On the Nature of F‐Region Bottom‐Type Echoing Layer Over Gadanki

Abstract

Bottom‐type echoing layers observed from Gadanki are presented and analyzed. The analysis is based on observations made using a substantial database of the 30 MHz Gadanki Ionospheric Radar Interferometer (GIRI) during 2017–2019, collocated digisonde observations, and a few days of overlapping volume observations made using the GIRI and the 53 MHz Advanced Indian MST Radar (AIR) . The echoes commence well before the E‐ and F‐region sunsets and last as late as 23:00 Local Time. The echoing layers occur in the height range of 220–300 km with a thickness of 10–15 km and the Doppler spectra are narrow with spectral width confined to 10 m s−1. The echoing layers are very common during the entire observational period and do not show any noticeable seasonal dependence. The zonal velocities of the irregularities responsible for the radar echoes are close to zero irrespective of the height of the echoing region. The echoes are stronger at 30 MHz than at 53 MHz indicating strong Bragg scale dependence. The height of the echoing layer agrees very well with the height of the F‐region peak electron density (hmF2). Also, early commencement of the echoing layer is found to be associated with low hmF2 and corresponding high electron density (foF2). While the results indicate toward the wind‐driven interchange instability as their origin, the early onset of the echoing layer and its relationship with the background ionospheric parameters call for explanation. The results are discussed in the light of current understanding on the bottom‐type echoing layer.

Multi‐Source Perturbations in the Evolution of a Low‐Latitudinal Equatorial Plasma Bubble Event Occurred Over China

“…Moreover, the statistical study by Hu et al. (2020) found no relationship between occurrences of BLSs and plasma plumes over Sanya (here note that the Sanya is very near the Fuke; besides, the same result was also obtained by Pavan Chaitanya and Patra (2021) over Gadanki). This is why Li et al.…”

“…(2020) found that almost all the BLSs observed in Sanya appeared generally at the altitude range of 195–235 km during the descending phase of solar cycle (2015–2018 years). A similar statistical study conducted by Pavan Chaitanya and Patra (2021) found that BLSs over Gadanki, India during 2017–2019 years commenced well before sunset and lasted late as 23:30 LT in the height range of 220–300 km with a thickness of 10–15 km; the most interesting finding in their study is that the height of the observed BLSs over Gadanki agreed very well with the height of the F ‐region peak electron density, and only those early commencement of BLSs before sunset were found to be associated with low h′f (<250 km).…”

Occurrence of Postmidnight Bottom‐Type Scattering Layer Over Low Latitude

“…The BSL was first observed by Jicamarca radar operated at magnetic equator (Woodman & La Hoz, 1976). Then based on observations from other instruments, the BSL was found in low latitude and other longitudes (Hu et al., 2020; Hysell et al., 2005, 2006; Li et al., 2017; Lyu et al., 2021; Patra et al., 2014; Pavan Chaitanya & Patra, 2021; Rodrigues et al., 2004; Takahashi et al., 2010). With the increase of research, its characteristics and corresponding mechanisms have gradually been revealed.…”

Daytime F Region Echoes at Equatorial Ionization Anomaly Crest During Geomagnetic Quiet Period: Observations From Multi‐Instruments

“…During the past several decades, compared to the high occurrence rate of F region echoes at night, some cases of daytime F region echoes were reported since the background conditions in the daytime F region with a larger field‐line‐integrated Pedersen conductivity and a smaller plasma density gradient at the bottom of F region are not conducive to the development of R‐T instability or Perkins instability (Chaitanya & Patra, 2021; Hu et al., 2020; Kelly, 2009; Xie et al., 2020). Woodman et al.…”