On the Seeding of Periodic Equatorial Plasma Bubbles by Gravity Waves Associated With Tropical Cyclone: A Case Study

Abstract

Understanding the day-today variability of equatorial plasma bubble (EPB) irregularities has been a major challenge for many decades that makes the deterministic prediction of EPBs remain elusive. In the present study, we report a case of intense and periodic EPBs observed during 8 and 9 April 2013 by the 47-MHz Equatorial Atmosphere Radar at Kototabang, Indonesia. The periodic EPBs separated by about 200-250 km were initiated before sunset. The presunset onset and development of these periodic EPBs were discussed in light of the gravity waves (GWs) excited in connection with the deep convection due to the tropical cyclone (TC) Victoria. The outgoing long-wave radiation measurement by very high-resolution radiometer (VHRR) onboard Indian meteorological satellite Kalpana-1 shows the occurrence of deep convective activity during these days. The presence of upward propagating GWs from the deep convective region associated with TC Victoria was confirmed using the GPS radio occultation (GPS-RO) observations in the troposphere and stratosphere. The GW signatures at ionospheric altitudes were also observed from the Ionosonde observations over magnetic equator, and medium-scale (~300 km) GWs were observed from the GPS-TEC (Total Electron Content) data near to the magnetic equator and cyclone center. From the GW parameters observed from GPS-TEC and GPS-RO, we surmise that the secondary GWs generated by the dissipation of primary GWs associated with TC Victoria could have served as a seeding source on the generation of periodic EPBs during these two consecutive days.

The Study of Daytime Ionospheric E‐Region Radar Echoes Simultaneously Observed by Qujing VHF Radar and Multi‐Ionosondes

“…Tsunoda (2010) and Ajith et al. (2020) found that upward propagating gravity waves associated with the deep convective region from the troposphere and stratosphere affected the ionospheric plasma structures. To examine the presence of upward propagating gravity wave in the ionospheric during the observation period, Figure 9 shows the time series of band pass filtered virtual height deviations of spread F (dhF) observed by Qujing ionosonde during 14:00–19:00 LT on 20 June 2020.…”

“…To examine the presence of upward propagating gravity wave in the ionospheric during the observation period, Figure 9 shows the time series of band pass filtered virtual height deviations of spread F (dhF) observed by Qujing ionosonde during 14:00–19:00 LT on 20 June 2020. The significant periodic oscillation occurred in the dhF time series with the phase propagating downward, indicating the existence of upward propagating gravity wave in the ionosphere (Ajith et al., 2020; Takahashi et al., 2018). The mean period of dhF disturbance was about 30 min by using the wavelet analysis.…”

“…Horinouchi et al (2002) and Vadas (2007) proposed that gravity waves generated in the troposphere could propagate to the lower thermosphere. Generally, the convective activity in the tropospheric region is one of the major sources for the generation of gravity waves (Ajith et al, 2020;Fritts & Alexander, 2003;Fritts & Nastrom, 1992). Xu et al (2015) deep convective region from the troposphere and stratosphere affected the ionospheric plasma structures.…”

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

“…In effort to examine the existence of gravity wave from this deep convective region, atmospheric temperature distribution from FY‐4A satellite measurements in the altitude range of 10–60 km was shown in Figure 5. The atmospheric temperature perturbations were generally on the order of ±6 K. Gravity wave signatures can be extracted from atmospheric temperature perturbations (Ajith et al., 2020; Kaifler et al., 2015). Considering that the vertical wavelength of gravity waves is generally below 20 km, the atmospheric temperature perturbation profiles were filtered by using a low pass filter with a cut‐off at 20 km for eliminating the effect of planetary wave or tides (the vertical wavelength is larger than 30 km) (Kaifler et al., 2015).…”

Stepping Into an Equatorial Plasma Bubble With a Swarm Overfly

“…Growth and decay processes of EPBs lead to the formation of ionospheric irregularities covering the full range of spatial spectrum, from thousands of km down to tens of meters (Balan et al., 2018; Li et al., 2021). The suggested mechanism triggering ionospheric irregularities formation is the Rayleigh‐Taylor (R‐T) instability, which amplifies the bottomside gradient at F‐layer, whose principal driver—but not the sole (see e.g., Ajith et al., 2020)—is the pre‐reversal enhancement (PRE) of the zonal electric field. The initial density perturbations at the bottomside F‐layer can then rise and grow in the topside ionosphere and reach the Swarm altitudes (see e.g., Park et al., 2013; Spogli et al., 2016; Wan et al., 2018; Xiong et al., 2016; Zakharenkova et al., 2016), if the vertical E x B drift and the field‐line‐integrated conductivity are enough intense to increase the growth rate of the R‐T instability (Abdu, 2001; Li et al., 2021).…”