|
|
 |
|
|
Ann. Geophys., 24, 355-366, 2006
www.ann-geophys.net/24/355/2006/
© European Geosciences Union 2006
Sub-keV ring current ions as the tracer of substorm injection
M. Yamauchi and R. Lundin
Swedish Institute of Space Physics, SE-98128 Kiruna, Sweden
Abstract. The dynamics of the energy-latitude dispersed sub-keV trapped ions inside the
ring current region, the so-called wedge-like dispersions structure, were
statistically studied using Viking satellite data. Probabilities with/without
these signatures at various local times in the dayside are obtained in terms
of different time-lags from the substorm activity monitored by the AE index.
The structure appears in the early morning sector within a few hours after
the substorm, and it slowly propagates eastward while decaying with a time scale
of several hours. The result qualitatively confirmed the previous model that
the wedge-like dispersions are originated from past substorm-related plasma
injections into the nightside ring current region, and that the dispersion is
formed when these injected plasma slowly moves eastward to the dayside by the
drift motion (E×B (eastward), grad-<|B| (westward), and
curvature (westward) drifts). However, the appearance of the structure is
twice or three times faster than the model prediction, and some structure
reaches even to the evening sector. The results indicate that the start
location of the drift is not as far as midnight and that the drift speed is
slightly faster than the model prediction. The former means that the
substorm-related increase of hot plasma in the ring current region shifts or
extends to the early morning sector for large substorms, and the latter means
that the substantial electric field driving the sub-keV ion drift is slightly
different from the model field. We also detected the evacuating effect
starting right after the substorm (or storm) onset. The electric field
imposed in the dayside magnetosphere seems to remove the remainder of trapped
ions.
Full Article in PDF (873 KB) |
|
|
