Variation in Pedersen Conductance near Jupiter’s Main Emission Aurora:
Comparison of Hubble Space Telescope and Galileo Measurements
Abstract
We present the first large-scale statistical survey of the Jovian main
emission (ME) to map auroral properties from their ionospheric locations
out into the equatorial plane of the magnetosphere, where they are
compared directly to in-situ spacecraft measurements. We use
magnetosphere-ionosphere (MI) coupling theory to calculate currents from
the auroral brightness as measured with the Hubble Space Telescope and
from plasma flow speeds measured in-situ with the Galileo spacecraft.
The effective Pedersen conductance of the ionosphere
(\(\Sigma_P^*\)) remains a free parameter in this
comparison. We first show that the field-aligned currents per radian of
azimuth calculated from the auroral observations, found to be
\(I_{||}=9.54^{+11.5}_{-6.35}\) MA
rad-1 and
\(I_{||}=10.64^{+11.1}_{-6.11}\) MA
rad-1 in the north and south, respectively, are consistent
with previous results. Then, we calculate the Pedersen conductance from
the combined datasets, and find it ranges from
\(0.02<\Sigma_P^*<2.26\) mho
overall with averages of \(0.14^{+0.31}_{-0.08}\) mho in the
north and \(0.14^{+0.26}_{-0.09}\) mho in the south. Taking the
currents and effective Pedersen conductance together, we find that the
average ME intensity and plasma flow speed in the middle magnetosphere
(10-30 RJ) RJ) are broadly consistent with one another under MI
coupling theory. We find evidence for peaks in the distribution of
\(\Sigma_P^*\) near 7, 12, and 14 hours magnetic
local time (MLT). This variation in Pedersen conductance with MLT may
indicate the importance of conductance in modulating MLT- and
local-time-asymmetries in the ME, including the apparent subcorotation
of some auroral features within the ME.