A Case Study of the Daytime Intense Radar Backscatter and Strong Ionospheric Scintillation Related to the Low‐Latitude E‐Region Irregularities

Abstract

The special daytime echoes, which present the V‐shaped echo pattern between 90–180 km ranges in the range‐time‐intensity (RTI) plot, were occasionally recorded by the Hainan coherent scatter phased array radar (HCOPAR) located at the low latitude of China. Four cases with distinct echo traces are presented to display the common characteristics of the V‐shaped echoes. They usually occur between 10:00–15:00 LT in the daytime with the enhanced top frequency and blanketing frequency of Es layer (ftEs and fbEs). Their left/right wings present negative/positive Doppler velocity. A case on 16 August 2015 was investigated by the joint observation of the HCOPAR, the Hainan Digisonde, and a scintillation receiver. The echo spectra show that the V‐shaped echoes were backscattered from the type 2 irregularities. The formation of the V‐shaped echo pattern was due to the leakage of the antenna sidelobe for the very intense scatter from Es layer. The irregularities were found traveling westward with the velocity of 41.12 ± 2.08 m/s. While the occurrence of the intense irregularities, there were periodic peaks appearing on the ftEs and fbEs curves, and the maximum ftEs‐fbEs reached 10.31 MHz. At the same time, the strong ionospheric scintillation event was recorded by the scintillation receiver. The wind shear is considered to produce the sharp density gradient in the Es plasma and then induce the gradient drift instability. The large‐scale gravity waves have the possibility to induce the E‐region wind shear.

Statistical Characteristics of the Low‐Latitude E‐Region Irregularities Observed by the HCOPAR in South China

“…Therefore, the steep plasma density gradient, but not the high background plasma density, is favorable for the gradient drift instability to generate Type‐Ⅱ irregularities. The SNR of the scattered echoes are also suggested to reflect the density gradient of the irregularities (Chen et al., 2020). As shown in Figure 3, the nighttime irregularities have higher mean SNR than the daytime irregularities, and the summer irregularities have higher mean SNR than those in other seasons.…”

“…Before long, the wind shear driven Kelvin‐Helmholtz (K‐H) instability became very popular as soon as it was put forward (Choudhary et al., 2005; Larsen, 2000). However, there are still many E‐region abnormal structures hard to explain, such as the solar eclipse associated FAIs, the intense daytime scattered echoes, and so on (Chen et al., 2014, 2020; Patra et al., 2012; Thampi et al., 2010). Moreover, the irregularities have presented a significant regional characteristics (Chau et al., 2002; Patra et al., 2004).…”

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

“…Traditionally, E s layers were detected with ionosondes and characterized with observational parameters such as the critical frequency ( f o E s ), the blanketing frequency and the virtual height (e.g., Zhou et al., 2017). Over mid‐to‐low latitude regions, the meter‐scale irregularities associated with E s were usually investigated based on observations from traditional very high frequency (VHF) coherent radars (e.g., Chen et al., 2020; Hysell et al., 2009; Ning et al., 2012; Ogawa et al., 2002; Yamamoto et al., 1991) and all‐sky meteor radars (Xie et al., 2019; Wang et al., 2019). However, both ionosondes and VHF radars suffer from a scarcity of site distribution that cannot form a dense network for routinely monitoring of E s with a high spatial resolution.…”

“…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.…”

Synthesis of Planar Circular Arrays with Quantized Amplitude Weights

“…Unlike the turbulence echo in the neutral atmosphere, the FAIs are also very sensitive to the weak radio frequency signals. In some ionospheric strong scattering events, part of the radar echo may be received by the sidelobes [ 25 ]. In this case, the range-time-intensity plot displays the combination of the mainlobe and the sidelobe echoes, which leads to the misjudgment of the actual height and angle of arrival of the FAI echoes.…”