Flow burst-induced Kelvin-Helmholtz waves in the terrestrial magnetotail

The Kelvin-Helmholtz instability (KHI) on the boundary of a flow channel in the Earth's plasma sheet is investigated using Cluster and Double Star TC1 data. It is shown that when Cluster moves into the flow channel the magnetometer measures strong oscillations of the magnetic field, that increase as the spacecraft move further into the flow channel. These waves are identified as Kelvin Helmholtz waves. DoubleStar TC1, closer to the Earth, also observes these waves when entering the flow channel but at larger amplitude and with only little flow. The increase in wave amplitude agrees with the KHI wave growth. It is argued that the development of the KHI can play a major role in flow braking in the magnetotail, which is an important aspect of magnetotail dynamics. The large amount of kinetic energy released by a reconnection event or bursty bulk flow gets converted to other kinds of energy such that in the near Earth region the flow is stopped.