Magnetic Field Fluctuations on the Earth and in Space

Abstract

The recent development of rubidium vapor magnetometers as practical instruments for measuring magnetic fields has led to extremely precise and accurate determinations of magnetic fields on the earth and in space. Because of the unique manner in which the data are presented in the frequency domain, the data are very amenable to analysis by automatic digital computers. As a result, measurements of fluctuations of the terrestrial magnetic field have enabled accurate determinations of the frequency spectrum characteristics of the fluctuations. Magnetometer measurements of the field in space have been made from the space probe Explorer X launched March 25, 1961. The terrestrial measurements are continuous over intervals of several days. These data were sampled once per second. Power spectrum analyses have indicated distinct frequency bands in which the fluctuating magnetic field energy is concentrated. Data collected at the Fredericksburg Magnetic Observatory show a strong spectral peak for fluctuations with a period of around 10 seconds. These peaks are found to be both amplitude and frequency modulated on a daily basis. Additional spectral peaks have been observed and studied in the terrestrial data. The data obtained from measurements in space are less extensive at present. Hence, they do not allow sophisticatedmore » analyscs to be performed as indicated above. Time correlations with terrestrial data have been made to study these fluctuations. The fluctuation of the field is then viewed with respect to the existence and propagation characteristics of hydromagnetic waves. (auth)« less