Research Article

Signatures of wedgelets over Fennoscandia during the St Patrick’s Day Storm 2015

¹ Department of Physics, Umeå University, Linneaus väg, 90187 Umeå, Sweden
² School of Physics and Astronomy, University of Leicester, LE1 7RH, United Kingdom
³ Thales Alenia Space, 26 Av. Jean François Champollion, 31100 Toulouse, France
⁴ Finnish Meteorological Institute, Dynamicum Erik Palménin aukio 1, 00560 Helsinki, Finland
⁵ Space Science and Applications Group, Los Alamos National Laboratory, Los Alamos, NM 87545, USA
⁶ Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Rd., Laurel, MD 20723, USA

^* Corresponding author: audrey.schillings@space.umu.se

Received: 6 October 2022
Accepted: 30 May 2023

Abstract

During the long main phase of the St Patrick’s Day storm on March 17, 2015, we found three separate enhancements of the westward electrojet. These enhancements are observed in the ionospheric equivalent currents computed using geomagnetic data over Fennoscandia. Using data from the IMAGE magnetometer network, we identified localised field-aligned current (FAC) systems superimposed on the pre-existing ionospheric current system. We suggest that these localised current systems are wedgelets and that they can potentially contribute to a larger-scale structure of a substorm current wedge (SCW). Each wedgelet is associated with a negative B_X spike. Each spike is recorded at a higher latitude than the former one and all three are very localised over Fennoscandia. The first spike occurred at 17:34 UT and was observed at Lycksele, Rørvik and Nurmijärvi, the second spike was recorded at 17:41 UT and located at Lycksele and Rørvik, whereas the last spike occurred at 17:47 UT and was observed at Kevo and Abisko. Simultaneous optical auroral data and electron injections at the geosynchronous orbit indicate that one or more substorms took place in the polar ionosphere at the time of the wedgelets. This study demonstrates the occurrence of small and short-lived structures such as wedgelets at different locations over a short time scale, 15 min in this case.