The Cusp as a VLF Saucer Source: First Rocket Observations of
Long-Duration VLF Saucers on the Dayside
Abstract
Auroral whistler mode radio emissions called saucers are of fundamental
interest because they require an unusually stationary emission process
in the dynamic auroral environment, and it is a mystery how that can
happen in this or similar conditions elsewhere in geospace. The Cusp
Alfven and Plasma Electrodynamics Rocket (CAPER-2), launched into the
polar cusp and obtained the first rocket measurements of a large-scale,
multiple-armed dayside saucers, similar to those recently observed by
the the DEMETER satellite, with the addition of in situ particle
measurements and simultaneous conjugate ground-based measurements. For
300 s prior to cusp entry, CAPER-2 detected ~15
truncated saucer arms lasting 5–50 s. Directional analysis using
waveforms, combined with ground-based data, suggests that these
originate within the cusp. Ray-tracing analysis indicates source
altitudes ~2500 km. On-board particle instruments show
dispersed electron bursts in the cusp, presumed Alfvenically
accelerated, corresponding to approximately the same source heights as
the saucers.