Intense Localised Currents during the St. Patricks Day Magnetic Storm, March 17, 2015

Abstract:

The St. Patrick’s day Storm on March 17, 2015 was a text-book example of a two phase magnetic storm initiated by an interaction between a CIR shock front and a CME at 1 AU, causing a two phase magnetic storm at Earth. While the first part of the magnetic storm is relatively smooth in its magnetic signatures the second part contains a number of very short-lived magnetic spikes of the order of 1-2000 nT for as short as 3-5 minutes at auroral and sub-auroral latitudes. The dB/dt effect of these spikes is causing induced electric fields of the order of several hundred mV/km at ground level, which is of the order of earlier events like during the Halloween storm, which had recorded damaging effects on ground-based technology systems.

We will analyse the difference in magnetospheric activity and solar wind drivers between the two markedly different storm phases and discuss possible physical reasons for the spikes occurring in the second phase. Ground-based data from the Scandinavian sector reveals that these features are indeed very localised, of the order of 1000 km or so, and thus they must, just like similarly sized substorm onset features, be associated with violent localised field-aligned currents.