Empirical selection of Auroral Kilometric Radiation during a multipoint
remote observation with Wind and Cassini
Abstract
Auroral Kilometric Radiation (AKR) is radio emission that originates in
particle acceleration regions along magnetic field lines, coinciding
with discrete auroral arcs. Found in both hemispheres, an increase in
the amplitude of a particular AKR source denotes the strengthening of
parallel electric fields in the auroral zone, while the emission
frequency gives insight into source region morphology. AKR viewing
geometry is complex due to the confinement of the source regions to
nightside local times and the anisotropy of the beaming pattern, so
observations are highly dependent on spacecraft viewing position. We
present a novel, empirical technique that selects AKR emission from
remote radio observations made with the spin-axis aligned antenna of the
Wind/WAVES instrument, based on the rapidly varying amplitude of AKR
across spacecraft spin timescales. This selection is applied to 30 days
of data in 1999, during which the Cassini spacecraft flew close to Earth
and recorded AKR for the majority of the period, while the Wind
spacecraft completed close to two, precessing petal orbits. We examine
the flux density and integrated power, which gives an occurrence
distribution with spacecraft local time that is typical of AKR, with an
increase in power of around $10^{3}$ Wsr$^{-1}$ between
dayside and nightside observations. We also find a statistically
significant ($p < 10^{-5}$), previously observed
diurnal modulation of the AKR integrated power for the period, further
verifying the empirical selection of AKR and showing the promise of its
application to larger subsets of Wind/WAVES observations.