Large-scale motions of the tropics in observations and theory

Recent observations of the tropical and subtropical atmosphere are interpreted in terms of scaling arguments and wave propagation theory advanced byCharney (1963, 1969).Charney’s idealizations describe the tropical atmosphere in terms of large regions of quasi-nondivergent flow containing small subdomains of heavy convection and divergence, and place emphasis upon the quasi-rotational regions. FGGE (First GARP Global Experiment) observations suggest that strongly divergent local tropical circulations are forced by latent heating and produce important direct modifications of the total wind field. We describe the extent to which the resulting field consists of divergent and rotational components in different analyses of the FGGE data, and present independent supporting documentation of the results in terms of heating estimates and rainfall observations. Local tropical heating rates on the order of 10°C/day are apparently due to latent heat release associated with precipitation rates as large as 6 cm/day during extended periods. The large contribution of the divergent wind is generally underestimated in models that do not retain such energetic local forcings, and this deficiency may be related to general underestimation of tropical-extratropical connections of many linear models. Such connections are commonly cited in relation to El Niño events, the Southern Hemisphere stationary-wave pattern, and in FGGE studies, but are not well simulated in most linear theories. It is not yet clear whether this is an inherent limitation of linear models, or whether the linear models have not yet explored all the potentially relevant ambient states. We explore the latter possibility by construction of a basic state that allows reasonable latitudinal evolution of the wave field. This basic state has zero absolute vorticity gradient throughout the tropics, and deviations linearized about this state are dynamically analogous to a “local” Hadley cell. To the extent that it is appropriate to regard the results in terms of wave propagation, our analysis suggests a prominent role for gravity-inertia waves in the tropics and for the extratropical connections. The relevance of gravity modes to observations and the theoretical explanation of the flat vorticity field remain to be established.     

Sr and Nd isotope geochronology,geologic history,and origin of the Adirondack Anorthosite

We have analyzed samples from the Adirondack Marcy massif for Rb-Sr and Sm-Nd isotopes in an attempt to determine directly the primary crystallization age of a Proterozoic massif-type anorthosite rock suite. The oldest age obtained (1288 ± 36Ma) is from a 4 point Sm-Nd isochron defined by igneous-textured whole-rock and mineral separate data from a local layered sequence gradational from oxiderich pyroxenite to leuconorite. This age is older than Silver's (1969) 1113 Ma zircon age of associated charnockites, but is within the window of permissible anorthosite ages based on previous geochronology and field relationships. As such, 1288 Ma may represent the time of crystallization of the massif. For the most part, however, both Sm-Nd and Rb-Sr isotopic systems did not survive granulite facies metamorphism. Internal isochrons based on whole rocks and minerals yield ages between 995 and 919 Ma. These isotopic data suggest that the granulite fades metamorphism experienced by the massif was a prograde event that occurred a minimum of 100 Ma and as much as 350 Ma after crystallization of the massif. The relatively large range in Rb abundance, and in calculated initial ${}^{87}\text{Sr}{}^{86}\text{Sr}$ (0.7039–0.7050) and ${}^{143}\text{Nd}{}^{144}\text{Nd}$ ratios among anorthosite suite rocks, particularly those at or near the contacts of the Marcy massif is explicable by variable contamination with “crustal” materials and/or fluids, derived from surrounding acidic metaplutonic rocks, paragneisses, and marbles. Despite uncertainies caused by crustal contamination and metamorphic resetting of primary ages, Marcy samples have epsilon Nd values between +0.44 and +5.08, implying a source for the massif with long-term depletion in light rare earth elements. A probable source material would be depleted mantle.     

