Coronal line-width variations

Line-width measurements of the coronal ion Si VIII confirm earlier observations which show an increase in the non-thermal velocity above the solar limb. The present data, taken at the equatorial limb, show an increase from 24 km s(-1) at the limb to 28 km s(-1) some 25 000 km above the limb. The electron density as measured from the Si VIII line pair shows a decrease from 3.5 x 10(8) cm(-3) to 1.8 x 10(8) cm(-3) over the same distance. These data imply that the non-thermal velocity is inversely proportional to the quadratic root of the electron density, in excellent agreement with that predicted for undamped radially propagating Alfven waves.