Sandra Catherine Chapman

The 2024 Hannes Alfvén Medal is awarded to Sandra Catherine Chapman for her pioneering work and leadership in advancing our understanding of space plasma physics in the solar system and beyond.

Sandra Catherine Chapman was a pioneer of the idea that Earth’s magnetosphere is a driven-dissipative system, far from equilibrium, which therefore releases energy in a ‘bursty’ and unpredictable manner. By making the connection with concepts from non-equilibrium statistical mechanics, Chapman argued that energy release is therefore expected to occur across a broad range of scales, and that the relevant physics is fundamentally multi-scale. Whilst the importance of coupling across multi-scale processes is now a commonplace throughout heliospheric physics, it was quite new when, in 1998, Chapman and colleagues linked this idea to the paradigm of self-organised criticality.

Chapman led several breakthroughs in our understanding of plasma turbulence in the solar wind. With colleagues, she was among the first to isolate, and thoroughly quantify, the distinction between the physical properties of magnetohydrodynamic turbulence, and turbulence on sub-ion Larmor scales, the dissipation range. This work is central to the fundamental question of how dissipation can occur in collisionless plasmas. She furthermore pioneered techniques that distinguish intermittent turbulence from noise fluctuations in observations and simulations.

Chapman has also made key contributions in High Performance Computing (HPC) approaches to the fully nonlinear kinetic physics of space plasmas. Her work led to the realisation that resolving full electron physics fundamentally changes the behaviour of supercritical shocks, from static to reforming. With colleagues, Chapman showed that once electron dynamics is properly resolved in quasiperpendicular shock simulations, the physics of ion acceleration yields a scaling of ion energy consistent with required values for ion injection energies at supernova remnant shocks.

The imperative to quantify uncertainties has been a central theme of Chapman’s development and application of novel approaches to heliospheric plasma observations. This has recently become a hot topic in the geosciences, and Chapman is a leader here too. She is devising new statistical approaches to utilise imperfect historical data to quantify the risk of extreme space weather events.

Chapman’s work is truly interdisciplinary, with important contributions in magnetically confined plasmas for fusion, and in earth climate change, as well as in space plasma physics. As co-founder of the interdisciplinary Centre for Fusion, Space and Astrophysics at Warwick University she has also supported the next generation of scientists, and supervised more than thirty PhD candidates to successful completion – many now hold permanent academic positions.

Chapman is not only a worthy recipient of the prestigious Hannes Alfvén Medal – her way of thinking and addressing problems is indeed the very personification of the award.