Vertical Velocity Variance Research Articles

Three‐dimensional seismic velocity structure in the Sichuan basin, China

AbstractWe present a new three‐dimensional velocity model of the crust in the eastern margin of the Tibetan Plateau. The model describes the velocity structure of the Sichuan basin and surrounding thrust belts. The model consists of 3‐D surfaces representing major geologic unit contacts and faults and is parameterized with Vp velocity‐depth functions calibrated using sonic logs. The model incorporates data from 1166 oil wells, industry isopach maps, geological maps, and a digital elevation model. The geological surfaces were modeled based on structure contour maps for various units from oil wells and seismic reflection profiles. These surfaces include base Quaternary, Mesozoic, Paleozoic, and Proterozoic horizons. The horizons locally exhibit major offsets that are compatible with the locations and displacements of important faults systems. This layered, upper crustal 3‐D model extends down to 10–15 km depth and illustrates lateral and vertical variations of velocity that reflect the complex evolution of tectonics and sedimentation in the basin. The model also incorporates 3‐D descriptions of Vs and density for sediments that are obtained from empirical relationships with Vp using direct measurements of these properties in borehole logs. To illustrate the impact of our basin model on earthquake hazards assessment, we use it to calculate ground motions and compare these with observations for the 2013 Lushan earthquake. The result demonstrates the effects of basin amplification in the western Sichuan basin. The Sichuan CVM model is intended to facilitate fault systems analysis, strong ground motion prediction, and earthquake hazards assessment for the densely populated Sichuan region.

Exploring Stratocumulus Cloud-Top Entrainment Processes and Parameterizations by Using Doppler Cloud Radar Observations

Abstract Observations made at the Atmospheric Radiation Measurement (ARM) Program’s Southern Great Plains (SGP) site during uniform nonprecipitating stratocumulus cloud conditions for a 14-h period are used to examine cloud-top entrainment processes and parameterizations. The observations from a vertically pointing Doppler cloud radar provide estimates of vertical velocity variance and energy dissipation rate (EDR) terms in the parameterized turbulent kinetic energy (TKE) budget of the entrainment zone. Hourly averages of the vertical velocity variance term in the TKE entrainment formulation correlated strongly (r = 0.72) with the dissipation rate term in the entrainment zone, with an increased correlation (r = 0.92) when accounting for the nighttime decoupling of the boundary layer. Independent estimates of entrainment rates were obtained from an inversion-height budget using the local time derivative and horizontal advection of cloud-top height together with large-scale vertical velocity at the boundary layer inversion from the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis model. The mean entrainment rate from the inversion-height budget during the 14-h period was 0.74 ± 0.15 cm s−1 and was used to calculate bulk coefficients for entrainment parameterizations based on convective velocity scale w* and TKE budgets of the entrainment zone. The hourly values of entrainment rates calculated using these coefficients exhibited good agreement with those calculated from the inversion-height budget associated with substantial changes in surface buoyancy production and cloud-top radiative cooling. The results indicate a strong potential for making entrainment rate estimates directly from radar vertical velocity variance and the EDR measurements.

Improving horizontal resolution of high-frequency surface-wave methods using travel-time tomography

In surface-wave methods, horizontal resolution can be defined as the ability to distinguish anomalous objects that are laterally displaced from each other. The horizontal length of a recognizable geological anomalous body is measured by the lateral variation of shear (S)-wave velocity. Multichannel analysis of surface waves (MASW) is an efficient tool to determine near-surface S-wave velocities. The acquisition of the MASW method involves the same source-receiver configuration moved successively by a fixed distance interval (a few to several stations) along a linear survey line, which is called a roll-along acquisition geometry. A pseudo-2D S-wave velocity section is constructed by aligning 1D models, and each inverted 1D S-wave velocity model reflects the vertical S-wave velocity variation at the midpoint of each geophone spread. Although the MASW method can improve the horizontal resolution of S-wave velocity sections to some degree, the amount of fieldwork is increased by the roll-along acquisition geometry. We propose surface-wave tomography method to investigate horizontal resolution of surface-wave exploration. Phase-velocity dispersion curves are calculated by a pair of traces within a multichannel record through cross-correlation combined with a phase-shift scanning method. Then with the utilization of travel-time tomography, we can obtain high resolution pure-path dispersion curves with diverse sizes of grids at different frequencies. Finally, the pseudo-2D S-wave velocity structure is reconstructed by inverting the pure-path dispersion curves. Travel-time tomography of surface waves can extract accurate dispersion curves from a record with a short receiver spacing, and it can effectively enhance the ability of random noise immunity. Synthetic tests and a real-world example have indicated that travel-time tomography has a great potential for improving the horizontal resolution of surface waves using multi-channel analysis.

