Statistical Survey of Ion Cyclotron Wave Signatures around Earth’s Magnetotail Dipolarizations

In the Earth’s Magnetotail fast earthward plasma flows (so-called Bursty Bulk Flows) with a duration of several minutes and velocities of several hundreds of km/s are regularly observed in in-situ measurements. These flows are frequently accompanied by embedded co-moving, and more dipolar-shaped, magnetic flux bundles. The leading edge of such flux bundles is called a Dipolarization Front (DF). Such Earthward moving flux bundles and DFs can be formed by magnetic reconnection in the Magnetotail, as well as by the Ballooning/Interchange Instability (BICI). For the latter mechanism, simulations of the BICI suggest that, away from the central plasma sheet, the BICI heads are accompanied by electromagnetic ion cyclotron waves, and such wave signatures were indeed observed by the MMS and THEMIS spacecraft between the neutral sheet and the magnetospheric lobes.

In the present study we use years of data from NASA’s Magnetospheric Multiscale Mission (MMS) to compile a database of several hundred events. We analyze this database with the goal of a statistical description of such flux bundles with respect to ion cyclotron wave occurrence, and compare them to several parameters, such as magnetic field and plasma conditions, to further enhance the understanding of the large-scale context and origin of magnetotail dipolarizations.