The Evolution of Complex E_s Observed by Multi Instruments Over Low‐Latitude China

Abstract

A complex daytime sporadic E (Es) case with extremely high critical frequency (foEs) was observed over the low latitude of China on 19 May 2018. Simultaneous observational results from two very high frequency (VHF) radars, two ionosondes, and multiple Global Navigation Satellite System total electron content and scintillation receivers are analyzed to investigate the evolution of the complex Es occurrence, which consisted of a relatively weak ambient Es layer (foEs < 8 MHz) and band‐like strong Es structures (foEs > 17 MHz) drifting from higher latitude. The strong Es structures elongated more than 500 km in the northwest‐southeast direction, drifted southwestward at a speed of ~65 m/s. VHF radar backscatter echoes were generated when the strong Es structures passed the radar field of view, with different echo patterns due to different radar and antenna configurations. No VHF radar backscatter echo was associated with the ambient Es layer. The mechanisms responsible for the formations of the ambient Es layer and band‐like strong Es structures are addressed and discussed.

Temporal Evolution of Three‐Dimensional Structures of Metal Ion Layer Around Japan Simulated by a Midlatitude Ionospheric Model

“…Under such conditions, the MILs deform to patchy structures rather than planar ones on horizontal cross sections, Figures 6 and 11d-11f. Recent total electron content (TEC) researches have reported that horizontal shapes of the Es layer, the MIL appearing in the ionospheric E region, are characterized by narrow, elongated structures, which were typically elongated in the east-west direction both in the daytime and nighttime (e.g., Maeda & Heki, 2014Sun et al, 2020). In the TEC studies, TEC was detrended to detect Es layers.…”

Occurrences of Regional Strong Es Irregularities and Corresponding Scintillations Characterized Using a High‐Temporal‐Resolution GNSS Network

“…It was demonstrated that scintillations due to E s can be greatly influenced by the thickness of the layer, the elevation angle of ray paths, and the frequency of radio signals (e.g., Beach & Kintner, 1999;Kintner et al, 2007). Recent studies found that the scintillation level of GNSS signals also depends on the satellite constellation and the receiver type (e.g., Liu et al, 2019;Sun, Ning, et al, 2020). Whereas the correlation between ROTI and S 4 index was occasionally reported (e.g., Luo et al, 2018;Yang & Liu, 2016), a statistical correlation between strong E s irregularities and S 4 index based on ground-based GNSS observations is not performed yet.…”

“…The superimposed gray dots in the bottom panel represent the collocated S 4 index of BD-GEO satellites. This case was investigated bySun, Ning, et al (2020). The unique V-shape echoes were due to the process of strong E s structures/irregularities passing over the field of view of the ionosonde/VHF radar.…”

“…For example, strong E s structures are usually slim band-like, with elongations ranging from tens to thousands of kilometers. They can drift at the speed of ∼60 m/s toward specific directions and cause unique V-shape backscatter echoes when passing the field of view of VHF radars, while the weaker ambient E s layer may not correspond to E-region radar echoes (e.g., Chen et al, 2020;Sun, Ning, et al, 2020). These unique features indicate that the occurrence of strong E s structures is a different phenomenon from the regular E s layer, which are possibly generated under different mechanisms.…”

High‐Resolution 3‐D Imaging of Daytime Sporadic‐E Over Japan by Using GNSS TEC and Ionosondes

“…Of course, the accuracy of STEC and spatial resolution in this analysis is not sufficient to resolve such density inhomogeneity. However, Sun et al (2020) have analyzed the high Doppler spectral width of the radar echoes in E s , which indicated severe perturbation inside the layer. The band-like main structure reach maximum in scale at ∼17:30 LT, which can be extended to ∼400 km in E-W. E s structures start to dissipate after around 17:42 LT, the lifetime of this strong E s with foEs exceeding 20 MHz can reach approximately 30 min.…”