Geomagnetic Conditions in Ireland during the St. Patrick’s Day 2015 Storm
Seán Blake
Trinity College Dublin
Peter T. Gallagher (TCD), Alan Jones (DIAS), Colin Hogg (DIAS), Joe McCauley (TCD), Ciarán Beggan (BGS), Alan Thomson (BGS), Gemma Kelly (BGS), David Bell (Eirgrid)
On March 15, 2015, two coronal mass ejections were launched in quick succession from the Sun. Two days later, on March 17 (St. Patrick's Day), they impacted the Earth's magnetosphere, resulting in a geomagnetic storm with a planetary K-index of 8.

A local K-index of 7, which was sustained for 9 hours, was derived from magnetic observations at the Rosse Solar-Terrestrial Observatory in the Irish midlands. This was the most geomagnetically disturbed day observed in Ireland in over a decade. This disturbance was also measured across a new network of magnetometers at Valentia, Birr, Leitrim, and Armagh in Northern Ireland.

Using these magnetic measurements, electric fields were calculated using both a plane-wave approximation and a thin-sheet surface electric field model supplied by the British Geological Survey. The calculated electric fields were then coupled to a model of the power grid to estimate the geomagnetically induced currents in the power network across the island. Preliminary calculations for the electric field suggest values of greater than 5 V/km during the peak of the storm. These are similar to condition observed in Britian during the Halloween 2003 storms.