Composition measurements of warm equatorially trapped ions near geosynchronous orbit

The mass composition of the intense warm (E ∼ 10‐500 eV) ion populations trapped within a few degrees of the geomagnetic equator in the range L = 5.3‐6.5 are examined using data from the Lockheed Ion Mass Spectrometer on the SCATHA spacecraft. The equatorially trapped ions, within the measured energy range E/q ≥ 100 eV, are found to be predominantly protons. These ions can be removed and replenished from the region sampled on time scales shorter than one day. Several recent works have focused on the energization of He+ in the equatorial region by ion cyclotron waves. It is now evident that an energization and/or transport process is required which produces equatorial H+ populations similar to those that have been predicted for He+.