Lidar Characterization of Boundary Layer Transport and Mixing for Estimating Urban-Scale Greenhouse Gas Emissions

A compact commercial Doppler lidar has been deployed in Indianapolis for two years to measure wind profiles and mixing layer properties as part of project to improve greenhouse measurements from large area sources. The lidar uses vertical velocity variance and aerosol structure to measure mixing layer depth. Comparisons with aircraft and the NOAA HRDL lidar generally indicate good performance, although sensitivity might be an issue under low aerosol conditions.

Analytical fundamentals of migration in reflection seismics

AbstractWe consider migration in reflection seismics from a completely analytical perspective. We review the basic geometrical ray-path approach to understanding the subject of migration, and discuss the limitations of this method. We stress the importance of the linear differential wave equation in migration. We also review briefly how a wavefield, travelling with a constant velocity, is extrapolated from the differential wave equation, with the aid of Fourier transforms. Then we present a non-numerical treatment by which we derive an asymptotic solution for both the amplitude and the phase of a planar subsurface wavefield that has a vertical velocity variation. This treatment entails the application of the Wentzel-Kramers-Brillouin approximation, whose self-consistency can be established due to a very slow logarithmic variation of the velocity in the vertical direction, a feature that holds more firmly at increasingly greater subsurface depths. For a planar subsurface wavefield, we also demonstrate an equivalence between two apparently different migration algorithms, namely, the constant-velocity Stolt Migration algorithm and the stationary-phase approximation method.

A Real-time Fall Detection System for Maintenance Activities in Indoor Environments

Abstract: A real-time, multi-camera incident detection system for indoor environments is presented in this paper. The paper focuses on the detection of fall incidents while it highlights the leverage that such a system can provide to the human resources department of a shop-floor especially referring to the maintenance procedures. The proposed detection method extracts features that characterize a falling person’s trajectory, like vertical velocity and area variance, while the fall is described by Hidden Markov Models (HMM). The system utilizes only privacy preserving sensors. Experimental results illustrate its efficiency.

Langmuir Turbulence and Surface Heating in the Ocean Surface Boundary Layer

AbstractThis study uses large-eddy simulation to investigate the structure of the ocean surface boundary layer (OSBL) in the presence of Langmuir turbulence and stabilizing surface heat fluxes. The OSBL consists of a weakly stratified layer, despite a surface heat flux, above a stratified thermocline. The weakly stratified (mixed) layer is maintained by a combination of a turbulent heat flux produced by the wave-driven Stokes drift and downgradient turbulent diffusion. The scaling of turbulence statistics, such as dissipation and vertical velocity variance, is only affected by the surface heat flux through changes in the mixed layer depth. Diagnostic models are proposed for the equilibrium boundary layer and mixed layer depths in the presence of surface heating. The models are a function of the initial mixed layer depth before heating is imposed and the Langmuir stability length. In the presence of radiative heating, the models are extended to account for the depth profile of the heating.

Discussion of ‘Geomorphology, internal structure, and successive development of a glacier foreland in the semiarid Chilean Andes (Cerro Tapado, upper Elqui Valley, 30°08′ S, 69°55′ W.)’, by S. Monnier, C. Kinnard, A. Surazakov and W. Bossy, Geomorphology 207 (2014), 126–140

Recently, Monnier et al. (2014, Geomorphology 207, 126–140) suggested that diffraction events with air-wave velocities along profile CD were caused by an air-filled void at depth within one of the glaciers of the Cerro Tapado, Chile. This is not physically possible. The velocity at which radar travels to and from the scattering feature that causes a diffraction is at the velocity that surrounds and overlies the scatterer. Thus, their air-wave velocity features are on the surface of the glacier, not at depth. Their three-layer model for profile CD, therefore, is more appropriately a two-layer model, with a lower density layer, with more air and debris, overlying a denser layer, likely corresponding to the firn–ice transition. In addition, they carried out common mid-point (CMP) velocity profiles. While it is encouraging that they have made such an attempt, the results will be affected significantly by the surface and subsurface topography, truncated beds, unconformities, etc., because CMP profiles inherently assume flat-lying surface and subsurface boundaries. The CMP results, while useful, must therefore be treated with caution and assumed to be highly inaccurate and only be used as general guides to vertical velocity variations.