A Probabilistic Displacement-based Vulnerability Assessment Procedure for Earthquake Loss Estimation

Earthquake loss estimation studies require predictions to be made of the proportion of a building class falling within discrete damage bands from a specified earthquake demand. These predictions should be made using methods that incorporate both computational efficiency and accuracy such that studies on regional or national levels can be effectively carried out, even when the triggering of multiple earthquake scenarios, as opposed to the use of probabilistic hazard maps and uniform hazard spectra, is employed to realistically assess seismic demand and its consequences on the built environment. Earthquake actions should be represented by a parameter that shows good correlation to damage and that accounts for the relationship between the frequency content of the ground motion and the fundamental period of the building; hence recent proposals to use displacement response spectra. A rational method is proposed herein that defines the capacity of a building class by relating its deformation potential to its fundamental period of vibration at different limit states and comparing this with a displacement response spectrum. The uncertainty in the geometrical, material and limit state properties of a building class is considered and the first-order reliability method, FORM, is used to produce an approximate joint probability density function (JPDF) of displacement capacity and period. The JPDF of capacity may be used in conjunction with the lognormal cumulative distribution function of demand in the classical reliability formula to calculate the probability of failing a given limit state. Vulnerability curves may be produced which, although not directly used in the methodology, serve to illustrate the conceptual soundness of the method and make comparisons with other methods.     

Environmental predictions for the Beagle 2 lander, based on GCM climate simulations

The Mars climate database (MCD) is a database of statistics based on output from physically consistent numerical model simulations which describe the climate and surface environment of Mars. It is used here to predict the meteorological environment of the Beagle 2 lander site. The database was constructed directly on the basis of output from multiannual integrations of two general circulation models, developed jointly at Laboratoire de Météorologie Dynamique du Centre National de la Recherche Scientifique, France, and the University of Oxford, UK. In an atmosphere with dust opacities similar to that observed by Mars Global Surveyor, the predicted surface temperature at the time of landing (L_s=322°, 13:00 local time), is , and varying between ∼186 and over the Martian day. The predicted air temperature at above the surface, the height of the fully extended Beagle 2 robot arm, is at the time of landing. The expected mean wind near the surface on landing is north-westerly in direction, becoming more southerly over the mission. An increase in mean surface pressure is expected during the mission. Heavy global dust storm predictions are discussed; conditions which may only occur in the extreme as the expected time of landing is around the end of the main dust storm period. Past observations show approximately a one in five chance of a large-scale dust storm in a whole Mars year over the landing region, Isidis Planitia. This statistic results from observations of global, encircling, regional and local dust storms but does not include any small-scale dust “events” such as dust devils.     

Push-pull tests for assessing in situ aerobic cometabolism

Three types of single-well push-pull tests were developed for use in assessing the feasibility of in situ aerobic cometabolism of chlorinated aliphatic hydrocarbons (CAHs). These included transport tests, biostimulation tests, and activity tests. Transport tests are conducted to evaluate the mobility of solutes used in subsequent tests. These included bromide or chloride (conservative tracers), propane (growth substrate), ethylene, propylene (CAH surrogates), dissolved oxygen (electron acceptor), and nitrate (a minor nutrient). Tests were conducted at an experimental wellfield of Oregon State University. At this site, extraction phase breakthrough curves for all solutes were similar, indicating apparent conservative transport of the dissolved gases and nitrate prior to biostimulation. Biostimulation tests were conducted to stimulate propane-utilizing activity of indigenous microorganisms and consisted of sequential injections of site ground water containing dissolved propane and oxygen. Biostimulation was detected by the increase in rates of propane and oxygen utilization after each injection. Activity tests were conducted to quantify rates of substrate utilization and to confirm that CAH-transforming activity had likely been stimulated. In particular, the transformation of injected CAH surrogates ethylene and propylene to the cometabolic byproducts ethylene oxide and propylene oxide provided evidence that activity of the monooxygenase enzyme system, responsible for aerobic cometabolic transformations of CAHs, had likely also been stimulated. Estimated zero-order transformation rates decreased in the order propane > ethylene > propylene. The series of push-pull tests developed and field tested in this study should prove useful for conducting rapid, low-cost feasibility assessments for in situ aerobic cometabolism of CAHs.     

