Waves within magnetic clouds: STEREO observations

Complex events are formed by two or more large-scale structures which interact in the solar wind. Typical cases are interactions of: (i) a magnetic cloud/interplanetary coronal mass ejection (MC/ICME) with another MC/ICME transient; (ii) a MC/ICME embedded within a stream interaction region (SIR); and (iii) a MC/ICME followed by a fast stream. Using data from the STEREO mission during the years 2007-2011 we found 17 ICMEs forming complex events with an associated shock wave. All the ICMEs included in this study showed a smooth rotation of the magnetic field and low proton beta plasma, and were classified as MCs. We use magnetic field and plasma data to study the waves observed within these MCs. To determine wave characteristics we perform Fourier Power Spectra and Minimum Variance Analysis. We also analyze 9 MCs driving shocks which were not associated with complex events. We compare wave characteristics within the Magnetic Clouds forming Complex Events (MCCE), with those waves observed within the Magnetic Clouds that were isolated (IMC), i. e., not associated with complex events. Transverse, almost parallel propagating and nearly circular polarized ion cyclotron waves (ICWs) were observed within both, MCCE and IMC. We find that both, left-handed ICWs and right- handed ICWs were present within MCCE and IMC. Compressive mirror mode waves (MM) were observed only within MCCE. We study plasma conditions inside the MCs to get insight about wave origin. Most of the mirror mode events found within MCCE, were observed in regions with enhanced plasma beta. This is in agreement with kinetic theory, which predicts that mirror mode growth is favored by high plasma beta values.