Morphological Characteristics of Thousand‐Kilometer‐Scale E_s Structures Over China

Abstract

Sporadic E (Es) structures have been observed occasionally covering a large horizontal scale of more than 1,000 km over China. Their onset locations and propagation features, and related generation mechanisms still remain unknown. In this study, a statistical analysis of large‐scale Es structures is performed based on the ionospheric total electron content obtained from ground‐based receiver networks, in combination with data from multiple ionosondes in China. The large‐scale strong Es structures mainly occur during summer months, with dominant horizontal azimuth in the east‐west and northwest‐southeast directions and dimensions of 1,000–3,000 km along the elongation. They predominantly drift southwestward at the speed of 30–210 m/s. The main onset region for the large‐scale Es structures over China is identified for the first time, which is around 20°–45°N and 100°–125°E. Based on the morphological features of large‐scale Es structures, and the observation of concurrent cases of traveling ionospheric disturbances, we surmise that gravity waves could play an important role in the generation of large‐scale Es structures.

Study of structures of the sporadic E layer by using dense GNSS network observations

“…With the frontal structures identified by the HT This velocity is consistent with the Es layer velocity reported using the TEC perturbation (Maeda & Heki, 2015). Recently, Sun et al (2021) showed with the TEC perturbation method that the Es layer over China moved predominantly southward. To understand such differences within the northeast Asian region, more observations and comparison with numerical models such as GAIA (Andoh et al, 2020;Shinagawa et al, 2017Shinagawa et al, , 2021 are necessary.…”

Comparison of Seasonal foEs and fbEs Occurrence Rates Derived from Global Digisonde Measurements

“…Kelvin-Helmholtz instabilities [44] can modulate E s layers to form billowy, small-scale structures [26,27,45] that affect both the spatial profiles and ionosonde measurements of the layers. This supports previous global [5,37,38] and regional [28] occurrence rate studies with large variations over relatively short distances.…”

“…In addition to ionosondes, sporadic-E can be measured from other instruments, such as incoherent scatter radars (ISRs) [25], ground-based global navigation satellite system (GNSS) measurements [26][27][28], and GPS radio occultation (RO) [29,30]. ISR measurements provide the most detailed observations of E s characteristics and structure [13,31,32], but the limited number of sites across the globe and measurement cadence are lacking for global climatological studies.…”

“…ISR measurements provide the most detailed observations of E s characteristics and structure [13,31,32], but the limited number of sites across the globe and measurement cadence are lacking for global climatological studies. Ground-based GNSS measurements allow for unprecedented largescale studies of E s morphology for strong layers (foEs > 14 MHz) over areas with GNSS networks, such as Japan [26] and China [27,28]. These ground-based measurements provide detailed information on the elongation, orientation, scale-size, and horizontal motion of the layers in addition to regional occurrence rates for exceptionally strong E s layers.…”

Altitudinal and Latitudinal Variations in Ionospheric Sporadic‐E Layer Obtained From FORMOSAT‐3/COSMIC Radio Occultation

“…(2021) compared the Es layer traces (with lifetimes larger than 6 h) with the wind shear region and found that the Es traces and the wind shear nodes are not completely overlapped in the vertical direction. Also, the height of the Es layer (foEs > 14 MHz) traces recorded by the ionosondes is ∼5 km higher than the meridional wind shear nodes obtained from the HWM93 and meteor radars (Sun et al., 2021). Back to this study, the discrepancies between the EsOR/EsI and CWS (Figure 9) also imply that the wind shear cannot explain the vertical evolution of the Es layer fully.…”