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.