A two million year old signal of 60Fe was detected in several terrestrial deep-sea archives and in lunar samples. This long-lived isotope is not produced on Earth, however, it is generated in massive stars and ejected during supernova explosions. The recent injection of 60Fe into the solar system coincides with the formation of the Local Bubble - a large cavity in the interstellar medium produced by multiple supernovae - into which our solar system is embedded. The most likely sources are stellar explosions within a moving group that passed the solar neighborhood, and whose surviving members are now in the Sco-Cen association. We have traced the trajectories of the member stars back in time and calculated the most probable explosion sites of the perished stars. By determining their masses and explosion times, we found a sequence of supernovae starting 13 Myr ago. With analytical and numerical methods we modeled the Local Bubble and, as a consequence of its formation, the terrestrial 60Fe signature. Similar calculations with another long-lived radionuclide, 26Al, show only a marginal supernova-signal. Accelerator mass spectrometry measurements of 26Al within samples of four deep-sea sediment cores from the Indian Ocean confirm this result. The data decreases exponentially towards larger depths as expected from 26Al produced in the Earth's atmosphere, which hides a contribution from nearby supernovae. [mehr]

Mit unserer Sprache beschreiben wir unsere Wirklichkeit. Was wir benennen ist auch vorhanden. Für was wir kein Wort haben, kann sich auch unser Hirn schlecht vorstellen. Unser Sprachgebrauch ist Teil unserer Wirklichkeit und sie beeinflusst unsere Wahrnehmung. Soweit die Sprachphilosophie. [mehr]

While the dynamics of the atmosphere can be described by model equations which are derived from first principles, the climate is ruled by feedback loops many of which are known only on a phenomenological level. Irrespective of the foundations of the model, both weather and climate are chaotic: their evolution depends sensitively on initial conditions and on control parameters. Therefore, predictions by modeling are usually complemented by the analysis of empirical data and their extrapolation into the future. In this talk, we present some relevant aspects of model based and statistical forecasting of weather and climate. Although the quality of the weather forecast for most of us is just an issue of convenience, I will discuss the possibility for a strict limit to the number of days ahead for which weather forecast can be successful. More relevant, a clear prediction of how climate will change will be crucial for mitigation and adaptation strategies, which have to be implemented in due time. Climate change goes along with changes in the dynamics, visible through the change of frequency of different regional weather patterns and in the meandering of the jet stream. Predictions here suffer from large time scales of relaxation and of exploration of the phase space, as we will exemplify for the warming trend in Germany. [mehr]