A Case Study of the Enhancements in Ionospheric Electron Density and Its Longitudinal Gradient at Chinese Low Latitudes

Abstract

The day-to-day variability of the ionospheric electron density and its longitudinal gradient challenges our description and understanding of the ionosphere, which is also essential for reliable applications of the Global Navigation Satellite System (GNSS). In this paper we conduct a case study of the anomalous enhancements in ionospheric electron density and its longitudinal gradient to reveal the spatial extent and related drivers of the enhancements. The ionospheric data analyzed include the vertical total electron content (TEC) by the Global Navigation Satellite System receivers, peak electron density (NmF2) and height (hmF2) of the F layer by a chain of ionosondes, and electron density profiles recorded by the Qujing incoherent scatter radar (103.8°E, 25.6°N) during the period from 29 May to 2 June 2015. Electron density enhancements are found in the region around the northern crest of equatorial ionization anomaly on the first 2 days of June 2015. It is the first time to report that, during the anomalous enhancement, the increase in electron density over Qujing depends on altitude, being stronger at higher altitudes. Further, there are strong longitudinal gradients in vertical TEC in the regions during the course of the electron density enhancements. Low latitude hmF2 and especially the equatorial electrojet become much larger on the enhancement days, implying the important role of equatorial zonal electric fields in the formation of the electron density enhancements at low latitudes.

The Ionosphere at Middle and Low Latitudes Under Geomagnetic Quiet Time of December 2019

“…Recently Liu et al. (2020) conducted a case study of the anomalous enhancements in electron density at low latitudes in China, showing strong longitudinal and altitudinal gradients during the whole process of the enhancements. They suggested that equatorial zonal electric fields play an important role in forming the electron density enhancements at low latitudes.…”

“…For instance, during geomagnetic storms the energy and energetic particles deposited in the polar upper atmosphere drive great changes in the chemical, electrodynamical, and thermodynamical processes in the whole ionosphere, and induce significant disturbances compared with the quiet time ionosphere (e.g., Buonsanto, 1999; Kuai et al., 2017; Lei et al., 2014; Liu et al., 2004; Mendillo, 2006; Prölss, 1995). Moreover, the ionospheric variations caused by lower atmospheric sources have also been studied in the past decades such as the ionospheric day‐to‐day variations (e.g., Depuev et al., 2008; Forbes et al., 2000; Huang et al., 2017; Liu et al., 2020, 2008; Mikhailov et al., 2009; Rishbeth & Mendillo, 2001; S.‐R. Zhang et al., 2005) or the anomalous changes during drastic meteorological events, such as sudden stratosphere warming (SSW) (e.g., Chau et al., 2012; Goncharenko et al., 2010; Liu et al., 2013, 2014, 2010; Matsuno, 1971; O'Neill, 2003; Pedatella & Liu, 2013; Yue et al., 2010; R. Zhang et al., 2020).…”

“…Even under geomagnetically quiet conditions, the anomalous enhancements in ionospheric electron density or TEC are observed frequently (e.g., David & Sojka, 2010;Mikhailov et al, 2007;Pezzopane et al, 2011;Zhao et al, 2008). Recently Liu et al (2020) conducted a case study of the anomalous enhancements in electron density at low latitudes in China, showing strong longitudinal and altitudinal gradients during the whole process of the enhancements. They suggested that equatorial zonal electric fields play an important role in forming the electron density enhancements at low latitudes.…”

Persistent Eastward EEJ Enhancement During the Geomagnetic Storm Recovery Phases

“…Thus, the similar occurrence climatology of two types of enhancement seems further support that the lower atmospheric forcing may modulate the ionospheric dynamo and cause the electric field eastward enhancement. The PEE seems belong to the “quiet‐time disturbance” (Q‐disturbance; David & Sojka, 2010; F. Huang et al., 2020; Kuai et al., 2021; L. Liu et al., 2020; Mikhailov et al., 2007; Zhao et al., 2008). However, like the prestorm enhancement of the electric field or EIA in the low‐latitude ionosphere (Burešová & Laštovička, 2007; Danilov, 2001; Danilov & Konstantinova, 2019; Kane, 1973; L. Liu et al., 2008; Mikhailov & Perrone, 2009), we still do not completely exclude the effects from the storm‐induced source.…”

“…Thus, the similar occurrence climatology of two types of enhancement seems further support that the lower atmospheric forcing may modulate the ionospheric dynamo and cause the electric field eastward enhancement. The PEE seems belong to the "quiet-time disturbance" (Q-disturbance; David & Sojka, 2010;Kuai et al, 2021;L. Liu et al, 2020;Mikhailov et al, 2007;Zhao et al, 2008).…”