Tidal tails in cold dark matter cosmologies

We study the formation of tidal tails in pairs of merging disc galaxies with structural properties motivated by current theories of cold dark matter (CDM) cosmologies. In a recent study, Dubinski, Mihos & Hernquist showed that the formation of prominent tidal tails can be strongly suppressed by massive and extended dark haloes. For the large halo-to-disc mass ratio expected in CDM cosmologies their sequence of models failed to produce strong tails like those observed in many well-known pairs of interacting galaxies. In order to test whether this effect can constrain the viability of CDM cosmologies, we construct N ‐body models of disc galaxies with structural properties derived in analogy to the recent analytical work of Mo, Mao & White. With a series of self-consistent collisionless simulations of galaxy–galaxy mergers we demonstrate that even the discs of very massive dark haloes have no problems developing long tidal tails, provided the halo spin parameter is large enough. For our class of models, the halo-to-disc mass ratio is not a good indicator of the ability to produce tails. Instead, the relative size of disc and halo or, alternatively, the ratio of circular velocity to local escape speed at the half mass radius of the disc is a more useful criterion. This result holds in all CDM models. While tidal tails can provide useful information on the structure of galaxies, it thus appears unlikely that they are able to constrain the values of the cosmological parameters within these models.     

Antarktis: Das CCAMLR-Übereinkommen (Convention on the Conservation of Antarctic Marine Living Resources) und die illegale Überfischung der südlichen Ozeane

Ocean Dynamics - Die Konvention zum Schutz der marinen lebenden Ressourcen der Antarktis (CCAMLR) wurde 1982 ins Leben gerufen. Im Hinblick auf die sich in der Antarktis rapide entwickelnde...     

Very high electrical conductivity beneath the Münchberg Gneiss area in Southern Germany: implications for horizontal transport along shear planes

New magnetotelluric data from the Münchberg Gneiss complex in Southern Germany reveal a zone of extremely high electrical conductivity. 1-D modelling of the data is justified in the period range 0.01 to 10  s. At least three layers are required to explain the steepness of the apparent resistivity curves, and the best-fitting models comprise four layers with successively higher conductivities. The layers of highest conductivity at depths between 2.2 and 3.6  km correlate with pronounced bands of high seismic reflectivity (profile DEKORP 85-4N). The Münchberg complex is today widely recognized as a tectonic klippe, consisting of rocks whose metamorphic and stratigraphic order is inverted rather than overturned. The material was transported into its present position by predominantly horizontal tectonic forces along shear zones. We interpret the high conductivity and high reflectivity as remnants of this transport process.     

Digital elevation models derived from airborne laser scanning point clouds: appropriate spatial resolutions for multi‐temporal characterization and quantification of geomorphological processes

Digital terrain models (DTMs) are a standard data source for a variety of applications. DTM differencing is also widely used for detection and quantification of topographic changes. While several investigations have been made on the accuracy of DTMs, calculated from different kinds of input data, little has been published on the error of DTM differencing, specifically for the quantification of geomorphological processes. In this study, an extensive, multi‐temporal set of airborne laser scanning (ALS) data is used to investigate the accuracy of topographic change calculations in a high alpine environment, caused by different geomorphic processes. Differences from DTMs with cell sizes ranging from 0.25 m to 10 m were calculated and compared to very accurate point‐to‐point calculations for a variety of processes and in nearby stable areas which show no significant surface changes. The representativeness of the DTM differences is then compared to the terrain slope and surface roughness of the investigated areas to show the influence of these parameters on the errors in the differences. Those errors are then taken into account for analyses of the applicability of different cell sizes for the investigation of geomorphic processes with different magnitudes and over different time periods. The analyses show that the error of DTM differences increases with lower point densities and higher roughness and slope values. The higher the error, the greater the differences between two elevation datasets have to be in order to quantify certain morphodynamic processes. Lower point densities and higher roughness and slope values require greater process rates or longer time intervals in order to obtain valid results. Copyright © 2013 John Wiley & Sons, Ltd.     

From new political organizations to changing moral geographies: Unpacking global civil society

The discourse of globalization suggests that territorial and cultural boundaries are increasingly insignificant or even disappearing in today's `world of flows'. More recently, this notion of borderlessness has also suffused broad reaches of the imagination of policy-makers and social scientists in the Western world. Thus, the term `global civil society' was coined to capture the experience and impact of transnational environmental and human rights activism. In this paper, however, it is argued that the concept remains both undertheorized and empirically dubious. In order to analytically `unpack' the concept, I provide a brief summary of an empirical research project on networks of new political organizations in South Asia and the West. The evidence assembled suggests the need to reconceptualize the geographies of transborder solidarity and concern beyond the rhetoric of global civil society.     

Twenty years of soil erosion on-farm measurement: Annual variation,spatial distribution and the impact of conservation programmes for soil loss rates in Switzerland

