First Simultaneous Observation of a Night Time Medium‐Scale Traveling Ionospheric Disturbance From the Ground and a Magnetospheric Satellite

Abstract

Medium‐scale traveling ionospheric disturbances (MSTIDs) are a phenomenon widely and frequently observed over the ionosphere from high to low latitudes. Night time MSTIDs are caused generally by the polarization electric field in the ionosphere. However, propagation of this polarization electric field to the magnetosphere has not yet been identified. Here, we report the first observation of the polarization electric field and associated density variations of a night time MSTID in the magnetosphere. The MSTID event was observed by an all‐sky airglow imager at Gakona (geographical latitude: 62.39°N, geographical longitude: 214.78°E, magnetic latitude: 63.20°N), Alaska. The Arase satellite passed over the MSTID in the inner magnetosphere at 0530–0800 UT (2030–2300 LT) on November 3, 2018. This MSTID, observed in 630 nm airglow images, was propagating westward with a horizontal wavelength of ∼165 km, a north–south phase front, and a phase velocity of ∼80 m/s. The Arase satellite footprint on the ionosphere crossed the MSTID in the direction nearly perpendicular to the MSTID phase fronts. The electric field and electron density observed by the Arase satellite showed periodic variation associated with the MSTID structure with amplitudes of ∼2 mV/m and ∼150 cm−3, respectively. The electric field variations projected to the ionosphere are mainly in the east‐west direction and are consistent with the direction of the polarization electric field expected from MSTID growth by E × B drift. This observation indicates that the polarization electric field associated with the MSTID in the ionosphere is projected onto the magnetosphere, causing plasma density fluctuations in the magnetosphere.

Multi‐Event Analysis of Magnetosphere‐Ionosphere Coupling of Nighttime Medium‐Scale Traveling Ionospheric Disturbances From the Ground and the Arase Satellite

“…These good correspondences between electric field and airglow deviations are very similar to the observation reported by Kawai et al. (2021).…”

“…The amplitude of mapped electric field variations is ∼10 mV/m. These good correspondences between electric field and airglow deviations are very similar to the observation reported by Kawai et al (2021). In this event, the MSTIDs had a wavefront elongated from northwest-southeast (NW-SE) and propagated westward.…”

“…As shown by Figure 11 of Kawai et al. (2021), the polarization electric field can also cause electron density variations in the magnetosphere due to E × B drift of magnetospheric plasma which usually has an inward radial gradient (e.g., Carpenter & Anderson, 1992). Thus, we also expect correlation between the electron density variations observed by Arase and the airglow intensity variations at the footprint locations.…”

Statistical Study on Small‐Scale (≤1,000 km) Density Irregularities in the Inner Magnetosphere

“…These ionospheric disturbances can be mapped along the field lines to the conjugate regions (Huba et al, 2015;Valladares & Sheehan, 2016), causing FAIs inside the plasmasphere (Helmboldt, 2020;Helmboldt et al, 2020). The direct relationship between MSTIDs and plasmaspheric density fluctuations was confirmed by simultaneous observation of the two (Kawai et al, 2021).…”

Tandem Observations of Nighttime Mid‐Latitude Topside Ionospheric Perturbations

“…Because no previous studies have performed such coherence analysis with MSTIDs, this paper provides the first quantitative measure of distance‐dependent coherence of MSTID substructures. The decrease of coherence (Rmax) with increasing inter‐satellite distance (|ΔGLON|) gives firm observational evidence that an MSTID is not such an infinite plane wave (i.e., perfect homogeneity along the wavefront direction) as is commonly assumed in simplified descriptions (e.g., Tsunoda, 2006, Figure 3; Ogawa et al., 2009, Figure 13; Kawai et al., 2021, Figures 10c–10d), but can have inhomogeneous or finite wavefronts. This inhomogeneity or finiteness of MSTID wavefronts was demonstrated earlier in realistic simulation results (e.g., Yokoyama & Hysell, 2010, Figures 3 and 4) or individual 2D images (e.g., Kelley & Makela, 2001, Plate 1), but our Figure 3 gives its statistical proof for the first time.…”