Optimal deflection of NEOs en route of collision with the Earth

Recently, a method for the n-body analysis of the velocity change required to deflect a hazardous near-Earth object (NEO) was presented by Carusi et al. [Carusi, A., Valsecchi, G.B., D'Abramo, G., Boattini A., 2002. Icarus 159, 417-422]. We extent this method in order to optimize the velocity change vector instead of its along-track magnitude. From an application of both methods to a fictitious NEO we find Carusi's parallel approach to be reasonable for phases of unperturbed two-body motion. But, for orbit phases inhering third-body perturbations, i.e., for planetary close approaches or prior to a collision, the results obtained from the new method show the radial component of deflection impulse to play a major role. We show that a fivefold greater efficiency can be achieved by a deflection impulse being non-parallel to orbital velocity. The new method is applied to two possible 99942 Apophis impact trajectories in order to provide constraints for future Apophis deflection mission analysis.     

Multiforced statistical assessments of greenhouse-gas-induced surface air temperature change 1890–1985

Based on univariate correlation and coherence analyses and considering the physical basis of the relationships, a simple multiforced (multiple) statistical concept is used which correlates observational climatic time series simultaneously with volcanic, solar, ENSO, and the anthropogenic greenhouse gases forcing. This is appropriate to remove some natural climate noise in the observed data and to evaluate the components (signals) possibly due to the anthropogenic greenhouse gas forcing (CO₂, or equivalent CO₂ implying additional gases) during industrial time. In this paper, we apply this technique to 100 global box data time series 1890–1985, of the surface air temperature, using observed data from Hansen and Lebedeff. The results are presented in terms of latitudinal-seasonal and regional trends, where the observed trend patterns are compared with the hypothetical signals (statistical assessments) possibly due to anthropogenic greenhouse forcing. These latter signals can be amplified to enable a comparison with corresponding results from general circulation model (GCM) CO₂ doubling experiments. These observed-statistical assessments lead to results which are, at least qualitatively and in respect to the zonal mean temperatures, very similar to some GCM experiments indicating the maximum CO₂ doubling signals (statistical assessment > 12 K) in the arctic winter. However, these signals are moderate in the tropics and in the Southern Hemisphere (global average 2.8–4.4 K). As far as the industrial signals are concerned (observed period) these signals are somewhat larger (maximum 7 K, global average 0.5–0.9 K) than the observed trends (maximum 5 K, global average 0.5 K). Phase shifts of cause and effect may amplify these signals but are very uncertain.This paper was presented at the International Conference on Modelling of Global Climate Change and Variability, held in Hamburg 11–15 September 1989 under the auspices of the Meteorological Institute of the University of Hamburg and the Max Planck Institute for Meteorology. Guest Editor for these papers is Dr. L. Dümenil     

Groundwater flow and contaminant transport modelling at an air weapons range

Numerical modelling was done at the Cold Lake Air Weapons Range, Canada, to test whether the dissolved RDX and nitrate detected in groundwater come from the same sources, and to predict whether contamination poses a threat to the surface water receptors near the site. Military live fire training activities may indeed pose a risk of contamination to groundwater resources, however field investigations on military bases are quite recent, and little information is available on the long-term behaviour of munition residues related contaminants. Very limited information was available about the contaminant source zones, which were assigned based on our knowledge of current training activities. The RDX plume was well represented with the model, but the heterogeneous distribution of nitrate concentrations was more difficult to reproduce. It was nonetheless determined that both contaminants originate from the same areas. According to the model, both contaminants should reach the nearby river, but concentrations in the river should remain very low if the source zone concentration does not change. Finally, the model allowed the recommendation of a new location for the main bombing target, which would offer added protection to the river and the lake into which it flows.     