Thermodynamic and Turbulence Characteristics of the Southern Great Plains Nocturnal Boundary Layer Under Differing Turbulent Regimes

The nocturnal stable boundary layer (SBL) can generally be classified into the weakly stable boundary layer (wSBL) and very stable boundary layer (vSBL). Within the wSBL, turbulence is relatively continuous, whereas in the vSBL, turbulence is intermittent and not well characterized. Differentiating characteristics of each type of SBL are still unknown. Herein, thermodynamic and kinematic data collected by a suite of instruments in north central Oklahoma in autumn 2012 are analyzed to better understand both SBL regimes and their differentiating characteristics. Many low-level jets were observed during the experiment, as it took place near a climatological maximum. A threshold wind speed, above which bulk shear-generated turbulence develops, is found to exist up to 300 m. The threshold wind speed must also be exceeded at lower heights (down to the surface) in order for strong turbulence to develop. Composite profiles, which are normalized using low-level jet scaling, of potential temperature, wind speed, vertical velocity variance, and the third-order moment of vertical velocity ( $$\overline{w'^3}$$ ) are produced for weak and moderate/strong turbulence regimes, which exhibit features of the vSBL and wSBL, respectively. Within the wSBL, turbulence is generated at the surface and transported upward. In the vSBL, values of vertical velocity variance are small throughout the entire boundary layer, likely due to the fact that a strong surface inversion typically forms after sunset. The temperature profile tends to be approximately isothermal in the lowest portions of the wSBL, and it did not substantially change over the night. Within both types of SBL, stability in the residual layer tends to increase as the night progresses. It is thought that this stability increase is due to differential warm air advection, which frequently occurs in the southern Great Plains when southerly low-level jets and a typical north–south temperature gradient are present. Differential radiative flux divergence also contributes to this increase in stability.

Characterization of the geological and geotechnical properties of soil using the surface wave approach

<p>As part of the efforts to examine the elastic and engineering properties of the subsurface sequence at a proposed new power plant site in Edo State, a geophysical survey involving Multichannel Analysis of Surface Waves (MASW) was carried out. The MASW was adopted to determine the vertical and lateral variations in velocity beneath each seismic line. The MASW was carried out on two seismic lines each trending NE-SW. A geophone interval of 3 m was used, and the length of the seismic lines ranged from 60 – 90 m. The ES-3000 seismograph was used for the surface wave data acquisition and the Shear-Wave velocity structures of the area were obtained through the inversion of the acquired surface wave data. The one dimensional (1D) S-Wave velocity profiles along the lines were diagnostic of generally low velocity lithologies that suggest sand, clayey sand and sandy clay formations with relatively varying thicknesses. The subsurface layers delineated had shear-wave velocity values in the range of 63-400 m/s. They were classified using the NEHRP Seismic Site Classification, and all of them were in the range of stiff soil to soft clay soil. The bulk moduli (k) for these soils were in the range of 3.22-3.98 GPa. This depicts relatively low strength of the subsurface materials. The shear moduli (μ) values range from 7.15-7.43 MPa, which is indicative of low to moderate strength. The information provided in this study will aid the structural engineer or architect in foundation design of the proposed power plant. From the results of this study, it is concluded that although the subsurface layers are of relatively low strength, with the right intervention of the civil engineer, a suitable foundation can be designed for the gas plant.</p>

Sensitivities of Lagrangian modelling of mid-latitude cirrus clouds to trajectory data quality

