Magnetopause structure during the magnetic storm of September 24, 1961

Abstract

Explorer-12 magnetic-field observations of the magnetopause current layer were made on the inbound pass of September 24, 1961, which occurred during the main phase of a moderately strong magnetic storm. The satellite was located near the subsolar point. The accuracy of the Explorer-12 data reported here has been increased by use of an improved filtering procedure. Five magnetopause penetrations were observed in a time period of about 20 min and for each of these the data were used to calculate the vector normal to the current layer, the magnetic-field component along that vector, and the polarization of the current layer. Normal magnetic-field components significantly different from zero were obtained, and it is suggested that the observations during this pass in general are consistent with the so-called open magnetosphere model. In fact, it appears that the first and last of the boundary penetrations may have occurred on opposite sides of, but very near, the X-type magnetic null line, which is located on the front side of the open magnetosphere model. The direction of the normal magnetic-field component as well as the sense of rotation of the tangential magnetic-field component in the current layer were found to be opposite for these two boundaries.