--------------------------------------------------------------------- REPORT FROM THE CONVENORS OF CHAPMAN CONFERENCE ON MAGNETIC STORMS --------------------------------------------------------------------- From: Bruce Tsurutani (BTSURUTANI@jplsp1.jpl.nasa.gov) More than 100 scientists from 20 countries met at the Jet Propulsion Laboratory, Pasadena, California, during the week of February 12-16, 1996, to discuss recent developments of research on magnetic storms. In spite of the importance of magnetic storms in the science of Solar-Terrestrial relationship, surprisingly this was, to our knowledge, the first large-scale international conference on this topic ever held. A press conference was held followed by an article in Science. The conference focused on many different aspects of magnetic storms, starting with its origin at the Sun and in the interplanetary medium, followed with the storm dynamics and structure in magnetospheric and ionospheric regions, and ending with studies about its main atmospheric and ground effects. The present efforts to forecast its occurrence were also discussed. Twenty invited review talks covered a vast number of topics, addressing not only tutorial perspectives but also very recent unpublished research contributions. The invited talks will be published as a special Monograph of the American Geophysical Union. These review talks were complemented by about one hundred contributed (oral and poster) papers, many of which will be published in a special issue of the Journal of Geophysical Research - Space Physics (with regular review procedures). The editor of the special JGR issue (Y. Kamide) also welcomed papers on magnetic storms by authors who had not participated in this Chapman Conference. SOLAR AND INTERPLANETARY PROCESSES. Certainly our ultimate answer about the origin of geomagnetic storms resides in the knowledge of associated solar and interplanetary processes. Toward this search, in this Conference important new clues were unveiled among the review and contributed papers. T. Kosugi presented new evidence for magnetic reconnection at the solar corona using YOHKOH images, both for active region-scale lengths and for larger regions at the solar corona, probably related to CMEs, in which observable morphological changes can be identified. Referring also to YOHKOH observations, H. Hudson discussed an important new coronal feature associated with a CME: a dimming of the corona. If this effect can be substantiated it will certainly represent a key factor for forecasting geomagnetic storms associated with CMEs, although critical information about the origin of a substantial southward (perpendicular to the ecliptic) component of the IMF, necessary for the growth of storms, will still need to be added toward a more precise forecasting. With respect to the origin of intense geomagnetic storms, Gonzalez et al. presented evidence about combined solar structures of the "coronal hole-active region-current sheet" (CHARCS for short) type, as being candidates for the origin of intense storms, especially when the associated coronal hole grows in size rapidly near the active region-current sheet structures. With respect to the solar-interplanetary coupling, J. Chen summarized several theoretical and observational aspects of the CME/prominence association and of the solar ejecta's transport in the interplanetary medium as a magnetic cloud structure. Toward the interest of forecasting geomagnetic storms, B. V. Jackson summarized heliospheric- remote sensing observations using ground and satellite techniques, both for transient as well as for corotating solar-interplanetary features. Concerning the interplanetary structures that cause magnetic storms, C. F. Farrugia summarized our present understanding about magnetic clouds, whereas B. T. Tsurutani and W. D. Gonzalez reviewed other structures which also involve large-amplitude and long-duration Bs fields, mainly of the "sheath" field type. These two complementary presentations focused also on the currently unsolved problems about the interplanetary origin of storms. In addition to those two presentations, D. Odstrcil presented a 3-dimensional, time-dependent MHD numerical model to investigate the interaction between magnetic clouds and the heliospheric current sheet, which could lead to an additional source of Bs structures and consequently to the development of storms. MAGNETOSPHERIC PROCESSES. The above mentioned interplanetary structures involving substantial Bs fields are expected to effectively transfer energy to the magnetosphere which, after being stored mainly in the tail, gets channeled to the inner magnetosphere. Among the magnetospheric processes that signal the occurrence of storms, it has been classically accepted that the most accepted one is the intensification of the ring current. Thus, in this Conference some reviews and contributed papers have dealt with such basic magnetospheric processes as a general background for the understanding of storm dynamics. V. M. Vasyliunas presented an overview of the global energetics of the magnetosphere during magnetic storms, starting with the solar wind MHD dynamo concept and following with general concepts about energy storage and dissipation processes in the magnetosphere. Toward a more quantitative understanding of those processes, R. A. Wolf presented an updated overview of the Rice convection model as applied to the understanding