The Influence of Sudden Commencements on the Rate of Change of the Surface Horizontal Magnetic Field in the United Kingdom

Smith, Andy, Freeman, M. P., Rae, Jonathan and Forsyth, C. (2019) The Influence of Sudden Commencements on the Rate of Change of the Surface Horizontal Magnetic Field in the United Kingdom. Space Weather, 17 (11). pp. 1605-1617. ISSN 1542-7390

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Sudden commencements (SCs) are rapid increases in the northward component of the surface geomagnetic field, related to sharp increases in the dynamic pressure of the solar wind. Large rates of change of the geomagnetic field can induce damaging currents in ground power networks. In this work, the effect of SCs on the (1 min) rate of change of the surface magnetic field (R) at three U.K. stations is investigated. The distributions of R during SCs are shifted to higher values than the data set as a whole. Rates of change greater than 10 nT/min are 30–100 times more likely during SCs, though less than 8% of the most extreme R (≥99.99th percentile) are observed during SCs. SCs may also precede geomagnetic storms, another potential source of large R. We find that the probability of observing large a R is greatly enhanced for 3 days following an SC. In the 24 hr following an SC it is 10 times more likely than at any given time to observe rates of change between 10 and several hundred nT/min. Additionally, between 90% and 94% of data (depending on station) above the 99.97th percentile is recorded within 3 days of an SC. All values of R ≥ 200 nT/min in the United Kingdom have been observed within 3 days of an SC. These results suggest that accurately predicting SCs is critically important to identify intervals during which power networks at similar geomagnetic latitudes to the United Kingdom are at risk from large geomagnetically induced currents.

Item Type: Article
Additional Information: Funding Information: The magnetometer data used in this study were collected at the Hartland, Eskdalemuir, and Lerwick observatories. We thank the British Geological Survey for supporting their operation and INTERMAGNET for promoting high standards of magnetic observatory practice. The data were downloaded from and are freely available there. We acknowledge and thank NASA GSFC's Space Physics Data Facility's OMNIWeb (or CDAWeb or ftp) service for the use of OMNI data ( ). The results presented in the paper also rely on the SC list made available by the International Service on Rapid Magnetic Variations ( ) and published by the Observatorio de l'Ebre in association with the International Association of Geomagnetism and Aeronomy (IAGA) and the International Service of Geomagnetic Indices (ISGI). We thank the involved national institutes, the INTERMAGNET network and the ISGI. A. W. S. and I. J. R. were supported by STFC Consolidated Grant ST/S000240/1 and NERC Grant NE/P017150/1. C. F. was supported by the NERC Independent Research FellowshipNE/N014480/1 and STFC Consolidated Grant ST/S000240/1. M. P. F. was supported by NERC Grant NE/P016693/1. The analysis in this paper was performed using python, including the pandas, numpy, scipy, and matplotlib libraries.
Subjects: F300 Physics
F500 Astronomy
Department: Faculties > Engineering and Environment > Mathematics, Physics and Electrical Engineering
Depositing User: Rachel Branson
Date Deposited: 07 Nov 2022 11:07
Last Modified: 07 Nov 2022 11:15

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