Freitag, 27. Juni 2025 17:00 Uhr  Melting of ice

Prof. Dr. Detlef Lohse , Max-Planck-Institut für Dynamik und Selbstorganisation, Göttingen und University of Twente

The quantitative understanding of glacial ice melting into the ocean is one of the most outstanding challenges in environmental fluid dynamics. The lack of understanding is on a fundamental level, due to the highly complex multi-scale, multi-physics nature of the problem. The process involves intricate multi- way coupling effects, including thermal convection, salinity, ocean current, and radiation, etc. As ice melts into the surrounding salty water, a decrease in local salt concentration leads to reduced water density, inducing upward buoyant forces and, consequently, upward flow. This flow dynamically interacts with the ice, resulting in a feedback loop of further melting (Stefan problem). Our investigation employs direct numerical simulations with the phase field method. To capture the intricacies of melting dynamics within turbulent flows, we implement a multiple-resolution strategy for salinity and phase field simulations [3]. The versatility of our method is demonstrated through successful applications to diverse melting scenarios, including the formation of melt ponds [2], melting in Rayleigh-Bénard convection [4], vertical convection with fresh water [1], and vertical convection with salty water [3]. In this presentation, we showcase results obtained across these various geometries. This work contributes to advancing our understanding of the complex dynamics involved in glacial ice melting within oceanic environments.

References

1. Rui Yang, Kai Leong Chong, Hao-Ran Liu, Roberto Verzicco, and Detlef Lohse. Abrupt transition from slow to fast melting of ice. Phys. Rev. Fluids, 7(8):083503, 2022.

2. Rui Yang, Christopher J. Howland, Hao-Ran Liu, Roberto Verzicco, and Detlef Lohse. Bistability in radiatively heated melt ponds. Phys. Rev. Lett., 131:234002, Dec 2023.

3. Rui Yang, Christopher J. Howland, Hao-Ran Liu, Roberto Verzicco, and Detlef Lohse. Ice melting in salty water: layering and non-monotonic dependence on the mean salinity. J. Fluid Mech., 969:R2, 2023.

4. Rui Yang, Christopher J Howland, Hao-Ran Liu, Roberto Verzicco, and Detlef Lohse. Morphology evolution of a melting solid layer above its melt heated from below. J. Fluid Mech., 956:A23, 2023.

NUCLEUS

Dr. Thierry Lasserre, Institute for Advanced Study, Technische Universität München

Dienstag, 17. Juni 2025 16:30 Uhr  The magnetic history of the Universe

Jennifer Schober, Argelander-Institute for Astronomy, University of Bonn Magnetic fields permeate nearly every astrophysical environment, from planets and stars to galaxies and galaxy clusters. In these cosmologically overdense regions, magnetic fields are thought to arise primarily from magnetohydrodynamic (MHD) dynamos. These mechanisms convert turbulent kinetic energy into magnetic energy through the stretching and twisting of field lines. In the first part of this talk, I will present recent advances in our understanding of MHD dynamos. In the second part, I will focus on the vast underdense regions of space, cosmic voids, where blazar observations have revealed the existence of magnetic fields. As voids lack turbulence and therefore the energy source of classical dynamos, these large-scale magnetic fields likely originate in the very early Universe shortly after the Big Bang and therefore offer a unique window into fundamental physics. I will outline key theoretical models of magnetogenesis and present new insights in the pre-recombination evolution of these primordial magnetic fields from state-of-the-art numerical simulations. To arrange a visit with the speaker during the visit, please contact their host: Philipp Girichidis

Mittwoch, 25. Juni 2025 16:30 Uhr  tba

Dr. Martin Robert-de-Saint Vincent, Laboratoire de Physique des Lasers, Université Sorbonne Paris Nord