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Pulsating aurorae in the growth phase of substorms

We have done a study of a number of auroral substorms, observing them with both the Kilpisjärvi Atmospheric Imaging Receiver Array (KAIRA) and the Finnish Meteorological Institute's all-sky camera located nearby.  KAIRA was measuring riometric absorption at 38.1 MHz and we used the 557.7nm optical data from the FMI camera.

Substorms can be divided into three phases: the growth phase, the expansion phase and the recovery phase. Here, we studied the long east–west band of aurora (known as the growth-phase arc), which forms at the start of substorms. We found that radio absorption was consistently south of the bright auroral arc and that optical pulsating aurora occurs in the boundary region between the radio absorption zone and the bright arc.

Optical pulsating aurora is a well known phenomenon in the recovery phase of the substorm. This is where the most dramatic part of the auroral display has occurred and there is optical emission all over the sky. During this time patches…

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