For the first time, direct comparisons of the equatorial ion partial pressure
and pitch angle anisotropy observed by TWINS and simulated by CIMI are
presented. The TWINS ENA images are from a 4-day period, 7–10 September
2015. The simulations use both the empirical Weimer 2K and the
self-consistent RCM electric potentials. There are two moderate storms in
succession during this period. In most cases, we find that the general
features of the ring current in the inner magnetosphere obtained from the
observations and the simulations are similar. Nevertheless, we do also see
consistent contrasts between the simulations and observations. The simulated
partial pressure peaks are often inside the observed peaks and more toward
dusk than the measured values. There are also cases in which the measured
equatorial ion partial pressure shows multiple peaks that are not seen in the
simulations. This occurs during a period of intense AE index. The CIMI
simulations consistently show regions of parallel anisotropy spanning the
night side between approximately 6 and 8 RE, whereas the
parallel anisotropy is seen in the observations only during the main phase of
the first storm. The evidence from the unique global view provided by the
TWINS observations strongly suggests that there are features in the ring
current partial pressure distributions that can be best explained by enhanced
electric shielding and/or spatially localized, short-duration injections.</p