ERIK MCLEAN / UNSPLASH

Physikalisches Kolloquium

Friday, 24. May 2024 5:00 pm  The role of aerosol - cloud interactions as driver of climate change in the past and in the future

Prof. Dr. Johannes Quaas, Theoretische Meteorologie, Universit├Ąt Leipzig Particles in the atmosphere - aerosols - may serve as cloud condensation nuclei. Increases in aerosol concentrations thus change cloud droplet concentrations and thus enhance the brightness of clouds. Such aerosol-cloud interactions exert a cooling effect on climate. The presentation will explain how we learned to quantify this climate forcing from climate models and satellite observations. It will detail where open questions are, and what implications small or large aerosol-cloud effects have on climate sensitivity as well as past and future climate change. The improvement of air quality implies reduced aerosol forcing and thus enhanced warming currently and in the future, but also climate intervention by artificially enhancing the cloud brightness is in discussion.

Particle Colloquium

Simulation-Basted Inference Techniques and its....

Aishik Ghosh, LBL, Berkeley, CERN

Astronomy colloquium

Tuesday, 21. May 2024 4:30 pm  Interchange magnetic reconnection as the driver of the fast solar wind

Professor James Drake, Institute for Physical Science and Technology, University of Maryland The mechanism that drives the solar wind has been a topic of extensive scientific debate since the 1960's when the existence of the solar wind was confirmed with spacecraft observations. In its recent closest approaches to the sun the Parker Solar Probe (PSP) spacecraft is revealing wind structure not seen by spacecraft at 1AU. The bursty radial flows and associated local reversals of the radial magnetic field (switchbacks) exhibit a spatial periodicity that is linked to that of network magnetic field near the solar surface (Bale et al. 2021; ApJ 923,174). The observations point to magnetic reconnection between open and closed magnetic flux in coronal holes (interchange reconnection) as the driver of these bursts. The corresponding enhancements in plasma pressure, wind speed, and energetic ions further suggest that interchange reconnection is the fundamental source of energy that drives the fast solar wind. We use the PSP data along with the basic characteristics of reconnection to deduce the local properties of interchange reconnection near the solar surface, including the characteristic strength of the reconnecting magnetic, the ambient density, the rate of reconnection and associated rate of energy release (Bale et al. 2023; Nature, vol. 628). An important conclusion of the analysis is that coronal interchange reconnection is in the collisionless regime and that the energy released by interchange reconnection is sufficient to drive the wind. Analytical estimates are supported by particle-in-cell simulations of interchange reconnection that establish that the structure of reconnection exhausts match PSP measurements. The spectra of energetic protons and alpha particles from the simulations, which take the form of powerlaws at high energy, also match the observations by the PSP. The bursty nature of interchange reconnection has implications for the development of the measured turbulence in the solar wind, which is currently being explored. These results have significant implications for understanding the winds produced by objects throughout the universe. Those unable to attend the colloquium in person are invited to participate online through Zoom (Meeting ID: 942 0262 2849, passcode 792771) using the link: https://eu02web.zoom-x.de/j/94202622849?pwd=dGlPQXBiUytzY1M2UE5oUDRhbzNOZz09 During his visit to Heidelberg, Professor Drake will be available for meetings by arrangement with his host, Brian Reville (brian.reville@mpi-hd.mpg.de)

Center for Quantum Dynamics Colloquium

Wednesday, 22. May 2024 4:30 pm  Dissipation in Bose-Einstein Condensates

Prof. Dr. Herwig Ott, Fachbereich Physik, TU Kaiserslautern