An investigation of auroral E region energy exchange using Poker Flat
Incoherent Scatter Radar observations during fall equinox conditions
Abstract
We present new results using data collected by the Poker Flat Incoherent
Scatter Radar (PFISR) of energy transfer rates which include the effects
from neutral winds in the high latitude E-region ionosphere-thermosphere
(IT) during Fall 2015. The purpose of our investigation is to understand
the magnetic local time (MLT) dependence of the peak energy transfer,
which occurs asymmetrically in the morning-evening (dawn-dusk) MLT
sector. The statistical characteristics of both altitude-resolved and
altitude-integrated energy transfer rates in the auroral E region local
to PFISR during different geomagnetic conditions are quantified. Our
analysis shows that the geomagnetic activity level has a large impact on
the energy transfer rates. In contrast with previous investigations, we
find both the altitude integrated electromagnetic (EM) energy transfer
rate and Joule heating rate are larger in the evening sector than in the
morning sector during all geomagnetic activity conditions. We also
observe non-negligible negative EM energy transfer rates below 110 km in
the morning sector during active conditions, which is associated with
neutral winds during this MLT interval. The statistical results show
that the neutral winds tend to increase the Joule heating rate in a
narrow altitude range in the morning sector and impact a broader region
with respect to altitude and time in the evening sector in the E region
under moderate and active conditions. We find that during quiet
conditions that the neutral winds have a significant contribution to the
Joule heating and contribute up to 75% of the Joule heating. However,
during active conditions, the enhanced fields are a dominant driver of
Joule heating, while the neutral wind effects can reduce the Joule
heating rates by 25% or more relative to the passive heating rates.