| 1. |
- Lundstedt, H., et al.
(författare)
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The extreme solar storm of May 1921: observations and a complex topological model
- 2015
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Ingår i: Annales Geophysicae. - : Copernicus GmbH. - 1432-0576. ; 33:1, s. 109-116
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Tidskriftsartikel (refereegranskat)abstract
- A complex solid torus model was developed in order to be able to study an extreme solar storm, the so-called "Great Storm" or "New York Railroad Storm" of May 1921, when neither high spatial and time resolution magnetic field measurements, solar flare nor coronal mass ejection observations were available. We suggest that a topological change happened in connection with the occurrence of the extreme solar storm. The solar storm caused one of the most severe space weather effects ever.
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| 2. |
- Wik, Magnus, et al.
(författare)
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Space weather events in July 1982 and October 2003 and the effects of geomagnetically induced currents on Swedish technical systems
- 2009
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Ingår i: Annales Geophysicae. - 1432-0576. ; 27:4, s. 1775-1787
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we analyse in detail two famous space weather events; a railway problem on 13-14 July 1982 and a power blackout on 30 October 2003. Both occurred in Sweden during very intensive space weather storms and each of them a few years after the sunspot maximum. This paper provides a description of the conditions on the Sun and in the solar wind leading to the two GIC events on the ground. By applying modelling techniques introduced and developed in our previous paper, we also calculate the horizontal geoelectric field at the Earth's surface in southern Sweden during the two storms as well as GIC flowing in the southern Swedish 400 kV power grid during the event in October 2003. The results from the calculations agree with all measured data available. In the July-1982 storm, the geomagnetic field variation, Delta B-x, reached values up to similar to 2500 nT/min and the geoelectric field reached values in the order of several volts per kilometer. In the October-2003 storm, the geomagnetic field fluctuations were smaller. However, GIC of some hundreds of amperes flowed in the power grid during the October-2003 event. Technological issues related to the railway signalling in July 1982 and to the power network equipment in October 2003 are also discussed.
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| 3. |
- Wintoft, P, et al.
(författare)
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Predictions of local ground geomagnetic field fluctuations during the 7-10 November 2004 events studied with solar wind driven models
- 2005
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Ingår i: Annales Geophysicae. - 1432-0576. ; 23:9, s. 3095-3101
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Tidskriftsartikel (refereegranskat)abstract
- The 7-10 November 2004 period contains two events for which the local ground magnetic field was severely disturbed and simultaneously, the solar wind displayed several shocks and negative B-z periods. Using empirical models the 10-min RMS Delta X and Delta Y at Brorfelde (BFE, 11.67 degrees E, 55.63 degrees N), Denmark, are predicted. The models are recurrent neural networks with 10-min solar wind plasma and magnetic field data as inputs. The predictions show a good agreement during 7 November, up until around noon on 8 November, after which the predictions become significantly poorer. The correlations between observed and predicted log RMS Delta X is 0.77 during, 7-8 November but drops to 0.38 during 9-10 November. For RMS Delta Y the correlations for the two periods are 0.71 and 0.41, respectively. Studying the solar wind data for other L1-spacecraft (WIND and SOHO) it seems that the ACE data have a better agreement to the near-Earth solar wind during the first two days as compared to the last two days. Thus, the accuracy of the predictions depends on the location of the spacecraft and the solar wind flow direction. Another finding, for the events studied here, is that the Delta X and Delta Y models showed a very different dependence on B-z The Delta X model is almost independent of the solar wind magnetic field B-z except at times when B-z is exceptionally large or when the overall activity is low. On the contrary, the Delta Y model shows a strong dependence on B-z at all times.
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| 4. |
- Wintoft, Peter
(författare)
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Study of the solar wind coupling to the time difference horizontal geomagnetic field
- 2005
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Ingår i: Annales Geophysicae. - 1432-0576. ; 23:5, s. 1949-1957
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Tidskriftsartikel (refereegranskat)abstract
- The local ground geomagnetic field fluctuations (AB) are dominated by high frequencies and 83% of the power is located at periods of 32 min or less. By forming 10-min root-mean-square (RMS) of A B a major part of this variation is captured. Using measured geomagnetic induced currents (GIC), from a power grid transformer in Southern Sweden, it is shown that the 10-min standard deviation GIC may be computed from a linear model using the RMS AX and Delta Y at Brorfelde (BFE: 11.67 degrees E, 55.63 degrees N), Denmark, and Uppsala (UPS: 17.35 degrees E, 59.90 degrees N), Sweden, with a correlation of 0.926 +/- 0.015. From recurrent neural network models, that are driven by solar wind data, it is shown that the log RMS Delta X and Delta Y at the two locations may be predicted up to 30 min in advance with a correlation close to 0.8: 0.78 +/- 0.02 for both directions at BFE; 0.81 +/- 0.02 and 0.80 +/- 0.02 in the X- and Y-directions, respectively, at UPS. The most important inputs to the models are the 10-min averages of the solar wind magnetic field component B, and velocity V, and the 10-min standard deviation of the proton number density a,. The average proton number density n has no influence.
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