VLBI-derived troposphere parameters during CONT08

Time-series of zenith wet and total troposphere delays as well as north and east gradients are compared, and zenith total delays (ZTD) are combined on the level of parameter estimates. Input data sets are provided by ten Analysis Centers (ACs) of the International VLBI Service for Geodesy and Astrometry (IVS) for the CONT08 campaign (12?C26 August 2008). The inconsistent usage of meteorological data and models, such as mapping functions, causes systematics among the ACs, and differing parameterizations and constraints add noise to the troposphere parameter estimates. The empirical standard deviation of ZTD among the ACs with regard to an unweighted mean is 4.6?mm. The ratio of the analysis noise to the observation noise assessed by the operator/software impact (OSI) model is about 2.5. These and other effects have to be accounted for to improve the intra-technique combination of VLBI-derived troposphere parameters. While the largest systematics caused by inconsistent usage of meteorological data can be avoided and the application of different mapping functions can be considered by applying empirical corrections, the noise has to be modeled in the stochastic model of intra-technique combination. The application of different stochastic models shows no significant effects on the combined parameters but results in different mean formal errors: the mean formal errors of the combined ZTD are 2.3?mm (unweighted), 4.4?mm (diagonal), 8.6?mm [variance component (VC) estimation], and 8.6?mm (operator/software impact, OSI). On the one hand, the OSI model, i.e. the inclusion of off-diagonal elements in the cofactor-matrix, considers the reapplication of observations yielding a factor of about two for mean formal errors as compared to the diagonal approach. On the other hand, the combination based on VC estimation shows large differences among the VCs and exhibits a comparable scaling of formal errors. Thus, for the combination of troposphere parameters a combination of the two extensions of the stochastic model is recommended.     

Effect of Ocean Spray on Vertical Momentum Transport Under High-Wind Conditions

Two mathematical models are proposed detailing the influence of ocean spray on vertical momentum transport under high-wind conditions associated with a hurricane or severe storm. The first model is based on a turbulent kinetic energy (TKE) equation and accounts for the so-called lubrication effect due to the reduction of turbulence intensity. The second model is based on Monin–Obukhov similarity (MOS) and uses available experimental data. It is demonstrated that the flow acceleration is negligible for wind speeds below a certain critical value due to the fact that the spray volume concentration is low for such speeds. For wind speeds higher than the critical value, the spray concentration rapidly increases, which results in significant flow acceleration. Both models produce qualitatively similar results for all turbulent flow parameters considered. It was found that the MOS-based model tends to predict a noticeably stronger lubrication effect than the TKE-based model, especially for lower wind speeds. The results of model calculations are in very good agreement with available experimental data for the spray production values near the upper bound. It is also shown that neither the value of the turbulent Schmidt number in the TKE-based model nor the choice of a stability profile function affects the spray-laden flow dynamics significantly.     

Scenarios with MIT integrated global systems model: significant global warming regardless of different approaches

A wide variety of scenarios for future development have played significant roles in climate policy discussions. This paper presents projections of greenhouse gas (GHG) concentrations, sea level rise due to thermal expansion and glacial melt, oceanic acidity, and global mean temperature increases computed with the MIT Integrated Global Systems Model (IGSM) using scenarios for twenty-first century emissions developed by three different groups: intergovernmental (represented by the Intergovernmental Panel on Climate Change), government (represented by the U.S. government Climate Change Science Program) and industry (represented by Royal Dutch Shell plc). In all these scenarios the climate system undergoes substantial changes. By 2100, the CO₂ concentration ranges from 470 to 1020 ppm compared to a 2000 level of 365 ppm, the CO₂-equivalent concentration of all greenhouse gases ranges from 550 to 1780 ppm in comparison to a 2000 level of 415 ppm, oceanic acidity changes from a current pH of around 8 to a range from 7.63 to 7.91, in comparison to a pH change from a preindustrial level by 0.1 unit. The global mean temperature increases by 1.8 to 7.0°C relative to 2000. Such increases will require considerable adaptation of many human systems and will leave some aspects of the earth??s environment irreversibly changed. Thus, the remarkable aspect of these different approaches to scenario development is not the differences in detail and philosophy but rather the similar picture they paint of a world at risk from climate change even if there is substantial effort to reduce emissions.     

