Alfvénic Fluctuations in an Interplanetary Coronal Mass Ejection Observed Near 1 AU

As for the present situation of coronal mass ejection(CME) triggering models,the distributions of Alfvén waves in flux ropes are different from model to model,and thus examining those distributions in interplanetary coronal mass ejection(ICME) is an effective way to connect ICME observations with these theoretical models of CME triggering.However,previous observations of Alfvénic fluctuations in ICMEs were rare with locations ranging from 0.3 AU to 0.68 AU only,which is usually explained as rapid dissipation of those remnant waves.Here we present an observation of Alfvén waves in a magnetic cloud(MC) near 1 AU,in situ detected by WIND in February 17～20,2011.The MC was generated by a CME accompanied with the first X-class flare in the 24 th solar cycle.The slope of the power spectral densities of magnetic fluctuation in the MC,are similar to those modes in ambient solar wind,but more anisotropic.The results will also be helpful for studies of CME theories and ICME thermodynamics.