Karl Friedrich Almstedt - scientist, teacher, and co-founder of the German Geophysical Society

The German Geophysical Society was founded in 1922 as the Deutsche Seismologische Vereinigung. One of the 24 founders of this society was Karl Friedrich Almstedt. Born in 1891 and deceased in 1964, Almstedt represents a generation of academics and scientists who grew up during the decline of the European empires, experiencing the devastations of the two World Wars and the cruelties of the Nazi era as well as the resurrection of academic and cultural life in post-war Germany. A detailed biographical sketch of Karl Almstedt’s life is presented through historical notes on his social, political, and scientific environment

Propagation pattern of low frequency waves in the terrestrial magnetosheath

International audiencePropagation pattern (distribution of phase velocities) is determined in three dimensions in the terrestrial magnetosheath on a statistical basis using Cluster spacecraft observations. It is found that the anti-sunward propagation dominates and that the propagation direction is toward the magnetosheath flank at smaller zenith angles, while it is toward the magnetopause at larger angles. This pattern is axially symmetric regardless of the interplanetary magnetic field direction and agrees qualitatively with the density gradient directions in a hydromagnetic flow model of the magnetosheath, suggesting that the wave refraction mechanism is more significant than the wave drift effect

On the Anthropogenic and Natural Injection of Matter into Earth's Atmosphere

Every year, more and more objects are sent to space. While staying in orbit at high altitudes, objects at low altitudes reenter the atmosphere, mostly disintegrating and adding material to the upper atmosphere. The increasing number of countries with space programs, advancing commercialization, and ambitious satellite constellation projects raise concerns about space debris in the future and will continuously increase the mass flux into the atmosphere. In this study, we compare the mass influx of human-made (anthropogenic) objects to the natural mass flux into Earth's atmosphere due to meteoroids, originating from solar system objects like asteroids and comets. The current and near future significance of anthropogenic mass sources is evaluated, considering planned and already partially installed large satellite constellations. Detailed information about the mass, composition, and ablation of natural and anthropogenic material are given, reviewing the relevant literature. Today, anthropogenic material does make up about 2.8 % compared to the annual injected mass of natural origin, but future satellite constellations may increase this fraction to nearly 40 %. For this case, the anthropogenic injection of several metals prevails the injection by natural sources by far. Additionally, we find that the anthropogenic injection of aerosols into the atmosphere increases disproportionately. All this can have yet unknown effects on Earth's atmosphere and the terrestrial habitat.Comment: 24 pages, 4 figures, submitted to Advances in Space Researc

BepiColombo - Zur Genese eines Weltraumprojektes

Reisen in den Weltraum sind nicht nur weite Reisen, sondern fordern auch Zeit. Für den Sommer 2013 planen die europäische Weltraumagentur ESA und ihr japanischer Partner JAXA den Start zweier Satelliten, die sechs Jahre später in eine Umlaufbahn um den Planeten Merkur einschwenken sollen, um dort mindestens zwei Jahre den der Sonne nächsten Planeten unseres Sonnensystem wissenschaftlich zu erkunden. Die ersten Planungen für dieses Projekt gehen auf Überlegungen Mitte der achtziger Jahre des vergangenen Jahrhunderts zurück. Wenn also die BepiColombo-Raumschiffe 2021 ihre Mission erfüllt haben, dann sind mehr als 30 Jahre vergangen, während derer sich die europäische Wissenschaftsgemeinde mit der Planung und Realisierung einer Merkurmission beschäftigt hat. Die BepiColombo-Mission ist somit ein Beispiel wissenschaftlicher Großforschung, für das nicht nur politische und finanzielle, wissenschaftliche und technische Probleme zu lösen waren, sondern für das auch über mindestens eine Wissenschaftlergeneration hinweg Kontinuität in der Projektabwicklung zu fordern ist

A mode filter for plasma waves in the Hall-MHD approximation

International audienceA filter method is presented which allows a qualitative and quantitative identification of wave modes observed with plasma experiments on satellites. Hitherto existing mode filters are based on the MHD theory and thus they are restricted to low frequencies well below the ion cyclotron frequency. The present method is generalized to cover wave modes up to the characteristic ion frequencies. The spectral density matrix determined by the observations is decomposed using the eigenvectors of the linearized Hall-MHD equations. As the wave modes are dispersive in this formalism, a precise determination of the k->-vectors requires the use of multi-point measurements. Therefore the method is particularly relevant to multi-satellite missions. The method is tested using simulated plasma data. The Hall-MHD filter is able to identify the modes excited in the model plasma and to assign the correct energetic contributions. By comparison with the former method it is shown that the simple MHD filter leads to large errors if the frequency is not well below the ion cyclotron frequency. Further the range of validity of the linear theory is examined rising the simulated wave amplitudes

Concerning the detection of electromagnetic knot structures in space plasmas using the wave telescope technique

The wave telescope technique is broadly established in the analysis of spacecraft data and serves as a bridge between local measurements and the global picture of spatial structures. The technique is originally based on plane waves and has been extended to spherical waves, phase shifted waves as well as planetary magnetic field representation. The goal of the present study is the extension of the wave telescope technique using electromagnetic knot structures as a basis. As the knots are an exact solution of Maxwell's equations they open the door for a new modeling and interpretation of magnetospheric structures, such as plasmoids.</p

Spin axis offset calibration on THEMIS using mirror modes

A newly developed method for determining spin axis offsets of magnetic field instruments on spacecraft is applied to THEMIS. The formerly used determination method, relying on solar wind Alfvénic fluctuations, was rarely applicable due to the orbital restrictions of the mission. With the new procedure, based on magnetic field observation of mirror modes in the magnetosheath, updated spin axis offsets can be estimated approximately once per year. Retrospective calibration of all THEMIS magnetic field measurements is thereby made possible. Since, up to this point, spin axis offsets could hardly ever be calculated due to the mission's orbits, this update represents a substantial improvement to the data. The approximate offset stability is estimated to be &lt; 0.75 nT year−1 for the complete course of the mission