Summary

To take maximum advantage of the opportunity afforded by this suite of prime spacecraft, the worldwide space research community has determined that intensive data collection campaigns are necessary. This report summarizes the first Inter-Agency Consultative Group for Space Science (IACG) campaign that has been defined, for the study of "Magnetotail Energy Flow and Non-Linear Dynamics." Two other campaigns have so far been identified: "Boundaries in Collisionless Plasmas" and "Solar Events and their Manifestations in Interplanetary Space and in Geospace," both to take place in 1996.

The Airlie House Workshop on Magnetotail Energy Flow and Non-Linear Dynamics at Airlie House, Virginia, U.S.A., June 1-3, 1992, was organized by the IACG Working Group-1 (Science) around three science topics: (1) Plasma Dynamics of the Distant Tail; (2) Equilibrium Tail Structure; and (3) Tail Dynamics and the Interplanetary Magnetic Field (IMF). These topics were listed in the IACG Core Report of November, 1991, (Appendix A of this Report) as important goals for the first campaign, and, in addition, were appropriate goals to address with the available prime IACG spacecraft in late 1993 and early 1994--GEOTAIL, WIND, and INTERBALL. All workshop participants were assigned to a sub-group, chaired by the Project Scientists for these three prime IACG spacecraft, and were charged with developing a campaign plan to address one of these three science topics.

The workshop began with a discussion of lessons learned from previous spacecraft campaigns: with Dynamics Explorers, International Sun-Earth Explorers, Active Magnetospheric Particle Tracer Explorers, and the Polar Region and Outer Magnetosphere International Study. Successful campaigns require a central planning focus, formal procedures for making campaign operating plans and for communications, common rules for data exchange and use, and a mechanism for planning and carrying out coordinated data analysis.

Each sub-group then presented a straw-man campaign plan, which had been prepared in advance on the sub-group topic, along with descriptions of the prime IACG spacecraft and orbits. This was followed by presentations describing other resources that will provide an enabling environment for the campaign. During the second and third days, the participants alternately met in sub-groups to refine their strategies and presented their latest versions in plenary sessions.

The success of the campaign will be greatly facilitated by the "enabling environment," which includes other spacecraft to provide complementary data, ground observations, theoretical modeling and simulations, other related research initiatives to be coordinated through the Solar Terrestrial Energy Program (STEP), spacecraft operation facilities, and data handling, exchange and storage capabilities. A centralized science planning facility will coordinate campaign planning by combining spacecraft ephemeris and model software to predict advantageous times for campaign intervals.

The final result of the workshop was the definition of two overarching science research themes, and a two-phase campaign plan, which is presented in this report, focusing on: (1) The Structure of the Global Magnetotail System, especially during quiet periods; and (2) Magnetotail Effects of the Global Solar Wind-Magnetosphere Interaction, especially during active periods.

The first of these themes (Section 2 of the Report) recognizes that, despite decades of magnetospheric research, our spacecraft have systematically explored only the relatively near-Earth region of space. An immense amount remains to be learned about the quiescent structure of the distant tail, about the evolution of the tail plasma regions, about the relative contributions of the sources of the tail plasma population, and about the ultimate fate of these plasmas as they convect toward, and away from, the Earth. Thus, the prime objective of this campaign phase is to use the widely spaced IACG satellites-along with ground-based data, other spacecraft, and modeling tools-to gain a true understanding of the large-scale configuration of the magnetotail system.

A second dominant research theme (Section 3) concerns the time-dependent behavior of the coupled solar wind-magnetosphere system. Time variations can arise very naturally in this system owing to major solar wind perturbations: interplanetary shock waves, large pressure pulses, changes in the interplanetary magnetic field, etc. But significant internal magnetospheric instabilities can also cause profound, global changes throughout the magnetosphere. Thus, the second phase of this campaign deals with the storage and release of energy within the magnetotail, especially during both sub-storm and storm conditions, and with the many macroscale manifestations of these energy transfer processes in the near-Earth and distant-tail regions. The IACG suite of spacecraft is ideally suited for such studies.

It is envisaged that a prototypical spacecraft arrangement for this campaign would have WIND or IMP-8 in the upstream solar wind to monitor the interplanetary conditions and sense the kind of changes that will induce global dynamical responses in the magnetosphere. INTERBALL-AURORAL, AKEBONO, and/or FREJA should be in the polar regions to image the polar cap and monitor the low-altitude plasma population. Ground-magnetometer chains, all-sky camera stations, and HF radar facilities will be used to provide correlative data. An operational set of geostationary spacecraft at several different local times will also provide important data.

A key component of the configuration strategy is to have INTERBALL-TAIL in the mid-magnetotail during this campaign, optimally being relatively near the midnight meridian, and probably near apogee (~30 Re). However, INTERBALL-TAIL could be at any local time in the tail--including near the flanks--and still return very useful information.

The GEOTAIL spacecraft is the cornerstone of this campaign, spending most of its time near apogee in the relatively distant tail region. Apogee can range from ~80 Re for 1-month period orbits to ~220 Re for 4-month orbits. A wide range of INTERBALL-GEOTAIL separation strategies are possible in this campaign. Moreover, if IMP-8 is in the magnetotail along with INTERBALL and GEOTAIL, there are a very wide variety of 3-spacecraft location possibilities available to study the way in which disturbances propagate in the tail after their initiation.

The general campaign starts when INTERBALL-TAIL enters the magnetotail from the dawn boundary. The timeframe of April, 1994, when GEOTAIL reaches a distance of 220 Re in the magnetotail, will allow a number of campaign sub-intervals in which measurements in the distant tail are possible. Intervals will be selected (i) either in retrospect by referring to appropriate signatures in the solar wind or inside the magnetosphere, or (ii) according to orbit predictions when INTERBALL-TAIL (or IMP-8) crossings of key physical regions (e.g., flanks of the magnetotail, inner edge of the plasma sheet) are identified.

A crucial aspect determining the overall success of the IACG effort is the definition of an effective campaign organization. A detailed implementation scheme must be filled out by creating operating plans and timelines. This responsibility lies with the Project Scientists for the prime IACG missions and with IACG Working Group-1. It is important to identify a central planning focus for the campaign, to define procedures for decision-making and communication, to agree on a set of "rules of the road" for data exchange and use, and to begin planning for coordinated campaign data analysis. Supplements to this report will be issued describing these subsequent developments.

A subcommittee of the IACG Working Group-1 consisting of the WG-1 Chairman, E. Whipple, together with A. Nishida, M. Acuna, L. Zelenyi, and R. Schmidt, is charged with overseeing the campaign. The IACG, in its coordinating function, will assure that all spacecraft are optimally utilized, that ground-based facilities are involved to the greatest extent possible, and that summary information about the campaign is widely distributed both before and after the campaign.