Upper mantle structure of the Apulian plate from Rayleigh waves

Phase velocities of Rayleigh waves for the Adriatic Sea area are obtained in the period range 25–190 sec along the path (l'Aquila-Trieste) AQU-TRI and 20–167 sec along the path (Trieste-Bari) TRI-BAI.The phase velocities are systematically higher than the known values for the surrounding regions. The data inversion indicates the presence of a lithosphere typical of stable continental areas with clear high-velocity lid (V _s 4.6 km/sec) overlying a well developed low velocity zone (V _s 4.2 km/sec).P. F. Geodinamica C.N.R., Roma Pubbl. N. 189.     

A Lagrangian stochastic model for the trajectories of particle pairs and its application to the prediction of concentration variance within plant canopies

A simple Lagrangian stochastic model for the trajectories of particle pairs in high Reynolds-number turbulent flows is presented. In this model, the velocities of particle pairs are initially correlated but subsequently each particle moves independently. The independent single-particle trajectories are simulated using Thomson's model [J. Fluid Mech. 180, 529–556, 1987]. This two-particle model exactly satisfies the well-mixed condition for Gaussian turbulence when length scales, characterizing the two-point Eulerian velocity correlation function, vanish. Temperature variances, due to heat released as a passive scalar from an elevated plane source, within a model plant canopy (Coppin et al. Boundary Layer Meteorol. 35, 167–191, 1986) are shown to be well predicted by the model. It is suggested that for strongly inhomogeneous flows, the two-point Eulerian velocity function is of secondary importance in determining the simulated trajectories of particle pairs compared to the importance of ensuring satisfaction of the two-to-one constraint (Borgas and Sawford. J. Fluid Mech. 279, 69–99, 1994); i.e ensuring that one-particle statistics obtained from the two-particle model are the same as those obtained from the corresponding one-particle model. Limitations of this modelling approach are discussed.     

Mode identification of terrestrial ULF waves observed by Cluster: A case study

Using multipoint measurements from the Cluster mission wave identification techniques are applied to observations of ULF waves made in the terrestrial foreshock with the aim of identifying the modes and properties of the waves taking into account the effects of a high beta plasma. The wave properties in the spacecraft and plasma rest frames are experimentally derived using minimum variance analysis. Two waves with periods of 30 and 3 s dominate the dynamic frequency spectrum. The results indicate that these waves propagate in the fast magnetosonic and Alfvén/Ion Cyclotron modes, respectively. Both waves propagate in the upstream direction in the plasma rest frame but are convected downstream in the spacecraft frame. The measured wave properties in the plasma rest frame are in good agreement with those obtained from the theoretical kinetic dispersion relation taking into account the effects of different plasma beta. The dispersion results show a rather significant deviation from fluid model, especially when high beta plasma conditions occur. These experimentally derived foreshock ULF wave properties are in good agreement with previous results but when the effects of a high beta plasma are considered it is not as straight forward to choose the correct wave mode branch.     

Continuous inline mapping of a dissolved methane plume at a blowout site in the Central North Sea UK using a membrane inlet mass spectrometer – Water column stratification impedes immediate methane release into the atmosphere

The dissolved methane (CH₄) plume rising from the crater of the blowout well 22/4b in the Central North Sea was mapped during stratified water column conditions. Geochemical surveys were conducted close to the seafloor at 80.3 m water depth, below the thermocline (61.1 m), and in the mixed surface layer (13.2 m) using membrane inlet mass spectrometry (MIMS) in combination with a towed CTD. Seawater was continuously transferred from the respective depth levels of the CTD to the MIMS by using an inline submersible pump. Close to the seafloor a well-defined CH₄ plume extended from the bubble release site ∼460 m towards the southwest. Along this distance CH₄ concentrations decreased from a maximum of 7872 nmol l⁻¹ to less than 250 nmol l⁻¹. Below the thermocline the well-defined CH₄ plume shape encountered at the seafloor was distorted and filaments were observed that extended towards the west and southwest in relation to current direction. Where the core of the bubble plume intersected this depth layer, footprints of high CH₄ concentrations of up to 17,900 nmol l⁻¹ were observed. In the mixed surface layer the CH₄ distribution with a maximum of up to 3654 nmol l⁻¹ was confined to a small patch of ∼60 m in diameter. The determination of the water column CH₄ inventories revealed that CH₄ transfer across the thermocline was strongly impeded as only ∼3% of the total water column inventory was located in the mixed surface layer. Best estimate of the CH₄ seabed release from the blowout was 1751 tons yr⁻¹. The fate of the trapped CH₄ (∼97%) that does not immediately reach the atmosphere remains speculative. In wintertime, when the water column becomes well mixed as well as during storm events newly released CH₄ and the trapped CH₄ pool can be transported rapidly to the sea surface and emitted into the atmosphere.     

Tropical Cyclone Energy Dispersion and Possible Self Maintenance Mechanism of the Synoptic Scale Wave Trains

The interaction between tropical cyclone (TC) and the large-scale mean flows such as the inter-tropical convergence zone (ITCZ) is investigated using a three-dimensional primitive equation model. Once a TC develops in the vicinity of the ITCZ region where satisfies both barotropic and baroclinic instabilities, the southeastward energy dispersion from the TC may disturb the ITCZ and thus help its breakdown. Cumulus convection can be organized in the region of cyclonic circulation, and the interaction between convective heating and the perturbation circulation may enhance the development of the waves, leading to the generation of a new tropical cyclone to the east. While the TC moves to the high latitude, the ITCZ will reform. Though repeating of this process, a synoptic-scale wave train oriented in the northwest-southeast direction can be generated and self-maintained. The results suggest that the mutual interaction among the low-frequency background flow, wave train pattern and TCs provides a possible mechanism for the origin of the summer synoptic scale wave train pattern over the western North Pacific.     

