Quiet-time mid-latitude trough: influence of convection, field-aligned currents and proton precipitation

• Published in: Annales Geophysicae
• Main Authors: H. Nilsson, T. I. Sergienko, Y. Ebihara, M. Yamauchi
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2005
• Subjects: Science; Q; Physics; QC1-999; Geophysics. Cosmic physics; QC801-809; EISCAT
• Online Access: https://doi.org/10.5194/angeo-23-3277-2005; https://doaj.org/article/f2182c791be44e5f9cf522c162ce0ee9

A combination of EISCAT CP-3 (latitude scans) and satellite (DMSP) data have been used to study the structure of the quiet-time evening-sector auroral and subauroral ionosphere, in particular the mid-latitude trough. The main mechanism behind trough formation in the quiet-time evening sector ionosphere is believed to be flow stagnation in a region where convection and corotation counteract each other. However, there is also the possibility that field-aligned currents (FAC) more directly modify the ionospheric density if the current is carried by thermal ionospheric electrons. A quantitative test of the flow-stagnation scenario and an estimate of the possible direct effects caused by field-aligned currents have been performed. We found that the electron densities observed can indeed be explained by the flow-stagnation scenario, but the electron density altitude profiles in the trough sometimes differ from what should be expected from flow stagnation. The effect of a downward field-aligned current cannot be identified in the data, but a simple estimate shows that it can affect the ionospheric plasma density, causing decreased ionospheric densities. In the quiet-time region 2 current/trough region there is typically a significant ion production resulting from proton precipitation which may counteract this effect. Charge exchange of the precipitating protons causes a lateral spread and a smooth associated conductance enhancement. Thus, whereas the proton number flux is insufficient to directly carry the evening sector region 2 current, the precipitation in practice produces the necessary charge carriers. We suggest that precipitating protons do play a crucial role in the electrodynamics of the dark evening sector ionosphere by causing a small but smooth conductance enhancement and producing the charge carriers necessary to carry the trough-associated downward field-aligned current.