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Ann. Geophys., 17, 642-649, 1999
www.ann-geophys.net/17/642/1999/
© European Geosciences Union 1999
Heliospheric current sheet inclinations at Venus and Earth
G. Ma, K. Marubashi, and T. Maruyama
Communications Research Laboratory, 4-2-1 Nukui-Kitamachi Koganei-shi Tokyo, Japan
Correspondence to: G. Ma; e-mail: ma@crl.go.jp
Abstract. We investigate the inclinations of
heliospheric current sheet at two sites in interplanetary space, which are
generated from the same solar source. From the data of solar wind magnetic
fields observed at Venus (0.72 AU) and Earth (1 AU) during December 1978-May
1982 including the solar maximum of 1981, 54 pairs of candidate sector boundary
crossings are picked out, of which 16 pairs are identified as sector boundaries.
Of the remainder, 12 pairs are transient structures both at Venus and Earth, and
14 pairs are sector boundaries at one site and have transient structures at the
other site. It implies that transient structures were often ejected from the
coronal streamer belt around the solar maximum. For the 16 pairs of selected
sector boundaries, we determine their normals by using minimum variance
analysis. It is found that most of the normal azimuthal angles are distributed
between the radial direction and the direction perpendicular to the spiral
direction both at Venus and Earth. The normal elevations tend to be smaller than
~ 45° with respect to the solar equatorial plane, indicating high
inclinations of the heliospheric current sheet, in particular at Earth. The
larger scatter in the azimuth and elevation of normals at Venus than at Earth
suggests stronger effects of the small-scale structures on the current sheet at
0.72 AU than at 1 AU. When the longitude difference between Venus and Earth is
small (<40° longitudinally), similar or the same inclinations are
generally observed, especially for the sector boundaries without small-scale
structures. This implies that the heliospheric current sheet inclination tends
to be maintained during propagation of the solar wind from 0.72 AU to 1 AU.
Detailed case studies reveal that the dynamic nature of helmet streamers causes
variations of the sector boundary structure.
Key words. Interplanetary physics (interplanetary
magnetic fields; sources of solar wind)
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