FESOM under coordinated ocean-ice reference experiment forcing

Characteristics of the ocean state simulated with the Finite-Element Sea-Ice Ocean Model (FESOM) under the normalized year forcing of Coordinated Ocean-ice Reference Experiments (COREs; Griffies et al., Ocean Model 26:1–46, 2009) are compared with those of other models participating in COREs. In contrast to these models, FESOM is run on an unstructured mesh (with resolution varying between 20 and 150 km). It is shown that the ocean state simulated by FESOM is in most cases within the spread of other models, demonstrating that the unstructured mesh technology has reached the stage when it becomes a reliable tool for studying the large-scale ocean general circulation.     

Heat budget of the surface mixed layer south of Africa

ARGO hydrographic profiles, two hydrographic transects and satellite measurements of air–sea exchange parameters were used to characterize the properties and seasonal heat budget variations of the Surface Mixed Layer (SML) south of Africa. The analysis distinguishes the Subtropical domain (STZ) and the Subantarctic Zone (SAZ), Polar Frontal Zone (PFZ) and Antarctic Zone (AZ) of the Antarctic Circumpolar Current. While no Subantarctic Mode Water forms in that region, occurrences of deep SML (up to ∼450 m) are observed in the SAZ in anticyclones detached from the Agulhas Current retroflection or Agulhas Return Current. These are present latitudinally throughout the SAZ, but preferentially at longitudes 10–20° E where, according to previous results, the Subtropical Front is interrupted. Likely owing to this exchange window and to transfers at the Subantarctic Front also enhanced by the anticyclones, the SAZ shows a wide range of properties largely encroaching upon those of the neighbouring domains. Heat budget computations in each zone reveal significant meridional changes of regime. While air–sea heat fluxes dictate the heat budget seasonal variability everywhere, heat is mostly brought through lateral geostrophic advection by the Agulhas Current in the STZ, through lateral diffusion in the SAZ and through air–sea fluxes in the PFZ and AZ. The cooling contributions are by Ekman advection everywhere, lateral diffusion in the STZ (also favoured by the ∼10° breach in the Subtropical Front) and geostrophic advection in the SAZ. The latter likely reflects an eastward draining of water warmed through mixing of the subtropical eddies.     

Trace-element study and age dating of zircon from chromitites of the Bushveld Complex (South Africa)

The layered Bushveld Complex hosts a number of chromitite layers, which were found to contain significant amounts of zircon grains compared with adjacent silicate rocks. Cathodoluminescent-dark, partially metamict cores and transparent rims of composite zircon grains were analyzed for trace elements with SIMS and LA-ICPMS techniques. The cores are enriched in REE, Y, Th and U and are characterized by distinctly flatter REE patterns in contrast to those of the rims and transparent homogenous crystals. Zircon from the different stratigraphic units has specific Th/U ratios, the highest of which (1.5–4) occurs in a Merensky Reef zircon core. The Ti content of Bushveld zircon ranges from 12 to 52 ppm correlating to a crystallization temperature range of 760–930 °C. The geochemical characteristics of the first zircon generation are consistent with its high-temperature crystallization as the first major U, Th and REE acceptor from a highly-evolved residue of the high-Mg basalt magma, whereas the rims and coreless crystals have crystallized from percolating intercumulus liquid of new influx of the same magma. U-Pb SHRIMP dating of zircon cores and rims does not reveal a distinguishable difference between their ages indicating the absence of inherited zircon. Concordia ages of 2,051?±?9 Ma (2σ, MSWD?=?0.1) and 2,056?±?5 Ma (2σ, MSWD?=?0.05) for zircons from the Merensky Reef and the Upper Platreef located equally near the top of the Critical Zone are in agreement with published ages for the Merensky Reef. Zircon from the deeper-seated Lower Group, Middle Group and Lower Platreef chromitites yields younger concordia ages that may reflect prolonged late-stage volatile activity.     

