The seasonal cycle in coupled ocean-atmosphere general circulation models

We examine the seasonal cycle of near-surface air temperature simulated by 17 coupled ocean-atmosphere general circulation models participating in the Coupled Model Intercomparison Project (CMIP). Nine of the models use ad hoc “flux adjustment” at the ocean surface to bring model simulations close to observations of the present-day climate. We group flux-adjusted and non-flux-adjusted models separately and examine the behavior of each class. When averaged over all of the flux-adjusted model simulations, near-surface air temperature falls within 2?K of observed values over the oceans. The corresponding average over non-flux-adjusted models shows errors up to ～6?K in extensive ocean areas. Flux adjustments are not directly applied over land, and near-surface land temperature errors are substantial in the average over flux-adjusted models, which systematically underestimates (by ～5?K) temperature in areas of elevated terrain. The corresponding average over non-flux-adjusted models forms a similar error pattern (with somewhat increased amplitude) over land. We use the temperature difference between July and January to measure seasonal cycle amplitude. Zonal means of this quantity from the individual flux-adjusted models form a fairly tight cluster (all within ～30% of the mean) centered on the observed values. The non-flux-adjusted models perform nearly as well at most latitudes. In Southern Ocean mid-latitudes, however, the non-flux-adjusted models overestimate the magnitude of January-minus-July temperature differences by ～5?K due to an overestimate of summer (January) near-surface temperature. This error is common to five of the eight non-flux-adjusted models. Also, over Northern Hemisphere mid-latitude land areas, zonal mean differences between July and January temperatures simulated by the non-flux-adjusted models show a greater spread (positive and negative) about observed values than results from the flux-adjusted models. Elsewhere, differences between the two classes of models are less obvious. At no latitude is the zonal mean difference between averages over the two classes of models greater than the standard deviation over models. The ability of coupled GCMs to simulate a reasonable seasonal cycle is a necessary condition for confidence in their prediction of long-term climatic changes (such as global warming), but it is not a sufficient condition unless the seasonal cycle and long-term changes involve similar climatic processes. To test this possible connection, we compare seasonal cycle amplitude with equilibrium warming under doubled atmospheric carbon dioxide for the models in our data base. A small but positive correlation exists between these two quantities. This result is predicted by a simple conceptual model of the climate system, and it is consistent with other modeling experience, which indicates that the seasonal cycle depends only weakly on climate sensitivity.     

Coral Recruitment and Regeneration on a Maldivian Reef 21 Months after the Coral Bleaching Event of 1998

Abstract. This paper describes the quantitative inventory of stony corals on a Maldivian reef after the bleaching event of 1998. The detailed data, collected in March 1999 and March 2000, comprise survival, new recruitment and regenerates. They were obtained in 6 transects laid out randomly on the reef flat, on 22 Acropora tables on 6 sites at the reef edge and on 39 Porites lobata blocks and 1 Diploastrea heliopora colony. The present cover of living zooxanthellate corals is reduced to ca. 2 – 5 % of its previous state. Acroporidae and Pocilloporidae were practically wiped out, while Poritidae survived partly and Agariciidae (esp. Pavona) are now the dominant group. New settlements on dead Acropora tables were mainly Agariciidae, followed by Acroporidae and Pocilloporidae. Regenerates on Porites were pronounced and the apparent yearly increase in mass was about threefold that of Diploastrea, which is 3 – 4 mm per year. The influence on reef ecology in terms of coral substrate and species, possible sources of larvae, change of guilds in reef builders, other species and the prospect for further development of the reef, with respect to growth versus erosion, is discussed.     

Microbial Degradation of Tar Oil Compounds under Different Redox Conditions

The microbial transformation of typical tar oil compounds such as acridine, benzo(b)thiophene, dibenzofuran, indane, and indene under different redox conditions was investigated in microcosm studies. Under aerobic conditions the inherent contamination in polluted soil as well as the added N‐, S‐, O‐ heterocyclic and homocyclic compounds were transformed predominantly apart from thiophene. 1‐Indanone was detected by RP‐HPLC‐DAD and GC‐MS as an intermediate metabolite from indane and indene. Under nitrate and sulfate reducing conditions indane, benzo(b)thiophene, and dibenzofuran were transformed in assays with the polluted soil samples from well B 65 and B 66 within 426 days, whereas they were persistent in assays with the highly polluted soil B 67. All heterocyclic and homocyclic compounds added to the non‐contaminated soil from well B 85 were not degraded under nitrate and sulfate reducing conditions, too. The results indicate that for the decision, wether natural attenuation can be implemented in the remediation of contaminated site, in addition to BTEX and PAHs especially the fate of further tar oil compounds in anoxic aquifers has to be considered.     

