Wavelike Structures of E‐Region Irregularities Observed by All‐Sky Radar at Low Latitude

Abstract

We report for the first time a case of wavelike structures of E‐region irregularities observed by an all‐sky radar at Ledong (18.44°N, 108.97°E), China. The wavelike structures covered up to 250 km zonally, fluctuated in the vertical and horizontal planes, and were observed in the directions perpendicular and significantly off‐perpendicular to the geomagnetic field. The wavelength, and vertical and horizontal oscillating amplitudes were estimated at about 20–70, 5, and 2 km, respectively. Eventually, the large‐scale wavelike structure broke into spatially separated small‐scale patches and disappeared. The case provides observational evidence for the wave modulating sporadic E (Es) mechanism, which suggests that the wavelike structures of E‐region irregularity were primarily generated by wind shears and modulated by gravity waves. The wavelike structure was possibly an intermediate state between the continuous‐type and quasiperiodic‐type E‐region irregularities. The mechanism responsible for the echoing structure observed in off‐perpendicular directions is unclear. The possible contributions from refraction and reflection by intense Es layer/structure were discussed.

Wind Shear Driven Double Layer Structures of E‐Region Irregularities at Low Latitudes

“…The results indicate that the generation of the structures at the two layers could be under the same driving force, that is, GWs. Besides, according to previous studies, the slant Es trace in ionograms (e.g., 12:00 UT in Figure 2a) and the wavelike manifestation of the irregularity structure (e.g., 12:11 UT in Figure 1i) may indicate the possible presence of GWs (e.g., Resende et al, 2023;Sun, Li, Han, et al, 2023). Therefore, comparing with K-H instability, GWs were more likely to provide simultaneous modulation on the two separated FAI layers in the present study.…”