Altitude variation of ion composition in the midlatitude trough region: Evidence for upward plasma flow

Abstract

Midday ion composition measurements made by the Explorer 32 ion mass spectrometer in the midlatitude trough region (L = 5.0 -10.5) are compared with measurements made within the plasmasphere (L= 1. 8 -2.2).In the trough the light ion (H+ and He +) concentrations are observed to decrease with altitude between 600 and 2500km-a region in which 0+ is the major ion.Within the plasmasphere, however, the concentrations of the light ions, when minor, increase with altitude.Model calculations indicate that the behavior of the plasmasphere profiles is consistent with a state of stationary diffusive equilibrium, whereas a dynamic plasma state is required to account for the trough distributions.Upward directed H+ fluxes having near sonic E'peeds above 2000 km are required to reproduce the meas ured trough variations.This 'trough wind' , consisting of a rapid upward flow of H+, can be interpreted as evidence for the convection of the supersonic polar wind onto closed trough field lines.