Die wachsende Bedeutung der Ingenieurgeologie im Zeitalter der Umweltzerstörung

Zusammenfassung Die Entwicklung der Technik führt zu immer größeren Bauprojekten im Bereich des Talsperrenbaus, Verkehrswegebaus, Untertagebaus, Bergbaus und Grundbaus. Diese großen Bauprojekte stellen in vielfacher Hinsicht eine erhebliche Belastung der Natur sowie eine Beeinträchtigung ihres Gleichgewichts dar und rufen teilweise unvorhergesehene Wechselwirkungen von Bauwerk und Baugrund hervor. Die technische Entwicklung überrollte die Natur so stürmisch, daß ihre ökologischen Folgen weder von den Wissenschaftlern noch von den Praktikern erkannt und bedacht wurden. Die Aufgaben, die sich in diesem Rahmen dem Ingenieurgeologen stellen, bestehen nicht nur in der möglichst genauen Erfassung der geologischen Parameter zur Gewährleistung der Sicherheit des Bauwerks, wirtschaftlich vertretbarer Baukosten unter optimaler Berücksichtigung geologischer Gegebenheiten, sondern sie haben auch die Vorhersage der Wechselwirkungen von Bauwerk und Baugrund sowie von Störungen des oft erstaunlich labilen Gleichgewichts von Geo-, Bio- und Atmosphäre einzubeziehen. Dabei spielen oft rezente geologische Vorgänge eine bisher in der Ingenieurgeologie viel zu wenig gewürdigte Rolle. Die Notwendigkeit, die Ingenieurgeologie schon bei der allerersten Planung, beim Entwurf und der Bauwerksüberwachung mitbestimmen zu lassen, wird an einzelnen Projekten erläutert.

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Summary Technical development leads to dams, roads, tunnels, mines and foundations of always larger dimensions. Various aspects of these projects represent a serious encumbrance of nature and an impairment of her equilibrium and can cause unforeseen interactions between structure and the earth. Development has taken place so quickly, that the ecological consequences have not been recognised or considered in many cases — neither by the scientists nor by the practitioners. The tasks, confronting the engineering geologists in this regard, consist not only in an exact investigation of the geological parameters to guarantee the safety of the construction project and to achieve project costs by taking into consideration the geological conditions, but must encompass the recognition of the interactions of construction and the earth as well as the disturbance of the often astonishingly fragile equilibrium of the geo-, bio- and atmosphere. Specifically recent geological processes are often not accounted for, despite their possibly disadvantageous effects. The necessity, that the engineering geologist contributes in all project stages from the first planning, to the design upto the surveillance of the construction, is stressed by giving examples.

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Résumé Le développement technique a conduit à des projets de construction toujour plus grands dans le domain des barrages, des routes, des tunnels, des mines et des fondations. Ces grands projets représentent sous beaucoup d'aspects une immense contreinte pour l'environnement naturel, un préjudice pour son équilibre et conduisent parfois à une interaction imprévue entre la construction et le sol. Le développement fut si rapide que les conséquences écologiques ne furent pas reconnues et prises en compte, ni par la science ni par la pratique. Les taches, qui se présentent au géologue ingénieur sur le terrain, comprennent non seulement l'investigation exacte des paramètres géologiques dans le but d'assurer la securité de la construction pour des frais raisonnables tout en prenant en compte d'une façon optimale les conditions géologiques, mais aussi la prévision de ces interactions entre l'ouvrage et le sol, ainsi que les perturbations de l'équilibre de l'environnement géologique, biologique et atmosphérique, équilibre qui est souvent éxtrêmement fragile.Les phénomènes géologiques récents ne sont que très peu considérés dans ces études. La necessité de la participation du géologue ingénieur dès le début des études pendant la conception et la surveillance de l'ouvrage est illustrée à l'aide de projets particuliers.

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Atmospheric superrotation on Saturn and Jupiter

The problem is discussed whether atmospheric superrotation is driven by internal or external torques. An integral constraint is derived which under certain conditions forbids geostrophic flow, and suggests corkscrew-shaped motion along zones of constant latitude. A momentum balance consideration restricts effective viscosities in the upper atmospheres to be much smaller than maximal eddy viscosity, perhaps as small as molecular viscosity.     

