*************************** ** THE GEM MESSENGER ** *************************** Volume 22, Number 20 August 26, 2012 ---------------------------------------------------------------------- 2012 WORKSHOP REPORT: Dayside Field Aligned Currents and Energy Deposition (FED) Focus Group ---------------------------------------------------------------------- From: Delores Knipp The Field Aligned Currents and Energy Deposition (FED) Focus Group held two sessions at the 2012 GEM Meeting. The primary aspects of the ten presentations focused on: 1) Data-model comparisons for dayside energetics: a. AMPERE, DMSP, CHAMP, GRACE, SuperDARN b. LFM, OpenGGCM, TIMEGCM, AMIE, HASDM and JB2008 2) Relative role of dayside Poynting flux and particle deposition in creating dayside neutral density perturbations The data-model comparisons for field aligned currents and associated dynamics reveal improving agreement. Model sophistication is increasing and data sets are providing better global coverage. Getting to agreement with the neutral density response to energy deposition is still a challenge, although recent efforts to include both dayside Poynting flux and particle deposition as a source of energy is showing promise. The relative roles of these energy sources were discussed at length. Slava Merkin compared Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) data and an ultra-high resolution (~60 km in the ionosphere) Lyon-Fedder-Mobarry (LFM) global MHD simulation for an interval during the August 3-4 2010 storm, wherein there was a solar wind dynamic pressure jump and a south to north rotation of the IMF Bz component with By <0. The LFM and AMPERE current patterns showed remarkable agreement during this period. The dayside peak of the upward current moved from post- noon to pre-noon in response to the IMF Bz rotation. He showed that the magnetic perturbations underlying AMPERE patterns were very consistent with the simulated response. He also noted that, particularly during northward IMF conditions, if the orbit crossing point is far from the locus of the NBZ current system, the AMPERE fit may not capture the true geometry of the currents because the pole of the inversion basis functions is at the orbit crossing point rather than the magnetic pole. The new generation of AMPERE inversions fixes this problem by putting the basis function pole at the magnetic pole. Athanasios Boudouridis presented a case study of the effect of solar wind dynamic pressure fronts on dayside field-aligned currents and thermospheric density for April 5 2010 using Challenging Minisatellite Payload (CHAMP) data and TIMEGCM simulations. The challenge is to separate pressure pulse effects from IMF effects and determine their relative importance, since often both happen at same time. The pressure and IMF front passed ACE at ~ 0830 UT. The first responses were in the post-noon/afternoon MLT sector; these appear to coincide with intense FACs and Joule heating as produced in the AMIE procedure. The CHAMP and TIMEGCM results enhanced neutral density in the same general region, but the magnitudes of the perturbations are not yet in agreement. The associated traveling atmospheric disturbance traveled to the equator in ~ 3.5 hr. More effort will be devoted to determining how common the response is and to determining the relative roles of the IMF and dynamic pressure. Wenhui Li discussed Thermospheric Density Enhancements in Dayside High latitude Region. He showed comparisons between OpenGGCM-CTIM and CHAMP observations for three cases. Lühr et al. [2004] showed that, under relatively quiet geomagnetic conditions, the CHAMP satellite often observes regions of enhanced density at ~ 400 km altitude in the noon sector at high latitudes correlated with small scale field- aligned currents (FACs) associated with the dayside cusp. Knipp et al., [2011] reported localized Poynting flux in the near cusp region, during northward IMF with strong By component (quiet magnetosphere, Kp<2). This study looked at large Poynting flux and Joule heating during NBZ with large By. The CHAMP neutral enhancements are matched by OpenGGCM/CTIM but quantitative differences exist and are being explored. He is exploring effects of soft electrons and is varying the IMF clock angle to determine its effects. Rick Wilder investigated intense Joule heating, thermospheric upwelling, and large- scale gravity waves and their association with reverse convection under northward IMF for April 5 2010. He showed that the TIMEGCM output agrees better with CHAMP data when the high latitude driver (AMIE) ingests AMPERE data. During intervals of strong northward IMF there can be intense reverse convection that produces vertical winds and enhanced thermospheric density. Large- scale gravity waves with 700 m/s wave speed and 1000 km wavelength can arise from the density perturbations. Again the challenge for this event is separating solar wind dynamic pressure effects from IMF change effects. Ceren Kalafatoglu (student at Istanbul University) compared Joule heating outputs from