Global Development of the Supersubstorm of May 28, 2011

The paper gives an analysis of the isolated supersubstorm observed during the main phase of the moderate magnetic storm on May 28, 2011 ( SYM / H ~ –95 nT), which was caused by the solar wind magnetic cloud. This supersubstorm peaked at around ~0850 UT ( SML = ~–2600 nT). The study was based on data from the global SuperMAG and IMAGE magnetometer networks and satellite data from the AMPERE project. Like those in other supersubstorms, the ionospheric currents in this event were found to develop on a global scale: an intense and extended westward electrojet (with a maximum around midnight) was observed in the midnight, morning, and daytime sectors and an intense eastward electrojet was observed in the afternoon and evening sectors. The development of global currents was accompanied by intense positive bays. This was reflected by large values of the MPB index (~4000 nT 2 ). It has been shown that, during the peak development of the supersubstorm, there was a significant increase in the eastward electrojet in the evening sector (~15–18 MLT), an additional affluent longitudinal electric current, and an additional ring current that appeared concurrently in this sector. These facts suggest the hypothesis about the development of an additional substorm current wedge that appeared on the evening side during the supersubstorm and closed on the eastward electrojet.