By Gemma Bower (University of Leicester)
Horse collar aurora (HCA) are an auroral phenomena that occurs under northward IMF where the polar cap becomes teardrop shaped due to the poleward motion of the dusk and dawn sectors of the auroral oval. Their formation has been linked to prolonged periods of dual-lobe reconnection (DLR). This occurs when the same IMF magnetic field line reconnects in both the northern and southern hemisphere lobes when the IMF clock angle is small. This leads to the closure of magnetic flux at the dayside magnetopause. In order to further study the motion of HCA a list of HCA events previously identified in UV images captured by the Special Sensor Ultraviolet Spectrographic Imager (SSUSI) instrument on-board the Defense Meteorological Satellite Program (DMSP) spacecraft F16, F17 and F18 has been used. Events that have concurrent 630.0 nm all-sky camera (ASC) data from the Redline Geospace Observatory (REGO) Resolute Bay site are studied in more detail, making use of the higher cadence of the ASC images compared to DMSP/SSUSI. 11 HCA events are classified based on the IMF conditions at the end of the event. A southward turning of the IMF ends five events, two end with positive By dominated IMF and four with negative By dominance. The figure shows one of the studied events that ends with a southward turning of the IMF. Under positive (negative) By the arcs move duskward (dawnward) in the northern hemisphere with the opposite true in the southern hemisphere. Under a southward turning the arcs move equatorward. These results are in agreement with previously proposed models. Understanding the evolution of HCA will allow DLR to be studied in more detail.
Please see paper for full details: Bower, Bower, G. E., Milan, S. E., Paxton, L. J., Spanswick, E., & Hairston, M. R. (2023). Formation and motion of horse collar aurora events. Journal of Geophysical Research: Space Physics, 128, e2022JA031105. https://doi.org/10.1029/2022JA031105
We are pleased to announce that following Spring MIST 2023 the Rishbeth Prizes this year are awarded to Sophie Maguire (University of Birmingham) and Rachel Black (University of Exeter).
Sophie wins the prize for the best MIST student talk which was entitled “Large-scale plasma structures and scintillation in the high-latitude ionosphere”. Rachel wins the best MIST poster prize, for a poster entitled “Investigating different methods of chorus wave identification within the radiation belts”. Congratulations to both Sophie and Rachel!
As prize winners, Sophie and Rachel will be invited to write articles for Astronomy & Geophysics, which we look forward to reading.
MIST Council extends their thanks to the University of Birmingham for hosting the Spring MIST meeting 2023, and to the Royal Astronomical Society for their generous and continued support of the Rishbeth Prizes.
By Cameron Patterson (Lancaster University)
Railway signalling is one of the many ground-based systems that are susceptible to the impacts of space weather. A popular signalling system is the track circuit, where a line is split into smaller sections called ‘blocks’, each containing a power supply and a relay that sets the signal based on the level of current. Currents induced in the rails during geomagnetic events disrupt this balance, and have the potential to cause signalling misoperations, which can create delays and/or possibly be hazardous. Using recent theoretical work and parameters from industry standards documents, we have developed realistic models of two railway lines in the United Kingdom to study the impacts that geomagnetically induced currents have on signalling systems. In this study, we have focused on right side failures, which is when there are no trains occupying the blocks and green signals are turned red. Our results show that the susceptibility of a track circuit to induced currents is dependent on its length, orientation and position along the line. We found that the threshold electric field strength for a misoperation to occur is approximately what would arise during a storm expected to occur once every 30 years. Finally, we showed that with a 1 in 100 year extreme electric field, there would be a significant number of misoperations across the line.
Please see the following paper for a more in depth look: Patterson, C. J., Wild, J. A., & Boteler, D. H. (2023). Modeling the impact of geomagnetically induced currents on electrified railway signaling systems in the United Kingdom. Space Weather, 21, e2022SW003385. https://doi.org/10.1029/2022SW003385.