Observations of ionospheric magnetospheric coupling: DE and Chatanika coincidences

Abstract

Observations from several experiments on board the Dynamics Explorer 1 and 2 (DE 1 and 2) spacecraft and ground‐based radar measurements from the Chatanika radar are combined in order to examine the details of ionospheric/magnetospheric coupling in the local evening sector. DE 1 and DE 2 were in coplanar polar orbits that provided measurements almost simultaneously in time and magnetically coincident with the Chatanika radar from L = 3 to L = 17. The coupling processes are inferred from the density, temperature, composition, and angular distributions of the low‐energy plasma observed from the E region of the ionosphere to magnetospheric altitudes of 2.5 earth radii (RE). Plasma characteristics of the plasmasphere, main trough, auroral zone, and polar cap can be studied in this data set. In the comparison of the data, it is clear that the only ionospheric trace of the plasmapause is seen as an increase of the electron temperature. The minimum plasma density in the high‐latitude trough of the ionosphere is magnetically coincident with a region of observed low‐energy bidirectional conical distributions of H+ and He+ at the DE 1 altitude of 1.5 to 1.8 RE. Polarward of this region, DE 1 observes unidirectional conies consisting of H+ and He+ ions that are magnetically coincident with low‐altitude (150‐km) auroral ionization as observed by the Chatanika radar. Over the polar cap, only field‐aligned outward flows of H+, He+, and O+ are seen. These observations imply that as L increases, the dominant coupling mechanism between the ionosphere and magnetosphere in the measured energy range changes from equilibrium diffusion to perpendicular acceleration and, finally, to parallel acceleration.