A representation of the magnetic neutral line on the solar source surface in terms of the Sun's axial dipole at the center and two equatorial dipoles in the photosphere

Saito, Takao; Ôki, T.; Olmsted, C.; Akasofu, S.‐I.

doi:10.1029/ja094ia11p14993

Cited by 11 publications

(3 citation statements)

References 10 publications

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“…It seems clear that the average velocity, at least as measured beyond 0.4 AU, is intrinsically smoother than the coronal density or magnetic field. Saito et al [1989] have recently given an alternative to the spherical multipole analysis, in characterizing the neutral line of the coronal magnetic field. They pose the existence of a Suncentered dipole aligned with the solar rotation axis and two additional dipoles on the photosphere itself.…”

Section: Here B Is the Heliographic Latitude I Is The Carrington Lonmentioning

confidence: 99%

Evolution of the solar wind structure over a solar cycle: Interplanetary scintillation velocity measurements compared with coronal observations

Rickett¹,

Coles

1991

J. Geophys. Res.

122

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Sixteen years of solar wind observations via the technique of interplanetary scintillation 0PS) are presented. By an ecliptic comparison with in situ spacecraft observations, these data are shown to be valuable estimates of the large-scale slowly evolving structures in the solar wind speed, but to underestimate the speed in small-scale or rapidly evolving structures. These 1PS observations allow the large structures to be studied over solar latitudes from 60 ø north to 60 ø south over more than a solar cycle. The o•ervations are presented as half-yearly averages in Cartington longitude and latitude. These are compared with plots of coronal density estimated from coronameter observations and radial magnetic field estimated from solar magnetograph observations and the potential field method. •n low and declining solar activity, there is the expected relationship between fast wind and 1ow'clensity open-field regions, and between slow wind, dense corona and proximity to the neutral sheet. The dipolar field component wanders up to 30 ø from the rotation axis and is followed by dipolar distributions of density and velocity. Near solar maximum, average wind speeds are uniformly slow over the entire range of latitudes covered, the coronal density becomes more spherically distributed (though it retains a somewhat lower density over the solar poles), and the neutral sheet ranges over all latitudes and sometimes forms disconnected surfaces. The relationship between wind speed, density and angular separation from the neutral sheet are then broken. The results confirm the controtiing influence of the coroo•l magnetic field in dete•g the threedimensional structure of the solar wind. INTRODUCFIONIn the more than twenty years that spacecraft have been exploring the solar wind an enormous wealth of information has been acquired on its properties. However, the great bulk of the observations come from spacecraft in orbits near the ecliptic. Thus direct information on the solar wind out of the ecliptic comes only from a few spacecraft. In particular, Pioneer 11 and Voyager I have spent extended periods of time at latitudes in the range 10 ø to 20 ø solar latitude. Remote sensing techniques such as comet tail and radio propagation observations, in contrast, are not constrained in latitude but are more difficult to interpret as they provide less direct measurements of the basic plasma parameters. This paper presents the results of a long-i•'m study of the solar wind velocity using the method of interplanetary scintillations 0PS) and a comparison of the large-scale velocity structure with that of the coronal density and magnetic field. Comet observations have shown some latitudinal variation of solar wind speed [Brandt et al., 1975], but the sporadic nature of comet passages makes them difficult to use for a long-term study. Similarly, 2 years of early IPS observations at Cambridge, England showed conflicting results on wind speed versus latitude [Hewish and Symotuts, •969]. The results of the long-term IPS study at the University of C...

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Section: Here B Is the Heliographic Latitude I Is The Carrington Lonmentioning

confidence: 99%

Evolution of the solar wind structure over a solar cycle: Interplanetary scintillation velocity measurements compared with coronal observations

Rickett¹,

Coles

1991

J. Geophys. Res.

122

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“…It is interesting to note here that these active longitudes correspond to giant bipolar magnetic regions (GBMR) situated on the global neutral line (Saito et al 1993). On the basis of the 'triple dipole model' (Saito et al 1989) of global solar magnetic field distribution, Saito predicted the existence of very large coronal loop structures above GBMRs in active longitudes. Such very large coronal loop structures have actually been observed on the limb in FFI images when the GBMR crosses the limb (Saito et al 1993).…”

Section: Long Term Evolution Of Global Structure Of Coronamentioning

confidence: 99%

The Variable Structure of the X-ray Corona as Viewed by Yohkoh

Shibata

1994

International Astronomical Union Colloquium

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“…One of the most important aspects on the source surface is the magnetic equator (or the socalled "neutral line"). The axis of the dipolar field on the source surface rotates from 0° to 180° (or from 180° to 0°) during the sun's 11-year cycle variations (Saito et al, 1989). We found that we can reproduce much of the main feature of solar wind variations during the sunspot mini mum period at the earth or at any point to about a dis tance of 2 au by assuming that the solar wind speed is minimum at the sinusoidal magnetic equator and increases toward higher latitudes (see the top diagram of Figure 2a).…”

Section: Modeling the Background Solar Wind Flowmentioning

confidence: 99%

Space Weather

2001

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A representation of the magnetic neutral line on the solar source surface in terms of the Sun's axial dipole at the center and two equatorial dipoles in the photosphere

Cited by 11 publications

References 10 publications

Evolution of the solar wind structure over a solar cycle: Interplanetary scintillation velocity measurements compared with coronal observations

Evolution of the solar wind structure over a solar cycle: Interplanetary scintillation velocity measurements compared with coronal observations

The Variable Structure of the X-ray Corona as Viewed by Yohkoh

Space Weather

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