Abstract. Simulations of cirrus are subject to uncertainties in model physics and meteorological input data. Here we model cirrus clouds along air mass trajectories, whose extinction has been measured with an elastic backscatter lidar at Jungfraujoch research station in the Swiss Alps, with a microphysical stacked box model. The sensitivities of these simulations to input data uncertainties (trajectory resolution, unresolved vertical velocities, ice nuclei number density and upstream specific humidity) are investigated. Variations in the temporal resolution of the wind field data (COSMO-Model at 2.2 km resolution) between 20 s and 1 h have only a marginal impact on the trajectory path, while the representation of the vertical velocity variability and therefore the cooling rate distribution are significantly affected. A temporal resolution better than 5 min must be chosen in order to resolve cooling rates required to explain the measured extinction. A further increase in the temporal resolution improves the simulation results slightly. The close match between the modelled and observed extinction profile for high-resolution trajectories suggests that the cooling rate spectra calculated by the COSMO-2 model suffice on the selected day. The modelled cooling rate spectra are, however, characterized by significantly lower vertical velocity amplitudes than those found previously in some aircraft campaigns (SUCCESS, MACPEX). A climatological analysis of the vertical velocity amplitude in the Alpine region based on COSMO-2 analyses and balloon sounding data suggests large day-to-day variability in small-scale temperature fluctuations. This demonstrates the necessity to apply numerical weather prediction models with high spatial and temporal resolutions in cirrus modelling, whereas using climatological means for the amplitude of the unresolved air motions does generally not suffice. The box model simulations further suggest that uncertainties in the upstream specific humidity (± 10 % of the model prediction) and in the ice nuclei number density (0–100 L−1) are more important for the modelled cirrus cloud than the unresolved temperature fluctuations if temporally highly resolved trajectories are used. For the presented case the simulations are incompatible with ice nuclei number densities larger than 20 L−1 and insensitive to variations below this value.

CLUBB as a unified cloud parameterization: Opportunities and challenges

AbstractCLUBB (Cloud Layers Unified by Binormals) is a higher‐order closure (HOC) method with an assumed joint probability density function (PDF) for the subgrid variations in vertical velocity, temperature, and moisture. CLUBB has been implemented in the atmospheric component (AM3) of the Geophysical Fluid Dynamics Laboratory general circulation model AM3‐CLUBB and successfully unifies the treatment of shallow convection, resolved clouds, and planetary boundary layer (PBL). In this study, we further explore the possibility for CLUBB to unify the deep convection in a new configuration referred as AM3‐CLUBB+. AM3‐CLUBB+ simulations with prescribed sea surface temperature are discussed. Cloud, radiation, and precipitation fields compare favorably with observations and reanalyses. AM3‐CLUBB+ successfully captures the transition from stratocumulus to deep convection and the modulated response of liquid water path to aerosols. Simulations of tropical variability and the Madden‐Julian oscillation (MJO) are also improved. Deficiencies include excessive tropical water vapor and insufficient ice clouds in the midlatitudes.

Importance of Vertical Variations of Velocity for Shear Dispersion in Rivers

AbstractAn expression for the dispersion coefficient in a rectangular channel is derived to evaluate the importance of transverse and vertical variations in velocity for dispersion. The contribution of vertical variations to dispersion depends not on the ratio of the width B and depth H of the channel—as is usually assumed—but on the ratio of mixing times, τ=(H2/Dz)/(B2/Dy), where Dy and Dz are the transverse and vertical mixing coefficients, respectively. The analysis allows the role of vertical variations to be assessed quantitatively as a function of the time scale ratio and the shape of the velocity profile. The time scale ratio is estimated using data sets compiled by others and several empirical formulas for Dy. In almost all cases, vertical variations contribute a small amount to the overall dispersion. The results support the usual practice of considering only transverse variations in computing the dispersion coefficient, and the analysis provides an approach for including vertical variations in c...

