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This is the first volume in the new COSPAR Colloquia series which will provide a forum for an in-depth discussion on selective topics of importance to the international community. The International Heliospheric Study (IHS) was initially approved by COSPAR in 1982 when it was anticipated that the study would centre on the ESA/NASA Ulysses spacecraft. This mission was delayed until October 1990, but it was decided to commence the study in 1986 in order to exploit the existence of the Pioneer 10 and 11 and the Voyager 1 and 2 spacecraft in the outer heliosphere. The primary purpose of Physics of the Outer Heliosphere is to study the three-dimensional structure of the solar wind and interplanetary magnetic field carried by it, the propagation of energetic solar particles throughout the heliosphere and the modulation of galactic cosmic rays by the heliosphere. This volume provides information for scientists interested in spectroscopic studies of the local interstellar medium, galactic and solar cosmic ray populations in the outer heliosphere and also plasma and magnetic field aspects of the distant solar wind.

The 1969 ESLAB symposium ''Intercorrelated Satellite Observations Related to Solar Events'' was held at a time when the importance of bringing together measure­ ments made simultaneously in different regions of space was beginning to be appreciated. To-day it is universally accepted that the major experimental steps forward in understanding the physics of the Sun-Earth relationships are likely to be made through pre-planned correlated satellite studies. Such considerations have led to the organisation of the International Magnetospheric Study and the joint ESROj NASA International Magnetospheric Explorer, (Mother-Daughter-Heliocentric) mission. The seventh ESLAB symposium was planned as a follow up to that of 1969 with the aim of deriving maximum benefit from those spacecraft which through good fortune found themselves simultaneously operating in different regions of the magnetosphere and interplanetary space. ESRO had launched in early 1972 its HEOS-2 satellite to investigate fields and particles in the unexplored region far above the North pole of the Earth and it became clear that the interesting new results arriving from that mission could profitably be linked with those from various American and the U.S.S.R. PROGNOZ satellites. The book follows the order of the symposium (unfortunately the PROGNOZ contribution did not materialise) concentrating, through both review lectures and of new experimental results, on the nature of the boundaries between the presentation the interplanetary medium and the magnetosphere and the interaction of each region on the other.

The 1969 ESLAB symposium 'Intercorrelated Satellite Observations Related to Solar Events' was held at a time when the importance of bringing together measure­ ments made simultaneously in different regions of space was beginning to be appreciated. To-day it is universally accepted that the major experimental steps forward in understanding the physics of the Sun-Earth relationships are likely to be made through pre-planned correlated satellite studies. Such considerations have led to the organisation of the International Magnetospheric Study and the joint ESROj NASA International Magnetospheric Explorer, (Mother-Daughter-Heliocentric) mission. The seventh ESLAB symposium was planned as a follow up to that of 1969 with the aim of deriving maximum benefit from those spacecraft which through good fortune found themselves simultaneously operating in different regions of the magnetosphere and interplanetary space. ESRO had launched in early 1972 its HEOS-2 satellite to investigate fields and particles in the unexplored region far above the North pole of the Earth and it became clear that the interesting new results arriving from that mission could profitably be linked with those from various American and the U.S.S.R. PROGNOZ satellites. The book follows the order of the symposium (unfortunately the PROGNOZ contribution did not materialise) concentrating, through both review lectures and of new experimental results, on the nature of the boundaries between the presentation the interplanetary medium and the magnetosphere and the interaction of each region on the other.

The European Space Research Organisation put its first satellite into orbit in March 1968 and was successful with two more before the end of that year. It was not entirely surprising therefore that the third annual ESLAB/ESRIN Symposium should in some way deal with the results obtained. This book is the Proceedings of that Sym­ posium which, for reasons which Dr. Trendelenburg explains in the introductory talk, concentrated on intercorrelating phenomena occurring during solar events and in particular during the event of 25 February 1969. It is generally acknowledged that space data could yield a much more fruitful harvest if measurements taken simulta­ neously in different regions of space could be compared and the detectors inter­ calibrated. ESRO therefore sought right from the start to encourage this comparison of data. The first two days of the Symposium (16 and 17 September 1969) were devoted to review lectures on inter-related phenomena occurring on the sun, through inter­ planetary space and the magnetosphere right down to the earth''s ionosphere. The last two days were used to hear papers presenting results obtained from the ESRO and certain U. S. S. R. and U. S. A. satellites during the solar events around 25 February 1969. The Proceedings published here follow the same sequence as the Symposium presentations. Because of the short time interval between the solar event and the Symposium, some of the data presented in the second part must be regarded as preliminary.