Comparison of seismic activity for Llaima and Villarrica volcanoes prior to and after the Maule 2010 earthquake

Llaima and Villarrica are two of the most active volcanoes in the Chilean Southern Volcanic Zone and presently show contrasting types of activity. Llaima is a closed vent edifice with fumarolic activity, while Villarrica has an open vent with a lava lake, continuous degassing and tremor activity. This study is focused on characterizing the relationships between volcanic and seismic activity in the months before and after the 2010 M8.8 Maule earthquake, which was located in NNW direction from the volcanoes. Time series for tremors, long-period and volcano-tectonic events were obtained from the catalogue of the Volcanic Observatory of the Southern Andes (OVDAS) and from the SFB 574 temporary volcanic network. An increase in the amount of tremor activity, long-period events and degassing rates was observed at Villarrica weeks before the mainshock and continued at a high level also after it. This increase in activity is interpreted to be caused by enhanced magma influx at depth and may be unrelated to the Maule event. In Llaima, an increase in the volcano-tectonic activity was observed directly after the earthquake. The simultaneous post-earthquake activity at both volcanoes is consistent with a structural adjustment response. Since this enhanced activity lasted for more than a year, we suggest that it is related to a medium-term change in the static stress. Thus, the Maule earthquake may have affected both volcanoes, but did not trigger eruptions, from which we assume that none of the volcanoes were in a critical state.     

Hotspot distribution, gravity, mantle tomography: evidence for plumes

Thermal convection is the motor of Earth dynamics and therefore is the link between plate motions, hotspots, seismic velocity variations in the mantle, and anomalies of the gravity field. Small scale mantle anomalies, such as plumes, do, however, generally escape detection by tomographic methods. It is attempted to approach the problem of detection in a somewhat statistical manner. Correlations are sought between spherical harmonic expansions of the fields under study: the hotspot distribution, mantle velocity variations, gravity, heat flow. Using spherical harmonic representations of global fields implies integration and averaging over the whole globe. Thus, although relationships may remain masked in the space domain by a multitude of effects, tendencies may become visible in the spectra or in appropriate averages.The main results are the following: There is a significant long wavelength (n=2,3) negative correlation between the hotspot density and the P-wave velocity variation in the lower mantle. Positive hotspot density of degree 2 to 9 generally correlates with low seismic velocity in all depths of the upper mantle and with positive gravity. This fits well with plume-type convection. These results are also confirmed regionally for a number of individual mid-ocean ridges and hotspots. The hotspot density and the free air anomalies are distinctly positive above regions of low velocity extending to great depth. The effect is not distinct at ridges with shallow velocity anomalies. In a general way, we suggest that the antipodal upwellings (Pacific, Africa) are divided by downwelling currents around the shrinking Pacific. Plate boundaries can easily move away from their past connections with the deeper mantle. Small scale plume currents seem to be depicted in the hotspot expansion. © 1999 Elsevier Science Ltd. All rights reserved.     

Turnover of Eastern Caribbean deep water from 14C measurements

A¹⁴C balance for the Eastern Caribbean deep water indicates the average inflow of Atlantic water into the basin to be 2.3 × 10⁵ m³/sec (±30%), or about 2–4 times the values estimated previously. The balance uses a model representation of the deep-water turnover, and is based on¹⁴C concentrations at a station in the Venezuelan Basin which average Δ¹⁴C= 89‰ below 800 m depth with a total range of only 9‰, as well as on a¹⁴C concentration of the Atlantic inflow of Δ¹⁴C= ?71%. as obtained from measurements outside the Antilles Arch. The turnover time of the basin water below 2500 m depth is 55 years, which corresponds to an average upwelling velocity at this depth of about 35 m/year. With such upwelling, the temperature profile below 1800 m (the depth of the sill determining the inflow of new water) requires a vertical eddy diffusivity of about 5 cm²/sec. The oxygen consumption, and silica and CO₂ regeneration, rates below 2500 m depth are obtained as ?0.18, + 0.08, and + 0.2 μmole kg^?1 yr^?1, respectively. The CO₂ regeneration has but a negligible effect on the¹⁴C balance.     

An FDTD method for analysis of scattering from rough fluid-fluidinterfaces

A finite-difference time-domain (FDTD) method for scattering by one-dimensional, rough fluid-fluid interfaces is presented, modifications to the traditional FDTD algorithm are implemented which yield greater accuracy at lower computational cost. These modifications include use of a conformal technique, in which the grid conforms locally to the interface, and a correction for the numerical dispersion inherent to the FDTD algorithm, Numerical results are presented for fluid-fluid cases modeling water-sediment interfaces. Two different roughness spectra, the single-scale Gaussian roughness spectrum and a multiscale modified power-law spectrum, are used. The Gaussian results are calculated as a function of the dimensionless parameters kh and kl, where k is the wavenumber in water, h is the rms surface height, and l is the surface correlation length. For the modified power-law spectrum, statistical parameters consistent with an insonification frequency of 7.5 kHz are used. Results are compared with those obtained using an integral equation technique both for scattering from single-surface realizations and for Monte Carlo averages of scattering from an ensemble of surface realizations. Scattering strengths are calculated as a function of scattering angle for an incident angle of 70° (20° grazing). The results agree well over all scattering angles for the cases examined