Long-term field assessments of soil erosion on the landscape scale are very scarce. Such monitoring programmes create sound data regarding severity, extent, frequency and types of soil erosion and the vulnerability of particular crops. In a 20-year monitoring programme between 1997 and 2017, accurate erosion damage mapping was carried out on 203 fields on arable land in the Canton of Berne (Switzerland). During 115 field inspections, 4060 field years and 2165 mapped erosion systems were recorded. Because several soil conservation programmes were implemented during this period, two 10-year time periods (1st October 1997 to 30th September 2007 [P1] and 1st October 2007 to 30th September 2017 [P2]) were established and compared. The soil erosion rate was already low in P1 (mean: 0.74 t ha⁻¹ year⁻¹), but decreased significantly in P2 (mean: 0.20 t ha⁻¹ year⁻¹). During P1 and P2, respectively, 12 and 42% of the fields were without any visible erosion. Within 10 years, erosion occurred on each field on average 3.2 times in P1 and only 1.3 times in P2. Soil losses are spatially concentrated and linked to topographically defined pathways (thalwegs, slope depressions) or human-made flow pathways (wheel tracks, tramlines, headlands). Financial incentives, rising awareness among farmers, innovative contractor farmers and good extension service of cantonal agencies helped conserve 85% of the arable land in the study area with conservation tillage methods by 2015. As a result, soil erosion was significantly reduced. The field-based measurements show that a significant decrease in soil erosion is possible by changes in soil tillage practices and that erosion control is feasible almost everywhere under real-life conditions on farmers’ fields. In this respect, the Frienisberg region is a case example of successful erosion control. © 2020 John Wiley & Sons, Ltd.     

Annual deformation signals from homogeneously reprocessed VLBI and GPS height time series

The first part of this paper compares homogeneously reprocessed Very Long Baseline Interferometry (VLBI) and Global Positioning System (GPS) long-term height series from 1994 to 2007. The data analysis used fully adapted state-of-the-art models (like VMF1 and a priori zenith delays from ECMWF) for the GPS and VLBI processing. The series are compared in terms of long-term non-linear behaviour, harmonic and mean annual signals (not necessarily of harmonic nature). The similarity between both techniques is very good (especially the mean annual signals), which is assumed to be due to the adapted models and consistent reprocessing of both series. As two almost independent observing techniques see the same annually recurring signals at almost all co-located sites, we expect a good geophysical interpretability as integral vertical deformation. For the second part of this paper, the height time series of 161 suitable GPS sites (of the same solution as before) are used to determine a harmonic and a mean annual signal for each of them. Comparing the annual signals for this big dataset visually to GRACE-determined load deformations described in other publications, we find good agreement. This puts emphasis to the assumption that our height data have a lot of potential to be interpreted as geophysical signals. Out of these 161, 131 are grouped to 55 clusters, if at least two nearby (some thousand kilometres) sites show similar mean annual signals, which are thus confirmed to be real regional deformation, not local or technical artefacts. These 55 signals are presented on a “world map” of regional average mean annual height signals, as easy-to-handle tool to validate geophysical models. The data of these measured regional mean annual signals can be downloaded from a web-page for numerical analysis.     

A parameterization for modelling the meteorological effects of tall forests — A case study of a large clearing

A parameterization scheme has been developed to describe the effects of a tall forest on the mean structure of the atmospheric boundary layer (ABL). The main advantage of the scheme is that dynamical and thermodynamical effects of a forest surface can be simulated satisfactorily using only a coarse-grid resolution within numerical models. Thereby, the canopy layer is parameterized as a quasi-subgrid phenomenon. This makes it possible to study meteorological phenomena within the ABL in a very economical way (with respect to computational time) whereby, nevertheless, more detailed information concerning the forest surface is taken into account than could be done using the same grid resolution and quite simple assumptions describing the canopy, e.g., the effective roughness.The applicability in numerical models is shown by using a slightly modified two-dimensional version of the mesoscale model FITNAH. For comparison, simulations with a high numerical grid resolution within the canopy have been carried out.Model results reproduce the known meteorological phenomena in forested areas, e.g., a stable thermal stratification near the surface during the day, and at night, a neutral — or slightly unstable condition — and, in general, reduced windspeed within the canopy layer.Diurnal variations and spatial distributions of temperature and humidity are found to be similar for both cases. Also, a thermally-induced local circulation system in the vicinity of a large clearing has been simulated satisfactorily.A comparison of the calculated results verifies that the parameterization scheme is quite suitable for simulating the effects of plant canopies on the distributions of meteorological variables in the ABL.     

Can Water Vapour Raman Lidar Resolve Profiles of Turbulent Variables in the Convective Boundary Layer?

High-resolution water vapour measurements made by the Atmospheric Radiation Measurement (ARM) Raman lidar operated at the Southern Great Plains Climate Research Facility site near Lamont, Oklahoma, U.S.A. are presented. Using a 2-h measurement period for the convective boundary layer (CBL) on 13 September 2005, with temporal and spatial resolutions of 10 s and 75 m, respectively, spectral and autocovariance analyses of water vapour mixing ratio time series are performed. It is demonstrated that the major part of the inertial subrange was detected and that the integral scale was significantly larger than the time resolution. Consequently, the major part of the turbulent fluctuations was resolved. Different methods to retrieve noise error profiles yield consistent results and compare well with noise profiles estimated using Poisson statistics of the Raman lidar signals. Integral scale, mixing-ratio variance, skewness, and kurtosis profiles were determined including error bars with respect to statistical and sampling errors. The integral scale ranges between 70 and 130 s at the top of the CBL. Within the CBL, up to the third order, noise errors are significantly smaller than sampling errors and the absolute values of turbulent variables, respectively. The mixing-ratio variance profile rises monotonically from ≈0.07 to ≈3.7 g² kg⁻² in the entrainment zone. The skewness is nearly zero up to 0.6 z/z _i , becomes −1 around 0.7–0.8 z/z _i , crosses zero at about 0.95 z/z _i , and reaches about 1.7 at 1.1 z/z _i (here, z is the height and z _i is the CBL depth). The noise errors are too large to derive fourth-order moments with sufficient accuracy. Consequently, to the best of our knowledge, the ARM Raman lidar is the first water vapour Raman lidar with demonstrated capability to retrieve profiles of turbulent variables up to the third order during daytime throughout the atmospheric CBL.