Heliospheric magnetic field strength and polarity from 1 to 81 AU during the ascending phase of solar cycle 23

Abstract

[1] The Voyager 1 (V1) observations of the heliospheric magnetic field strength B agree with Parker's model of the global heliospheric magnetic field from 1 to 81.0 AU and from 1978 to 2001.34 when one considers the solar cycle variations in the source magnetic field strength and the latitude/time variation in the solar wind speed. In particular, Parker's model, without adjustable parameters, describes the general tendency for B to decrease with increasing distance R from the Sun, the three broad increases of B around 1980, and 2000 , and the minima of B in 1987 . During 1987, B appears to be lower than Parker's model predicts, but that can be attributed to the presence of a heliospheric vortex street at these times and/or uncertainty in the observations. There is no evidence for a significant flux deficit increasing monotonically from 1 to 81.0 AU. By extrapolating these results and considering the limitations of the observations, V1 should continue to make useful measurements during the next few years at least. The magnetic field polarity in the distant heliosphere at V1 and Voyager 2 (V2) changed during the ascending phase of solar cycle 23. In the Northern Hemisphere, V1 observed a decrease in the percentage of positive polarities from %100% during 1997 to %50% during 2000. In the Southern Hemisphere, V2 observed the opposite behavior, an increase in the percentage of positive polarities from %0% during 1997 to %50% during 2000. The variation of magnetic polarity observed by V1 and V2 was caused by the increasing latitudinal width of the sector zone with increasing solar activity, which in turn was related to the increasing maximum latitudinal extent and the decreasing minimum latitudinal extent of the footprints of the heliospheric current sheet (HCS). There was a tendency for the speed and proton temperature to decrease and the density to increase at V2 from 1997 (when it observed flows from polar coronal holes) to 2001 (when it observed more complex and dynamic flows).

The Structure and Dynamics of the Corona—Heliosphere Connection

“…At some locations it extends up to 30 • from the HCS, which explains the observations of slow wind at high latitudes. The HCS is not always symmetrically located inside the S-Web but can lie near one edge and, in fact, the HCS is often observed in the heliosphere to occur close to one of the slow wind boundaries rather than symmetrically between them (Burlaga et al 2002). Although the Q layers are densely spaced, they are not space filling, so we expect that the wind in the S-Web region will actually consist of a mixture of slow and fast, as observed.…”

“…2. The HCS appears as the dark red line and the contours of high Q as white, (adapted from Antiochos et al 2011) observed photospheric flux distribution, but less structured than in Fig. 2, and two "magnetic carpet" bipoles.…”

“…(b) The slow wind is associated with the heliospheric current sheet (HCS), which is always embedded in slow wind, not fast (Burlaga et al 2002). On the other hand, the slow wind is observed to extend in the heliosphere to angles far from the HCS, up to 30 • or so.…”

Structures in the Outer Solar Atmosphere

“…The slow wind is found at low latitudes and surrounds the HCS (heliospheric current sheet) (Burlaga et al 2002). The HCS is always observed to be embedded in slow wind, which is sometimes observed to extend as much as 30 or more from the HCS.…”

Solar cycle variations of solar wind dynamics and structures

“…1. At solar minimum, the magnetic field is dipolar and the average solar wind magnetic field magnitude at 1 AU is small (Burlaga et al, 2002 streamer belt and current sheet are near the equator and are a source of low-speed, 400 km/s solar wind (see Gazis, 1996). Few interplanetary coronal mass ejections (ICMEs) occur near solar minimum, so few shocks form (see Cane and Richardson, 2003), and the average helium abundance (averaged over all solar wind conditions) is low, 1-2% (Aellig et al, 2001).…”