Possible evidence for small-scale wave seeding of equatorial plasma bubbles Kangkang Liu a,b , Guozhu Li a,b,c,⇑ , Baiqi Ning a,c a Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China b College of Earth and Planetary Sciences, University of Chinese Academy of Science, Beijing, China c Beijing National Observatory of Space Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China Received 19 November 2018; received in revised form 17 February 2019; accepted 18 February 2019 Available online 23 February 2019 Abstract The small-scale wave-like structure (SSWS) of F region bottomside plasma density was proposed to be an important seeding for equa- torial plasma bubble (EPB) generation, and employed in theoretical simulations of EPBs in recent years. The seeding role of SSWS, how- ever, is waiting to be demonstrated by observation. Here we present two cases of SSWS and EPB observed by the Fuke all-sky airglow imager (19.3°N, 109.1°E; dip latitude 14.3°N). For each case, the results show that two large-scale wave-like structures (LSWSs) initially appeared around sunset in the longitude regions separated by 3–4°, but EPB irregularities were only generated in one of the LSWSs where SSWSs were seen riding on LSWS. For the other LSWS, no SSWS and EPB irregularities were seen. Considering that the two LSWSs were situated closely in longitude where the amplitude of pre-reversal enhancement of background eastward electric field should be similar, the observation that EPB was only generated in the longitude with simultaneous LSWS and SSWS could provide supporting evidence for SSWS seeding of EPB. Ó 2019 COSPAR. Published by Elsevier Ltd. All rights reserved. Keywords: Equatorial plasma bubble; Wave-like structure; Airglow image 1. Introduction Equatorial plasma bubble (EPB) is the product of gener- alized Rayleigh-Taylor (GRT) instability driven convective activity in the equatorial ionospheric F layer. There are many factors that could affect the growth rate of GRT instability. The post-sunset rise of the F layer caused by pre-reversal enhancement (PRE) of background eastward electric field can enhance the growth rate of GRT instability that well explain the climatological characteristics of EPB occurrence (e.g., Fejer et al., 1999; Li et al., 2007). However, the PRE, by itself, is difficult to explain the day-to-day vari- ation of EPB occurrence. Under similar PRE, EPB might occur on one night and be absent on another (Hysell et al., 2002). By using the EPB observations from the Sanya and Kototabang VHF radars which are separated by about 1000 km in longitude, Li et al. (2016) reported that the gen- eration rate of EPBs over Kototabang is significantly higher than that over Sanya. The EPB occurrence differences over the two stations were suggested to be linked with the inter- tropical convergence zone in East/Southeast Asia. More factors besides PRE are needed to well explain the day-to- day, and the extremely large longitudinal variation of EPBs. The F layer bottomside plasma density wave-like structure, which could be induced by gravity waves from lower atmo- sphere convective activity, was considered as one of the most important factors that determine the day-to-day and https://doi.org/10.1016/j.asr.2019.02.025 0273-1177/Ó 2019 COSPAR. Published by Elsevier Ltd. All rights reserved. ⇑ Corresponding author at: Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China. E-mail address: gzlee@mail.iggcas.ac.cn (G. Li). www.elsevier.com/locate/asr Available online at www.sciencedirect.com ScienceDirect Advances in Space Research 63 (2019) 3612–3620