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Large-scale structure of the interplanetary medium
Authors:J. T. Nolte  E. C. Roelof
Affiliation:(1) Dept. of Physics, Univ. of New Hampshire, Durham, N.H., U.S.A.
Abstract:We propose that the coronal source longitude and latitude of solar wind plasma can be estimated within sim 10°. Previous writers have argued that the solar wind in the ecliptic should originate near the equator and that a quasi-radial hypervelocity (QRH) approximation (constant radial flow) is valid beyond the magnetohydrodynamic critical points. We demonstrate that an extension of the QRH approximation (as if the solar wind flowed radially with constant velocity from the center of the Sun) yields a proper estimate of the high coronal source location at the lsquorelease zonersquo where the solar wind makes its transition to radial interplanetary flow. This lsquoextrapolatedrsquo QRH (or EQRH) approximation succeeds because the two main corrections to this source estimate, coronal corotation and interplanetary acceleration, tend to cancel (the former correcting the source location eastward, the latter westward). Although this lsquoideal spiralrsquo approximation was first suggested by Snyder and Neugebauer (1966), only recently has it been demonstrated that it relates a wide range of interplanetary plasma, magnetic field and energetic particle data to observed coronal magnetic structure. We estimate quantitatively the error in the EQRH approximation by comparison with steady-state streamlines predicted by azimuthally independent and dependent theoretical solutions to the steady-state plasma equations. We find the error in both cases les 10° in longitude and therefore suggest that the EQRH approximation offers the means to relate observed solar lsquoinitial conditionsrsquo in the lsquorelease zonersquo directly to interplanetary measurements. If, in addition, the EQRH approximation also leads to agreement with low coronal structure, then there should be a straightforward correspondence to otherwise unobservable high coronal structure.
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