Evidence for convected Alfvén ion-cyclotron and fast magnetosonic-whistler waves inside an interplanetary coronal mass ejection

Intervals of enhanced fluctuations are relatively rare within the magnetic cloud region of an interplanetary coronal mass ejection (ICME). We investigated two such intervals inside an ICME observed by the Wind spacecraft on 8–9 June 2000 and characterized their associated wave populations. A spectral analysis of magnetic and velocity fluctuations was used to characterize Alfvénicity. We examined the power spectral density (PSD), magnetic helicity, and ellipticity to determine wave properties. Minimum variance analysis (MVA) was used to investigate wave polarization, while wavelet transform coherence (WTC) between density and magnetic fluctuations was employed to assess compressibility. In addition, a linear plasma dispersion solver was used to evaluate the growth and damping rates of the observed wave modes. The ion-scale normalized magnetic helicity reveals a left-handed circularly polarized signature in both intervals. Moreover, the second interval is characterized by an additional right-handed population at higher frequencies. All these fluctuations propagate in a quasi-parallel direction to the local magnetic field. Therefore, the left-handed fluctuations are consistent with Alfvén ion-cyclotron (AIC) waves, while the right-handed fluctuations are consistent with fast magnetosonic-whistler (FM/W) waves. The ICME plasma accesses resonance conditions supporting multiple ion-scale wave modes. Although the observed fluctuations exhibit characteristics consistent with AIC-like and FM/W-like modes, the enhanced wave activity near ion scales is unlikely to originate from locally growing instabilities under the observed bulk plasma conditions. Instead, these fluctuations are more plausibly convected from regions outside the local plasma environment.