Testing the Electrodynamic Method to Derive Height-Integrated Ionospheric Conductances

Abstract

Abstract. We have used empirical models for electric potentials and the magnetic fields in both space and on the ground to obtain maps of the height-integrated Pedersen and Hall ionospheric conductivities at high latitudes. This calculation required use of both "curl-free" and "divergence-free" components of the ionospheric currents, with the former obtained from magnetic fields that are used in a model of the field-aligned currents. The second component is from the equivalent current, usually associated with Hall currents, derived from the ground-level magnetic field. Conductances were calculated for varying combinations of the Interplanetary magnetic field (IMF) magnitude and orientation angle, as well as the dipole tilt angle. The results show that reversing the sign of the Y component of the IMF produces substantially different conductivity patterns. The Hall conductivities are largest on the dawn side in the upward, Region 2 field-aligned currents. Low electric field strengths in the Harang discontinuity lead to inconclusive results near midnight. Calculations of the Joule heating, obtained from the electric field and both components of the ionospheric current, are compared with the Poynting flux in space. The maps show some differences, while their integrated totals match to within 1 %. Some of the Poynting flux that enters the polar cap is dissipated as Joule heating within the auroral ovals, where the conductivity is greater.

Testing the electrodynamic method to derive height-integrated ionospheric conductances

“…(10). This model version (Edwards et al, 2020) had fit the spacecraft magnetic field measurements to the duskward and sunward components in order to reduce the spurious, circular harmonics in the FAC that tend to result when using polar coordinates. The total sums of the upward (negative) and downward (positive) FAC, integrated over the spherical cap, are indicated in the upper left and right corners of the contour map in units of millions of amperes (MA).…”

“…The field-aligned current maps obtained from different data sets are also similar and repeatable. For examples, compare the results from magnetometers on Dynamics Explorer 2 (Weimer, 2001(Weimer, , 2005a, DMSP , the Iridium constellation (Anderson et al, 2008), CHAMP and Swarm (Laundal et al, 2018), and the Ørsted-CHAMP-Swarm combination (Edwards et al, 2020) that we use here. Laundal et al (2018) also show maps of the equivalent currents that resemble the ones shown here.…”

“…The new FAC model that we use was developed using a very large database of magnetic field measurements from the Ørsted, Challenging Mini-satellite Payload (CHAMP), and Swarm missions, along with IMF values from ACE (Edwards et al, 2020). The magnetic field instruments on these satellites have better accuracy and sampling rates than the Iridium satellites used for the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) (Anderson et al, 2008(Anderson et al, , 2014.…”

“…Additionally, this gradient is rotated 90 • from the direction of the toroidal component of the magnetic field, and vice versa. The newest model by Edwards et al (2020) differs from the predecessors in that, rather than first integrating the magnetic field measurements to obtain a magnetic potential, the magnetic field values measured on the spacecraft are used directly in the least-error fits. Preprocessing of the data involves subtraction of the Earth's internal field and translation into magnetic apex coordinates.…”

“…In this paper we use a similar calculation to generate 34 D. Weimer and T. Edwards: Testing the electrodynamic method more detailed maps of the conductivity for a wider range of conditions, including variations in IMF clock angle and dipole tilt angle. Our input data consist of outputs from three separate empirical models that were derived from large data sets: a new model of the electric potentials (Edwards, 2019), a model of the ground-level geomagnetic perturbations (Weimer, 2013), and a new FAC model from satellite magnetometers (Edwards et al, 2020). Due to the need for both electric fields and currents, from magnetic field measurements both on the ground and in space, we prefer to call this the "electrodynamic method".…”