Structure of the extended solar magnetic field and the sunspot cycle variation in cosmic ray intensity

It is stated that the interplanetary magnetic field within several astronomical units of the Sun appears to have one polarity in most of the hemisphere north of the solar equatorial plane and the opposite polarity in most of the hemisphere south of the equatorial plane. The two hemispheres are separated by a curved current sheet that crosses the solar equatorial plane in two or four places, dividing the equatorial region into either two or four sectors. Near sunspot minimum, at 1AU, the current sheet has a latitude spread of typically +- 150 and the sector boundary is almost parallel to the solar equatorial plane. In the photosphere, however, the sector boundary makes an angle of approximately 900 with the equatorial plane. A schematic diagram of the structure for the case of four sectors in shown. It is proposed that a connection exists between the extent of the magnetic fields and the observed variations in cosmic ray intensity at the Earth. Geometrical effects that may be the principal cause of the 11 year modulation of cosmic ray intensity observed at the Earth are discussed. The fraction of the heliosphere occupied by sector-structure fields as a function of time through an average sunspot cycle are estimated and the results are shown graphically. It is assumed that galactic cosmic rays have relatively difficult access to the inner solar system in the portion of the heliosphere occupied by the changing fields of the sector structure, and relatively easy access through the portions of the heliosphere occupied by the extended uniform solar polar fields, and it is also assumed that high speed solar wind streams are contained within sectors. The solid cycle of the heliosphere occupied by the extended solar polar fields through an average cycle is also shown graphically. (U.K.)