*************************** ** THE GEM MESSENGER ** *************************** Volume 6, Number 40 July 8, 1996 --------------------------------------------------------------------------- 1996 SNOWMASS REPORT BOUNDARY LAYER CAMPAIGN WG 1: RECONNECTION ELECTRIC FIELD AND MAGNETOPAUSE BOUNDARY NORMAL MAGNETIC FIELD --------------------------------------------------------------------------- From: "Larry Lyons" This year's working group met for about 1.5 days. It carried out four main tasks. a) Completed studies of intervals discussed at previous Snowmass workshops, b) Began studies capitalizing on the unique opportunities provided by ISTP. c) Initiated detailed comparisons between data and a variety of models in an attempt to assess the strengths of each model. d) Made detailed plans for studies that will be presented and discussed at the next Snowmass meeting. The following sections summarize by scientific topic the state of various studies. The scientist taking the lead on each interval is identified in parentheses. I. Dayside reconnection and convection studies A. Determination of the dayside reconnection rate using SuperDARN measurements (Baker) 1. 22 Aug. 1995: excellent data from Goose Bay and Saskatoon radar pairs from ~12-23 UT. Bz ~ -3 nT. High latitude magnetometers (MACCS and Greenland) show interesting spike events extending over at least 6 h of MLT. 2. 21-22 Nov. 1995: good data from six northern hemisphere radars (first time) for ~8-22 UT on both days. Supporting ground B data from MACCS (Engebretson, Zesta) and Greenland (Friis-Christensen, Moretto) to be made available. Gentle IMF changes on 21 Nov., large IMF changes on 22 Nov. Halley shows good scatter on 22nd during interval when IMF is southward. Papitashvili to run IZMEM model for this interval. 3. 5-7 Dec. 1994: good data from two northern hemisphere pairs from ~13-22 UT. Smooth IMF changes on 5 Dec., large rapid By and Bz changes on 6 & 7 Dec. Dayside auroral observations available from Svalbard (Smith) on 6 Dec. Halley shows important time variation of cusp location (Pinnock/Rodger to pursue). B. Dayside reconnection studies under sunlit conditions with IS radar at Sondrestrom (Blanchard): Useful addition to other studies since have data for many of the above periods; statistical evaluation of reconnection rates versus MLT and IMF possible; separatrix identification technique development in progress. II. First study of 2-D electric fields relative to poleward progression events (Engebretson): 24 Aug. 95; weak southward IMF; ~1/2 hr period progressions of the type described by Stauning (JGR, 1995) seen in MACCS B data; good SuperDARN data available from two pairs. III. Ground magnetic field responses poleward and equatorward of separatrix and their relation to electric fields (Joint WG-1 and 3 study; Friis-Christensen, Moretto, Clauer, Ridley): 22 Aug. 95 plus other dates showing well defined ground response in Greenland B, MACCS, and low-latitude Japanese stations (night side). IV. Dayside-substorm association (first studies). A. Ground electric field measurements to be combined with near-Earth nightside GEOTAIL data for isolated substorm onsets at 1108 and 1502 UT on 22 Nov. 1995, including flows during recovery periods. Reasonable data from Halley ~1500 UT. (R. Nakamura) B. Dayside-nightside optical comparisons during substorms (R. Smith): 12 Jan. 1994 plus other dates; available electric and magnetic field data to be included. V. ISTP 18-19 Oct. 1995 magnetic cloud event, studies in progress: A Global convection response to cloud (Lu) B. Saturation effects in polar cap size and cross-polar-cap potential (Lu, Reiff) C. Dayside electric field response to large interplanetary pressure and magnetic field discontinuities; e.g., 60 to 5 cm-3 reduction in density without large change in B (Senior) D. IZMEM and comparison with Lu/Reiff results (Papitashvili) E. Vector magnetic field comparisons with models (Reiff's idea, needs Interball B data) VI. Conjugate reconnection study using Halley and Goosed Bay radar (Pinnock - study in progress): 21 July 1992 plus other dates; IMF By associated differences between hemispheres are seen, and temporal structure is to be related to time-dependent model of reconnection. VII. Identification of three kinds of convection boundaries (Ridley): a) Stationary with character modified by IMF, b) shear reversal moving equatorward and poleward in