Can an impulsive variation of the solar wind plasma pressure trigger a plasma bubble? A case study based on CSES, Swarm and THEMIS data M. Piersanti a , M. Pezzopane b,⇑ , Z. Zhima c,d , P. Diego e , C. Xiong f , R. Tozzi b A. Pignalberi b , G. D’Angelo e , R. Battiston g , J. Huang d , P. Picozza a , Y. Rui c,d , X. Shen c,d , R. Sparvoli h , P. Ubertini e , Y. Yang c,d , S. Zoffoli i a INFN – University of Rome ‘‘Tor Vergata”, Rome, Italy b Istituto Nazionale di Geofisica e Vulcanologia, Rome, Italy c Institute of Earthquake Forecasting, China Earthquake Administration, Beijing, China d Institute of Crustal Dynamics, China Earthquake Administration, Beijing, China e INAF-Istituto di Astrofisica e Planetologia Spaziali, Rome, Italy f GFZ German Research Centre for Geosciences, Potsdam, Germany g TIFPA and University of Trento, Trento, Italy h University of Rome ‘‘Tor Vergata”, Rome, Italy i Agenzia Spaziale Italiana, Rome, Italy Received 19 June 2020; received in revised form 18 July 2020; accepted 29 July 2020 Available online 13 August 2020 Abstract During the August 25, 2018 geomagnetic storm, the new borne CSES-01 satellite and the Swarm A satellite detected a really large equatorial plasma bubble (EPB) in the post-midnight sector over western Africa. We investigated the features of this deep ionospheric plasma depletion using data from the Langmuir probes on-board CSES-01 and Swarm A satellites, and data from the high-precision magnetometer and the electric field detector instruments on-board CSES-01. Using also plasma and magnetic field data from THEMIS-E satellite we found that, during the passage of the magnetic cloud that drove the geomagnetic storm, an impulsive variation lasting about ten minutes characterized the solar wind (SW) pressure. The analysis of the delay time, between the occurrence of such impulsive variation and the detection of the plasma bubble, suggests a possible link between the SW pressure impulsive variation as iden- tified by THEMIS-E and the generation of the EPB as detected by CSES-01 and Swarm A. We put forward the hypothesis that the SW pressure impulsive variation might have triggered an eastward prompt penetrating electric field that propagated from high to equatorial latitudes, overlapping in the nightside region to the zonal westward electric field, causing either a reduction or an inversion, at the base of the EPB triggering. Ó 2020 COSPAR. Published by Elsevier Ltd. All rights reserved. Keywords: Equatorial plasma bubble; Solar wind-magnetosphere-ionosphere coupling; Geomagnetic storm; CSES; Swarm; THEMIS 1. Introduction Plasma density depletions, which are observed in the equatorial ionosphere at different spatial (~50–1000 km) and temporal scales, are called equatorial plasma bubbles (EPBs). Typically, EPBs are detected within a narrow band https://doi.org/10.1016/j.asr.2020.07.046 0273-1177/Ó 2020 COSPAR. Published by Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail addresses: mirko.piersanti@roma2.infn.it (M. Piersanti), michael.pezzopane@ingv.it (M. Pezzopane), piero.diego@inaf.it (P. Diego), bear@gfz-potsdam.de (C. Xiong), roberta.tozzi@ingv.it (R. Tozzi), roberto.battiston@unitn.it (R. Battiston), picozza@roma2. infn.it (P. Picozza), shenxuhui@vip.sina.com (X. Shen), roberta. sparvoli@roma2.infn.it (R. Sparvoli), pietro.ubertini@inaf.it (P. Ubertini), simona.zoffoli@asi.it (S. Zoffoli). www.elsevier.com/locate/asr Available online at www.sciencedirect.com ScienceDirect Advances in Space Research 67 (2021) 35–45