ULF Waves Modulating and Acting as Mass Spectrometer for Datside Ionospheric Outflow Ions

Ionospheric outflow has been shown to be a dominant ion source of Earth's magnetosphere. However, most studies in the literature are about ionospheric outflow injected into the nightside magnetosphere. We still know little about ionospheric outflow injected into the dayside magnetosphere and its further energization after it enters the magnetosphere. Here, with data from MMS mission, we report direct observations of the modulation of dayside ionospheric outflow ions by ultra-low frequency (ULF) waves. The observations indicate the modulation is mass-dependent, which demonstrates the possibility of using ULF waves as a mass spectrometer to identify ion species. Moreover, the measurement suggests polarization drift may play a role in O⁺ modulation, which may lead to a true acceleration and even non-adiabatic behavior of O⁺. This interaction scenario can work throughout the whole magnetosphere, and impact upon the plasma environment and dynamics.