Interplanetary sector structure in the rising portion of the sunspot cycle

Abstract

The interplanetary sector structure during the rising portion of the sunspot cycle in 1966 and 1967 has been investigated. The sector pattern is often quasi-stationary for a few rotations, followed by an appreciable change in the next rotation. When a sector boundary passes the earth geomagnetic activity tends to increase, an effect rather similar to that observed near sunspot minimum. The recurrence period of the interplanetary field during the interval investigated was 27.5 ± 0.1 days. (1968).In the present study the determination of sector polarity has been made in a manner similar to that previously used by Wilcox and Ness (1965).Three-hour average values of the azimuthal direction of the observed interplanetary magnetic field component parallel to the ecliptic are used.Although the direction of the interplanetary magnetic field is usually variable, an averaging interval of three hours almost always results in a direction that can be associated with a basic Archimedes spiral field directed either toward or away from the sun.The present results have been added to Figure 13 of Wilcox (1968) and are shown here as Figure 1, in which the observed sector structure of the interplanetary magnetic field is overlayed on the daily geomagnetic character index C9. This figure provides an overall view of the sector structure from midway in the decline of the last sunspot cycle to midway in the rise of the present sunspot cycle. The first point to observe is that even though we are approaching the maximum of the solar cycle, the interplanetary field retains the property that almost always several consecutive days have the same polarity, with field predominantly either toward the sun or away from the sun. The sector pattern is often quasistationary for a few rotations, followed by appreciable change in the On at least three occasions, namely January 13, 196713, , February 7, 1967 and November 3, 1967, a sudden commencement occurs near a sector boundary.A similar case was previously observed on December 2, 1963 (Wilcox and CIE Ness, 1965) . Thus we see that a sudden commencement is not necessarily associated with a flare-induced shock wave, but may also be caused by a corotating sector boundary.During the quasi-stationary sector structure at solar minimum, geomagnetic activity was observed to reach a maximum about two days after a sector boundary had passed. In the present investigation there is a tendency for geomagnetic activity to increase after the passage of a sector boundary, although there are also some exceptions. The average structure of geomagnetic activity with respect to a sector boundary has been investigated using the superposed epoch technique. Boundaries were selected in which the field polarity was the same for at least four days on each side of the boundary, i.e. reasonably well-established sector boundaries were considered. Sixteen boundaries in the present investigation met this criteria; they are listed in Table I. Figure 3 shows the resulting average response of the geomagnetic activity in...

Heliocentric distance dependence of the interplanetary magnetic field

“…Mariner 4, for example, observed considerable evolution of the sector pattern from one solar rotation to the next just after solar minimum, and variable to quasi stationary conditions continued through 1967 (Ness and Wilcox, 1967;Wilcox and Colburn, 1969).…”

“…The sector pattern evolves with time, with the number of sectors and the dominant polarity in a given hemisphere apparently related to the solar activity and magnetic cycles, respectively (Ness and Wilcox, 1967;Rosenberg and Coleman, 1969;Hirshberg, 1969;Wilcox and Colburn, 1969Wilcox and Scherrer, 1972;Svalgaard, 1972;Russell and Mc~herron, 1973;Fairfield and Ness, 1974;Svalgaard and Wilcox, 1975;Hedgecock, 1975;King, 1976).…”

Large‐scale properties of the interplanetary magnetic field

“…Figure 16 from Wilcox and Colburn (1970) illustrates the evolutionary changes of the interplanetary magnetic sectors over six years. The observed sector structure is overlayed on the daily geomagnetic character index C9.…”

“…Figure 22 from Wilcox and Colburn (1970) The <FI> symbol represents the average instantaneous magnetic field from Ness (1970b) obtained at 20.5 second intervals.…”

Magnetometers for space research

“…The sampling rate was not uniform but averaged one vector sample every 6.15 seconds during the scan of the three ranges. Results from these experiments have contributed to the mapping of the geomagnetic tail and the tail magnitude gradient Mihalov et al, 1968) and the solar wind interaction with the moon (Colburn et al, 1967) and the interplanetary sector structure (Wilcox and Colburn, 1969 Figure 26.…”