Deformation of Ionospheric Potential Pattern by Ionospheric Hall Polarization

Abstract

The present study shows that the ionospheric Hall polarization can deform the high‐latitude ionospheric convection field, which is widely considered to be a manifestation of the convection field in the magnetosphere. We perform the Hall polarization field separation with a potential solver by changing the conductance distribution step by step from a uniform one to a more realistic one. We adopt dawn‐dusk and north‐south symmetric distributions of conductance and region 1 (R1) field‐aligned current (FAC). The pair of the primary field of the R1 system and each gradient of off‐diagonal component of conductance tensor (Hall conductance) generates the Hall polarization field and consequently causes potential deformations as follows. (a) The equatorward gradient causes clockwise rotation. (b) The gradient across the terminator, together with the effect of the equatorward gradient, causes the dawn‐dusk asymmetry. (c) The high conductance band in the auroral region causes kink‐type deformations. In particular, a nested structure at the equatorward edge of the band in the midnight sector well resembles the Harang Reversal. Result (a) can explain the clockwise bias inexplicable by the IMF‐By effect alone, the combination of (a) and (b) can explain the clearness and unclearness in the round or crescent shapes of the dawn‐dusk cells depending on the IMF‐By polarity, and (c) suggests that the ionosphere may not need the upward‐FAC for the formation of the Harang Reversal. We suggest that the final structure of the ionospheric potential is established by the combined effects of the magnetospheric requirements (external causes) and ionospheric polarization (internal effect).

Testing the Electrodynamic Method to Derive Height-Integrated Ionospheric Conductances

“…Shue and Weimer (1994) had proposed that polarization electric fields around areas of enhanced conductivity are responsible for forming the Harang discontinuity; the effect is to block the divergence of Hall currents where there are gradients in the Hall conductivity. Further evidence of this concept has been provided by Nakamizo and Yoshikawa (2019), and our results are consistent with this hypothesis. Equations 7and 8are not accurate where there are conductivity gradients, so the derived conductivity values near midnight, from 22 to 2 MLT, should not be trusted.…”

Testing the electrodynamic method to derive height-integrated ionospheric conductances

“…Data used in the development of the fieldaligned current model are available through Edwards et al (2020). The electric potential model (Edwards, 2019) was developed with the Swarm cross-track ion drift data available at https://swarm-diss.eo.esa.int/#swarm/Advanced/Plasma_Data/ 2Hz_TII_Cross-track_Dataset (Burchill and Knudsen, 2020) and Dynamics Explorer 2 Vector Electric Field measurements at https://cdaweb.gsfc.nasa.gov/pub/data/de/de2/electric_fields_vefi/ (last access: 12 January 2021, Maynard et al, 1981 Frandsen et al, 1978;Coplan et al, 1978), and data from ACE are available at https://cdaweb.gsfc.nasa.gov/pub/data/ace/mag/level_2_cdaweb/ and https://cdaweb.gsfc.nasa.gov/pub/data/ace/swepam/level_2_ cdaweb/swe_h0 (last access: August 2019, Smith et al, 1998;McComas et al, 1998).…”

Temporal and Spatial Variations of Total Electron Content Enhancements During a Geomagnetic Storm on 27 and 28 September 2017

“…According to their results, the pattern of the equivalent currents related to the high‐latitude convection showed a clockwise rotation for all the cases of the IMF By pattern under the negative value of the IMF Bz . Recently, Nakamizo and Yoshikawa (2019) clarified that the deformation of the high‐latitude convection pattern is established by the combined effects of the solar wind and ionospheric polarization due to the spatial inhomogeneity of ionospheric conductivities with the use of an electric potential solver (Nakamizo et al, 2012). In this study, it was newly shown that the SED plume can expand from the afternoon or evening sector to the prenoon sector and move toward the high‐latitude region from the throat region between the dawn and dusk convection cells due to the clockwise rotation of the high‐latitude convection pattern.…”

“…Therefore, based on the above discussion, it can be considered that the structure of the SED plume strongly depends on the high‐latitude convection pattern. According to Nakamizo and Yoshikawa (2019), since the spatial distribution of the high‐latitude convection depends on both the solar wind and ionospheric conductivities, the statistical feature of the SED plume will be established by a statistical analysis in future studies.…”