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We present the first high resolution global MHD with coupled inner magnetosphere simulation results of an observed theta aurora event. We use the Space Weather Modeling Framework in the Geospace configuration, which produces accurate field aligned current closure in the ionosphere that is integral to theta aurora formation. At the location of the observed theta aurora, the simulation produces a narrow channel of Joule heating along both open and closed field lines, and between a pair of oppositely directed field‐aligned current sheets in the ionosphere. We demonstrate that this Joule heating pattern that we identify as theta aurora maps to a reconnection region at the magnetotail flanks as well as in the distant magnetotail. The theta aurora maps to a cross‐tail current disruption and field‐aligned current source region in a highly twisted magnetotail. Plain Language Summary: The light of the aurora observed in the Earth's atmosphere is a signature of magnetic processes in outer space. The Sun produces hot magnetized plasma that blows through the solar system like a wind. The Earth's magnetic field shields us from the harmful impacts of the Sun's magnetized plasma wind. The interaction between the Earth's magnetic field and the Sun's plasma wind causes the ring of auroral light we see in the polar regions. Sometimes the ring of auroral light grows a bar of auroral light across its center (over the Earth's magnetic poles), transforming the ring into a structure like the Greek letter theta. We call this the theta aurora. It is unknown what physical processes in the Earth's magnetic field create the theta aurora. In this study we show the first realistic simulation that uses solar wind driver conditions of an observed theta aurora event, and demonstrate that we can successfully produce the theta aurora structure in the simulation. We find that the theta aurora's center bar of auroral light comes from multiple regions in the vast Earth's magnetotail. This new result helps us better understand the dynamics of the Earth's space environment and better protect ourselves against the Sun's hazardous plasma wind effects. Key Points: We show first global MHD simulation event study that successfully produces a Joule heating signature that we identify as theta auroraSimulation associates transpolar arc signatures with reconnection at the magnetospheric flank and in the distant magnetotailThe transpolar arc maps to a cross‐tail current disruption and field‐aligned current source region in a highly twisted magnetotail [ABSTRACT FROM AUTHOR]

In this study, we explore the evolution of long-duration transpolar arcs observed during an exceptionally quiet period by the Fengyun-3D and Defense Meteorological Satellite Program satellites on 17 January 2019. Leveraging the extensive field of view of WAI, we captured the complete structure and evolution of the TPA over a very quiet period exceeding 7 h, with AE<30 nT. The TPA initially manifested at the poleward boundary of the auroral oval in the dawn sector, gradually migrating towards the dusk as the y-component of the interplanetary magnetic field (IMF BY) transitioned from negative to positive. Throughout this phase, the TPA underwent a distortion, transforming from a straight line to an "l-shape". Following a reversal in interplanetary magnetic field BY to negative, the TPA retraced its path towards dawn and ultimately dissipated when the IMF turned southward. Of particular interest is the observation that when the TPA approached the noon-midnight line, small-scale spiral structures became apparent within the TPA. This suggests the presence of intricate small-scale magnetic field topologies or plasma instabilities/shears in the source region. These observations highlight the likelihood of complex field and particle dynamics in the high-latitude reconnection region and the twisted tail plasma sheet. [ABSTRACT FROM AUTHOR]

Abstract We present the first high resolution global MHD with coupled inner magnetosphere simulation results of an observed theta aurora event. We use the Space Weather Modeling Framework in the Geospace configuration, which produces accurate field aligned current closure in the ionosphere that is integral to theta aurora formation. At the location of the observed theta aurora, the simulation produces a narrow channel of Joule heating along both open and closed field lines, and between a pair of oppositely directed field‐aligned current sheets in the ionosphere. We demonstrate that this Joule heating pattern that we identify as theta aurora maps to a reconnection region at the magnetotail flanks as well as in the distant magnetotail. The theta aurora maps to a cross‐tail current disruption and field‐aligned current source region in a highly twisted magnetotail.

This paper reviews our current understanding of auroral features that appear poleward of the main auroral oval within the polar cap, especially those that are known as Sun-aligned arcs, transpolar arcs, or theta auroras. They tend to appear predominantly during periods of quiet geomagnetic activity or northwards directed interplanetary magnetic field (IMF). We also introduce polar rain aurora which has been considered as a phenomenon on open field lines. We describe the morphology of such auroras, their development and dynamics in response to solar wind-magnetosphere coupling processes, and the models that have been developed to explain them. [ABSTRACT FROM AUTHOR]