Abstract
Statistical distributions are investigated for magnetic storms, sudden commencements (SCs), and substorms to identify the possible amplitude of the one in 100-year and 1000-year events from a limited data set of less than 100 years. The lists of magnetic storms and SCs are provided from Kakioka Magnetic Observatory, while the lists of substorms are obtained from SuperMAG. It is found that majorities of events essentially follow the log-normal distribution, as expected from the random output from a complex system. However, it is uncertain that large-amplitude events follow the same log-normal distributions, and rather follow the power-law distributions. Based on the statistical distributions, the probable amplitudes of the 100-year (1000-year) events can be estimated for magnetic storms, SCs, and substorms as approximately 750 nT (1100 nT), 230 nT (450 nT), and 5000 nT (6200 nT), respectively. The possible origin to cause the statistical distributions is also discussed, consulting the other space weather phenomena such as solar flares, coronal mass ejections, and solar energetic particles.
Highlights
It is important to understand the characteristics and possible amplitudes of extreme events of substorms, sudden commencements (SCs), and magnetic storms to mitigate the space weather hazard, especially from geomagnetically induced currents (Kataoka and Ngwira 2016; Pulkkinen et al 2017)
One of the extreme geomagnetic activity events was observed associated with an episodic solar flare on 1 September 1859 (Carrington 1859), which has been considered as a measure of extreme events
Note that the log-normal fit for above 200 nT level can be meaningful to give an estimate of the extreme amplitude because those large storms were caused by only Coronal mass ejection (CME), while relatively weak magnetic storms are driven by both CMEs and corotating interaction regions (Richardson et al 2006; Kataoka and Miyoshi 2006)
Summary
It is important to understand the characteristics and possible amplitudes of extreme events of substorms, sudden commencements (SCs), and magnetic storms to mitigate the space weather hazard, especially from geomagnetically induced currents (Kataoka and Ngwira 2016; Pulkkinen et al 2017). It is still hard to predict the amplitude of unprecedented extreme events by physicsbased simulations, and the statistical analysis is necessary to estimate the quantitative amplitude of possible extreme events. One of the extreme geomagnetic activity events was observed associated with an episodic solar flare on 1 September 1859 (Carrington 1859), which has been considered as a measure of extreme events. From the statistical comparison among several space weather phenomena of magnetic storms, solar flares, and coronal mass ejections, Riley (2012) estimated a probability of 12% to have another Carrington event in coming 10 years. Kataoka (2013) applied the same analysis to the 90-year list of magnetic storms and estimated the probability of another Carrington storm in 10 years as 4 ~ 6%
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