of magnetic storms, including the relationship between time-dependent convection and diffusion. For completeness, S. Kokubun presented a summary of our present knowledge about the dynamic behavior of the distant magnetotail during magnetic storms, using GEOTAIL and ISEE-3 data. Three additional contributions dealt with the tail behavior during storms. W. Baumjohann et al. presented data from the IRM satellite in the near magnetotail to discuss tail signatures during isolated substorms as compared to intervals with substorms occurring within storm events. They concluded that not all substorms are alike and that the near-earth neutral line scenario may apply only to the storm-time substorms. L. Frank presented plasma velocity distributions obtained from GEOTAIL measurements also at the near-earth magnetotail, showing that during storm intervals there are clear field-aligned electron beams and field-aligned beams of singly charged oxygen ions flowing from the ionosphere. On the other hand, C. M. Ho and B. T. Tsurutani, using ISEE-3 data collected at the distant magnetotail, presented evidence of strong earthward flowing events probably originated at distances beyond ISEE-3. It is not thought that such distant tail reconnection/jetting is important for near-Earth substorms, however. Such events are probably associated with additional flux sloughing. The issue of magnetospheric energization and its dissipation in storms and substorms was discussed by R. M. MacMahon et al. They presented results associated with superstorms, for which it was found that about 1% of the energy transferred by the solar wind to the magnetosphere is used to build up the ring current. STORM DYNAMICS The topic of storm dynamics, involving ring current evolution and population as well as the issue of storm/substorm relationship(s), was certainly one of the hottest and busiest in this Conference. I. A. Daglis, while discussing the role of magnetosphere- ionosphere coupling in storm dynamics, raised the very interesting issue of the role of the ionosphere in ring current population and evolution. He presented evidence from the CRRES and AMPTE/CCE spacecraft about the dominance of oxygen ions over the other ring current constituents during the main phase of intense storms. D. C. Hamilton added more evidence to these findings by also contrasting the ring current population during the maximum and minimum phases of the solar cycle. Further, M. Grande complemented these talks with a review about ring current composition contrasting the solar wind material and the ionospheric one as competitive sources. He also raised the subject of the difference between substorms during storm times and quiet times. Modeling ring current formation and decay is a key subset of storm research. This was addressed by M. W. Chen et al., who reviewed our present understanding of the transport and loss processes, involving large-scale electric and magnetic field variations, wave generation and convection versus diffusion processes under both quiescent and storm-time conditions. This talk was complemented by another review given by J. V. Kozyra et al. about the role of electromagnetic ion cyclotron (EMIC) waves in storm-time ring current erosion. On the other hand, L. M. Kistler concentrated on the pitch angle distributions of ring current ions during the main phases of storms, showing statistical results of the distributions of four major species, namely H+, O+, He+ and He++. Dealing with the evolution of the storm-ring current, A. L. Clua de Gonzalez et al. examined the energy balance equation in order to understand the role of the energy input variability, as governed by the solar wind. Some analytic solutions for Dst variations were found for simple solar wind governing structures. Two interesting presentations also addressed the role of electric fields in the energization of ring current and radiation belt particles. J. R. Wygant, using electric field observations from CRRES during major magnetic storms, showed clear associations between intense convection electric fields and large changes in the ring current injection rate, as well as between intense fluctuations in the electric field (with large power) and abrupt appearance of trapped radiation belt-electron population. To complement this, M K. Hudson et al. presented results from MHD simulations of the radiation belt formation during storm sudden commencements. Among new experimental projects which are expected to help us to better understand the processes associated with ring current formation and decay, G. Haerendel reviewed the instrumentation and scientific goals of the EQUATOR-S satellite, expected to be launched in early 1997. The very important issue of storm/substorm relationship was reviewed by R. L. McPherron and by G. Rostoker. They presented complementary talks showing that the ring current is mainly controlled by changes in the interplanetary electric field variability and that substorms, despite the fact that they occur more intensively and frequently during the storm's main phase, may not play an important role in ring current development. However, the final (panel) session of the Conference considered this issue as one deserving further future studies (in fact, a small workshop was held at Lake Arrowhead, California, right after the Conference, to discuss this matter). Showing in fact that the topic of storm/substorm relationship is