Geobarometry for Peridotites: Experiments in Simple and Natural Systems from 6 to 10 GPa

Experiments with peridotite minerals in simple (MgO–Al₂O₃–SiO₂,CaO–MgO–SiO₂ and CaO–MgO–Al₂O₃–SiO₂)and natural systems were conducted at 1300–1500°Cand 6–10 GPa using a multi-anvil apparatus. The experimentsin simple systems demonstrated consistency with previous lowerpressure experiments in belt and piston–cylinder set-ups.The analysis of spatial variations in pyroxene compositionswithin experimental samples was used to demonstrate that pressureand temperature variations within the samples were less than0·4 GPa and 50°C. Olivine capsules were used in natural-systemexperiments with two mineral mixtures: SC1 (olivine + high-Alorthopyroxene + high-Al clinopyroxene + spinel) and J4 (olivine+ low-Al orthopyroxene + low-Al clinopyroxene + garnet). Theexperiments produced olivine + orthopyroxene + garnet ±clinopyroxene assemblages, occasionally with magnesite and carbonate-richmelt. Equilibrium compositions were derived by the analysisof grain rims and evaluation of mineral zoning. They were comparedwith our previous experiments with the same starting mixturesat 2·8–6·0 GPa and the results from simplesystems. The compositions of minerals from experiments withnatural mixtures show smooth pressure and temperature dependencesup to a pressure of 8 GPa. The experiments at 9 and 10 GPa producedandradite-rich garnets and pyroxene compositions deviating fromthe trends defined by the lower pressure experiments (e.g. higherAl in orthopyroxene and Ca in clinopyroxene). This discrepancyis attributed to a higher degree of oxidation in the high-pressureexperiments and an orthopyroxene–high-P clinopyroxenephase transition at 9 GPa. Based on new and previous resultsin simple and natural systems, a new version of the Al-in-orthopyroxenebarometer is presented. The new barometer adequately reproducesexperimental pressures up to 8 GPa. KEY WORDS: garnet; mineral equilibrium; multi-anvil apparatus; orthopyroxene; geobarometry     

Die Windverhältnisse im Davoser Hochtal

Zusammenfassung Die Davoser Windverh?ltnisse werden in ihrem tages- und jahreszeitlichen Ablauf sowie in ihrer Abh?ngigkeit von verschiedenen typischen Wetterlagen untersucht. Neben den ungest?rten Sch?nwetterlagen mit ihrem ausgepr?gten Talwind, der wie der Malojawind talabw?rts weht, werden die F?hnstr?mung aus Südwest und die Nordoststr?mung bei Staulagen und Bise kurz besprochen. Gegenüber dem benachbarten Dischmatal zeigt sich ein sp?terer Beginn des Talwindes bei Sch?nwetterlagen, w?hrend im Vergleich zu anderen T?lern, z. B. zum Wallis, ein früheres und schw?cheres nachmitt?gliches Windmaximum auftritt.

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Summary The wind at Davos is analysed in his diurnal and annual variation and in the depence on the different weather types. The fair and undisturbed weather shows a typical valley breeze during the day, but not in the normal direction towards the higher part of the valley, but downstream, similar to the Malojawind in the Engadine. The opposite wind direction, from southwest, characterises the foehn-situation. Northeasterly winds develop in the case of higher pressure north of the Alps (e. g. in situations of barrage). The valley-breeze begins later than in the adjacent Dischma Valley, but it is weaker and reaches the highest intensity earlier than in other valleys, as e. g. in the Valais.

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Résumé Les vents de Davos sont analysés selon leurs variations diurnes et annuelles et selon des types de temps caractéristiques. La situation de beau temps montre un vent de vallée assez accentué, soufflant du haut en bas, donc dans une direction anormale, mais analogue au vent de la Maloja en Engadine. En cas de ?foehn? le vent souffle du sud-ouest tandis qu'un vent du nord-est se manifeste par situations de surpression au nord des Alpes. Le vent de vallée se met à souffler plus tard à Davos que dans la vallée de Dischma toute proche. Il y atteint par contre sa vitesse maximale plus t?t que les vents correspondants d'autres vallées p. ex. du Valais. Le maximum y est cependant moins élevé.

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Mit 6 Textabbildungen

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Herrn Dr.W. M?rikofer zu seinem 70. Geburtstag gewidmet.     

Präparationstechnik für Aufbereitungsprodukte zur quantitativen erzmikroskopischen Untersuchung

Zusammenfassung Mikroskopische Anschliffe feinkörniger Aufbereitungsprodukte können nur dann quantitativ ausgewertet werden, wenn ihre Schliffqualität so hoch ist, daß auch feinste Partien sicher zu bestimmen sind. Daneben muß gewährleistet sein, daß die an der Schliffoberfläche erfaßten Körner die tatsächliche Verteilung der Mineralien der Probe repräsentieren. Diese Forderung kann nur durch zweckentsprechende Präparation, die dem eigentlichen Schleif- und Polierprozeß vorausgeht, erfüllt werden. Als günstigste Lösung erscheint es, das Korngemisch exakt als Einkornschicht zu präparieren und anschließend wie Stückproben anzuschleifen. Die Schliffe können dann nach den gleichen statistischen Gesetzmäßigkeiten ausgewertet werden, wie sie bei praktisch zweidimensionalen Dünnschliffen oder bei Streupräparaten nichtopaker Korngemische vorliegen.

