On the generation of Pi2 pulsations due to plasma flow patterns around
magnetosheath jets
Abstract
We report observations of a magnetosheath jet followed by a period of
decelerated background plasma. During this period, THEMIS-A magnetometer
showed abrupt disturbances which, in the wavelet spectrum, appeared as
prominent and irregular pulsations in two frequency bands (7.6–9.2 and
12–17 mHz) within the Pi2 range. The observations suggest–for the
first time to our knowledge–that these pulsations were locally
generated by the abrupt magnetic field changes driven by the jet’s
interaction with the ambient magnetosheath plasma. Furthermore, similar
pulsations, detected by THEMIS-D inside the magnetosphere with a 140
seconds time-lag (which corresponds to the propagation time of a
disturbance travelling with Alfvenic speed), are shown to be directly
associated with the ones in the magnetosheath, which raises the question
of how exactly these pulsations are propagated through the magnetopause.