Auroral arcs as current transformers

Abstract

[1] We treat the effects of an electric field tangential to an auroral arc on the basis of an analytical model according to which auroral arcs are energized by the release of magnetic shear stresses and associated internal energy (Haerendel, 2007). If the tangential field exceeds a certain (low) threshold, the ionosphere acts as a current generator, or better transformer, and the magnetosphere as the load. The reason is that energy supplied by a longitudinal Type I current system, as defined by Boström in 1964, is transformed into energy of the latitudinal Type II current system attached to the arc and is mostly consumed by the auroral acceleration process. Closure of the transformer current in the upper magnetosphere and energy deposition in form of internal energy and shear stresses, although small, are crucial for the operation of this process. It can be visualized as a dragging of magnetic field and plasma along the arc in the direction of higher magnetospheric pressure enforced by the electric polarization field. This energy deposition from below is superimposed on the release of free energy supplied by the magnetospheric generator. Formulation of this scenario leads to a set of algebraic equations, whose solution provides quantitative answers on the interdependence of current closure, energy deposition, and enhanced auroral energy flux in relation to the imposed tangential electric field. Contrary to earlier expectations, the polarization field appears not as a consequence of current blockage, but as manifestation of its continuation by field-aligned currents and their closure in the magnetosphere. Another consequence of the energy deposition from below is a small modification of the arc's proper motion in the ambient plasma frame. A procedure for evaluating applicable measurements in terms of the underlying physics is given and a concrete example added.

What can we learn from HF signal scattered from a discrete arc?

“…The arc described above has several interesting features from the viewpoint of the theoretical arc models by Haerendel (2007Haerendel ( , 2008, and references therein). The arc was observed in the midnight sector where the total pressure should have its maximum and significant plasma flow perpendicular to the arc was recorded by the CUTLASS radar.…”

“…A more comprehensive testing of the model (e.g. according to the guidelines given in Haerendel, 2008) is left for future studies with the hope of finding an event where observations are available also from the magnetospheric generator and auroral acceleration regions.…”

“…The arc model of Haerendel (2007) is upgraded in the continuation work by Haerendel (2008) where an auroral arc acts as a current generator (or transformer) in the M-I current circuit. This can happen when the ambient electric field has a component tangential to the arc.…”

Solar wind effects on Jupiter non-Io DAM emissions during Ulysses distant encounter (2003–2004)

“…These results may imply that fast pressure changes have a higher longer impact on the auroral and magnetospheric processes than slower pressure changes. The former are expected to be accompanied by steep pressure gradients, which in turn could be associated with stronger auroral field aligned currents and related dissipation processes (e.g., Haerendel 2008).…”

Auroral Substorms: Search for Processes Causing the Expansion Phase in Terms of the Electric Current Approach

“…33 Possible cause of the expansion phase as a result of the deflation of the magnetosphere after the magnetosphere is inflated during the growth phase have been published on this subjects (cf. Rostoker and Bostrom 1976;Shiokawa et al 1998;Nakamura et al 2001;Haerendel 2007Haerendel , 2008Haerendel , 2009Birth et al 2012). However, it is important to distinguish between the DD and UL currents in explaining the expansion phase.…”