Long-lasting daytime equatorial plasma bubbles observed by the C/NOFS satellite

[1] We report the first observations of long-lasting daytime equatorial plasma bubbles with the Communication/Navigation Outage Forecasting System (C/NOFS) satellite. The most unusual features of the plasma bubbles are the persistence from the post-midnight sector through the afternoon sector and the extremely long lifetime of 12 h. In one case, the plasma bubbles were generated at 02:00―03:00 LT near the end of the main phase of a moderate magnetic storm and detected by C/NOFS over eight successive orbits, and the decrease of the ion density inside the bubbles was still as large as ∼30% at 14:00―15:00 LT. In another case, one group of plasma bubbles was generated near the sunset terminator and existed over the entire nighttime until the post-sunrise sector (06:00―08:00 LT), and another group of plasma bubbles was first detected at 04:00―06:00 LT and lasted until ∼11:00 LT. The latter group of bubbles occurred following a sharp northward turning of the interplanetary magnetic field (IMF) near the end of the main phase of a weak magnetic storm, and the overshielding electric field caused by the IMF northward turning and the storm time disturbance dynamo might both have contributed to the generation of the bubbles. The plasma bubbles reached 800 km or higher in altitude during daytime. The high altitudes may be critical for the long lifetime of the bubbles: the photo-ionization rate decreases rapidly with altitude. The photo-ionization process may take a long time to produce enough new plasma particles to fill the daytime bubbles at high altitudes.