Frequency-dependent multi-offset phase analysis of surface waves: an example of high-resolution characterization of a riparian aquifer

Multi-offset phase analysis of seismic surface waves is an established technique for the extraction of dispersion curves with high spatial resolution and, consequently, for the investigation of the subsurface in terms of shear wave velocity distribution. However, field applications are rarely documented in the published literature. In this paper, we discuss an implementation of the multi-offset phase analysis consisting of the estimation of the Rayleigh wave velocity by means of a moving window with a frequency-dependent length. This allows maximizing the lateral resolution at high frequencies while warranting stability at the lower frequencies. In this way, we can retrieve the shallow lateral variability with high accuracy and, at the same time, obtain a robust surface-wave velocity measurement at depth. In this paper, we apply this methodology to a dataset collected for hydrogeophysical purposes and compare the inversion results with those obtained by using refraction seismics and electrical resistivity tomography. The surface-wave results are in good agreement with those provided by the other methods and demonstrate a superior capability in retrieving both lateral and vertical velocity variations, including inversions. Our results are further corroborated by the lithological information from a borehole drilled on the acquisition line. The availability of multi-offset phase analysis data also allows disentangling a fairly complex interpretation of the other geophysical results.

Numerical modeling of turbulence above offshore helideck – Comparison of different turbulence models

The turbulent flow over an offshore oil-rig helideck has been simulated by a commercial engineering CFD code, Star-CCM+, with nine different turbulence models: two Reynolds-stress transport equation (RSE) models, six k–ε models and one k–ω model. Simulations by the same code and models were compared to experimental data for simpler test cases, including flows over a backward-facing step and a surface-mounted cube. The primary aim was to compare RSE models to two-equation models on the background of a new industry standard for helicopter operation with requirements on the vertical velocity variance over the helideck. It was found that RSE models do not outperform two-equation models for separated flows and wakes. The RSE models seem to underpredict the turbulence energy more than the two-equation models and hence, also the vertical velocity variance. Among the two-equation models, the realizable k–ε model and Menter׳s k–ω model performed better than the standard k–ε model, while a cubic k–ε model predicted unphysical, negative normal Reynolds stresses. Attempts on adjusting the coefficients of the k–ε model, as promoted by some authors, worked fine for undisturbed atmospheric flow but quite poor for more complex flows.

Langmuir Turbulence under Hurricane Gustav (2008)

AbstractExtreme winds and complex wave fields drive upper-ocean turbulence in tropical cyclone conditions. Motivated by Lagrangian float observations of bulk vertical velocity variance (VVV) under Hurricane Gustav (2008), upper-ocean turbulence is investigated based on large-eddy simulation (LES) of the wave-averaged Navier–Stokes equations. To realistically capture wind- and wave-driven Langmuir turbulence (LT), the LES model imposes the Stokes drift vector from spectral wave simulations; both the LES and wave model are forced by the NOAA Hurricane Research Division (HRD) surface wind analysis product. Results strongly suggest that without LT effects simulated VVV underestimates the observed VVV. LT increases the VVV, indicating that it plays a significant role in upper-ocean turbulence dynamics. Consistent with observations, the LES predicts a suppression of VVV near the hurricane eye due to wind-wave misalignment. However, this decrease is weaker and of shorter duration than that observed, potentially due to large-scale horizontal advection not present in the LES. Both observations and simulations are consistent with a highly variable upper ocean turbulence field beneath tropical cyclone cores. Bulk VVV, a TKE budget analysis, and anisotropy coefficient (ratio of horizontal to vertical velocity variances) profiles all indicate that LT is suppressed to levels closer to that of shear turbulence (ST) due to misaligned wind and wave fields. VVV approximately scales with the directional surface layer Langmuir number. Such a scaling provides guidance for the development of an upper-ocean boundary layer parameterization that explicitly depends on sea state.

Relationship between vertical and horizontal jump variables and muscular performance in athletes.

This study investigated the relationship between vertical and horizontal measures in bilateral and unilateral countermovement jump, drop jump and squat jump (SJ), and sprinting speed and muscle architecture of both the vastus lateralis and gastrocnemius. Subjects (n = 17) completed a 30-m sprint test, muscle stiffness test; ultrasound measures, and a jump testing session. Measures of horizontal peak and mean force, in both bilateral and unilateral jumps, tended to have greater relationships to sprint speeds (R = 0.132-0.576) than peak and mean force in the vertical plane (R = 0.008-0.504). Vertical velocity variables also showed some large and very large correlations to sprint speed (R = 0.062-0.635). Unilateral measures of velocity tended to have larger correlations to sprint performance than their bilateral counterparts across all jump types and peak and mean velocity in SJ showed large and very large correlations to sprint speed (bilateral R = 0.227-0.635; unilateral 0.393-0.574). Few large correlations were shown between muscle stiffness measures of muscle architecture and kinetic and kinematic variables in either vertical or horizontal jumps. The present findings suggest that sport scientists and strength and conditioning practitioners concerned with the prognostic value of kinetic variables to functional movements such as sprint speed should also use horizontal jumps in addition to vertical jumps in testing and training.

