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.

This sixth volume in the ISSI Space Sciences Series is a fully integrated book that gives an authoritative overview of all aspects of the topic in a well-organized form. Leading international scientists from all over the world contributed consistent, cross-referenced articles of high scientific standard.

In this report, the calculation of riometer absorption during several PCA events of particular interest is presented. These calculations are based on earlier work in which an improved effective recombination coefficient was derived and an atmospheric model for (1) each month of the year, (2) day and night, and (3) 60 deg N and 90 deg N latitude was presented. In this report, the calculated values of riometer absorption are presented for 5 PCA events: 2 Nov. 69, 7 Mar. 70, 25 Jan. 71, 2 Sep. 71, and 3 Aug. 72. The calculated values of riometer absorption are compared with experimental values measured for both day and night conditions at Thule, Greenland. An approximate connection between riometer absorption and the square-root of the proton flux for nighttime conditions is presented. This relationship, which has previously been applied only for daytime conditions, is discussed both on a fundamental level and on the level of verification by comparison with experiment. In addition, the basic equation widely used to calculate riometer absorption is compared with the original Sen-Wyller result.