--an effect that was affectionately called "Knudsen's diffuse aurora eraser". Throughout the off phase the brightness of the diffuse aurora gradually increases back to the average intensity. Allison Jaynes presented results from work being done at the University of New Hampshire, in collaboration with NOAA, showing GOES 13 particle fluctuations relation to pulsating aurora. Data from the GOES 13 MAGnetospheric Electron Detector mapped to the THEMIS ASI at The Pas, Manitoba for a pulsating aurora event on March 15, 2008. Fluctuations in the electron fluxes measured by the MAGED were cross correlated with the brightness fluctuations for each pixel in the all- sky images to identify regions of highest correlation, for 30 minute and 1 minute correlations. In this way, the patch that is magnetically conjugate to GOES 13 is identified. The GOES analysis (by Juan Rodriguez) used in-situ magnetometer data to confirm that precipitating electrons were field-aligned. Robert Michell presented slides showing high-resolution all-sky imager observations of "fast pulsations". He and Marilia Samara are currently exploring the connection between enhanced wave power in situ, as measured by THEMIS, and active fast pulsating to enable identification of the wave modes responsible for pitch-angle scattering electrons into the loss cone. Yoshizumi Miyoshi reported on a time-of-flight analysis of precipitating electrons associated with pulsating aurora observed by the REIMEI satellite and suggested that the modulation region of the pitch angle scattering is near the magnetic equator. Their estimated parameters, such as wave-frequency and latitudinal distribution of the modulation region, are consistent with previous statistical studies of whistler waves in the magnetosphere. Toshi Nishimura and Jacob Bortnik described a multi-event study performed using conjugate measurements of the THEMIS spacecraft and an all-sky imager during periods of intense lower-band chorus waves. The thirteen identified cases support their previous finding that the intensity modulation of lower-band chorus near the magnetic equator is remarkably well correlated with quasi-periodic pulsating auroral emissions near the spacecraft magnetic footprint, indicating that lower-band chorus is the driver of the pulsating aurora. Wen Li discussed the origin of the pulsating aurora due to modulation of whistler-mode chorus waves and their coherent size. Using coordinated in-situ spacecraft and ground-based all-sky imager observation from the THEMIS mission, she showed that the luminosity of pulsating aurora over a single auroral patch is closely related to the modulation of the chorus wave intensity. Furthermore, a one-to-one correlation exists between depletions in total plasma density and increases in chorus wave intensity, thus suggesting that density variations may play an important role in modulating chorus wave intensity and thus controlling the luminosity of the pulsating aurora. Using simultaneous observations by multiple THEMIS spacecraft, she estimated the transverse coherent size of chorus waves in the equatorial magnetosphere to be a couple of thousands km. Yoshi Miyoshi presented the spatial distribution of plasma sheet electrons statistically using the THEMIS/ESA data. The electron phase space density decreases monotonically along the electron drift path. The electron life times estimated from the radial profile of the electron phase space density are consistent with the theoretical life times due to chorus-wave particle interactions. The results suggest that the main loss mechanisms of plasma sheet electrons at dawn side are the pitch angle scattering with chorus waves. Remaining outstanding problems related to pulsating aurora include: 1. What is the relationship between pulsating aurora and substorms? Do substorms provide the seed populations of energetic electrons as originally suggested by S. Akasofu? 2. What is the total energy involved in pulsating aurora events? How does this compare to substorm expansion phases? 3. What is the spatial extent of occurrences of pulsating aurora? Does it occur throughout the dayside? 4. What is the role of the ionosphere? How do the patches remain so incredibly persistent in terms of their shape and location during an event? 5. Do "worms" represent black aurora (i.e., does it represent a signature of current closure)? How do currents close in individual patches? Session II: Scattering Mechamisms for Diffuse Auroral Precipitation, Chaired by Binbin Ni and Xin Tao Xin Tao presented the temporal evolution of the phase space density of plasma sheet electrons injected into the nightside during disturbed times using a quasi-linear diffusion simulation. Scattering in energy and pitch angle during interactions with both whistler mode chorus waves and electron cyclotron harmonic waves are included using a wave model recently obtained using CRRES spacecraft data. The results demonstrate that the formation of the electron pitch angle distributions is consistent with pitch angle scattering by upper and lower band chorus waves. Jun Liang reported multi-instrumental observations of fast earthward flows, ECH waves, and diffuse auroras, during 8-9 UT on February 5, 2009. Following the fast earthward flows observed on mid-tail probe THEMIS-C and subsequent magnetic dipolarization in the near-Earth plasma sheet, strong ECH waves were observed by THEMIS A/D/E at