Abstract
<strong class="journal-contentHeaderColor">Abstract.</strong> Known as northern lights, auroral spirals are distinct features of substorm auroras composed of large-scale spirals (100s km Surges) mixed with smaller scale ones (10s km Folds, and 1 km Rays). Spiral patterns are generally interpreted in terms of the field line mapping of the upward field-aligned currents produced in the magnetosphere during the field line dipolarization. The field line mapping results in opposing spiral rotations of small- and large-scale auroras. Because of a rotational symmetry deformation and similarity in deformation speeds (6~8 km/s) of small- and large-scale spirals, it has been suggested that common physical processes may underlie the deforming processes. Internal processes in the polar ionosphere (ionospheric driver) will be proposed as the general dynamic for spiral auroras. The ionospheric driver rotated in the ionosphere to produce spirals that characteristically differ from the field line mapping scenario.
Highlights
Introduction onboard particle and field detectors revealed that a primary driver of auroras associated of Bursty Bulk Flows [Angelopoulos et al, 1992], Dipolarization Front [Runov et al, 2011], and Plasma Bubbles [Sergeev et al, 1996] from the tail may alter poleward boundary intensification, streamers, beading of the onset arc, and auroral bulge. (Westward Traveling Surges, 100s km) are distinct auroral forms associate with the polar ionosphere are determined by the field line mapping [Borovsky, 1993; Stenbaek-Nielsen et al, 1999; Forsyth et al, 2020]
Oguti (2010) described spiral auroras in the auroral bulge as a whole “STo explain consistent rotations from small-scale to large-scale spirals, we propose the new scenario is referred to as ionospheric injection [Saka, 2019, 2021] and is summarized
The evaporations of ions from negatively charged regions associated with parallel electric fields would interrupt the perfect neutralization of ionosphere
Summary
The ionospheric injection is first triggered by westward electric fields transmitted from the convection surge in the magnetosphere in association with dipolarization onset. The evaporations of ions (electrons) from negatively (positively) charged regions associated with parallel electric fields would interrupt the perfect neutralization of ionosphere. Ions/electrons traveling in accelerating potential gradients lose perpendicular and lower velocities in parallel component, leaving only the energetic part of ionospheric plasmas collimated along the field lines. The potential drop would develop to retain sufficient excited locally in the negatively charged regions, and black auroras are from positively the ionosphere correspond to electron rich and ion rich regions and are referred to as ion geometry, pitch angle anisotropies of evaporated ions/electrons further develop initial energies for driving auroral precipitations in low altitude acceleration regions.
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