Revisiting the edge of chaos
Solar eruptions causing geomagnetic storms as they impact Earth's magnetic field are just an indication that the Sun-Earth system is in a state far from equilibrium. Instabilities, waves and turbulence, all play key roles in the system's behaviour. Chaos is ubiquitous in the near-Earth space, with alternating periods of quiescent low-level fluctuations with active high-level waves of magnetic and electric fields. Scientists working on the 'Nonlinear dynamics of the solar-terrestrial environment' (PLASMADYNAMICS) project studied the chaotic nature of the space environment using non-linear dynamics tools. Non-linear dynamics offers powerful mathematical and computational techniques to probe the origin and nature of turbulence. Turbulence in space is governed by Alfvén waves, which are moving disturbances of the plasma and magnetic field. Nonlinear interactions between Alfvén waves travelling up and down, colliding with each other to create new waves are the fundamental building blocks of turbulence. The PLASMADYNAMICS scientists modelled the evolution of Alfvén waves by means of non-linear equations. In particular, they employed derivatives of the Schrödinger equations, describing the motion of individual particles. The PLASMADYNAMICS scientists were not only able to model the transition from order to chaos. The team led by the Observatoire de Paris in France also observed non-linear interactions between counter-propagating Alfvén waves. Specifically, during violent emissions of charged particles from the Sun, the source of gusty space winds, chaotic motions in the ionised gas were observed. Moreover, the PLASMADYNAMICS project brought together scientists from different countries in Asia, America and Europe to drive models with solar observations. The results, presented in 12 papers will contribute to our increasing understanding of how turbulence can mediate the effects of gusty space winds on Earth.
Keywords
Chaos, Sun, Earth, geomagnetic storms, instabilities, waves, turbulence, non-linear dynamics, ionised gas