A comparative assessment of the distribution of Joule heating in
altitude as estimated in TIE-GCM and EISCAT over one solar cycle
Abstract
During geomagnetically active times, Joule heating in the Lower
Thermosphere - Ionosphere is a significant energy source, greatly
affecting density, temperature, composition and circulation. At the same
time, Joule heating and the associated Pedersen conductivity are amongst
the least known parameters in the upper atmosphere in terms of their
quantification and spatial distribution, and their parameterization by
geomagnetic parameters shows large discrepancies between estimation
methodologies, primarily due to a lack of comprehensive measurements in
the region where they maximize. In this work we perform a long-term
statistical comparison of Joule heating as calculated by the NCAR
Thermosphere - Ionosphere - Electrodynamics General Circulation Model
(TIE-GCM) and as obtained through radar measurements by the European
Incoherent Scatter Scientific Association (EISCAT). Statistical
estimates of Joule heating and Pedersen conductivity are obtained from a
simulation run over the 11 year period spanning from 2009 until 2019 and
from radar measurements over the same period, during times of radar
measurements. The results are statistically compared in different
Magnetic Local Time sectors and Kp level ranges in terms of median
values and percentiles of altitude profiles. It is found that Joule
heating and Pedersen conductivity are higher on average in TIE-GCM than
in EISCAT for low Kp and are lower than EISCAT for high Kp. It is also
found that neutral winds cannot account for the discrepancies between
TIE-GCM and EISCAT. Comparisons point towards the need for a
Kp-dependent parameterization of Joule heating in TIE-GCM to account for
the contribution of small scale effects.