27-10-2012, 03:41 PM
Coupling the Solar-Wind/IMF to the Ionosphere through the High Latitude Cusps
ABSTRACT
Magnetic merging is a primary means for coupling energy from the solar wind into the magnetosphere-ionosphere system.
The location and nature of the process remain as open questions. By correlating measurements form diverse locations and
using large-scale MHD models to put the measurements in context, it is possible to constrain out interpretations of the global
and meso-scale dynamics of magnetic merging. Recent evidence demonstrates that merging often occurs at high latitudes in
the vicinity of the cusps. The location is in part controlled by the clock angle in the interplanetary magnetic field (IMF) Y-Z
plane. In fact, B(sub Y) bifurcated the cusp relative to source regions. The newly opened field lines may couple to the
ionosphere at MLT locations of as much as 3 hr away from local noon. On the other side of noon the cusp may be connected
to merging sites in the opposite hemisphere. In face, the small convection cell is generally driven by opposite hemisphere
merging. B(sub X) controls the timing of the interaction and merging sites in each hemisphere, which may respond to planar
features in the IMF at different times. Correlation times are variable and are controlled by the dynamics of the tilt of the
interplanetary electric field phase plane. The orientation of the phase plane may change significantly on time scales of tens
of minutes. Merging is temporally variable and may be occurring at multiple sites simultaneously. Accelerated electrons from
the merging process excite optical signatures at the foot of the newly opened field lines. All-sky photometer observations of
557.7 nm emissions in the cusp region provide a ‘television picture’ of the merging process and may be used to infer the
temporal and spatial variability of merging, tied to variations in the IMF.