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Quantitative examination of fine-grained ore dressing products depends on good quality of the sections and on whether very small particles and areas of grains can be determined. Besides, it must absolutely be guaranteed that the grains at the section surface represent the actual distribution of the minerals in the sample. This condition can only be realized by suitable grain mounting prior to grinding and polishing. The best method for this purpose appears to be the preparation of a mono-grain layer. The polished sections can then be examined according to the same statistical laws as two-dimensional thin sections or immersion-liquid slides of non-opaque mixtures of grains.

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Mitteilung Nr. 141 aus dem Forschungsinstitut für Aufbereitung der Deutschen Akademie der Wissenschaften zu Berlin, Freiberg (Sachsen). Direktor: Prof. Dr.-Ing. habil. H. Kirchberg.     

Stable carbon isotope ratios of plankton carbon and sinking organic matter from the Atlantic sector of the Southern Ocean

The stable carbon isotope composition of particulate organic carbon (POC) from plankton, sediment trap material and surface sediments from the Atlantic sector of the Southern Ocean were determined. Despite low and constant water temperatures, large variations in the δ¹³C values of plankton were measured. ¹³C enrichments of up to 10‰ coincided with a change in the diatom assemblage and a two-fold increase in primary production. Increased CO₂ consumption as a result of rapid carbon fixation may result in diffusion limitation reducing the magnitude of the isotope fractionation. The δ¹³C values of plankton from sea-ice cores display a relationship with the chlorophyll a content. High ‘ice-algae’ biomass, in combination with a limited exchange with the surrounding seawater, results in values of about − 18 to − 20‰. It is assumed that these values are related to a reduced CO₂ availability in the sea-ice system. In comparison with plankton, sinking krill faeces sampled by traps can be enriched by 2–5‰ in ¹³C (e.g. central Bransfield Strait). In contrast, the transport of particles in other faeces, diatom aggregates or chains results in minor isotope changes (e.g. Drake Passage, Powell Basin, NW Weddell Sea). A comparison between the δ¹³C values of sinking matter and those of surface sediments reveals that ¹³C enrichments of up to 3–4‰ may occur at the sediment-water boundary layer. These isotopic changes are attributed to high benthic respiration rates.     

Microbial Biomass Dynamics Along a Trophic Gradient at the Atlantic Barrier Reef off Belize (Central America)

Abstract. Recent findings indicate that heterotrophic bacteria and not phytoplankton are the most numerous biomass components even in the euphotic zone of oligotrophic, open oceans. In this study it was hypothesized that the microbial biomass components change within a few hundred meters as oligotrophic water flows across the reef and becomes enriched with nutrients. Along a trophic gradient, four stations at the Atlantic Barrier Reef off Belize (Central America) were sampled for microbial biomass components. Phytoplankton biomass (measured as chlorophyll a) ranged from the most oligotrophic station (St. 1) to the most eutrophic station (St. 4) from 6.9–415.5 μg CI"' (assuming a C:chl a ratio of 30): heterotrophic bacterial biomass increased 4-fold (from 10.1–46.4μg C 1^-1), heterotrophic nanoflagellate (HNAN) biomass increased from 4.6-19ug C 1^-1, and cyanobacteria from 0.9-4.5 μg C-1^-1. Production estimates derived from seawater cultures revealed a 5-fold increase in bacterial production from the oligotrophic station (3.7 ug C 1^-1 d^-1) to the eutrophic St. 4 (17.8ug C-1-d1^-1)- Cyanobacterial production rose from 1.1–3.5ug C-1–d^-1 and HNAN production from 0.65-1.13 μg C-1^-1 -d^-1. While cyanobacteria contributed between 13 and 20% to the autotrophic plankton component in the oligotrophic waters, their contribution dropped to about 1 % at the eutrophic stations.