Example of BBF footpoint-Swarm conjunction for Swarm trace Δt = 15 min after end time of BBF detection. (Left) Swarm A, B, and C FAC measurements, and the BBF duration indicated with the two vertical dashed lines. (Right) Polar plot with Swarm traces across the Northern and Southern Hemispheres and the corresponding FAC intensity. The BBF footpoint for the different Tsyganenko models are represented by circles, with shaded areas indicating the errors Err_MLAT = ±1°, Err_MLT = ±1 h. The Q_fp and Q_cj indicate the footpoint quality and conjunction quality with Swarm A, B, and C.