*************************** ** THE GEM MESSENGER ** *************************** Volume 2, Number 10 July 15, 1992 ------------------------------------------------------------------- Reports of Boundary Layer Campaign Working Group Meetings, Part II Snowmass, Colorado, June 28-30, 1992 ------------------------------------------------------------------- Report of GEM Working Group 1: Reconnection Electric Field and Magnetopause Boundary Normal Magnetic Field O. de la Beaujardiere and L. R. Lyons (co-chairs) Our working group had an 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 evaluate ionospheric plasma transport in the vicinity of the boundary between open and closed field lines and dayside boundary layers and 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 workshop. Specific campaign dates and approximate UT times are: 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 - 18 UT; 28 and 29 March 92, 05 - 20 UT; 2 and 3 Aug. 1991, 1200 - 1600 UT. Data from four of the campaigns were considered during the workshop, leading to a large number of planned joint studies. Enthusiasm was so high that a large number of individual wanted to present results from the GEM campaigns at the Fall, 1992 AGU meeting. As a result, a special AGU session entitled "Processes Near the Dayside Magnetic Separatrix and Boundary Layers as Observed in the Ionosphere" has been arranged, and we encourage the submittal to this session of papers describing results from GEM observing campaigns as well as other relevant results. We first focussed on the campaign period Jan. 27-29, 1992. There are long periods of relatively steady IMF having significant Bx and By components. Excellent, yet preliminary, polar-cap potentials from AMIE were presented by Gang Lu of NCAR/HAO. These patterns showed significant hemispheric differences and should be valuable for comparison with model results. A large amount of ground- based data is still to be incorporated into the AMIE runs, and we anticipate that the final potential patterns will be among the most accurate ever determined. Papers and Fall AGU talks on this campaign that were planned at the workshop by participants are: Lu, with data from many others: AMIE potential patterns (paper, talk) Rich et al.: Mantle flow patterns relative to the IMF direction (paper and talk if get good results): Lyons, Rich, Lu, de la Beaujardiere et al.: Determine particle boundaries and relate to AMIE potential patterns (paper) Baker, de la Beaujardiere, Lyons: Combine Sondrestrom and Goose Bay data to get two-dimensional electric field maps with high spatial and temporal resolution; add particle boundaries (at least one paper, talk) Watermann, de la Beaujardiere: Fold Sondrestrom ne and Te data into study (paper, talk) Rogers, Lu: Relate F-region patches on night side to potential patterns on day side (paper, talk) Papitashvili: Results from electrodynamic parameter model (talk) Onsager: Use f(v) plots to map particle distributions back to the magnetopause (paper, talk?) Lyons et al.: Test models with AMIE potential patterns and boundaries from this and other campaigns (paper eventually) Excellent data is also available for the campaign period March 28-29, 1992, and cusp coverage is particularly good on the 29th from Goose Bay. We decided to pursue the analysis of data from this campaign by first combining the Goose Bay and Sondrestrom data to obtain local 2-D convection patterns. AMIE will be applied by Gang Lu after completing her analysis of the Jan. 27-29 campaign data. The campaign period Jan. 6-7, 1992 has unique radar, optical and induction coil B cusp observations from Svalbard in darkness, as well as excellent global data from polar- orbiting satellites, radars, and magnetometers. AMIE runs for this period will be pursued by Gang Lu, but only after she analyzes her results from the above two campaigns. Specific plans for this campaign at this time are: Lockwood, McHarg, Minnow: Bring radar, optical, and induction coil data together (at least one paper, 3 talks) Lu et al.: AMIE runs (paper eventually) de la Beaujardiere, Lockwood: Sondrestrom-Eiscat comparisons (paper) Dramatic dayside field oscillations directly related to oscillations in the IMF By-component were observed on the day side during the campaign period Aug. 2-3, 1991. These oscillations demonstrate strong coupling between the interplanetary and convection electric fields. Specific plans for this campaign at this time are: Stauning et al.: Greenland and IMF data showing direct connection (paper almost ready, talk) Rosenberg, Stauning, AT&T magnetograms: Conjugate study of oscillations (paper, talk) Fraser, Arnoldy: Antarctic wave data on day side (paper?) Rogers: PACE data oscillations (paper?) de la Beaujardiere, Clauer, Stauning, Baker: Comparison of oscillations with Sondrestrom and Goose Bay day (paper, talk?) ===================================================================== Report of GEM Working Group 2: Particle Entry, Boundary Structure, and Transport Pat Newell (chair) Our group debated a number of topics concerning reconnection sites and time scales, ionospheric convection and transients, and related subjects. Although there was lively debate, the underlying disagreements are in many (but not all) cases less severe than might be thought. A scenario emerged in which the IMF is constantly changing on a variety of time scales (as pointed out by Mike Lockwood), and the magnetosheath field is even more variable (as pointed out by Nelson Maynard). Hence it is not surprising that in situ observations of reconnection indicate merging is variable on all time scales of observation. Jack Gosling reports that on a given pass through the magnetopause, the chance of observing some clear signature of merging (such as accelerated flow speeds) is quite high (probably between 25% and 50%). Although one (presumably) rarely passes through the magnetopause precisely at the merging site, the fact that one is so often close enough to observe merging signatures strongly suggests the possibility that merging is always occurring somewhere on the magnetosphere, with the location and size of the merging region shifting according to the constantly ongoing shifts in the magnetosheath field. Nancy Crooker suggests that the resulting magnetopause is a "zoo" with a multitude of transient effects and reconnection changes ongoing simultaneously. The location and rate of merging is strongly influenced by magnetic shear. Especially along the tail and flanks of the magnetopause, the experimental evidence presented by Jack Gosling reveals the importance of magnetic shear, although a 180 degree