response to IMF changes, and c) oscillations on boundary in response to strong shears associated with large By. (2 papers now published, and one submitted) VIII. Synoptic Space Weather Maps for stable IMF intervals (Lyons, Lu). The purpose of these maps is to produce detailed ionospheric maps of the electric field, magnetic separatrix, currents and boundary layers for detailed comparison with models, and especially the Global Geospace Circulation model. Several intervals of steady but different IMF conditions have been identified. A. 27-28 Jan. 1992: Paper submitted and results being used for model comparisons - see below (cases with large IMF negative By and positive and negative Bz, one case with small |By| and positive Bz). B. 12-13 Jan. 1989, |B| ~ Bx, small |Bz| and |By|, preliminary results: Convection strength more strongly affected by small |By| than might have thought; large polar-cap regions of soft electrons (SEZ) and intermittent polar-cap arcs; size of polar cap stays large, even when convection weak for |B| =~ Bx ~ 8 nT. C. Future stable IMF intervals for maps: 20-21 July 1992 (3 intervals: Bz ~ Bx ~ 0; |By| large, B ~ Bz ~ 12 nT; Bz ~ 0, |By| large, Bx negative) and 18-19 Oct. 1995 (2 intervals: 4 hr of B ~ Bz ~ -20 nT; large positive Bz interval) IX. High-altitude cusp signatures in POLAR energetic particles (Spence): Ion energy dispersion seen up to ~200 keV in "traditional cusp"; See strong fluxes of ~20-200 keV ions well within polar caps in events which last ~4 hr. These occur when have Bz large and positive, and when have small positive Bz and large |Bx|. Many of examples on line for correlation with ground data; signatures in ionosphere not yet identified. X. Joint WG1/GGCM session on model comparisons with Synoptic Space Weather Maps for stable IMF intervals on 27 and 28 January 1992. This activity arose as a result of a suggestion at the last GEM steering committee meeting, and has been termed the 'Grand Challenge'. These periods were selected because the IMF was relatively stable. The models were of three basic types: empirical models, large-scale codes, and field construction models. Predictions included the cross polar cap potential, the location of the separatrix between open and closed field lines, the convection pattern, and geomagnetic indices. Also, preliminary results of Onsager provided an explanation for the observations of a "SEZ (soft electron zone)" in the polar caps as a region magnetosheath particle access from the flanks to the polar caps along open field lines. It was agreed that the 10 modellers will write up their comparisons by 1 October 1996 for (hopefully) publication in a special section of JGR. **The Future** It was decided that there would not be a WG1 meeting associated with the Fall AGU. At the next Snowmass meeting, results from this year's continuing and planned studies will be emphasized. Also, a subset of definitive results will be selected for possible additional GGCM tests. Our program is likely to include several cross working group sessions to address some remaining issues such as the relationship between small scale and large scale dayside structures (joint with WG3). The GEM steering committee has agreed to produce an interim report on the progress of GEM to date. Therefore in the coming months we will be soliciting input from members of WG1, and seeking a complete list of publications where the GEM initiative has played a critical role. The steering committee also agreed that the Boundary Layer campaign will wind down. However the role of the dayside studies will continue to play a critical role in GEM, through scientific topics such as dayside-nightside links and through providing data to test and validate the General Geospace Circulation Model and its component parts. 8 July 1996 LARRY LYONS ALAN RODGER. Larry_Lyons at qmail2.aero.org A.Rodger at bas.ac.uk +-------------------------------------------------------------------------+ |To add name to the mailing list, send a message to: editor at igpp.ucla.edu | |For message to whole GEM mailing list, send to: gem at igpp.ucla.edu | | | |URL of GEM Home Page: http://igpp.ucla.edu/gem/Welcome.html | |Please update your e-mail address. | |CAUTION: Do not send messages to gem at igpp.ucla.edu unless you want | | your message to go to everyone in the GEM mailing list! | +-------------------------------------------------------------------------+