Daytime Ionospheric Large‐Scale Plasma Density Depletion Structures Detected at Low Latitudes Under Relatively Quiet Geomagnetic Conditions

Abstract

According to the Chapman theory (Rishbeth & Garriott, 1969), the plasma density of the ionosphere is expected to continuously increase after sunrise under the control of continuously enhancing photoionization production until local noon. However, various sources from the solar, geomagnetic, or meteorological activities can significantly influence the plasma density via modulating the production, recombination, and transportation processes. The complex interplay among multiple drivers can result in either enhancements or depressions of ionization to varying degrees over different regions. Thus, instead of a continuously enhancing ionization, the plasma density of the daytime ionosphere may also undergo remarkable depletions, especially under geomagnetic disturbed conditions.During severe geomagnetic storms, significant plasma density depletions were frequently detected and termed as negative storm effects (Prölss, 2008, and the references therein). The duration of the storm-time plasma density depletion can vary from several hours to a few days and can be observed over wide longitude and latitude regions

Latitude Variation of the Post‐Sunset Plasma Density Enhancement During the Minor Geomagnetic Storm on 27 May 2021

“…Sun et al. (2022) reported an anomalous large‐scale ionospheric TEC depletion structure preceded by an increase of NmF2 and a reduced hmF2 propagating northward occurring in morning hours over low latitudes in China under relatively quiet geomagnetic conditions on 10 July 2018. The depletion observations from multiple ionosondes revealed a net downward plasma movement during the TEC depletion.…”

Ionospheric Super Bubbles Near Sunset and Sunrise During the 26–28 February 2023 Geomagnetic Storm

“…This corresponded well with previous studies that the increase in F layer height at middle latitudes due to equatorward neutral wind originated from auroral energy input usually lag ∼1–2 hr behind the rise of AE index (e.g., Prölss, 1993). In addition, the upward plasma drifts driven by equatorward neutral wind should be more significant and start earlier at middle and low latitudes than over the magnetic equator where the magnetic field line is nearly horizontal (e.g., Sun, Li, et al., 2022). This was consistent with the larger and earlier vertical plasma drift toward higher latitudes in the present study (Figure 8c–8e).…”

Anomalous Disturbance of the Ionosphere in the East Asia Region During the Geomagnetically Quiet Day on 1 November 2016

“…(2005) analyzed the ionospheric disturbance in the equatorial region and qualitatively discussed its possible mechanism. Subsequently, some scholars have studied the Q disturbances through O/N2, equatorial eastward electric field, NmF2, and peak electron density of the E region, respectively (e.g., Goncharenko et al., 2006; C. M. Huang, 2013; Mikhailov et al., 2007; Sun et al., 2022). Regarding the ionosphere/thermosphere disturbances during weak or minor geomagnetic disturbances, a recent study by Cai et al.…”