Left: Detection of the same hook-like signal observed on 19-Jan-2014 at the same altitude, for Swarm Alpha (A), Bravo (B), and Charlie (C). Spectrogram panels are aligned by magnetic local time and the power scale fixed to allow comparison of each event. Right: Inclination (I) calculated at 500 km altitude, with the zero contour shown as a thick black line. White points indicate the location corresponding to where each hook is seen to alias upon hitting the 125 Hz Nyquist frequency. Satellite tracks are shown by dashed arrows.