shear is not actually necessary. For reconnection in the equatorial plane on the dayside, magnetic shear is less crucial, with reconnection occurring for as little as 90 degrees of shear, and sometimes even less. Even at the subsolar magnetosphere, however, reconnection is still most likely for the highest shears, although a strictly anti-parallel merging model greatly underestimates the likelihood of merging at this location. We considered the question whether convection in the ionosphere is fairly steady or pulsed. This may have been the wrong question to ask, since Mike Lockwood presented arguments that inductive effects act as a low-pass filter smoothing out the sharp effects of pulsed reconnection. Moreover, the magnetopause results discussed above suggest that reconnection is not pulsed; indeed, as Mike Lockwood pointed out, even FTEs do not have any particular characteristic period -- there is nothing very prominent about the 8 minute number so often cited. Kile Baker presented results from the Goose Bay and Halley HF radars which indicate that convection in the ionosphere is also constantly undergoing changes on all time scales. Although "pulses" of rapid (< 2 minutes) changes in convection can indeed at times be observed, so can very slow gradual changes, and everything between. Convection in the near-noon ionosphere rarely if ever disappears, and rarely if ever is stable or consistently pulsed. Instead the dayside convection patterns reported by Kile Baker are quite consistent with the sorts of ionospheric patterns one might have expected from the "zoo" of constantly on-going and constantly changing reconnection observed at the magnetopause. Thus the idea of reconnection as a series of "pulses" driving the magnetosphere and ionosphere is as inaccurate as the idea of a steady IMF and magnetosheath field driving a steady convection. Since all present who spoke up agreed that reconnection occurs, and since all agree that significant changes occur, presumably everyone agrees that transient reconnection occurs. However the best studied signature of apparent transient reconnection, Flux Transfer Events (FTEs), is still somewhat controversial. David Sibeck pointed out more clearly than has been done previously how nearly all of the signatures of FTEs are in fact wave signatures, and would be shared by any other explanation which produced a "bump" on the magnetopause. Presenting evidence from two-spacecraft observations (AMPTE IRM and AMPTE CCE) showing magnetosheath dynamic pressure increases associated with FTE-like signatures observed at the magnetopause, Sibeck argued that pressure-driven waves on the magnetopause can explain many FTE observations. Several members of the group, including Chris Russell, argued that Sibeck's explanations of how waves produce FTE signatures are too qualitative ("hand-waving") and not rigorous enough to be convincing. Still the best argument that FTEs are merging related continues to be one of the oldest ones -- the evidence that the overwhelming number of magnetosheath FTE observations occur for southward IMF. Nelson Maynard and Jack Gosling both argued that ionospheric researchers who have tried to relate their observations of transient merging effects only to FTEs are making a mistake. They believe that FTEs are not the only type of transient merging signature observed at the magnetopause. Indeed, since merging is constantly changing, transients of all sorts are to be expected, and the search for a one-to-one correspondence between certain ionospheric effects and FTEs has probably been over-emphasized by our field in recent years. Ennio Sanchez reviewed the development of MHD model representations of the open magnetosphere. The most sophisticated model to date appears to be that of Siscoe, Lotko, and Sonnerup, in which the mantle continues to be represented by a slow mode expansion fan, the LLBL by a rotational discontinuity, and the transition between the two is smoothly joined through Ohms law in the ionosphere. Some of the predictions of this model are that the mantle (not the LLBL) is the main voltage generator, that the convection reversal would actually take place inside the LLBL (instead of at its Earthward edge), and that the region 1 currents flow within the LLBL. Although none of these predictions are agreed upon beyond dispute, the evidence appears to be in favor of the model (e.g, the ionospheric observations by Newell et al., December 1991 JGR). Sanchez also discussed how voltage changes observed in the mantle on time scales of less than an hour -- representing a large part of such changes -- are attenuated by self-inductance in the magnetosphere ionosphere circuit, leading to half or less of the voltage change amplitude ever being imposed on the ionosphere. His arguments were in some ways parallel or complementary to those made elsewhere by Mike Lockwood. Odile de la Beaujardierre presented clear evidence that particle and current boundaries in the ionosphere do not always precisely coincide. This is true no matter how the particle regions are identified, since one can at times observed dramatic changes in the particle precipitation which have no correspondence in the current signature, and vice versa. However generally the current 1 system seems to straddle the cusp or LLBL poleward boundary; although at times the R1 system is entirely within the LLBL. The mantle current system generally lies within the region of mantle precipitation, although it often continues poleward of where any ion precipitation can be observed. Finally Gerald Fasel reported some new observations -- or more properly new interpretation of neglected old observations. He showed instances of poleward moving auroral transients in the dayside ionosphere, at times when the auroral oval as a whole was shifting equatorward. A new facet of the observations is that the transients can experience multiple brightenings, suggestive of the scenario previously suggested by Lou Lee, in which dayside reconnected field lines can undergo additional subsequent reconnections before straighting out their kinks. +--------------------------------------------------------------------+ |To add name to the mailing list, send a mail to: guan at igpp.ucla.edu | |For message to whole GEM mailing list, send to: gem at igpp.ucla.edu | |For message to a specific working group, send to: | | gem_field at igpp.ucla.edu (WG1); gem_boundary at igpp.ucla.edu (WG2);| | gem_current at igpp.ucla.edu (WG3); gem_data at igpp.ucla.edu (WG4) | |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! | +--------------------------------------------------------------------+