On the Spatial Structure and Zonal Drift of Low Latitude E Region Irregularity Patches Over Hainan

Abstract

All‐sky radar measurements provide a unique capability to resolve the spatial structure of E region irregularities over a large zonal region. With the all‐sky radar interferometry observations at Ledong (18.4°N, 109.0°E) in Hainan, China, the spatial structure and zonal drift of low latitude E region field‐aligned irregularities (FAIs) over a large region are statistically investigated for the first time. It is revealed that the E region FAIs, including both the continuous and quasi‐periodic (QP) types shown in radar range‐time‐intensity maps, occurred most frequently in summer. The continuous type was observed being generated locally without obvious zonal drift. The QP type generally covered ∼40–500 km zonally, and consisted of up to 9 (peaking at 3–4) FAI patches separated by ∼20–130 km (peaking at ∼60 km). The spatially separated FAI patches predominantly drifted westward at the speed ∼50–200 m/s. Besides the Kelvin‐Helmholtz instability, gravity waves were surmised to be a major source for causing the spatial structures of low latitude QP type E region FAIs. Neutral wind was suggested to play an important role for their zonal drifts.

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

“…In previous studies, the spatially separated structures of QP‐type E‐region irregularities were presumed to be modulated by gravity waves (e.g., Sun et al., 2023; Yokoyama et al., 2004). However, any QP structures could not necessarily represent the existence of a modulating wave.…”

“…Based on numerical simulations, it was suggested that the E s layer accumulated by wind shears could be deeply modulated by the propagating gravity waves, and the polarization electric field due to the distorted E s layer could produce wavelike patterns of plasma density (e.g., Huang & Kelley, 1996; Ogawa et al., 2002; Yokoyama et al., 2003). However, such mechanisms were usually proposed to account for generating the spatially separated structures of QP‐type E‐region irregularities (e.g., Sun et al., 2023). It is not clear whether it could be employed to explain the wavelike E‐region irregularity structures elongating up to 250 km in the present case or not.…”

“…The most interesting feature of the present case that differs from previous observations of E‐region irregularity is the well‐resolved wavelike structure, which elongated up to 250 km zonally. Traditionally, the E‐region irregularities observed by VHF radars mainly fall into two categories, the continuous type due to large irregularity structure over the radar site, and the QP type due to spatially separated irregularity patches drifting through the radar FOV (e.g., Patra et al., 2004; Sun et al., 2023; Yamamoto et al., 1991). The present case differs from the two major types in both the echo pattern and the spatial features.…”

“…Based on the phase differences between the signals received by channels R1–R4 and channel R0, the interferometry technique was employed along the two baselines in the east‐west and north‐south directions, respectively. Then the azimuth and elevation angles, latitudes, longitudes, and altitudes of the backscatters could be derived by assuming the straight‐line propagation of radio signals (Sun et al., 2023; Wang et al., 2019).…”

“…Recently, facilitating from the large field‐of‐view (FOV) of all‐sky radars, which nearly covers all the sky, the spatial features of low‐ and middle‐latitude E‐region irregularities were derived over a large zonal region (Wang et al., 2019; Xie et al., 2019). It was revealed that the continuous‐type E‐region irregularities were linked with the tidal sporadic E (E s ) layer over the radar site, whereas the QP type was due to the drift of irregularity patches separated by tens of kilometers (e.g., Patra et al., 2007; Sun et al., 2023; Yamamoto et al., 1994). Previous studies suggested that the spatial features of the QP‐type E‐region irregularities could be attributed to E s modulated by gravity waves (e.g., Huang & Kelley, 1996; Woodman et al., 1991).…”