Possible role of auroral oval-related currents in two intense magnetic storms recorded by old mid-latitude observatories Clementinum and Greenwich

0506249 - GFÚ 2020 RIV FR eng J - Journal Article
Valach, F. - Hejda, Pavel - Revallo, M. - Bochníček, Josef
Possible role of auroral oval-related currents in two intense magnetic storms recorded by old mid-latitude observatories Clementinum and Greenwich.
Journal of Space Weather and Space Climate. Roč. 9, May (2019), č. článku A11. ISSN 2115-7251. E-ISSN 2115-7251
R&D Projects: GA ČR(CZ) GA17-19877S
Institutional support: RVO:67985530
Keywords : storm * substorm * geomagnetism * extreme events * historical records
OECD category: Environmental sciences (social aspects to be 5.7)
Impact factor: 3.095, year: 2019
Method of publishing: Open access
https://www.swsc-journal.org/articles/swsc/abs/2019/01/swsc180073/swsc180073.html

Some recent studies point out that currents related to the auroral oval, electrojets and field aligned currents (FACs), are serious candidates for the mechanism of the intense mid-latitude magnetic storms. It is interesting to re-analyse historical data under the light of this modern knowledge. In this aim, we analysed two intense magnetic storms that were recorded by observatories Clementinum (Prague) and Greenwich on 17 November 1848 and 4 February 1872, respectively. The latter has been marked as an extraordinary event by several authors, in particular in connection with auroras. The former, however, has been little known in the space weather community. Both these events possessed swift and extensive variations of the horizontal (H) component (>400 nT and >500 nT, respectively) and were accompanied by auroras sighted at very low magnetic latitudes. This implies that the auroral oval on the north hemisphere was vastly extended southward. The variations of the magnetic declination also indicate that during these events the auroral oval was situated at magnetic latitudes lower than those of the observatories. The storms studied in this paper occurred at different magnetic local times (MLTs), similar to 23 MLT and similar to 19 MLT. Therefore, they might represent mid-latitude events related to different parts of the auroral oval. In this paper, the H-variation recorded at Clementinum in 1848 is interpreted to be a substorm due to the ionospheric substorm electrojet. The Greenwich event registered in 1872 then seems to be a combination of the ring-current storm with a positive variation of the H-component caused by the eastward electrojet. Both the events of 1848 and 1872 appear to exemplify phenomena that are common in high magnetic latitudes but which may occasionally happen also at mid-latitudes.
Permanent Link: http://hdl.handle.net/11104/0297554