The geomagnetic field observed on the surface of the earth has been an important source of information on the dynamic behavior of the magnetosphere. Because the. magnetosphere and its environment are filled with plasma in which electric current can easily flow, dynamic processes that occur in the magnetosphere tend to produce perturba tions in the geomagnetic field. Geomagnetic data have therefore pro vided valuable means for sensing the processes taking place at remote locations, and such basic concepts as the magnetosphere, solar wind, and trapped radiation were derived in early,...

In the past two decades a succession of direct observations by satellites, and of extensive computer simulations, has led to the realization that the polar ionosphere plays a principal role in large-scale magnetospheric processes - a manifestation of the physics linkage involved in solar-terrestrial interactions. Spatial/temporal variations in high-latitude electromagnetic phenomena, such as dynamic aurorae, electric fields and currents, have proved to be extremely complex. Now the challenge is to comprehend the vast amount of complicated measurements made in this magnetosphere-ionosphere...

The subject of geomagnetic micropulsations has developed extremely rapidly and it is difficult to know when is an appropriate time to pause and assess the sum total of our knowledge-both observational and theoretical. There has in recent years been a tremendous increase in both the quantity and quality of data and also many theoretical ad vances in our understanding of the phenomenon. Undoubtedly there will be further progress in both areas but it seems worthwhile now to review both our knowledge and our ignorance. This book was essen tially completed by the end of April 1969 and tries to...