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


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 plane1–7. The two hemispheres are separated by a curved current sheet that typically crosses the solar equatorial plane in either two or four places, thus dividing the equatorial region into either two or four sectors. Near sunspot minimum, at 1 AU the curved current sheet has a spread in latitude of typically ± 15°, so that the sector boundary (the current sheet separating the two hemispheres of opposed field polarity) is almost parallel to the solar equatorial plane. In the photosphere, on the other hand, the sector boundary makes an angle of 90° with the equatorial plane8. At 1.5 R, in 1972 and 1973, the angle between the sector boundary and the equatorial plane was 45° (ref. 9), and at 3–10 R the angle between boundary and plane was 25° (ref. 10). A schematic diagram of this structure for the case of four sectors is shown in Fig. 1. We here propose that a connection exists between the extent of these magnetic fields and the observed variations in cosmic ray intensity at the Earth.

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