NOAA卫星探测数据对B-模式分析预报系统性误差的影响

本文报告极轨气象卫星探测数据对B-模式的海平面气压场预报和500hPa高度预报的系统性误差的影响.主要结果是:(1)B-模式预报海平面气压的强度偏弱,即高压系统太低,低压太高;(2)500hPa高度预报的系统性误差情况不如海平面气压场误差情况明显.但也能发现槽区的高度预报不够低,而脊区的高度预报不够高;(3)应用卫星数据对B-模式分析预报系统的预报有正作用,对海洋上的地面低压和500hPa槽区附近的系统性误差有明显减小,但对其它地区天气系统预报的正负影响参差不齐,其作用难下结论。     

Gravity changes accompanying volcanic activity at Pacaya volcano, Guatemala

Gravity changes of up to 1.2 ± 0.1 mgal (1 standard deviation) were measured at three points within 400 m of an active vent on Pacaya volcano, Guatemala during eleven days of January, 1975. For five continuous days gravity varied inversely with the average muzzle velocity of ejecta, the frequency of volcanic explosions, and the frequency of volcanic earthquakes. The gravity changes are most reasonably interpreted as the product of intravolcanic movements of magma with masses one to two orders of magnitude larger than any flow ever erupted from the volcano. However, elevation changes and/or combination of elevation and mass distribution changes could also have been an important factor in effecting the observed gravity variations. Because we lack elevation control on the gravity stations, we are unable to unequivocally conclude which factor or which combination of factors produced the gravity changes. The study indicates the possibility of gravity monitoring of hazardous volcanoes as a predictive tool, and as an added means for investigating the internal mechanism of volcanic eruptions.     

Back-arc spreading: Trench migration, continental pull or induced convection?

Mechanisms of the opening of back-arc systems are analyzed. Limited focal mechanisms of intraplate earthquakes are used to determine the stress regime of an overriding plate. Preliminary analyses show that compressive deviatoric stresses exist in the plate except near the spreading center. Based on this observation “trench suction” does not appear to be the primary force that drives back-arc spreading, since it will result in tensional deviatoric stresses within the overriding plate. Even though “continental pull” is able to satisfy the stress requirements, it does not appear to be a likely mechanism either because of the initiation and subsequent symmetric spreading difficulty associated with such a mechanism. The mechanism we favor is the one that involves the induced convective current in the mantle wedge immediately above the slab. Calculations show that the induced flow is able to generate sufficient stress to break up the overriding lithosphere if the tectonic stresses of the region are favorable. Both trench suction and continental pull may help to provide such a favorable tectonic stress regime.     

Sedimentary iron monosulfides: Kinetics and mechanism of formation

The reaction between hydrous iron oxides and aqueous sulfide species was studied at estuarine conditions of pH, total sulfide, and ionic strength to determine the kinetics and formation mechanism of the initial iron sulfide. Total, dissolved and acid extractable sulfide, thiosulfate, sulfate, and elemental sulfur were determined by spectrophotometric methods. Polysulfides, S₄^2? and S₅^2?, were determined from ultraviolet absorbance measurements and equilibrium calculations, while product hydroxyl ion was determined from pH measurements and solution buffer capacity.Elemental sulfur, as free and polysulfide sulfur, was 86% of the sulfide oxidation products; the remainder was thiosulfate. Rate expressions for the reduction and precipitation reactions were determined from analysis of electron balance and acid extractable iron monosulfide vs time, respectively, by the initial rate method. The rate of iron reduction in moles/liter/minute was given by $\text{d(}\text{reduction}\text{Fe)}\text{dt}\text{= kS}{}_{\mathrm{t}}{}^{0.5}\text{(J}{}^{\mathrm{+}}\text{)}{}^{0.5}\text{A}{}_{\mathrm{FeOOH}}{}^1$ where S_t was the total dissolved sulfide concentration, (H⁺) the hydrogen ion activity, both in moles/ liter; and A_FeOOH the goethite specific surface area in square meters/liter. The rate constant, k, was 0.017 ± 0.002m^?2 min^?1. The rate of reduction was apparently determined by the rate of dissolution of the surface layer of ferrous hydroxide. The rate expression for the precipitation reaction was $\text{d(FeS)}\text{dt}\text{= kS}{}_{\mathrm{t}}{}^1\text{(H}{}^{\mathrm{+}}\text{)}{}^1\text{A}{}_{\mathrm{FeOOH}}{}^1$ where $\text{d(FeS)}\text{dt}$ was the rate of precipitation of acid extractable iron monosulfide in moles/liter/minute, and k = 82 ± 18 mol^?1l²m^?2 min^?1.A model is proposed with the following steps: protonation of goethite surface layer; exchange of bisulfide for hydroxide in the mobile layer; reduction of surface ferric ions of goethite by dissolved bisulfide species which produces ferrous hydroxide surface layer elemental sulfur and thiosulfate; dissolution of surface layer of ferrous hydroxide; and precipitation of dissolved ferrous specie and aqueous bisulfide ion.     

The duisburg method of metro-construction, a successful application of the gap freezing method

Between March 1977 and August 1979 contract No.4 of the Stadtbahnbau (Metro-construction) in Duisburg was executed, making successful use of gap freezing.

The gap freezing was necessary because the Metro-tunnel is crossed by a groundwater stream (flow velocity up to 15 m/d) and it had to be assured that open cut construction of the tunnel was possible and that the original situation could be reinstated as far as possible after completion.

