Omega band pulsating auroras observed onboard THEMIS spacecraft and on the ground

<jats:title>Abstract</jats:title><jats:p>We examined a fortuitous case of an omega band pulsating aurora observed simultaneously on the ground at Sanikiluaq in Canada and onboard the Time History of Events and Macroscale Interactions during Substorm (THEMIS) spacecraft on 1 March 2011. We observed almost the entire process of the generation of the omega band aurora from the initial growth to the declining through expansion period. The omega band aurora grew from a faint seed, not via distortion of a preexisting east‐west band aurora. The size scale of the omega band aurora during the maximum period was ~500 km in the north‐south direction and ~200 km in the east‐west direction. The mesoscale omega band aurora consisted of more than 15 patches of complex‐shaped small‐scale auroras. Each patch contained an intense pulsating aurora with a recurrent period of ~9–12 s and a poleward moving form. The footprints of the THEMIS D and THEMIS E spacecraft crossed the poleward part of the omega band aurora. THEMIS D observed significant signatures in the electromagnetic fields and particles associated with the time at which the spacecraft crossed the omega band aurora. In particular, it was found that the <jats:italic>Y</jats:italic> and <jats:italic>Z</jats:italic> components of the DC electric field intensity, especially the <jats:italic>Z</jats:italic> component, modulated with almost the same period as that of the optical pulsating auroras. The electrostatic low‐frequency waves of less than 30 Hz showed quasiperiodic intensity variations similar to those of the DC electric field. These observations suggest that DC electric field variation and low‐frequency electrostatic waves may play important roles in the driving mechanism of omega band pulsating auroras.</jats:p>