Magnetohydrodynamical Processes of the Sector Structure in the Solar Wind

Abstract Effects of the spirally-twisted interplanetary magnetic field on the solar wind velocity and density are investigated in a scheme of linear approximation. It is clarified that the interplanetary magnetic field plays an important ro'.e on the solar wind density variations. The observed longitudinal variation in the solar wind velocity amounting to 100km/sec must exist already near the sun (r ≲ 0.2 AU): such large velocity variations cannot be generated by the interplanetary magnetic field. It is suggested that at r ~ 0.2 AU the solar wind with large kinetic energy is ejected from a narrow region less than 40° in the azimuthal angle, where the magnetic field is strong. The solar wind density variations are discussed under the hypothetical boundary condition that the solar wind plasma is spherically symmetric at r ~ 0.2 AU. It is concluded that the interplanetary magnetic field can generate a large density variation not only in the ecliptic plane but also in the regions away from it.