Sources of plasma in the high altitude cusp

Abstract

Ambiguities introduced by the inconsistent definitions of the low and high altitude cusp lead to the inconsistency that at low altitudes the region commonly known as the cusp does not include boundary layer plasmas, but at high altitudes it does. Here we examine plasma data from two high altitude cusp intervals where ∼100keV ionospheric ions were observed. We show that the data are an average over an interval that includes plasma from both boundary layer and newly injected solar wind plasmas. We find that the ∼100keV ionospheric ions reported in the high altitude cusp are energized by well-known magnetospheric processes bringing energetic ions to the dayside boundary layers. We conclude that there is no need to postulate new processes associated with waves in diamagnetic cavities commonly found in the high altitude cusp to explain the observation of ∼100keV ionospheric ions found there.