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A simple kinetic theory model of the interplanetary gaseous medium based on the evaporation of particles from the solar coronal exosphere is considered, using Jeans' equation for the escape of gases from planetary atmospheres. The exosphere is fixed in the corona at a level (four times the solar radius) where the mean free path is comparable with the scale height. Equality of flux for the protons and electrons at the exosphere is assumed, so that the sun may not build up an inordinately high charge. Ingham's density value is used at the exosphere, where the temperature is assumed to be 1,000,000 degrees K. The electric potential at the exosphere is found to be about 488 volts and is almost equal and opposite to the gravitational potential for the protons so that the protons are virtually weightless. Computed particle density values are in good agreement with the observational data of van de Hulst, Vitkevitch and Slee. The theoretical proton (particle) flux and velocity near the earth are, respectively, 1.47 x 10 to the 8th power 1/sq-cm sec, and 147 km/s. These values are in order-of-magnitude agreement with the Lunik II, Explorer X, and Mariner II data. The order-of-magnitude agreement does not depend critically on the value at the exospheric level or on making the protons actually weightless. (Author).
Little more than ten years have passed since spaceprobe-borne instruments con clusively demonstrated the existence of the solar wind. These observations con firmed the basic validity of a theoretical model, first proposed by E. N. Parker, predicting a continuous, rapid expansion of the solar corona. The subsequent decade has seen a tremendous growth in both the breadth and sophistication of solar wind observations; the properties of the interplanetary plasma near the orbit of the earth are now known in great detail. The theory of the coronal ex pansion has also been highly refilled both in the sense of including additional physical processes, and of treating more realistic (time-dependent and non spheri cally-symmetric) coronal boundary conditions. The present volume is an attempt to synthesize the solar wind observations and coronal expansion models from this decade of rapid development. The ultimate goal is, of course, the interpretation of observed solar wind phenomena as the effects of basic physical processes occurring in the coronal and interplanetary plasma and as the natural manifestations of solar properties and structures. This approach implies an emphasis upon the "large-scale" features revealed by the observations. It requires extensive use of the concepts and methods of fluid mechanics.