The Duisburg building ground also made a special construction method necessary. Ground strata: from surface to 2–4 m, civilisation deposits; from ˜ 4 m to ≈ 25–28 m below surface, glacial sand and gravel deposits, containing stones with a diameter > 20 cm and even boulders of 1 m³ and more; from approximately 28 m below surface, layers of Tertiary clay and silt; the groundwater table is ˜ 8 m below the surface, the stream flowing within the sand and gravel deposits from SE to NW (towards the Rhine).

Installing a groundwater barrier, for instance by erecting a continuous diaphragm wall enclosure, was already ruled out in early design stages as was the use of driven steelpiles.

At the inception of the design in 1974, it was decided first to carry out a measuring scheme to establish the groundwater flow velocity. This was followed by a large scale (1:1) trial freezing to ascertain the feasibility of the gap-freezing method.

When these experiments were scientifically valued it was established, that the risk involved was acceptable. The contract documents were prepared prescribing a combination of “cover and cut” with gap-freezing, which is tentatively called the “Duisburg method of Metro-construction”.

During the construction a large scale measuring and scientific research programme was carried out.     

Spectral analysis of earthquake migration in South America

Earthquake migration along linear seismic belts is investigated by analyzing spacetime diagrams using spectral analysis. In order to sample the earthquakes in the space-time domain, they must first be convolved with a (sinx sint)/xt surface to obtain an unbiased and alias free twodimensional Fourier spectrum. Further enhancements are provided by selectively stacking patterns (a pattern is defined as the distribution of earthquakes in space and time before a particular earthquake), thereby reinforcing the similarities within the various patterns. With these techniques, it is possible to quantitatively estimate the migration rates (from theirspatial frequencies) and recurrence intervals (from theirtemporal frequencies) of large earthquakes in South America.Preliminary examination of the spectra for South America indicates that a low frequency peak occurs at approximately 2500 km and 27 years for earthquakes with magnitudes greater than 7.7. The results suggest a migration rate of approximately 95 km/yr from south to north and a recurrence interval of 27 years.     

The distribution of titanium on the lunar surface

Titanium concentrations have been derived from measurements with the lunar-orbiting gamma-ray experiment on Apollo 15 and 16 by analyzing a spectral interval in which the titanium signal is relatively enhanced. Landing site soil values provide the reference for a regression curve from which Ti concentrations in 137 regions of adequate counting statistics are calculated. Among the mare regions overflown, the southern portion of Mare Tranquillitatis contains the highest Ti concentration (4.4%), Mare Serenitatis, Mare Fecunditatis, and Mare Smythii have intermediate values corresponding to low-Ti basalts, and Mare Crisium is conspicuously low in Ti (0.9%). Regional values in the western maria range from 1.1% to 4.1%, somewhat higher in the north than in the south, with the highest values seen south and west of Aristarchus. The Aristarchus Plateau appears chemically distinct from the surrounding mare. The younger western basalts mapped by the experiment do not appear to be identical to the Apollo 11 and Apollo 17 high-Ti basalts. Low-Ti basalts predominate in the observed mare regions. Highland Ti concentrations range from undetectable to 1.5% with several exceptions; accuracy is limited by the relatively large uncertainty. Highland results suggest a north-south asymmetry which is not consistent with previously reported results for Fe and Th. Comparisons with telescopic spectral reflectance studies of the maria do not show complete agreement and suggest that effects due to Fe may not have been fully removed from the reflectance data.     

Der Permische Vulkanismus in Südtirol und das Problem der Ignimbrite

Zusammenfassung Anläßlich der Pfingstexkursion 1959 der Geologischen Vereinigung nach Südtirol, kam es zu einer Diskussion, ob und inwieweit die Quarzporphyre der Bozener Porphyrplatte Ignimbrite seien. Es wird versucht, unter Berücksichtigung der zugänglichen Literatur, den Begriff Ignimbrit in seiner eigentlichen Bedeutung zu fassen. Dabei wird auf die Gefahr hingewiesen, die in der Doppelverwendung als Gesteinsname und als Bezeichnung für einen Eruptionsmechanismus liegt. An Hand der jüngsten Literatur über die Bozener Quarzporphyre und eigener Beobachtungen wird die Beteiligung von Ignimbriten an dem komplexen vulkanischen Gesteinsaufbau der Porphyrplatte erörtert.     

Phosphoric acid fractionation factors for smithsonite and cerussite between 25 and 72°C

The intramolecular kinetic oxygen isotope fractionation between CO₂ and CO₃²⁻ during reaction of phosphoric acid with natural smithsonite (ZnCO₃) and cerussite (PbCO₃) has been determined between 25 and 72°C. While cerussite decomposes in phosphoric acid within a few hours at 25°C, smithsonite reacts very slowly with the acid at 25°C providing yields of CO₂ < 25% after 2 weeks. The low yields result in a low precision for oxygen isotope measurements of the acid-liberated CO₂ (±1.65‰, 1σ, n = 9). The yield and reproducibility of oxygen isotope values of the acid-liberated CO₂ from smithsonite can be improved, the latter to ∼±0.15‰, by increasing the reaction temperature to 50°C for 12 h or to 72°C for 1 h. Our new phosphoric acid fractionation factor for natural cerussite at 25°C deviates significantly from a previously published value on synthetic material. The temperature dependence of the oxygen isotope factionation factor, α between acid-liberated CO₂ and carbonate at 25 to 72°C is given by the following equations