Abstract
We present a characterization of transient-large-amplitude (TLA)
geomagnetic disturbances that occurred at six stations of the
Magnetometer Array for Cusp and Cleft Studies throughout 2015. TLA
events are defined as one or more short-timescale (< 60
seconds) dB/dt signature with magnitude > 6 nT/s. A
semi-automated dB/dt search algorithm was developed to identify TLA
events in ground magnetometer data and used to identify 40 TLA dB/dt
events. We demonstrate the existence of large-amplitude dB/dt with
timescale less than 10 seconds in nine of the events. The association of
these events to sudden commencements is relatively weak, rather the
events are more likely to occur in relation to substorm onsets. However,
15% of TLA events show no direct association to geomagnetic storms,
substorms or nighttime magnetic impulse events.