UVCS WLC Observations of Compressional Waves in the South Polar Coronal Hole

Abstract

Recent SOHO Ultraviolet Coronagraph Spectrometer (UVCS) white light channel (WLC) observations of the south polar coronal hole plumes and interplume regions produce signatures of quasi-periodic variations in the polarized brightness (pB) at a heliocentric distance of 1.9 solar radii (R_solar). The Fourier power spectrum of the pB time series shows significant peaks at about 1.6-2.5 mHz and additional smaller peaks at longer and shorter timescales. Wavelet analysis of the pB time series shows that the coherence time of the fluctuations is about 30 minutes. The new observations strongly suggest that the fluctuations are compressional wave packets propagating in the coronal hole high above the limb. The presence of compressional waves may have important implications that help to explain the heating of coronal holes and the fast solar wind acceleration.