still largely open for more research, I. V. A. Sergeev discussed about steady magnetospheric convection events involving strong recurrent substorms and near-earth cross tail intensified currents, whereas Y. I. Feldstein and A. Grafe dealt with latitudinal and intensity changes of auroral electrojets and of the ionospheric role in ring current development. THERMOSPHERIC, IONOSPHERIC AND GROUND EFFECTS - STORM FORECASTING. The thermospheric and ionospheric effects of storms are observationally an old field of research. However the processes which are involved are even at present not fully understood. Nevertheless, an excellent review about some of the key processes was given by G. W. Proelss, who concentrated on the large scale morphology and the physical processes associated with magnetic storm perturbations in the upper atmosphere. He also focused on the large-scale wind circulation at several latitudinal regions and on the associated compositional changes. In a complementary effort, T. Fuller-Rowell reviewed the present status of modeling the thermospheric response to magnetic storms, including the "positive" and "negative" ionospheric responses and their seasonal and local time variability. He also presented a summary of the sources for ionospheric and thermospheric perturbations at low latitudes, although a more detailed description of this subject, especially in terms of electric fields, was given by B. G. Fejer and L. Scherliess. Further, J. H. A. Sobral et al. discussed this same topic as applied to intervals with intense storms. On the other hand Szuszczewicz et al. presented an overview of storm- time characteristics of the global ionospheric-thermospheric system using a global network of observations carried during several observational campaigns, in an effort that exemplifies several of the points reviewed by the previous speakers. Two other talks focused on detailed aspects of ionospheric and thermospheric response to storms during particular events. B. A. Emery et al. presented the results of such a study for the storm of March 28-29, 1992, as well as the related TIGCM/AMIE simulations. D. J. Knipp presented the results of a similar collaborative study for the storm of November 3-4, 1993, including complementary observations at the sun, the interplanetary medium and the magnetosphere, as collected through the CEDAR and GEM campaigns. W. H. Campbell reviewed several aspects related to what he called a "societal impact of geomagnetic storms", including satellite damage and tracking, induction in long pipelines and electric power grids, communication and global positioning systems as well as association of geomagnetism with weather and life forms. The issue of geomagnetic effects on power systems were further discussed by D. H. Boteler and by J. G. Kappenman and W. A. Radasky, who described also the need of further research in this field towards a better protection of the electric utility industry, including delicate situations such as nuclear power plants. Finally, with regard to the important goal of geomagnetic storm forecasting, several presentations raised complementary aspects of this problem. H. Lundstedt, reviewed AI methods used in long, medium and short-term predictions of geomagnetic storms, using solar and solar wind data. He stressed the importance of using more advanced neural networks and hybrids of different AI-methods, which together with new observations can improve the accuracy of storm forecasting. T. R. Detman and D. Vassiliadis tried on the other hand to review different approaches of storm forecasting using linear and non-linear techniques in order to be able to obtain short term predictions for the geomagnetic indices as well as medium and longer term predictions of storms. For the latter case they discussed the importance of improving present heliospheric and magnetospheric models as well as remote sensing techniques of solar and interplanetary processes. Other talks on storm forecasting helped to visualize more the present problems for improving our forecasting ability. A. S. Sharma et al. discussed non-linear dynamic models involving phase space reconstruction techniques that allow quantitative predictions of the level of storm development as a function of solar wind data. J. Chen et al. discussed another approach to forecast storms, following the evolution of physical features of interplanetary structures rather than a simple time-series information. This approach is expected to help us better understand also the physical processes associated with the solar wind-magnetosphere interaction. On the other hand, S. Bravo focused on the difficult problem of long-term storm forecasting using soft x- ray imaging of coronal transients and the tracking of solar wind disturbances by means of interplanetary scintillations. The Conference was closed by a Panel Discussion, chaired by Y. Kamide and R. McPherron, in which S. W. Kahler, H. Hudson, W. D. Gonzalez, D. C. Hamilton, L. R. Lyons, E. P. Szuszczewicz, H. H. Lundstedt and J. A. Joselyn highlighted some of the main conclusions and also presented open questions for future research. The AGU Monograph (with the review papers of this conference) will contain also a chapter about this Panel Discussion. This summary was contributed by the Convenors of the Conference: W. D. Gonzalez (INPE - Brazil), Y. Kamide (STEL - Japan), and B. T. Tsurutani (Jet Propulsion Laboratory, Pasadena).