L~11 in the equatorial plasma sheet. Concurrently, ground optical instruments detected diffuse auroral intensifications around the THEMIS footprints. He established an observationally confirmative conjunction between the observed ECH waves and diffuse auroras. He also found that the ECH wave and diffuse auroral intensification was triggered by the fast flow activity from the mid-tail. Possible mechanisms linking the fast flow and its associated magnetic dipolarization to the intensification of ECH wave and diffuse aurora in the outer magnetosphere were discussed. Based on the simultaneous observations from THEMIS spacecraft and NORSTAR optical instruments during 8 – 9 UT on February 5, 2009, Binbin Ni presented an example where electrostatic electron cyclotron harmonic (ECH) waves are the main contributor to the diffuse auroral precipitation. Using the electron differential energy flux inside the loss cone estimated based upon the energy-dependent efficiency of ECH wave scattering, both the auroral electron transport model developed by Lummerzheim [1987] and Maxwellian fitting produced an intensity of ~ 2.3 kR for the green-line diffuse aurora, in good agreement with the ~2.4 kR green-line auroral intensity observed simultaneously at the magnetic footpoint. The presented results support the scenario that enhanced ECH emissions in the central plasma sheet (CPS) can be an important or even dominant driver of diffuse auroral precipitation in the outer magnetosphere. Mike Schulz introduced a fourth adiabatic invariant, which is essentially a phase-space volume, i.e., the product of a momentum- space volume and a flux-tube volume, and conserved in the limit of strong pitch-angle diffusion to pursue better understanding of the dynamics of magnetospheric particles. He presented some analytical formula that connects radial diffusion coefficients with pitch angle diffusion coefficients, enabling to evaluate the consequences of pitch-angle diffusion and to estimate the maximum radial diffusion coefficient. ---------------------------------------------------------------------- 2. Workshop Report: Scientific Magnetic Mapping and Techniques ---------------------------------------------------------------------- Focus Group Leaders: Eric Donovan, Robyn Millan, Elizabeth MacDonald The new GEM focus group on Magnetic Mapping held three sessions at the recent workshop. Strong participation from attendees underscored the critical importance of understanding the magnetic mapping between different geospace regions to many of the GEM science challenges. Considerable time was reserved for traditional GEM style discussions and there were a few invited talks to highlight mapping technique examples (E. Zesta, T. Nishimura) and generate discussion of MHD- related issues (V. Merkin). There were also seven contributed talks (Y. Shi, R. Strangeway, S. Zaharia, R. Denton, J. Yang, A. Pembroke, J. Baker) and an introduction to the focus group by E. Donovan. Sessions were chaired by R. Millan and M. Henderson, E. Donovan and A. Pembroke, and M. Thomsen and E. MacDonald. Present observational programs produce simultaneous observations from disparate geospace regions that cannot be properly interpreted without addressing the mapping issue. Global models and simulations imply mappings that need to be correct in order for the models to be as useful as possible for science and prediction. Techniques for such mappings include empirical and event-based models, simulations, utilizing auroral boundaries and phenomena, magnetoseismology, and multi-point in situ particle observations. Talks in the first two sessions focused on these elements. Emerging themes included resolving mapping from different perspectives (e.g. the ground, FAST altitudes, and magnetotail regions), and ways to assess the metrics of various techniques. Universal questions were brought up; e.g. given observation A, where is point B, how did one get there, and given B, can one get back to A uniquely? The third session was devoted to gathering community input to focus group planning. Planning discussions revolved around how to take stock of these techniques, assess their weaknesses and add to their strengths, and determine how global simulations compare with reality in terms of mapping. Results of this session were to plan the next steps for the mini-GEM workshop. We would like to collect a detailed list of magnetic mapping techniques, workers, and results. This list will help guide the focus group's efforts and inform cross-pollination and best practices of mapping techniques. It can also be used as a basis for a review of mapping techniques and their efficacy. It can further be used to begin identifying the relevant science questions that most rely on accurate mapping. Discussion was held with A. Runov regarding improved scheduling to reduce overlap with the substorm focus group and allow syncing of discussion topics. An email communication list was established with nearly 90 members already and will be used for collecting and distributing the information. More information including archived talks can be found on the GEM wiki: http://aten.igpp.ucla.edu/gemwiki/index.php/FG:_Scientific_Magnetic_Mapping_%26_Techniques +-------------------------------------------------------------------+ | 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 | +-------------------------------------------------------------------+