History often turns on extreme events, be they man-made or natural. Examples are global financial crises, military strikes or radical political events, or natural disasters such as floods and earthquakes, in the latter. Extreme events are often associated with catastrophes, and the word ’extreme’ is sometimes substituted by ’freak’ to suggest something unnatural and undesirable, or ’rogue’ in the case of ocean waves. Generally, the economic and social consequences of extreme events are a matter of enormous concern.
When such catastrophes strike, it is easy to look back and analyze mistakes. But how do we gain a better understanding that can be applied towards the next event? It is often argued that extreme events are so implausible as to be negligible for planning purposes. Of course, extreme events are, by their definition, rare. However, what is rarer still is that a rare event never occurs at all. In particular, extreme events have a number of key characteristics that are found over and over again. We know that records must be broken in the future, so if a flood design is based on the worst case of the past, then we are still not prepared for possible floods in the future. Materials will fail due to fatigue, so if the body of an aircraft looks fine to the naked eye, it must still fail seemingly out of the blue if the aircraft has been in operation over an extended period of time.
Much of science has concentrated, until recently, on understanding the mean behaviour of physical, biological or social systems and their “normal” variability. Extreme events, due to their rarity, have been hard to study and even harder to predict. The science of extreme value statistics aims to describe the occurrence of extreme events in a general and unified way. We focus on extreme value statistics suitable for cases where individual events are correlated with each other over a wide range of spatial and/or temporal scales. Such complex behavior arises due to nonlinear interactions between the components of the system and has recently been established as a general and significant phenomenon, space weather being one particular example.
Space weather arises from the interactions of solar activity, solar wind and Earth’s magnetosphere, with phenomena ranging from magnetic storm activity on short time scales to possible relationships with global warming on long time scales. Magnetic storm intensities and other space weather-related phenomena must be considered when designing ground-based electric power systems. The severe geomagnetic storm and associated province-wide power blackout in Quebec on 13 and 14 March 1989 illustrates the deleterious effects of extreme space weather activity on critical infrastructure systems.
We showed for the first time that well-defined extreme bursts exist in the solar wind that share many scale-free properties with their counterparts in solar activity. In addition to providing evidence for the direct influence of solar activity on the solar wind, our analysis also raised important questions in the context of the solar wind-magnetosphere interaction. For example, do such scale-free extreme bursts play a role for this interaction?