  Observations reveal an increase with height of the line width of several
coronal spectral lines probably caused by outwardly propagating Alfv{\'e}n
waves. However, the spectral line width sometimes shows a sudden decrease at a
height 0.1-0.2 R, where the ratio of sound to Alfven speeds may approach unity.
Qualitative analysis shows that the resonant energy conversion from Alfven to
acoustic waves near the region of the corona where the plasma $\beta$
approaches unity may explain the observed spectral line width reduction.