Observed winds,turbulence, and dispersion in built-up downtown areas of Oklahoma City and Manhattan

Wind and tracer data from the Oklahoma City Joint Urban 2003 (JU2003) and the Manhattan Madison Square Garden 2005 (MSG05) urban field experiments are being analyzed to aid in understanding air flow and dispersion near street-level in built-up downtown areas. The mean winds are separately calculated for groups of anemometers having similar exposures such as “near street level” and “on building top”. Several general results are found, such as the scalar wind speed at street level is about 1/3 of that at building top. Turbulent standard deviations of wind speed components and temperature, and vertical fluxes of momentum and sensible heat, are calculated from sonic anemometers near street level at 20 locations in JU2003 and five locations in MSG05, and from two rooftop locations in MSG05. The turbulence observations are consistent with observations in the literature at other cities, although the JU2003 and MSG05 data are unique in that many data are available near street level. For example, it is found that the local (i.e., at the measuring height) averages about 1.5 and the local averages about 0.25 in the two cities, where is the standard deviation of vertical velocity fluctuations, is the friction velocity, and u is the wind speed. The ratio of temperature fluctuations to temperature scale, , averages about −3 in both cities, consistent with similarity theory for slightly unstable conditions, where is the standard deviation of temperature fluctuations, and is the temperature scale. The calculated Obukhov length, L, is also consistent with slightly unstable conditions near street level, even at night during JU2003. The SF₆ tracer concentration observations from JU2003 are analyzed. Values of for the continuous releases are calculated for each release and arc distance, where is the 30-min average arc maximum concentration, Q is the continuous source emission rate, and u is the spatial-averaged wind speed in the downtown area. The basic characteristics of the JU2003 plot of averaged agree reasonably well with similar plots for other urban experiments in Salt Lake City and London (i.e., at . A is found to be about 3 during the day and about 10 during the night.     

Multi-resolution adaptive modeling of groundwater flow and transport problems

Many groundwater flow and transport problems, especially those with sharp fronts, narrow transition zones, layers and fingers, require extensive computational resources. In this paper, we present a novel multi-resolution adaptive Fup approach to solve the above mentioned problems. Our numerical procedure is the Adaptive Fup Collocation Method (AFCM), based on Fup basis functions and designed through a method of lines (MOL). Fup basis functions are localized and infinitely differentiable functions with compact support and are related to more standard choices such as splines or wavelets. This method enables the adaptive multi-resolution approach to solve problems with different spatial and temporal scales with a desired level of accuracy using the entire family of Fup basis functions. In addition, the utilized collocation algorithm enables the mesh free approach with consistent velocity approximation and flux continuity due to properties of the Fup basis functions. The introduced numerical procedure was tested and verified by a few characteristic groundwater flow and transport problems, the Buckley–Leverett multiphase flow problem, the 1-D vertical density driven problem and the standard 2-D seawater intrusion benchmark–Henry problem. The results demonstrate that the method is robust and efficient particularly when describing sharp fronts and narrow transition zones changing in space and time.     

A fast inversion method for ocean parameters based on dispersion curves with a single hydrophone

The dispersion characteristics of shallow water can be described by the dispersion curves, which contain substantial ocean parameter information. A fast ocean parameter inversion method based on dispersion curves with a single hydrophone is presented in this paper. The method is achieved through Bayesian theory. Several sets of dispersion curves extracted from measured data are used as the input function. The inversion is performed by matching a replica calculated with a dispersion formula. The bottom characteristics can be described by the bottom reflection phase shift parameter P. The propagation range and the depth can be inverted quickly when the seabed parameters are represented by on parameter P. The inversion results improve the inversion efficiency of the seabed parameters. Consequently, the inversion efficiency and accuracy are improved while the number of inversion parameters is decreased and the computational speed of replica is increased. The inversion results have lower error than the reference values, and the dispersion curves calculated with inversion parameters are also in good agreement with extracted curves from measured data; thus, the effectiveness of the inversion method is demonstrated.     

Distribution of stars perpendicular to the plane of the galaxy

We present here rigorous analytical solutions for the Boltzmann-Poisson equation concerning the distribution of stars above the galactic plane. The number density of stars is considered to follow a behaviour n(m,0) ∼H(m - m₀)m^−x, wherem is the mass of a star andx an arbitrary exponent greater than 2 and also the velocity dispersion of the stars is assumed to behave as < v²(m)> ∼ m^−θ the exponent θ being arbitrary and positive. It is shown that an analytic expression can be found for the gravitational field K_z, in terms of confluent hypergeometric functions, the limiting trends being K_z∼z for z →0, while K_z → constant for z → infinity. We also study the behaviour of < |z(m)|²>,i.e. the dispersion of the distance from the galactic disc for the stars of massm. It is seen that the quantity < |z(m)|²>∼ m^t-θ, for m→ t, while it departs significantly from this harmonic oscillator behaviour for stars of lighter masses. It is suggested that observation of < |z(m)|²> can be used as a probe to findx and hence obtain information about the mass spectrum.