VSR Seminar
1st talk: ICON Performance Analysis and Simulations for the Project “High Definition Clouds and Precipitation for advancing Climate Prediction – HD(CP)2”
Speaker: Dr. Catrin Meyer, JSC
Clouds and precipitation are an essential element of the climate system, but they are difficult to account for in theories and models. Clouds significantly influence the atmospheric radiative forcing and modulate many feedback processes of the Earth system. Interactions with the terrestrial biosphere, sea-ice interactions, and bio-geochemical interactions are critically dependent on the cloud-precipitation representation. Atmospheric clouds and precipitation are small- and meso-scale phenomena, which cannot be modeled explicitly on the global scale with current computer architectures and hence are parametrized in global climate models. Global climate simulations today show significant biases in precipitation patterns, which are related to insufficient parametrization of these processes.
HD(CP)2 is a coordinated initiative to improve our understanding of cloud and precipitation events, to increase the quality and number of available observations, and to evaluate and improve modeling capabilities. One group of project partners develops a highly scalable regional weather model which will be used to provide a series of ultrahigh resolution summer-season hind-casts over Germany. Aiming on a horizontal grid spacing of approximately 100 m (and vertical grid spacings considerably finer) over domains of 1000 km, the new HD(CP)2 model will help to understand current limits on cloud-precipitation modeling and parametrization skills. The scale of the simulation allows the explicit representation and analysis of entirely new phenomena.
Due to the fine horizontal grid resolution and simulation time steps the ICONLES model must be highly parallelized and optimized for Peta-scale systems. Numerous performance analyses of the ICON code with different MPI/OpenMP task/thread-combinations on JUQUEEN were done. The aim of the performance analyses was to find the best model-configuration, e.g. in terms of MPI/OpenMP splitting and to identify bottlenecks and scaling problems specifically related to massive-parallel systems. The performance analyses of the ICON code on JUQUEEN were done for different horizontal resolutions of 420 m, 240 m and 120 m. Our efforts lead to substantial performance improvements of the ICON code on JUQUEEN and will enable large-scale simulations of HD(CP)2 in phase 2 of the project.
2nd talk: Radionuclide uptake by secondary minerals: The role of solid solution formation
Speaker: Dr. Victor Vinograd, IEK-6
Currently, several European countries investigate the feasibility of a direct disposal of spent nuclear fuel in deep geological formations. The main concern is the long-term safety of the deposition. Evidently, the safety can be assessed and demonstrated only theoretically. One should be able to predict geochemical consequences of an interaction of a waste form with cladding materials, with surrounding rocks and with ground waters, which could also come into play. Although our abilities in geochemical modelling of such a complex system are still limited, we know already that the likely consequence of this interaction would be the formation of various secondary minerals. Importantly, the formation of such minerals would provide a mechanism for radionuclide re-immobilization.
For example, the migration of Ba out of a waste form into a host rock under oxidized conditions will likely cause a crystallization of barium sulfate, BaSO4, while the subsequent migration of Ra will lead to a re-crystallization of the previously formed barite and the formation of a Ba-rich (Ba;Ra)SO4 solid solution. Our recent research at the IEK-6 shows that in this scenario a further Ra migration will be essentially prevented. The main reason for the almost complete removal of Ra out of the aqueous phase is the formation of a dilute solid solution, where the contaminant is stabilized by the configurational entropy. Our efforts within the JIEK60 project consisted in the development of a thermodynamic model for the ternary (Ba;Ra; Sr)SO4 solid solution. This task required very demanding first-principles based calculations and extensive Monte Carlo simulations. Due to these efforts we are now able to quantitatively model the system of (Ba;Ra; Sr)SO4 + H2O and to demonstrate a close attainment of the thermodynamic equilibrium in our experimental studies.
Anyone interested is cordially invited to participate in this seminar.