|
|
 |
|
|
Ann. Geophys., 23, 3277-3288, 2005
www.ann-geophys.net/23/3277/2005/
© European Geosciences Union 2005
Quiet-time mid-latitude trough: influence of convection, field-aligned currents and proton precipitation
H. Nilsson1, T. I. Sergienko1, Y. Ebihara2, and M. Yamauchi1
1Swedish Institute of Space Physics, Kiruna, Sweden
2National Institute of Polar Research, Tokyo, Japan
Abstract. 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.
Full Article in PDF (1334 KB) |
|
|
