The 2018 Hannes Alfvén Medal is awarded to Eckart Marsch for fundamental contributions to our understanding of the kinetic processes and plasma turbulence in the heliosphere, as well as for work that helped HELIOS become a successful mission and initiated the Solar Orbiter.
Eckart Marsch’s has effectively combined observations and theory to reach important breakthroughs on the analysis of plasma turbulence in the inner heliosphere. His scientific efforts have always focused on understanding the global view of all physical processes driving the birth, heating and acceleration of the solar wind through plasma kinetic and magnetohydrodynamics (MHD) turbulence.
A large fraction of Marsch’s scientific production is based on the exploitation of the observations of the HELIOS mission. Some of his most important scientific achievements and pioneering studies were unravelling the stream structure dependence and discovering the radial evolution of the 3D velocity distribution function of solar wind protons inferred from HELIOS observations in the inner heliosphere. These studies provided the first evidence for wave-particle interaction and plasma heating via ion-cyclotron resonance, highlighted by pitch-angle diffusion in phase space and temperature anisotropy.
Another of Marsch’s important accomplishments was the development of kinetic models to explain solar-wind heating and acceleration, investigating the validity of MHD cascade and quasi-linear theory in the kinetic regime. Furthermore, Marsch has contributed to the concept of solar wind turbulence that is composed of two components, namely waves and advected structures, directly transferring this idea into innovative turbulence models that reconciled the long-lasting problem of turbulence description versus wave description.
Marsch was also the first to investigate the geometrical and scaling properties of the energy flux along the turbulent cascade and dissipation rate of kinetic energy, unravelling the multifractal nature of the dissipation field and estimated, for the first time in solar wind MHD turbulence, the associated singularity spectrum. Additionally, Marsch was the first to introduce Elsässer variables to show the basic properties of solar-wind turbulence.
Marsch’s scientific legacy is displayed in several excellent reviews on turbulence and kinetic physics. It is important to highlight Marsch’s extraordinary efforts and tenacity as a champion for the Solar Orbiter mission. This European mission was first introduced in the late 1990s and has had several vicissitudes before the final approval as the first medium-class mission of ESA’s Cosmic Vision 2015-2025 Programme. It is scheduled for launch in October 2018 (with an option for a February 2019 launch, waiting for final approval). Solar Orbiter will be realised more than four decades after the HELIOS mission and promises to bring major breakthroughs in solar and heliospheric physics.
Lastly, Marsch is an excellent teacher and educator in space plasma physics, who regularly gives lectures at International Max-Planck Research School and Göttingen University. He is a deserving recipient of the EGU 2018 Hannes Alfvén Medal.