  The large-scale magnetic cloud such as coronal mass ejections (CMEs) is the
fundamental driver of the space weather. The interaction of the multiple CMEs
in interplanetary space affects their dynamic evolution and geo-effectiveness.
The complex and merged multiple magnetic clouds appear as the in-situ signature
of the interacting CMEs. The Alfven waves are speculated to be one of the major
possible energy exchange/dissipation mechanism during the interaction. However,
no such observational evidence has been found in the literature. The case
studies of CME-CME collision events suggest that the magnetic and thermal
energy of the CME is converted into the kinetic energy. Moreover, the magnetic
reconnection process is justified to be responsible for the merging of multiple
magnetic clouds. Here, we present unambiguous evidence of sunward torsional
Alfven waves in the interacting region after the super-elastic collision of
multiple CMEs. The Walen relation is used to confirm the presence of Alfven
waves in the interacting region of multiple CMEs/magnetic clouds. We conclude
that Alfven waves and magnetic reconnection are the possible energy
exchange/dissipation mechanisms during large-scale magnetic clouds collisions.
The present study has significant implications not only in CME-magnetosphere
interactions but also in the interstellar medium where interactions of
large-scale magnetic clouds are possible.
