*************************** ** THE GEM MESSENGER ** *************************** Volume 13, Number 33 August 26, 2003 --------------------------------------------------------------------------- Meeting Report from Working Group 1 of Inner Magnetosphere Storms Campaign --------------------------------------------------------------------------- From: Anthony Chan GEM 2003: Inner Magnetosphere Storms, Working Group 1 Meeting Report Working Group Co-chairs: Mike Liemohn liemohn@umich.edu Dennis Gallagher Dennis.L.Gallagher@nasa.gov Report Contributors: Dick Wolf rawolf@rice.edu Margaret Chen Margaret.W.Chen@aero.org Joerg-Micha Jahn jjahn@swri.edu The Inner Magnetosphere Storms Working Group 1 (IMS/WG1) held four independent and three joint sessions during the June 2003 GEM Workshop. The sessions focused on new work regarding inner magnetospheric electric fields, the stormtime ring current morphology and dynamics, plasmaspheric density structure, and coupling between the ring current, plasmasphere, and ionosphere. IMS WG1 and WG2 cosponsored two tutorials at the Workshop: Michelle Thomsen presented "Storm-Time Dynamics of the Inner-Magnetosphere: Observations of Sources and Transport" and Vania Jordanova presented "Modeling Geomagnetic Storm Dynamics." Thomsen spoke about the importance of geosynchronous orbit observations in forming our opinion of the inner magnetosphere. This altitude is a natural boundary between the plasma sheet in the near-Earth tail and the plasmasphere/ring current/ radiation belts in the inner magnetosphere. She demonstrated how the local time and energy dependence of the ion and electron measurements across the dayside and nightside are being used to improve our understanding the dynamics of magnetic storms. Jordanova discussed some of the modeling techniques used for simulating the plasma distributions in the inner magnetosphere. A detailed description of her ring current model was given, along with a review of many recent results regarding the stormtime ring current. She also presented a new relativistic electron version of her model and some initial results. Both tutorials are online at the GEM website: http://www-ssc.igpp.ucla.edu/gem/tutorial/index.html In the kickoff session for WG1, the following questions were posed to the audience: What is the bare minimum set of physics a model needs in order to get a reasonable description of the subauroral E-fields? What is the full set of physics for a complete description? Which essential processes are going to be the most difficult to capture quantitatively? And finally, is self-consistency necessary, or is an imposed E-field model sufficient? These questions were continually raised during the sessions, and there were numerous presentations and discussions addressing each of these topics. Inner Magnetospheric Stormtime Electric Fields C:son Brandt began the session by summarizing findings from HENA concerning the local-time distribution of the main phase ring current, showing a regular skew toward post-midnight. Kintner described some of the practical impacts that magnetospherically-driven electric fields can have on the mid and low latitude ionosphere, specifically on the redistribution of electron density and the creation of troughs and steep density gradients. Boonsiriseth described her MACEP calculations for the May 1997 storm, showing good agreement with in situ observations from Polar. Sazykin presented RCM results of the March 31, 2001 storm, with SAPS structures arising through much of the main phase. The ion pressure peaked premidnight, in approximate agreement with HENA data for this event. Jahn then showed two proposed methods for measuring inner magnetospheric electric fields, one from multiple in situ particle measurements and the other from successive ENA images. Partial/Symmetry ring Current Transitions DeZeeuw showed results from his MHD-RCM coupled model for IMF turnings, illustrating overshielding and a rapid change from a partial to a symmetric ring current. Weygand presented a superposed epoch analysis of SYM-H and ASY-H, correlating it with Ey,sw, detailing the timings of symmetric and asymmetric delta-B observations as a function of storm phase. Lyons showed Geotail data that indicate that pV^gamma is not always conserved, with substorms reducing the ring current source populations at all energies. M. Chen presented ring current modeling results for the October 1998 storm, showing that AMIE E-fields can create a very asymmetric ring current that peaks on the duskside. Russell showed a compilation of inner magnetospheric magnetometer data, binned according to Dst*, MLT, R, and MLAT, concluding that the stormtime ring current is asymmetric and that the currents go up linearly with Dst (to -100 nT, at least). C:son Brandt showed that D_ENA, a perturbation extraction from HENA data, can have a different time history than Dst, and the peak of the disturbance can be off by up to 30 minutes. Valek showed MENA images of the plasma sheet, with high density times correlating to high solar wind densities. Plasmaspheric Density Structure Gallagher started off the session with an overview of the terminology being encouraged by the IMAGE Mission for observed features of the plasmasphere. With the advent of plasmasphere imaging through the extreme ultraviolet imager (EUV) and the radio plasma imager (RPI), many new terms were being introduced without coordination. The objective for the new lexicon is to reduce confusion as researchers strive to understand the physical processes that shape plasmaspheric density distributions. Song presented an analysis of mass loss and refilling for the storm on March 31, 2001. The depth of the equatorial density, the steepness of the density