Statistical Characteristics and Correlation of Low‐Latitude F Region Bottom‐Type Irregularity Layers and Plasma Plumes Over Sanya

Abstract

Ionospheric F region bottom‐type irregularity layer has been frequently detected at equatorial latitude and regarded as a possible precursor of equatorial backscatter plumes producing scintillations. In this study, the VHF radar observations of ionospheric F region bottom‐type irregularity layers and plasma plumes over the low‐latitude station Sanya (18.4°N, 109.6°E, dip lat. 12.8°N) during the equinoctial months (March, April, September, and October) of 2011–2018 are analyzed. The results show an equinoctial asymmetry in the occurrence of F region backscatter plumes, wherein the occurrence could be greater in spring or autumn months under different solar activities and background ionospheric conditions (F layer height and density). On the other hand, the bottom‐type irregularity layer occurred almost exclusively in the descending phase of solar cycle (2015–2018). No clear correlation is found between the occurrences of bottom‐type irregularity layer and plasma plume at low latitude. The F layer virtual height (h′F) observations from the Sanya ionosonde show that the average h′F is higher during the months when the plume occurrence is higher, suggesting that the asymmetric plasma vertical drift could play a role in the equinoctial asymmetry of plume occurrence. Larger vertical drift (and higher h′F) could cause higher occurrence of equatorial plasma plumes which extend to low latitudes along magnetic field lines. In contrast, during the days when bottom‐type irregularity layers occur, the h′F is relatively lower. We surmise that only when the background F region is situated at low altitudes (with h′F < ~250 km), the low‐latitude bottom‐type irregularity layer could be generated.

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.…”

“…However, actual observations (e.g., Kudeki & Bhattacharyya, 1999;Hysell & Burcham, 2002) indicate that the evening plasma vortex usually occurs on the bottomside of the ionosphere (∼250 km) above the geomagnetic equator. 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 (2017) suggested that the observed BLSs over Fuke/Sanya should be caused by the other physical process rather than the CSI mechanism occurred above the geomagnetic equator.…”

Characterization of ionospheric irregularities over Vietnam and adjacent region for the 2008-2018 period

“…The pattern of the thermospheric wind in the ascending phase needs further investigations. Recently, Hu et al (2020) measured the statistical characteristics of the appearance of plasma plumes based on VHF radar observations at Sanya during the equinoxes for the period 2011-2016. They found the opposite patterns in the equinoctial asymmetry of the plasma plumes in 2011 (in the solar ascending phase) and in 2015 (descending phase), which corresponded well with those in the sunset increases of h'F in 2011 and 2015.…”

A Statistical Study of F‐Region 3.2‐m‐Scale Field‐Aligned Irregularities Occurrence and Vertical Plasma Drift Over Hainan: Solar Activity, Season, and Magnetic Activity Dependences

“…Hu et al. (2020) studied the statistical characteristics and correlation of equinoctial bottom‐type and plume irregularities over Sanya during equinox of 2011–2018 and found that bottom‐type and plume irregularities showed opposite correlation with F‐layer virtual height. Statistical studies of the EPBs occurrence during the moderate solar activity years 2011–2012 at nearby longitude have been conducted by Ajith et al.…”

“…VHF radars have been used for detecting backscatter echoes caused by the Bragg scatter from FAIs with a scale size of half of the radar wavelength. For instance, Xie et al (2018) investigated the occurrences of ionospheric E-region, valley and F-region FAIs in the postsunset period by using the observations from the low-latitude fivebeam Sanya, Hainan Island of China (18.4°N, 109.6°E) VHF radar and Sanya Digisonde during equinoctial months of 2012. Hu et al (2020 studied the statistical characteristics and correlation of equinoctial bottom-type and plume irregularities over Sanya during equinox of 2011-2018 and found that bottom-type and plume irregularities showed opposite correlation with F-layer virtual height.…”