General solution for calculating polarization electric fields in the auroral ionosphere and application examples

Abstract

[1] We devise an approach to calculate the polarization electric field in the ionosphere, when the ionospheric conductances, the primary (modeled) or the total (measured) electric field, and the Cowling efficiency are given. In contrast to previous studies, our approach is a general solution which is not limited to specific geometrical setups, and all parameters may have any kind of spatial dependence. The solution technique is based on spherical elementary current (vector) systems (SECS). This way, we avoid the need to specify explicit boundary conditions for the searched polarization electric field of its potential which would be required if the problem was solved in a differential equation approach. Instead, we solve an algebraic matrix equation, and the implicit boundary condition that the divergence of the polarization electric field vanishes outside our analysis area is sufficient. In order to illustrate our theory, we then apply it to two simple models of auroral electrodynamic situations, the first being a mesoscale strong conductance enhancement in the early morning sector within a relatively weak southward primary electric field, and a morning sector auroral arc with only a weak conductance enhancement, but a large southward primary electric field at the poleward flank of the arc. While the significance of the polarization electric field for maximum Cowling efficiency is large for the first case, it is rather minor for the second one. Both models show that the polarization electric field effect may not only change the magnitude of the current systems but also their overall geometry. Furthermore, the polarization electric field may extend into regions where the primary electric field is small, thus even dominating the total electric field in these regions. For the first model case, the total Joule heating integrated over the analysis area decreases by a factor of about 4 for maximum Cowling efficiency as compared to the case of vanishing Cowling efficiency. Furthermore, for this case the resulting total electric field structurally shows a strong resemblance to that frequently observed during auroral omega band events.Citation: Amm, O., R. Fujii, H. Vanhama¨ki, A. Yoshikawa, and A. Ieda (2013), General solution for calculating polarization electric fields in the auroral ionosphere and application examples,

Height‐dependent energy exchange rates in the high‐latitude E region ionosphere

“…In this paper, we use the calculated total electric field, which in some cases may compose of a magnetospheric electric field plus a polarization electric field. Amm et al [] show that the polarization effect (described by the Cowling efficiency) may significantly decrease Joule heating.…”

Flow Shears at the Poleward Boundary of Omega Bands Observed During Conjunctions of Swarm and THEMIS ASI

“…Lühr and Schlegel () and Wild et al () found that the eastward flow in the poleward part of the area of omega band‐related magnetic pulsations is stronger than that in the equatorward part, indicating a flow shear, but these studies lacked optical observations and so could not determine the relative location of the flow shear to the omega bands' auroral forms. In a newer study, Amm et al () showed optical observation of an omega band together with electric field data inferred from radar measurements. While not considered in their paper, their Figure 4 shows a gradient of southward electric field at the poleward boundary of the omega band's bright arc, indicating a flow shear.…”

Ground-based and additional science support for SMILE

“…Those IMAGE locations forming a meridional chain are especially useful for studying the equivalent ionospheric currents. The IMAGE observations are the base for algorithms developed in FMI for deducing the 1D and 2D ionospheric currents that are successfully used to study the ionosphere− magnetosphere processes and are potentially important for the SMILE mission (Amm and Viljanen, 1999;Amm et al, 2013). The Auroral Large Image System 4D (ALIS4D) multi-wavelength auroral imager network is operated by the Swedish Institute of Space Physics.…”