distribution, and the flatness of the near-equatorial density distribution have been used to quantify the field-aligned density distributions. During this storm and after plasmaspheric erosion, the equatorial densities primarily below 40 degrees magnetic latitude are depleted. At lower altitudes there is little change in density resulting from erosion. No density maximum was observed at the magnetic equator during filling. Field lines were filled significantly in less than 28 hours during recovery. Denton presented the results of analyzing field-aligned density distributions in the plasmasphere and magnetospheric trough using POLAR wave observations. A power-law dependence of density along a field line as a function of L was assumed. Typically a power-law coefficient of 0.5 was found within the plasmasphere and 2.5 outside in the magnetospheric trough. No remaining dependence on magnetic local time or Kp was found. The average L dependence for the equatorial density agrees well with Carpenter and Anderson [1992]. Separate comparison between the Denton and Song approaches also appears to show reasonable agreement even though the functional forms used were different. Gallagher presented a preliminary statistical analysis approach for IMAGE EUV observations. In one technique images were grouped by the integrated Kp and Dst from the preceding 24-hours and by the linear trend in Kp and Dst during that time period. Without excluding low altitude ionospheric contributions to EUV observed intensities, the total plasmaspheric content was reduced from quiet to active times by 32% when binned by Kp and by 54% using Dst. The period from May to July 2000 was analyzed for dependence on solar rotation longitude following the example of Fred Rich [JGR, 2003]. At 800km, a 50% increase in density is found near noon for a solar longitude of about 70 degrees. At larger distances peaks appear at dawn and dusk. Goldstein presented an analysis of the plasmaspheric drainage plume. He showed a broad, initial plume surge in the sunward direction, a rotation of the eastern plume edge toward the west with a thinning plume, then the plume wraps during recovery. The plume also thins on its westward edge due to loss of the original outer plasmasphere on the dawn side of the plasmasphere. He reports that Spasojevic has just mapped a plume to the auroral zone where she sees a correspondence suggesting ring current collisional loss. He finds TEC plumes are not seen together with EUV plasmaspheric plumes unless SAPS are present. Freeman presented BATSRUS MHD flow simulations for the plasmasphere. Instantaneous snapshots of the flow pattern from BATSRUS were shown. In these simulations you can see replication of potential flow pattern corresponding to May 25, 2000 with a narrow tail. The simulations also show a distinct change in the evening flow pattern between southward and northward IMF. Undulations were seen in the IMS during another time period at ULF periods. He also showed a lobe feature around 10am local time that travels antisunward. This is a wave undulation at around L of 5 or 6. Ring current-Plasmasphere Interactions C:son Brandt started the session by describing two types of ring current-plasmasphere interactions. There are “direct” interactions between ring current ions and electrons, cold plasmaspheric electrons and waves (e.g., EMICW, plasmaspheric hiss) that lead to pitch-angle scattering into the ionosphere. There are also “indirect” interactions of ring current and plasmasphere that occur through M-I coupling. He showed ring-current associated field-aligned currents inferred from HENA observations. Ring-current associated field-aligned currents can cause ionospheric conductivity gradients that lead to the formation of a mid-latitude SAP electric field. Complementing this presentation, Goldstein showed EUV observations illustrating how SAP electric fields can affect plasmaspheric erosion and plume formation. By adding a simple model of the SAP potential, a localized potential drop on the dusk side, to the Stern-Volland electric field, he was able to reproduce qualitatively the plasmaspheric features seen in EUV images. S. Liu presented comparisons of storm-time ring-current electron simulations with CRRES observations that illustrated the “direct” interaction between the ring current and plasmasphere. He found good agreement between simulated and observed ring-current electron flux profiles at low energies if he invoked an electron loss model that incorporated the dynamic plasmaspheric boundary. Finally, Liemohn presented a study of the influence of ionospheric conductance on the morphology and intensity of the ring current and plasmasphere. He compared plasmaspheric results with EUV images using 3 different E-field models: the McIlwain, Weimer, and a self-consistent model, for the April 2002 storm. The conclusion is that the self-consistent simulation produced the best match to the data. MIC/IMS joint session: Electrodynamics of Inner/Midlatitude MI-Coupling as a Plasma Source Region Kintner led off the discussion with a challenge: can models of the inner magnetosphere explain ionospheric motion? And this: is the ionospheric response significant to the magnetospheric dynamics? He then gave a review of coupling between the inner magnetosphere and subauroral ionosphere and thermosphere. Ridley gave an overview of the strengths and weaknesses of using results from the AMIE model at midlatitudes. Makela then presented correlations of Jicamarca ISR data and solar wind parameters, showing that the interplanetary electric field can penetrate to the equator (undershielding) for hours at a time. Dick Wolf showed some results from the RCM of SAPS and other E-field features. He noted