On the symmetry of ionospheric polar cap patch exits around magnetic midnight

Abstract

In this paper we examine how polar cap patches, which have been frozen into the antisolar flow over the polar cap, are transported into the nighttime auroral oval. First we present a detailed case study from 12 January 2002, with continuous observations of polar cap patches exiting into the nighttime auroral oval in the Scandinavian sector. Satellite images of the auroral oval and all-sky camera observations of 630.0 nm airglow patches are superimposed onto Super Dual Auroral Radar Network convection maps. These composite plots reveal that polar cap patches exit on both the dusk and on the dawn convection cells. Then we present statistics based on 8 years of data from the meridian scanning photometer at Ny-Aalesund, Svalbard, to investigate the possible interplanetary magnetic field (IMF) B y influence on the distribution of patch exits around magnetic midnight. The magnetic local time distribution of patch exits is almost symmetric around magnetic midnight, independent of IMF B y polarity. Synthesizing these observations with previous results, we propose a three-step mechanism for why patch material exits symmetrically around midnight. First, intake of patch material occurs on both convection cells for both IMF B y polarities. Second, plasma intake by transient magnetopause reconnection stretches the newly cut polar cap patches into dawn-dusk elongated forms during their transport into the polar cap. And finally at exit, dawn-dusk elongated patches are split and diverted toward both the dawn and dusk flanks when grabbed by transient tail reconnection.

Morphology of high‐latitude plasma density perturbations as deduced from the total electron content measurements onboard the Swarm constellation

“…As for substorm regions, on the other extreme, we expect zonally elongated perturbations [e.g., Moen et al , , Figure 8] caused by the zonally diverging convection pattern near the nightside reconnection region. This can explain the Swarm/TEC observations of the largest |ΔTEC| on the unit circle (Figures b and b).…”

Polar cap precursor of nightside auroral oval intensifications using polar cap arcs

“…Although the MLT distribution of such collision has been studied by Moen et al . [], whether and how the oval responds to this exit from the polar cap has not been examined in detail. Optical observations of patches could thus be useful for future studies to provide information on the polar cap precursor of nightside auroral oval disturbances under various IMF conditions.…”

Horseshoes in the High‐Latitude Ionosphere

“…After initiating on the dayside cusp region, patches are transported across the center of the polar cap region toward night side (Moen et al, ; Oksavik et al, ) and may circulate back on the dawn and dusk sides. Of the unresolved questions regarding polar cap patches, in this work we focus on asking the following: What is the source of the plasma?…”