-------------------------------- REPORT ON 1993 SNOWMASS WORKSHOP -------------------------------- GEM WORKING GROUP 1: RECONNECTION ELECTRIC FIELD AND MAGNETOPAUSE BOUNDARY NORMAL MAGNETIC FIELD Co-chairs: L. Lyons and O. de la Beaujardiere Our working group had another extremely successful workshop that was filled with important contributions from a large number of individuals. The primary goals of our working group are to evaluate the dayside reconnection electric field and the normal component of magnetic field at the magnetopause. Our approach is to determine ionospheric plasma transport in the vicinity of the boundary between open and closed field lines and dayside boundary layers and to evaluate the large-scale transport over the polar caps. Our analysis is being performed using ground-based and polar-orbiting satellite data, and our results are to be compared with models (MHD and non-MHD) of high-latitude convection to test and improve the models' distribution of magnetic field normal to the magnetopause. To pursue our goals, six specific coordinated observing campaigns were organized prior to the 1992 workshop. Specific campaign dates and approximate UT times are: 2 and 3 Aug. 1991, 1200 - 1600 UT; 22 Dec. 91, 09 - 22 UT; 6 and 7 Jan. 92 , 05 - 13 UT; 27 Jan. 92, 0940 UT - 29 Jan., 18 UT; 20 March 92, 10 - 19 UT; 28 and 29 March 92, 05 - 20 UT. Between the 1992 and 1993 workshops, data were acquired for the following additional campaign periods: 21 July 1992, 0933 - 2156 UT; 13, 14, 17, 18 Aug. 1992, 1230 - 1800 UT; 23 - 26 Nov. 1992, 1152 - 1801 UT; 07 Dec. 1992, 2006 - 08 Dec., 2148 UT; 18, 22 Dec. 1992, 0700 - 1900 UT; 17 March 1993, 1200 UT - 18 March, 1444 UT; 24 March 1993, 00-08 UT; 26 March 1993, 1039-1704 UT. Data from seven of these campaigns were specifically considered during the workshop. Progress and plans that were discussed during the working group sessions are summarized below: 27-29 JAN. 1992 As we did last year, we first considered the 27-29 Jan. 1992 campaign. This period has long intervals of relatively steady IMF having significant Bx and By components. AMIE potential patterns have now been completed by Gang Lu for this entire period, and she presented selected results for both hemispheres for various IMF conditions. A paper describing these results is nearly complete. Lyons identified several extended intervals of relatively stable IMF that contained a number of DMSP satellite passes over each polar cap. Lu ran AMIE for these extended intervals, including all available DMSP data in such a way that "instantaneous" potential patterns were obtained. As of the time of the workshop, only preliminary AMIE results were available for these intervals, but final results should be forthcoming. Lyons, Lu and Rich plan to combine these potential patterns with particle data from the DMSP, EXOS-D and NOAA-12 satellites to locate as well as possible the magnetic separatrix. In this way, we plan to obtain a determination of the potential patterns over open polar cap field lines in both hemispheres that is as accurate as possible. This work has already been initiated. The results from the extended-interval AMIE runs are to be used to test various models of polar cap convection. Lyons plans to make comparisons with the Aerospace/Schulz source surface model that bases polar-cap potential patterns on having a uniform fraction of the IMF penetrate the magnetopause. Toffoletto plans to make comparisons with the Toffoletto and Hill open magnetosphere model that is based on assumptions concerning reconnection theory. Crooker plans to make comparisons with her model where the interplanetary electric field maps to only a limited region of the dayside ionosphere. By making these comparisons with theoretical models, we plan to assess the relative merits of the different models and to improve the models where feasible. Papitashvili is already making comparison of the extended-interval AMIE results with the IZMIRAN model of polar-cap convection that is based on polar-cap magnetic records. This model gives statistical potential patterns versus season and the IMF. His goal is to both improve the IZMIRAN model and to determine whether it can be used to augment AMIE results in regions where data are lacking. Papitashvili (with de la Beaujardiere and Clauer) is also in the process of directly comparing the model electric fields with radar electric field measurements. A detailed study of data near ~1500 UT on 27 Jan. is being pursued. At this time, Goose Bay was near