that there is positive feedback in the ionosphere: faster flow lowers the conductivity, which increases E and thus makes even faster flow. C:son Brandt presented comparisons of satellite and groundbased data, showing that Iridium FACs are morphologically consistent with HENA and ISR data. Finally, Goldstein showed that the Volland-Stern model gets most of the plasmapause structure correct, but adding a simple SAPS E-field gets the plasmaspheric plume shape even better. IM/S Joint Session (WG1, WG2, WG3): Recent GEM Storms Analysis Fraser kicked off this joint session with an introduction of the new ULF Waves Working Group. He defined ULF waves to run from 0.002-5 Hz with: Pc1 0.2-5 Hz, Pc2 0.1-0.2 Hz, and Pc3-4 7 mHz up to 100 mHz. Pc5's period can be longer of course. Pi1 oscillations are 1-40 seconds and Pi2 is 40-150 seconds in period. Pi is pulsation impulsive and Pc is pulsation continuous. All waves are present in the magnetosphere. Wavelengths scale to the size of the magnetospheric cavity. Propagating waves exit. ULF waves interact with particles, fields, and plasmas in many ways and locations in the magnetosphere, plasmasphere, and ionosphere. The working group was initiated in response to the increasing importance of the new methods and analysis of ULF waves in investigating the subjects of magnetospheric and ionospheric physics that are the focus of GEM campaigns. Brian considers WG3 to be a working group that contributes to the others. The Alfven velocity controls ULF waves in the magnetosphere. Mass loading leads to a double peak in the Alfven velocity, as you look inward. The first peak is perhaps just inside L=6 and the second inside L=2. The minimum between is due to mass loading in the plasmasphere. One of the motivations of having a ULF working group is to discuss the derivation of densities in the magnetospheres. They want to pick up on relevant campaigns and contribute where needed, e.g. plasma density measurements for WG1. ULF Working Group Aims: - Cooperate with IAGA on developing a ULF wave index for use in statistical studies and other applications. - Deliver products routinely to the community, e.g. plasma density profiles and heavy ion concentrations. - Consult with the GPS-TEC community on plasmaspheric density measurements. In the future they plan to meet at the Fall 2003 AGU MiniGEM workshop to plan specific "campaigns." The rest of the session was devoted to recent results on the selected GEM Storms. Barker et al discussed efforts to study and predict radiation belt (RB) electrons. They are using the radial diffusion equation, where they assume a radial diffusion coefficient that varies with L^6 at L=4 and L^10 at geosynchronous. Radial diffusion can describe the trends, but does not well describe the RB magnitude. For one storm in September they were able to reproduce both. Feidel presented their work with data assimilation using the Salammbo code. It takes considerable effort to insure that quality or correct data is fed into the modeling code, otherwise garbage-in leads to garbage-out. They took many conjunctions and looked for the best fit between observation sites. A LANL GEO and CRRES MEA conjunction on Sep 3, 1990 17:03 worked well. They did the same thing with GPS, LANL and CRRES on Sept. 15, 1991, which worked well. Each channel must be examined to determine sensitivity to contamination. With conjunction a sin(alpha-eq)^N pitch angle distribution can be determined. Without conjunction they must set the distribution function to a default profile. They intend to be able to input up to 20 satellite data measurements into the model. This form of data assimilation is called model nudging. Liemohn presented the influence of ionospheric conductance on their ring current modeling. They computed azimuthal currents in the magnetosphere to get field aligned currents (FAC) through a potential solver to compute electric fields. They include charge exchange, collisions, and vary the electric field model. They perform a Poisson solution for potential throughout the ionosphere. The self-consistent calculation does better than other (non-self-consistent) e-field approaches. A parametric study of how the ionospheric conductance changes the ring current was shown. Gallagher presented a brief overview of the quality and quantity of IMAGE Mission extreme ultraviolet imager (EUV) observations of helium ions during the IMS/WG1 storms. Observations are limited to between midnight and dawn for the October 2, 2000 storm. There are extensive observations of various structures, e.g. the convection plume and plasmapause erosion to slightly less than L=2 during the March 31, 2001 storm. For the October 21, 2001 storm, mostly nightside observations of plasmapause erosion and the plume are available. Observations during the April 17, 2002 storm are spotty. IMS joint session: Inner Magnetosphere Interconnectedness and IMS Wrapup The main decision about the future of IMS was that an IMS Challenge will be issued within the next year. All IMS researchers are requested and encouraged to contemplate possible candidate events and challenge format details. The challenge will be defined at the GEM Mini-Workshop before the Fall AGU meeting, on Sunday December 7, 2002. Everyone is invited to come and participate in this discussion. More information on this IMS Challenge will be given in a future GEM Messenger announcement. +-------------------------------------------------------------------------+ |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 | | | | | |URL of GEM Home Page: http://www-ssc.igpp.ucla.edu/gem/Welcome.html | |Workshop Information: http://gem.rice.edu/~gem | +-------------------------------------------------------------------------+