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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 34, issue 4
Ann. Geophys., 34, 485–491, 2016
https://doi.org/10.5194/angeo-34-485-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 34, 485–491, 2016
https://doi.org/10.5194/angeo-34-485-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Regular paper 02 May 2016

Regular paper | 02 May 2016

Extreme value analysis of the time derivative of the horizontal magnetic field and computed electric field

Peter Wintoft1, Ari Viljanen2, and Magnus Wik1 Peter Wintoft et al.
  • 1Swedish Institute of Space Physics, Scheelevägen 17, 22370 Lund, Sweden
  • 2Finnish Meteorological Institute, Erik Palménin aukio 1, 00560 Helsinki, Finland

Abstract. High-frequency ( ≈  minutes) variability of ground magnetic fields is caused by ionospheric and magnetospheric processes driven by the changing solar wind. The varying magnetic fields induce electrical fields that cause currents to flow in man-made conductors like power grids and pipelines. Under extreme conditions the geomagnetically induced currents (GIC) may be harmful to the power grids. Increasing our understanding of the extreme events is thus important for solar-terrestrial science and space weather. In this work 1-min resolution of the time derivative of measured local magnetic fields (|dBh∕dt|) and computed electrical fields (Eh), for locations in Europe, have been analysed with extreme value analysis (EVA). The EVA results in an estimate of the generalized extreme value probability distribution that is described by three parameters: location, width, and shape. The shape parameter controls the extreme behaviour. The stations cover geomagnetic latitudes from 40 to 70° N. All stations included in the study have contiguous coverage of 18 years or more with 1-min resolution data. As expected, the EVA shows that the higher latitude stations have higher probability of large |dBh∕dt| and |Eh| compared to stations further south. However, the EVA also shows that the shape of the distribution changes with magnetic latitude. The high latitudes have distributions that fall off faster to zero than the low latitudes, and upward bounded distributions can not be ruled out. The transition occurs around 59–61° N magnetic latitudes. Thus, the EVA shows that the observed series north of  ≈ 60° N have already measured values that are close to the expected maxima values, while stations south of  ≈ ° N will measure larger values in the future.

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Extreme value analysis has been applied to 1-minute-resolution magnetic fields and computed electric fields over Europe. We find that on average the largest disturbances of the fields are observed close to the auroral oval, as expected. However, the analysis indicates that as we move south from Scandinavia to northern continental Europe the distribution becomes more extreme. This could be due to that strong storms regularly occur at high latitudes, while the extreme storms push the oval south.
Extreme value analysis has been applied to 1-minute-resolution magnetic fields and computed...
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