The sediment and hydrographic characteristics of three horseshoe crab nursery beaches in hong kong

1　Introduction　Thelifecycleofhorseshoecrabsislengthywhencom paredtoothermarinearthropodssuchasbluecrabsandshrimpspecies (Sekiguchietal.,1988) .Thetwospecies,TachypleustridentatusandCarcinoscorpiusrotundicauda,knowntooccurinHongKongrequire ,respectively ,betweenthirteentofourteenandtentoelevenyearstomaturebeforedepartingtheirnurserybeachesfordeeperwaters (ChiuandMorton ,1999a ;Sekiguchietal.,1988) .Thelivingenvironmentofthenurserybeacheswheretheeggsarelaidandincu bated ,andfromwhichtheyoun…     

Résultats préliminaires sur la sédimentation pélagique de l'Atlantique tropical au Crétacé et au Tertiaire (plateau de Demerara,Leg ODP 207)

Five sites located on a bathymetric transect of the distal Demerara Rise were studied by ODP Leg 207. Albian sediments of essentially terrigenous nature (clay, siltstone, sandstone) are the oldest drilled stratigraphic levels and form apparently the top of the synrift sequence. They are overlain by Cenomanian to Santonian finely laminated black shales, rich in organic matter of marine origin, which accumulated on a thermally subsiding ramp. Early Campanian hiatuses are thought to be the result of final disjunction of Demerara Rise (South America) from Africa and the onset of deep water communication between the two Atlantic basins (south and central). The overlying Uppermost Cretaceous–Oligocene chalk includes rich and diversified calcareous plankton assemblages, as well as two radiolarian-rich intervals (Late Campanian and Middle Eocene). A complex erosional surface developed during the Late Oligocene–Early Miocene. Sedimentation was impeded since then on the intermediate and deep sites of Demerara Rise, possibly due to the action of deep submarine currents. To cite this article: T. Danelian et al., C. R. Geoscience 337 (2005).     

The Northern Cordilleran Mid-Cretaceous Plutonic Province: Ilmenite/Magnetite-series Granitoids and Intrusion-related Mineralisation

Abstract. Twenty-five Early and mid-Cretaceous (145–90 Ma) plutonic suites and belts are defined across Alaska and Yukon, in the northern North American Cordillera, on the basis of lithological, geochemical, isotopic, and geochronometric similarities. These features are combined with aeromagnetic characteristics, magnetic susceptibility measurements, and whole-rock ferric: ferrous ratios to ascertain the distribution of magnetite- and ilmenite-series plutonic belts. Magnetite-series plutonic belts are dominantly associated with the older parts of the plutonic episode and comprise subduction-generated metaluminous plutons that are distributed preferentially in the more seaward localities dominated by primitive tectonic elements. Ilmenite-series plutonic belts comprise slightly younger, slightly peraluminous plutons in more landward localities in pericratonic to continental margin settings. They were likely initiated in response to crustal thickening following terrane collision. The youngest plutonic belt forms a small, but significant, magnetite-series belts in the farthest inboard position, associated with alkalic plutons that were emplaced during weak extension.
Intrusion-related metallogenic provinces with distinctive metal associations are distributed, largely in accord with classical redox-sensitive granite-series. Copper, Au, and Fe mineralisation are associated with magnetite-series plutons and tungsten mineralisation associated with ilmenite-series plutons. However, there are some notable deviations from expected associations, as intrusion-related Ag-Pb-Zn deposits are few, and significant tin mineralisation is rare. Most significantly, many gold deposits and occurrences are associated with ilmenite-series plutons: these form the basis for the newly recognized reduced intrusion-related gold deposit model.     

It's life, Jim…

Lewis Dartnell wonders how astronomers find life on this and other planets. After all, they do it on Star Trek with just a scanner…