On using a double-thin-shell approach and TEC perturbation component to sound night-time mid-latitude E–F coupling

Abstract

Observations and theoretical analysis on the night-time mid-latitude ionospheric irregularities support the postulation of frequently coupled E and F regions. In this paper, we attempt at asserting this notion while using total electron content (TEC) measurements. The TECs are from a dense GNSS receiver network over Japan with more than 1200 stations and a mean distance of ~ 25 km between receivers; thus, ideal for analyzing small-scale perturbations in ionospheric electron density. We take an ansatz that mid-latitude night-time plasma instabilities concentrate at E and F layers. Then the integrated three-dimensional density perturbations are parameterized with a double-thin-shell model. At each shell, perturbation components are assumed identical at any point within a given grid block. Two days with events of night-time medium-scale traveling ionospheric disturbances (MSTIDs), but with different amplitudes, were investigated. Results show that the newly developed technique can infer several horizontal characteristics on E–F coupled instabilities; the coexistence of northwest–southeast (NW–SE) aligned irregular structures in E and F regions is evident. Both E- and F-region irregularities share similar propagation parameters, a shred of clear evidence of strong coupling. Graphical Abstract

Tandem Observations of Nighttime Mid‐Latitude Topside Ionospheric Perturbations

“…The left column belongs to the June solstice while the right column represents the December solstice. He et al, 2004;Oinats et al, 2016;Otsuka et al, 2021) while they are well-aligned with MLAT (Fu et al, 2022;Yokoyama et al, 2009). In summary, the dependence of 𝐴𝐴 𝐴𝐴mag (or perturbation directivity) on the hemisphere, |MLAT|, and MLT strongly supports that the perturbations observed by Swarm at nighttime mid-latitude topside ionosphere can be identified as topside signatures of MSTIDs, at least for strong and coherent events (i.e., Rmax > 0.5 and the standard deviation of ΔNe > 8,000 cm −3 ).…”

“…The complex dependence of wavefront directions on MLT conforms to previous ground‐based studies on MSTIDs. The MSTID wavefront directions in existing literature were not well organized by MLT (Chen et al., 2019; Cheng et al., 2021; He et al., 2004; Oinats et al., 2016; Otsuka et al., 2021) while they are well‐aligned with MLAT (Fu et al., 2022; Yokoyama et al., 2009). In summary, the dependence of $${\theta }_{\mathrm{m}\mathrm{a}\mathrm{g}}$$ (or perturbation directivity) on the hemisphere, |MLAT|, and MLT strongly supports that the perturbations observed by Swarm at nighttime mid‐latitude topside ionosphere can be identified as topside signatures of MSTIDs, at least for strong and coherent events (i.e., Rmax > 0.5 and the standard deviation of ΔNe > 8,000 cm −3 ).…”

“…(2009, and references therein) and Fu et al. (2022, Page 9). To summarize, the hemisphere‐dependent wavefront directions (i.e., the backward‐C shape) and their dependence on |MLAT| all support that the disturbances observed by Swarm in the nighttime mid‐latitude ionosphere can be practically identified as MSTIDs.…”

Nighttime Midlatitude E‐F Coupling in Geomagnetic Conjugate Ionospheres: A Double Thin Shell Model and a Multi‐Source Data Investigation

“…STEC with elevation angles smaller than 35° were negated to mitigate the multipath effects. Following the work of Fu et al (2022), we ingested the TEC perturbation (TECP) component, since typical TECPs caused by Es and MSTIDs are small and the accuracy of absolute GNSS TEC estimation is a few TEC units (TECU; 1 TECU = 10 16 el/m 2 ). Similarly, in this paper, TECPs were obtained after deducting a 30-min data running average (centered on the epoch of the LOS) from each LOS TEC, and data corresponding to arc segments less than 30 min were excluded to avoid spurious perturbations.…”

“…Ignoring the sparse distribution of GNSS data over the Australian region, the amplitude of TECPs caused by the MSTIDs in the winter hemisphere (geomagnetic conjugate region) is small. Following Fu et al (2022), the double-thin-shell approach and ground-based GNSS TEC of GEONET were used to analyze the E-F coupling process in the region with most data points over Japan (30°N-42°N, 130°E−140°E for the E shell and 28°N-45°N, 128°E−145°E for the F shell). From the results in Figures 2a-2d, this region also coincides with the fast-growing region of the MSTID structures.…”