Convection structure in the solar photosphere at granulation and mesogranulation scales

Vertical structure of the solar photospheric convection is investigated using the profiles of neutral iron line λ ≈ 639.3 nm measured in a non-pertubed region near the center of the solar disk. The observations were carried out using German Vacuum Tower Telescope (Canary Islands, Spain). They are characterized by a high spatial resolution. Spatial-temporal variations of the kinematic and ther-modynamic parameters were reproduced by solving the nonequilibrium inverse radiative transfer problem. The wave motions were eliminated using the k — ω filtration. Spatial variations of temperature, vertical velocity, density, and gas pressure in convective cells are analyzed on the scales of granules (0.5–5 Mm) and mesogranules (5–12 Mm), respectively, at various heights in the solar photosphere (h = −25–500 km). When moving to the upper photosphere layers, the convective structure undergoes the following changes: at heights h = 200–250 km, the temperature inversion occurs, as well as some-times the inversion of convective velocities; at heights h = 50–100 km, the inversion of relative density variations takes place, the relative variations in density and pressure inside convective cells increase with height and become positive in ascending flows and negative in descending flows.

Correction of a Non-orthogonal, Three-Component Sonic Anemometer for Flow Distortion by Transducer Shadowing

Abstract We propose that flow distortion within a non-orthogonal CSAT3 sonic anemometer is primarily due to transducer shadowing, which is caused by wakes in the lee of the acoustic transducers impinging on their measurement paths. The dependence of transducer shadowing on sonic path geometry, wind direction and atmospheric stability is investigated with simulations that use surface-layer data from the Horizontal Array Turbulence Study (HATS) field program and canopy roughness-sublayer data from the CHATS (Canopy HATS) field program. We demonstrate the efficacy of correcting the CSAT3 for transducer shadowing with measurements of its flow distortion in the NCAR wind tunnel, combined with 6 months of data collected in the atmospheric surface layer with adjacent CSAT3 and orthogonal ATI-K sonic anemometers at the NCAR Marshall field site. CSAT3 and ATI-K measurements of the variance of vertical velocity $$\sigma _w^2$$ σ w 2 and the vertical flux of sonic temperature agree within 1 % after correction of both sonics for transducer shadowing. Both the simulations of transducer shadowing and the comparison of CSAT3 and ATI-K field data suggest a simple, approximate correction of CSAT3 surface-layer scalar fluxes with an increase on the order of 4–5 %, independent of wind direction and atmospheric stability. We also find that $$\sigma _w/u_*$$ σ w / u ∗ (where $$u_*$$ u ∗ is the friction velocity) and $$r_{uw}$$ r u w (the correlation coefficient) calculated with corrected CSAT3 data are insensitive to wind direction and agree closely with known values of these dimensionless variables for neutral stratification, which is evidence for the efficacy of the correction of the horizontal wind components for transducer shadowing as well.

Net primary production in the Gulf Stream sustained by quasi‐geostrophic vertical exchanges

AbstractWe analyze 12 years of mesoscale vertical motion derived from an observation‐based product in the top 1000 m of the North West Atlantic Ocean. Vertical velocities (O(10 m d−1)) associated with Gulf Stream instabilities consist of alternating cells of upwelling and downwelling. Here we show that the magnitude of the vertical motions decays exponentially southward with an e‐folding length scale that is informative on the dynamics of the system. We further investigate the impact of the vertical supply of nutrients about phytoplankton growth with a conceptual model incorporating the mean effect of nutrient distribution, quasi‐geostrophic dynamics, and Ekman suction/pumping. Results confirm that the mean effect of mesoscale vertical velocity variability alone can sustain observed levels of net primary production in the immediate vicinity of the Gulf Stream, while other mechanisms, including horizontal advection and submesoscale dynamics, need to be considered when moving toward the subtropical gyre.