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Abstract This study investigates the distribution and formation mechanisms of ionization troughs inside an auroral oval (referred to as high‐latitude troughs) by analyzing Swarm observations from May–August 2014. Simultaneous measurements of plasma density, 3‐dimensional ion velocity, ionospheric radial current (IRC), and electron temperature are available during this period. Because high‐latitude troughs appear within an auroral oval while mid‐latitude troughs appear at the equatorward edge of the auroral oval, the positioning of troughs relative to the equatorward auroral boundary becomes critical for distinguishing between the two types of troughs. We ascertain the auroral boundary and the orientation of field‐aligned currents using IRC data derived from magnetic field measurements. The principal features of high‐latitude troughs identified from Swarm data include: (a) enhancements in ion velocity and electron temperature, (b) the presence of downward or absent field‐aligned current (FAC), and (c) a more frequent occurrence in the Northern (summer) Hemisphere than in the Southern (winter) Hemisphere and in the dawn and dusk sectors than in the noon and midnight sectors. The alignment of the density minimum with the velocity maximum underscores the role of high‐speed plasma convection in the formation of high‐latitude troughs; atmospheric frictional heating promotes the O+loss through dissociative recombination. The prevailing appearance of high‐latitude troughs at dawn and dusk sectors, coupled with downward field‐aligned currents, indicates the involvement of outward electron evacuation in trough formation.
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This content will become publicly available on July 1, 2026
Robust Global Analysis of Mid‐Latitude Ionospheric Trough Morphology
Abstract This study characterizes the main ionospheric trough (MIT) using a newly implemented detection method applied to ground‐based Global Navigation Satellite System data. The MIT is a region of plasma depletion occurring primarily in the nighttime sub‐auroral F‐region ionosphere. Analysis is based on ground‐based ionosphere total electron content (TEC) measurements from 2012 to 2024 and is applied to both hemispheres. The data are sorted by geomagnetic condition and season. We characterize MIT dynamics and compare the results with previous studies. Detection algorithm limitations, hemispheric asymmetry, trough depth, boundary wall steepness and position are statistically quantified and visualized. Main conclusions include: (a) Automatic trough detection is highest during geomagnetically active winter in the northern hemisphere (NH). (b) This detection method creates synoptic views of the trough which we can use to demonstrate control of sub‐auroral polarization streams (SAPS) over the dusk/afternoon sector and influence of storm onset on the MIT. (c) There is a noticeable morning preference for the southern hemisphere (SH) trough. (d) The dawn‐side SH trough appears equatorward relative to the NH, potentially due to influence from polar convection patterns. The dusk‐side NH trough appears slightly equatorward of the SH trough as a response to SAPS. (e) The deepest trough occurs during dawn hours and demonstrates more consistent longitudinal patterns during quiet local winter. (f) The steepest trough boundary is at the poleward wall with a positive gradient at 12–15 local time in NH summer. Synoptic maps illustrate asymmetries in the trough structure and the influence of density plumes.
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- Award ID(s):
- 2120511
- PAR ID:
- 10635870
- Publisher / Repository:
- Willy
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Space Physics
- Volume:
- 130
- Issue:
- 7
- ISSN:
- 2169-9380
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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