noon and obtained some radar echoes in the vicinity of the cusp. Baker plans to do a detailed analysis of this data. Sondrestrom was near 1400 MLT at this time and analysis of the radar data by de al Beaujardiere shows equatorward moving regions of soft auroral precipitation on what appear to be the closed field lines. A paper describing these results is currently in preparation. Rodger has nearly completed a paper on data from 28 Jan. that examines F- region ionization enhancements that drift across the polar cap, and relates their formation to IMF changes that modify the reconnection rate on the day side. 6-7 JAN. 1992 The campaign period 6-7 Jan. 1992 has exciting optical and induction coil magnetometer observations of the cusp from Svalbard in darkness, as well as excellent global radar, magnetometer, and polar orbiting satellite coverage. G. McHarg focused considerable attention on the Svalbard observations for this period, and has four papers in various stages of preparation. His studies are focusing on the identification of the cusp using a combination of 5577 and 6300 A emission measurements. With these wavelengths, the average energy of precipitating particles can be obtained, and the cusp shows up as a distinct region of low average energies with higher average energies identifiable to either side. McHarg has also used the Svalbard observations to infer conductivities, field-aligned currents, and precipitating particle fluxes. Gang Lu plans to run AMIE for this period, but only after her studies for the 27-29 Jan. and 28-29 March 1992 periods are completed. 2-3 AUG. 1991 The 2-3 Aug. 1991 GEM period has been a particularly fruitful period for study by P. Stauning and his colleagues. He has found a dramatic association between oscillations in the IMF By component and the ground H-component near the cusp. His results show a direct connection between the interplanetary and polar- cap electric fields, with perturbations propagating poleward across the polar cap from the magnetic separatrix. The poleward propagation of these events, which were termed "poleward progressions" by Stauning, appears to result from the motion of the IMF oscillations as they are carried across the magnetosphere by the solar wind. A paper describing these results has already been submitted for publication. An second paper has also been submitted, which describes the results of a statistical study of the poleward progressions. They are found only for IMF Bz < 0 and have a maximum occurrence rate near noon. Similar H-component perturbations are also found when the IMF Bz > 0, but the perturbations do not propagate poleward. Stauning et al. are pursuing two additional studies concerning the poleward progressions. The first relates field-aligned currents to the ionospheric velocity shears associated with the poleward moving H perturbations. The times of upward field-aligned current have the potential for giving poleward moving auroral forms that are often observed near noon. The second study focuses on the effects of the poleward progressions on other ionospheric phenomena. The poleward progressions during this campaign period are also seen simultaneously in the southern hemisphere and the northern hemisphere, and this conjugacy is being studied by Rosenberg, Clauer, and Rodger. Because high spatial-resolution data have been obtained from near the cusp for this GEM period, Knipp and Emery are planning to modify the AMIE procedure to pursue small spatial-scale phenomena near the cusp. They plan to compare their results with riometer as well as magnetometer data. 23-26 NOV. 1992 The next campaign period that was considered was 23-26 Nov. 1992. Interesting magnetometer features were found in the MACCS array west of Greenland on 23 Nov. A particularly large pulse was seen at ~15 UT, that was identified as a vortex by Zesta and may have an electric field signature in the Sondrestrom radar data. This data set is presently being analyzed by Zesta and Engebretson. The Sondrestrom radar was run continuously during this period, and several interesting events are being considered by de la Beaujardiere. Goose Bay data will also be made available for this period, and Baker is going to check whether usable echoes were obtained from near the cusp. 28-29 MARCH 1992 Considerable effort has already gone into analyzing data from the 28-29 March 1992 GEM equinox campaign. This is the second campaign period for which Lu is running AMIE and she now was good results for the entire campaign period. Unfortunately, IMF