Equatorial Plasma Bubble Occurrence Under Propagation of MSTID and MLT Gravity Waves

We observed a signature of equatorial plasma bubbles (EPBs) followed by a medium‐scale traveling ionospheric disturbance (MSTID) crossing the solar terminator over the geomagnetic equator during the period of post‐sunset rise (PSSR) of the F layer. Simultaneous observations of the EPBs and the MSTIDs by ground‐based Global Navigation Satellite System receivers and OI 630‐nm imagers, ionospheric parameters by ionosondes, and mesosphere–lower thermosphere (MLT) gravity waves (MLT‐GWs) by OH airglow imagers have been carried out in the equatorial and low‐latitude region of Brazil. On 16–17 September 2015, MSTIDs with very fast horizontal phase speeds, propagating toward northeast (NE), were observed over the latitude region of 0–30°S in the afternoon to evening time zone. It was geomagnetically quiet time (Kp: 2–3). An EPB development was observed after one of the MSTIDs crossed the solar terminator at 22:00 UT. Large‐scale MLT‐GWs with slower phase speeds were also observed both at São João do Cariri (7.5°S, 35.0°W) propagating from southwest (SW) to NE and Cachoeira Paulista (22.7°S, 45.0°W) propagating northward. This is to report on what we consider as a signature of direct seeding of EPBs by an MSTID that was likely induced by a secondary GW from tropospheric deep cloud convections to the south. This study highlights a possible dynamical process from the troposphere to ionosphere via this vertical coupling process over the 2,500 km of horizontal distance. Key Points We observed equatorial plasma bubbles (EPBs), traveling ionospheric disturbances (MSTIDs), and MLT‐gravity waves in the evening period A direct evidence of the northeastward propagation of MSTID and EPB seeding process during the solar terminator passage was observed We concluded that the observed MSTID was induced by a secondary gravity wave from dissipation of primary waves in the thermosphere