THE RADIAL AND ANGULAR VARIATION OF THE ELECTRON DENSITY IN THE SOLAR CORONA

摘要

We derive, for the first time, electron densities as a function of both radius (R) and position angle (θ) for the southwest quadrant of the off-limb corona, using the density-sensitive Si Ix λ349.9/λ 341.9 and Si x λ356.0/ λ347.7 extreme-ultraviolet line ratios. The observations were made with the coronal diagnostic spectrometer on board the Solar and Heliospheric Observatory over the ranges of 1.00 R⊙ < R < l.20 R⊙ and 180° < θ < 270°. Within the south polar coronal hole, the density varies from 2.3 x 10~8 cm~(-3) at 1.0 R⊙ to 8.3 × 10~7 cm~(-3) at 1.20 R⊙, while at the equator, the density vanes from 6.3 × 10~8 cm~(-3) at l.0 R⊙ to l.6 × 10~8 cm~(-3) at l.20 R⊙. The density falloff with height is therefore faster in the equatorial region. We also find that electron densities are, on average, a factor of 2.7 larger in the equatorial regions than in the polar coronal hole at a given radial distance. Finally, we find remarkable agreement between our measured densities as a function of radius and position angle and those predicted by a recent analytic MHD model of the solar wind, strongly supporting its basic premises.