IRI/SuperDarn/BATSRUS for two isolated substorms and will do future validation with DMSP. Marc Lessard presented for Brent Sadler: "Auroral Precipitation / Ion Upwelling as a Driver of Neutral Density Enhancement in the Cusp" [Sadler et al., 2012]. He investigated soft electron precipitation effects at higher altitude using the Otto model. The line of reasoning is: Auroral precipitation and Joule heating heat ambient electrons. The electron gas expands upward and the ions are pulled upward by the electric field. Ion momentum drags the neutrals upward. The estimated "cooking time" for this effect is 10-30 min: Electron temperatures rise in 1-3 min and upward ion velocity increases in 3-5 min. This should drive ion outflow. Much discussion on this soft electron cause - effect followed. Yi-Jiun Su discussed the high-altitude energy input to the thermospheric dynamics: for the August 4-7 2011 storm event. She compared density from DMSP and GRACE sensors and the HASDM, JB2008 andJB2008-with-Weimer-2005 models. She reported that the thermosphere responded immediately as the solar wind energy began to deposit energy into the high-latitude region; however, it took 6 hours to reach the maximum of the thermospheric energy. The thermosphere does not return to pre-storm level for a very long time. She estimated that the high latitude system transferred 3 x1016 J of energy to 2.5 x1016 J of heat--very efficient heat transfer. Jo Baker discussed SuperDARN / IMF By asymmetries. He reported that strong IMF By penetrates the dayside magnetosphere and produces interhemispheric field aligned currents [Kozlovsky et al, 2003]. For strong By <0 in the northern hemisphere there is a downward FAC in the polar cap and an outward FAC on closed field lines which drives eastward convection in the auroral zone. The opposite situation exists in the southern hemisphere. Thus there will be a velocity mismatch between hemispheres when IMF By<0. In the winter southern hemisphere the FAC reinforces afternoon convection; in the summer northern hemisphere the FAC counteracts afternoon convection. The width of the FAC channel is 3-6 deg. He presented evidence for a unipolar current in/out FAC and interhemispheric current. Delores Knipp showed dayside DMSP Poynting flux and soft particle asymmetries and compared those to CHAMP neutral enhancements. For all years and most conditions the enhancements were stronger in northern hemisphere cusp than in southern hemiisphere cusp. In many instances the cusp energy deposition overwhelms the nightside energy deposition. Temporal variability of this effect is under investigation. Delores Knipp also presented for Yue Deng on the relative roles of particles and Poynting flux in dayside energy deposition. She used the Global Thermosphere Ionosphere Model (GTIM) to investigate soft particles (~100 eV) and their roles in direct heating and ionization that leads to Joule heating redistribution. The investigation compares the result to strong driving by Poynting flux. The result is a non-linear enhancement of particle influence. She also showed spatial distribution of neutral density changes at 200 and 400 km. Model density changes were consistent with those reported by CHAMP. Binzheng Zhang presented the Roles of Particles in Heating in Dayside Near Cusp Region. He used the coupled magnetosphere-ionosphere thermosphere model (LFM+TIEGCM = CMIT) to investigate the effects of precipitating soft electrons. The study included two types of causally specified soft electron precipitation - direct-entry cusp precipitation and Alfven-wave induced, broadband electron precipitation - the effects of which are self-consistently included for the first time in a coupled global simulation model. Simulation results show that while both types of soft electron precipitation have relatively minor effects on the interaction between the magnetosphere and ionosphere, they can significantly modify the plasma distribution of the F-region ionosphere and the neutral density of the thermosphere. Enhancements in F-region electron density and temperature and bottomside Pedersen conductivity caused by soft electron precipitation are shown to enhance the Joule heating per unit mass and the mass density of the thermosphere at F-region altitudes. The simulation results provide a causal explanation of CHAMP satellite measurements of statistical enhancements in thermospheric mass density at 400 km altitudes in the cusp and premidnight auroral region. Subsequent Open discussion focused on: * Defining a modeling challenge? --Depends on whether the Focus Group is extended * Community effort to develop a PF index? --How could we create and verify a local vs global index? * Extending focus group? Some interest, but will need a volunteer to take this forward * Writing a final report? Will be done at year's end if no extension +-------------------------------------------------------------------+ | 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 | +-------------------------------------------------------------------+