Introduction
Penetrating electric field is a high latitude dawn-dusk field applied to
the mid and low latitudes at a much short time scale than
thermosphere-ionosphere interaction process such as ion neutral
collision. Penetration electric fields have been intensively studied in
the past [e.g., Nishida, 1968; Kikuchi et al., 2008; W. Wang et al.,
2008; Huang, 2019; Huang et al., 2005; Maruyama et al., 2005; Kelley et
al., 2003; Fejer et al., 2007; Lu et al, 2012].
While the basic underlying physics is known, many aspects of the
penetrating electric field (PEF) remain to be addressed. For example, it
is difficult to simulate the penetrating electric field, which changes
rapidly, using a first principle thermosphere and ionosphere model
driven by empirical high latitude convection models such as Heelis
et al. [1982] and Weimer [2005]. Lu et al. [2012]
used the AMIE (Assimilative Mapping of Ionospheric Electrodynamics)
[Richmond and Kamide, 1988] driven TIMEGCM
(Thermosphere-Ionosphere-Mesosphere-Electrodynamic General Circulation
Model) model to simulate penetrating electric field effects. While AMIE
uses real data as inputs, the derived convection pattern at high
latitudes still relies heavily on empirical data information. The case
examined by Lu et al. [2012] was a very strong storm event (November
9-10, 2004), which produced 120 m/s vertical ion drift at the equator.
High latitude model inputs with a high time resolution will enable the
examination of the penetrating electric field in great details and
improve the understanding of observed results, especially under weak to
moderate geomagnetic activity conditions. One of the outstanding
questions is how the penetration electric field is related to changes in
the IMF Bz and the cross polar cap potential (CPCP). Penetrating
electric field effect becomes complicated when the IMF Bz changes back
and forth between northward and southward.
Towards the goal of better understanding the penetrating electric field,
we use a coupled magnetosphere ionosphere model (MAGE, Multiscale
Atmosphere-Geospace Environment) to simulate the penetrating electric
field effect on the equatorial ionosphere [e.g., Lin et al., 2021;
Pham et al., 2022], specifically on the vertical ion drift. The MAGE
model provides much higher and more dynamic high latitude inputs of
convection pattern and auroral precipitation by coupling with a
magnetospheric model. The objective is to show how the IMF Bz component
controls the equatorial vertical ion drift, through the CPCP and
penetrating electric field. In addition to the latest modeling tools, we
also will use the NASA ICON mission ion drift measurement to observe the
effect of the penetrating electric field from an equatorial orbiting
satellite platform. MAGE simulations are used to facilitate
interpretation of the observational results.
We selected two geomagnetically active intervals during September 2020.
The first interval is from September 24, 5-6 UT when the IMF Bz turned
northward first and then turned southward within one hour, which is
highlighted (blue shaded) in the IMF Bz and By subplot of Figure 1. The
figure also includes solar wind speed and density, and the
interplanetary electric field (IEF) dawn-dusk component. The IMF Bz
variations led to changes in the IEF, which affects the dawn-dusk
electric potential and penetrating electric field. The second interval
is from September 26, 9-10 UT with the interval highlighted in Figure 2.
In this case, IMF Bz turned southward within the highlighted interval.
Moreover, we have ICON observations of the equatorial ExB meridional ion
drift, which is upward at the magnetic dip equator, for comparison. The
paper is organized by (1) a brief description of the model setup, (2)
discussion of the simulation results for the two intervals, (3)
comparison between the model results and ICON ion drift observations,
and (4) additional discussion on the ICON ion drift data.