The crystal structure of ilinskite, NaCu5O2(SeO3)2Cl3, and review of mixed-ligand CuOmCln coordination geometries in minerals and inorganic compounds

The crystal structure of ilinskite, NaCu₅O₂(SeO₃)₂Cl₃, a rare copper selenite chloride from volcanic fumaroles of the Great fissure Tolbachik eruption (Kamchatka peninsula, Russia), has been solved by direct methods and refined to R ₁?=?0.044 on the basis of 2720 unique observed reflections. The mineral is orthorhombic, Pnma, a?=?17.769(7), b?=?6.448(3), c?=?10.522(4) Å, V?=?1205.6(8) ų, Z?=?4. The The CuO_mCl_n coordination polyhedra share edges to form tetramers that have 'additional' O1 and O2 atoms as centers. The O1Cu₄ and O2Cu₄ tetrahedra share common Cu atoms to form [O₂Cu₅]⁶⁺ sheets. The SeO₃ groups and Cl atoms are adjacent to the [O₂Cu₅]⁶⁺ sheets to form complex layers parallel to (100). The Na⁺ cations are located in between the layers. A review of mixed-ligand CuO_mCl_n coordination polyhedra in minerals and inorganic compounds is given. There are in total 26 stereochemically different mixed-ligand Cu-O-Cl coordinations.     

A series expansion of the solid Earth tide effect on geopotential

We develop analytical series representing the main part of corrections to the geopotential coefficients caused by the solid Earth tides, where Love numbers are assumed to be frequency-independent. The series are compact, precise and valid over 1800 A.D.–2200 A.D. The maximum difference between the corrections given by the analytical series and their numerical values, obtained with use of the DE/LE-423 planetary/lunar ephemerides, does not exceed $0.7\times 10^{-12}$ . A new algorithm is proposed for calculating amplitudes of the additional variations of the geopotential coefficients for frequency dependence of Love numbers. It uses the representation of the Earth tide-generating potential in the standard HW95 format and takes into account the phase of tidal waves. Corrections of up to $2\times 10^{-12}$ to the published by the IERS Conventions (2010) amplitudes of the additional variations of the geopotential coefficients are suggested. Examples of use of the obtained series in analytical theories of motion of low-altitude STARLETTE and high-altitude ETALON-1 satellites are given.     

High-order kernels for Riemannian wavefield extrapolation

Riemannian wavefield extrapolation is a technique for one‐way extrapolation of acoustic waves. Riemannian wavefield extrapolation generalizes wavefield extrapolation by downward continuation by considering coordinate systems different from conventional Cartesian ones. Coordinate systems can conform with the extrapolated wavefield, with the velocity model or with the acquisition geometry. When coordinate systems conform with the propagated wavefield, extrapolation can be done accurately using low‐order kernels. However, in complex media or in cases where the coordinate systems do not conform with the propagating wavefields, low order kernels are not accurate enough and need to be replaced by more accurate, higher‐order kernels. Since Riemannian wavefield extrapolation is based on factorization of an acoustic wave‐equation, higher‐order kernels can be constructed using methods analogous to the one employed for factorization of the acoustic wave‐equation in Cartesian coordinates. Thus, we can construct space‐domain finite‐differences as well as mixed‐domain techniques for extrapolation. High‐order Riemannian wavefield extrapolation kernels improve the accuracy of extrapolation, particularly when the Riemannian coordinate systems does not closely match the general direction of wave propagation.     

Optimizing fixed observational assets in a coastal observatory

Proliferation of coastal observatories necessitates an objective approach to managing of observational assets. In this article, we used our experience in the coastal observatory for the Columbia River estuary and plume to identify and address common problems in managing of fixed observational assets, such as salinity, temperature, and water level sensors attached to pilings and moorings. Specifically, we addressed the following problems: assessing the quality of an existing array, adding stations to an existing array, removing stations from an existing array, validating an array design, and targeting of an array toward data assimilation or monitoring.