SOHO/UVCS Detection of Turbulence in a Coronal Mass Ejection

The intensity of the H I Ly alpha line measured by the UltraViolet Coronagraph Spectrometer (UVCS) onboard the Solar and Heliospheric Observatory (SOHO) is used to investigate the density turbulence within the coronal mass ejection (CME) occurred on 2006 December 24, in the South polar coronal hole. In order to compare the spectral index inside the CME with those found in the undisturbed coronal plasma, we examined the CME data by applying the wavelet technique. This temporal analysis reveals, during the whole observation time, the existence of large-scale density fluctuations of periods from tens of minutes to a few hours. However, during the CME, the power spectrum becomes less steep with a spectral slope about 5/3, typical of the turbulent regime, whilst prior to the CME and in the recovery phase the spectral slope is about 3. The Kolmogorov-like spectrum observed within the CME is evidence for the nearly incompressible turbulent character of the CME plasma. This spectrum is significantly different from that of the high-speed flow from coronal holes and the low-speed wind originating above closed-field coronal streamers. This result is particularly important to advance in the understanding of where the main source of CME flux injection resides.