data was only available for a few hours, but the AMIE potential patterns imply that the IMF Bz was negative most of the time. Two excellent opportunities were found for studying the cusp on 29 March, during the time when the IMF data are available. First, at 0932 UT, DMSP F10 was directly over EISCAT as the satellite traversed the inner edge of the cusp. There was good coverage by EISCAT at this time, and Denig volunteered to analyze the simultaneous EISCAT and DMSP data. There was also good AC and DC magnetic field data from Svalbard at this time that McHarg plans to analyze. Between ~1400 and 1600 UT there was excellent cusp data available from the Sondrestrom and Goose Bay radars. De la Beaujardiere has identified a region of cusp-like precipitation from Sondrestrom Te and Ne measurements, and has measured equatorward motion of this feature as the IMF Bz became increasingly negative. Excellent two-dimensional maps of the electric field over the cusps are also available from Goose Bay at this time, including the period during which it moved equatorward over Sondrestrom. This should be an ideal period for measuring the reconnection electric field and the electric field pattern near the dayside separatrix. Analysis of these data is to be pursued be de la Beaujardiere, Baker, and Lyons. During this same period, there is excellent data available from the Greenland magnetometer chain that can be used to look for the Stauning poleward progressions. A significant IMF By change that would be expected to be associated with a poleward progression was identified at 1400 UT. Stauning, de la Beaujardiere, and Lyons plan to combine the Greenland magnetometer data with the Sondrestrom data to study the poleward progressions, and to place the results in context with the other cusp measurements and the AMIE potential patterns. Lockwood has already published a paper in Nature using data from this campaign period. He identified poleward propagating auroral forms that were interpreted as the signature of pulsed reconnection. His event look very similar to the Stauning poleward progressions, but Lockwood's interpretation is considerably different form Stauning's. We hope to address these differing interpretations. 24 MARCH 1993 On 24 March 1993, there was some Goose Bay coverage close to noon, but Sondrestrom did not take data near noon. Excellent substorm data on the night side are available from de la Beaujardiere, Doe, Baker, Stauning, and Rosenberg, and it was decided that this would be an excellent period to use for the future tail/substorm GEM campaign. 17-18 MARCH 1993 During the 17-18 March 1993 campaign, Sondrestrom data shown by de la Beaujardiere show generally quiet conditions near magnetic noon on 17 March. However, an electric field disturbance has been identified. Ground magnetometer and riometer data show some interesting dayside activity, with a particularly good event at 1450-1500 UT that might be associated with the disturbance seen by the Sondrestrom radar. Unfortunately, the Goose Bay radar probably received no echoes near the cusp. Rosenberg, Stauning, Zesta, and de la Beaujardiere plan to combine and analyze the available data for this period. 21 JULY 1992 For the 21 July, 1992 campaign period, excellent data near noon are available simultaneously from Sondrestrom, Goose Bay, and Halley Bay. Poleward progressions are also clear in the Greenland magnetometer data. This period has great potential for future analysis. Using the data acquired during these campaigns, as well as other data, the ionospheric signatures of intense, soft particle precipitation in the cups/LLBL region can be investigated. De la Beaujardiere identified a particularly promising technique based on Sondrestrom radar measurements of electron densities and ion and electron temperatures in the F-region. She plans to evaluate these signatures, with the goal of being able to identify the cusp/LLBL region and hopefully its equatorward boundary. This could greatly improve our ability to measure the reconnection electric field. As a summary, we anticipate that there will be four main results from the studies of this working group: 1. The best possible determination of polar-cap convection patterns yet obtained. 2. Tests of models for polar-cap convection 3. Several evaluations of the reconnection electric field at the estimated ionospheric location of the magnetic separatrix 4. Evaluation of the Stauning poleward progressions as the cause of disturbances moving poleward from dayside separatrix.