Persistent Occurrence of Strip‐Like Plasma Density Bulges at Conjugate Lower‐Mid Latitudes During the September 8–9, 2017 Geomagnetic Storm

Abstract

Large-scale ionospheric density enhancements are frequently observed during geomagnetic storms. The enhancements could be the positive ionospheric storm at low-and mid-latitudes (e.g., Appleton & Ingram, 1935;Rajaram, 1977), or the storm enhanced density (SED) at mid-and high-latitudes. The SED terminology was first introduced by J. C. Foster (1993), to describe a stream-like structure of the enhanced plasma density spanning from its dusk-sector source at the subauroral region to the noontime cusp during the initial stage of the geomagnetic storm, that is, sunward and upward convecting cold plasma (Foster

Disturbance Neutral Winds Effects on the Ionospheric Strip‐Like Bulge at Lower‐Middle Latitudes

“…The enhancements showed a width of about 5° in latitudes and were distributed at conjugate quasi‐dipole (QD) latitudes of 30°∼45°N/S, which are consistent with the strip‐like bulges reported in Wan et al. (2021). In the northern hemisphere, those bulges resided well within the ridge‐like TEC enhancements (Figures 2a and 2g).…”

“…In this study, supporting evidence of the ion composition of the middle-latitude band structure can be given by ICON IVM measurements, which will be presented in Figure 7 in Subsection 5.3. Besides, DMSP satellites also reveal that the strip-like bulge is predominantly formed by the light ions of H + /He + rather than O + in Wan et al (2021). Note that as the ion density of the bulge was greater in the topside ionosphere and showed enhanced H + , for the density profile at the same location, there might be greater ion density around the F2 peak with elevated O + , which currently cannot be confirmed.…”

“…The numerical simulations suggest that the enhanced eastward electric field alone is not adequate to produce the observed EIA features, and the effects of the enhanced equatorward neutral wind (e.g., Emmert et al., 2001; Fejer et al., 2000; Wang et al., 2017; Xiong et al., 2015) must be involved (Balan et al., 2010; Lin et al., 2005), as the latter term would reduce (or stop) the downward diffusion of plasma along the geomagnetic field lines, lift the ionosphere to a high altitude, and hence accumulate the plasma due to the low chemical loss. Similarly, equatorward disturbance neutral winds could also be a plausible driver for the appearance of the bulges by stopping the downward diffusion of plasma at lower‐middle latitudes and shaping the sharp poleward boundary of the bulges (Wan et al., 2021). Nevertheless, this mechanism needs more observations, such as direct measurements of neutral winds.…”

“…Recently, by utilizing six high inclinations low earth orbit (LEO) satellites that flew at multiple local time sectors during the 8–9 September 2017 geomagnetic storm, Wan et al. (2021) had advanced the current understanding of the shoulders in various aspects: (a) The shoulder is indeed a local time independent phenomenon, though it is seen more evident in the nightside. (b) Its zonal extension exceeds 150° in longitudes, while its meridional scale is only a few degrees in latitude.…”

“…The shoulders appear as narrow plasma density bulges with clear poleward boundary and reside at conjugate lower-middle latitudes as seen in the meridional profiles of total electron content (TEC) (Mannucci et al, 2005;Tsurutani et al, 2004) or the in-situ plasma density (Heelis & Coley, 2007). Together with the aid of regional TEC maps, the shoulders had then been witnessed from time to time (Foster & Erickson, 2013;Horvath & Lovell, 2008), but only a few dedicated works had been carried out (Chartier et al, 2021;Datta-Barua et al, 2008;Maruyama et al, 2013;Wan et al, 2021). and Foster and Coster (2007) first reported the shoulders in a form of localized enhancement in regional TEC maps in the American sector.…”