A simple index for Pi2 pulsations to nowcast substorms by Regional Warning Centre Canada

Substorm onsets and intensifications are accompanied by Pi2 magnetic pulsation bursts. Thus Pi2 would seem to be ideal for inferring the occurrence of substorm. However, the full potential of Pi2 pulsations as a proxy for substorms has not been fully exploited by the space weather community, although they are sometimes used by researchers to identify substorm onsets. To this end, a simple Pi2 index has been devised for stations in the auroral zone and subauroral zone in Canada on the basis of the log of the integrated power of the Pi2 spectrum, in analogy to the quasi‐logarithmic Kp or K indices. The Pi2 power spectrum necessarily contains a contribution by the substorm electrojet, as a power law relationship between Pi2 powers and X ‐negative bay extremes found in this study indicates. The index is shown to detect distinct bay signatures of substorm events regionally around local midnight at Canadian latitudes and would thus compensate for the inadequacy of the global geomagnetic indices such as Kp . An automatic production of such a Pi2‐based substorm index, using near‐real‐time data from Canadian observatories, enables the Regional Warning Centre Canada of the International Space Environment Services to nowcast substorms in order to meet the demands of users for real‐time knowledge of nighttime localized extreme geomagnetic variability.