Warum uns das Eis unter den Fingern zerrinnt – Gletschereis und Klimawandel

Eingeladener Vortrag zum 2. Workshop zur Einstimmung auf die Generalversammlung der Internationalen Union für Geodäsie und Geophysik, Juli 2023 in Berlin. Der Vortrag gibt einen Überblick über ausgewählte Aspekte des Klimawandels, insbesondere die Auswirkungen in den Polarregionen und der Kryosphäre

Mass-loading and parallel magnetized shocks

Recent observations at comets Giacobini-Zinner and Halley suggest that simple non-reacting gas dynamics or MHD is an inappropriate description for the bow shock. The thickness of the observed (sub)shock implies that mass-loading is an important dynamical process within the shock itself, thereby requiring that the Rankine-Hugoniot conditions possess source terms. This leads to shocks with properties similar to those of combustion shocks. We consider parallel magnetized shocks subjected to mass-loading, describe some properties which distinguish them from classical MHD parallel shocks, and establish the existence of a new kind of MHD compound shock. These results will be of importance both to observations and numerical simulations of the comet-solar wind interaction

Hypervelocity dust particle impacts observed by the Giotto Magnetometer and Plasma Experiments

We report thirteen very short events in the magnetic field of the inner magnetic pile‐up region of comet Halley observed by the Giotto magnetometer experiment together with simultaneous plasma data obtained by the Johnstone plasma analyzer and the ion mass spectrometer experiments. The events are due to dust impacts in the milligram range on the spacecraft at the relative velocity between the cemetery dust and the spacecraft of 68 km/sec. They are generally consistent with dust impact events derived from spacecraft attitude perturbations by the Giotto camera [Curdt and Keller, private communication]. Their characteristic shape generally involves a sudden decrease in magnetic field magnitude, a subsequent overshoot beyond initial field values and an asymptotic approach to the initial field somewhat reminiscent of the magnetic field signature after the AMPTE releases in the solar wind. These observations give a new way of analyzing ultra‐fast dust particles incident on a spacecraft

Cenozoic plate driving forces

Past studies of plate driving forces have concluded that the forces due to subducted slabs in the upper mantle and those due to the thickening of the oceanic lithosphere are the principal driving forces. We reexamine the balance of driving forces for the present-day and extend our analysis through the Cenozoic, using an analytical torque balance method which accounts for interactions between plates via viscous coupling to the induced mantle flow, We use an evolving mantle density heterogeneity field based on the last 200 Myr. of subduction to drive plate motions, an approach which has proven successful in predicting the present-day mantle heterogeneity field. We find that for plausible upper mantle viscosities the forces due to subducted slabs in the Cenozoic and Mesozoic account for in excess of 90% of plate driving forces and those due to lithospheric thickening for less than 10%

Grundlagen der Geophysik

Die vorliegenden Lecture Notes wurden im Rahmen von Vorlesungen und Praktika zwischen 1999 und 2014 an den Universitäten Frankfurt, Hamburg und Potsdam entwickelt, insbesondere als Zusatzmaterial meines Moduls Einführung in die Geophysik an der Universität Hamburg. Ziel dieser Vorlesung war die breite Einführung in die Grundlagen der Geophysik, von der großskaligen, globalen Geophysik bis zur kleinskaligen oberflächennahen und angewandten Geophysik. Das Manuskript ist vom Niveau her für Anfangssemester in einem Diplom- oder Bachelor-Studiengang in der Geophysik/Ozeanographie, den Geowissenschaften oder der Physik geeignet. Die Theorie-Kapitel sind auf wenige wichtige Formeln und elementare Ableitungen beschränkt. Meßinstrumente, Meßverfahren und Anwendungen werden ausführlich besprochen und durch Beispiele vertieft. Der erste Teil beginnt mit der Entstehung der Erde und der Planeten. Der innere Aufbau der Erde und die Dynamik der Erde folgen im dritten Kapitel. Unterkapitel sind hier bereits die globale Plattentektonik, der Wärmehaushalt der Erde und die Entstehung des Erdmagnetfeldes. Im vierten Kapitel folgt das Schwerefeld der Erde und die Ansätze der angewandten Gravimetrie. Der Sto↵ des fünften Kapitels umfasst die Geomagnetik und den remanenten Gesteinsmagnetismus. In den folgenden Kapiteln wird in weitere Verfahren der angewandten Geophysik eingeführt. Die Gleichstromelektrik wird ebenso behandelt wie Verfahren, die mit elektromagnetischen Wellen arbeiten. Dabei wird auch die Arbeitsweise des Bodenradar und der Magnetotellurik beschrieben. Im vorletzten Kapitel wird in seismische Verfahren eingeführt, die in der angewandten Geophysik eine wichtige Rolle spielen. Hierbei werden nötige Grundlagen der Theorie elastischer Wellen ebenso wie praktische Aspekte der geometrischen Ausbreitung von Raumwellen durch die Erde kurz beschrieben. Das letzte Kapitel ist den Erdbeben und der Seismologie gewidmet. Begleitende Übungsaufgaben sind auf Anfrage erhältlich

Using pressure and seismological broadband ocean data model shear wave velocities in the North Atlantic

EGU2010-10518 Seafloor compliance is the transfer function between pressure and vertical displacement at the seafloor Infragravity waves in the oceanic layer have long periods in the range of 30 – 500 s and obey a simple frequencywavenumber relation. Seafloor compliance from infragravity waves can be analyzed with single station recordings to determinate sub-seafloor shear wave velocities. Previous studies in the Pacific Ocean have demonstrated that reliable near-surface shear wave profiles can be derived from infragravity wave compliance. However, these studies indicate that, beside the water depth the compliance measurements are limited by instrument sensitivity, calibration uncertainties and possibly other effects. In this work seafloor compliance and infragravity waves are observed at two different locations in the Atlantic Ocean: the Logatchev hydrothermal field at the Mid Atlantic Ridge and the Azores (Sao Miguel Island). The data was acquired with the broadband ocean compliance station developed at the University of Hamburg as well as ocean station from the German instrument pool for amphibian seismology (DEPAS) equipped with broadband seismometers and pressure sensors. Vertical velocity and pressure data were used to calculate power spectral densities and normalized compliance along two profiles (one in each location). Power spectral densities show a dominant peak at low frequencies (0.01-0.035Hz) limited by the expected cut-off frequency, which is dependent on the water depth at each station. The peak has been interpreted as a strong infragravity wave with values between 10-14 and 10-11 (m/s2)2/Hz and 104 and 106 (Pa2)2/Hz for acceleration and pressure respectively. The results show compliance values between 10-10 and 10-8 1/Pa and its estimations take into account the coherence between seismic and pressure signals in order to confirm that the seismic signals in the infragravity waves are caused by pressure sources. Shear wave velocity models, with depth resolution from 200 to 2500 m for the deep water stations, were derived from compliance. Preliminary results indicate shear wave velocity increasing from 200 to 3500 m/s

Radiation balances and the solar constant

The radiometric concepts are defined in order to consider various types of radiation balances and relate them to the diabetic form of the energy balance. Variability in space and time of the components of the radiation field are presented. A specific concept for sweeping which is tailored to the requirements is proposed. Finally, after establishing the truncated character of the present knowledge of the radiation balance. The results of the last observations of the solar constant are given. Ground and satellite measurement techniques are discussed

Ground- and surface water mass balances to ensure protection of St Lawrence River ecostystems

No abstract available