Open AccessExtreme Value Analysis of Induced Geoelectric Field in South Africa
Author(s) -
Lotz S. I.,
Danskin D. W.
Publication year - 2017
Publication title -
space weather
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.254
H-Index - 56
ISSN - 1542-7390
DOI - 10.1002/2017sw001662
Subject(s) - geomagnetic storm , earth's magnetic field , extreme value theory , storm , latitude , log normal distribution , return period , event (particle physics) , climatology , environmental science , meteorology , atmospheric sciences , physics , statistics , mathematics , geology , geography , geodesy , magnetic field , astrophysics , archaeology , quantum mechanics , flood myth
Extreme geomagnetic disturbances occur rarely but can have great impact on technological systems such as power supply networks. Long‐term planning for extreme events requires the estimation of event impact for occurrence periods greater than the length of observed data. With this in mind an analysis of extreme geomagnetic events observed in South Africa (middle geomagnetic latitude) is performed over four solar cycles (1974–2015). An algorithm to identify active periods with minimum S Y M ‐ H ≤−100 nT is demonstrated. The sum of induced electric field over the course of each event is used to characterize the severity of each active period. It is found that the severity index (accumulated electric field magnitude Σ E ) shares a highly linear relationship with accumulated S Y M ‐ H over each event. The index Σ E is lognormal distributed, with tail deviating greater than lognormal, confirming heavy‐tailed occurrence. A general Pareto distribution is fitted to the tail of the distribution and extrapolated to calculate the return levels of extreme events. Return levels of once in 100 and once in 200 year events are estimated to be 9.4 × 10 4 mV/km min and 1.09 × 10 5 mV/km min, respectively. The top three events, in ascending order of severity, are the March 1989 storm, the events of late October 2003, and the April 1994 event—a long interval of coronal‐hole driven disturbances, bookended by two intense geomagnetic storms.