Comments on “An Evaluation of Hurricane Superintensity in Axisymmetric Numerical Models”

In a recent paper Rousseau-Rizzi and Emanuel (2019) presented a derivation of an upper limit on maximum hurricane velocity at the ocean surface. This derivation was based on a consideration of an infinitely narrow (differential) Carnot cycle with the warmer isotherm at the point of the maximum wind velocity. Here we show that this derivation neglected a significant term describing the kinetic energy change in the outflow. Additionally, we highlight the importance of a proper accounting for the power needed to lift liquid water. Finally, we provide a revision to the formula for surface fluxes of heat and momentum showing that, if we accept the assumptions adopted by Rousseau-Rizzi and Emanuel (2019), the resulting velocity estimate does not depend on the flux of sensible heat.

RADAR DIFFRACTION HORIZONS IN SNOW AND FIRN DUE TO A SURFICIAL VERTICAL TRANSFER OF MASS

ABSTRACT. We focus here on three horizons conspicuously embedded in the rich radar stratigraphy revealed on the fixed-offset radar data obtained Plateau Detroit, Antarctic Peninsula. Spatial filtering removed the more energetic reflection field and the surface wave arrivals at the earlier time, leaving only the diffracted field. This is particularly striking for the early time horizon where the direct wave arrivals had shrouded the diffractions before filtering. The density estimates and the photographic datasets from a centrally located well at depths compatible with the diffraction horizons suggested they share a common origin: a vertical transfer of mass associated with the formation of surficial hoar from a strong vertical temperature gradient in the snow cover, followed by a quick burial by fresh snow in a high accumulation environment. We have inverted the fundamental mode of the phase velocity dispersion of the surface waves to obtain a group velocity estimate and its depth range, used to improve the 1–D velocity model from a CMP gather by correcting its first velocity estimate. The same inversion solved an apparent ambiguity in our data by associating the surficial horizon with a specific density residual. We have also shown through modeling that the diffraction horizons seen in our data can be explained by the existence of large coarse–grained faceted crystals which became denser with depth than the surrounding firn.Keywords: GPR, radar, campo difratado, modelo de velocidade, guia de ondas, estratigrafia polar, depth hoar, AntárticaRESUMO. Concentramo-nos aqui em três horizontes conspicuamente embutidos na rica estratigrafia revelada nos dados de radar de afastamento constante obtidos Platô Detroit, Península Antártica. Uma filtragem espacial removeu o campo de reflexão mais energético e as chegadas de onda de superfície das primeiras chegadas, deixando apenas o campo difratado. Isso é notável para o horizonte de primeiras chegadas, onde as ondas diretas encobriam as difrações antes da filtragem. As estimativas de densidade e os conjuntos de dados fotográficos do poço localizado no centro da aquisição mostra em profundidades cristais compatíveis com os horizontes de difração dos dados de GPR sugerindo uma origem comum: uma transferência vertical de massa associada à formação de hoar devido a um forte gradiente vertical de temperatura na cobertura de neve fresca em um ambiente de alta acumulação. Nós invertemos o modo fundamental da dispersão de velocidade de fase das ondas de superfície para obter uma estimativa de velocidade de grupo e sua faixa de profundidade usada para melhorar o modelo de velocidade 1-D a partir de um CMP, corrigindo sua primeira estimativa de velocidade. A mesma inversão resolveu uma ambiguidade aparente em nossos dados ao associar o horizonte superficial a uma densidade específica residual. Também mostramos através de modelagem que os horizontes de difração observados em nossos dados podem ser explicados pela existência de grandes cristais facetados de granulação grossa que se tornaram mais densos com a profundidade do que o firn circundante.Palavras-chave: GPR, radar, campo de difração, modelo de velocidade, guia de onda, estratigrafia polar, depth hoar, Antarctica

Distinct fNIRS-Derived HbO2 Trajectories During the Course and Over Repeated Walking Trials Under Single- and Dual-Task Conditions: Implications for Within Session Learning and Prefrontal Cortex Efficiency in Older Adults

Background Neural trajectories of gait are not well established. We determined two distinct, clinically relevant neural trajectories, operationalized via functional near-infrared spectroscopy (fNIRS) HbO2 measures in the prefrontal cortex (PFC), under Single-Task-Walk (STW), and Dual-Task-Walk (DTW) conditions. Course trajectory assessed neural activity associated with attention during the course of a walking task; the second trajectory assessed neural activity associated with learning over repeated walking trials. Improved neural efficiency was defined as reduced PFC HbO2 after practice. Methods Walking was assessed under STW and DTW conditions. fNIRS was utilized to quantify HbO2 in the PFC while walking. Burst measurement included three repeated trials for each experimental condition. The course of each walking task consisted of six consecutive segments. Results Eighty-three nondemented participants (mean age = 78.05 ± 6.37 years; %female = 49.5) were included. Stride velocity (estimate = −0.5259 cm/s, p = <.0001) and the rate of correct letter generation (log estimate of rate ratio = −0.0377, p < .0001) declined during the course of DTW. In contrast, stride velocity (estimate = 1.4577 cm/s, p < .0001) and the rate of correct letter generation (log estimate of rate ratio = 0.0578, p < .0001) improved over repeated DTW trials. Course and trial effects were not significant in STW. HbO2 increased during the course of DTW (estimate = 0.0454 μM, p < .0001) but declined over repeated trials (estimate = −0.1786 μM, p < .0001). HbO2 declined during the course of STW (estimate = −.0542 μM, p < .0001) but did not change significantly over repeated trials. Conclusion We provided evidence for distinct attention (course) and learning (repeated trials) trajectories and their corresponding PFC activity. Findings suggest that learning and improved PFC efficiency were demonstrated in one experimental session involving repeated DTW trials.

Reply to “Comment on ‘Using an ADCP to Estimate Turbulent Kinetic Energy Dissipation Rate in Sheltered Coastal Waters’”

This note is a comment in response to Gargett, who argues that a large-eddy estimate of turbulent dissipation rate using a horizontal length scale with a vertical velocity estimate, as in Greene et al., is a dubious approximation if the energy-containing eddies are anisotropic. A simulation of Langmuir cells and associated turbulence is used to support Gargett’s conclusions. This rebuttal reviews the approaches taken by Greene et al. and cites several instances of flawed reasoning by Gargett. This includes using Langmuir simulations to support the primary conclusion of Gargett, which seems unconnected to Greene et al.’s data and ignores a vast body of work on simulating Kelvin–Helmholtz instabilities, widely considered to be the dominant mechanism producing stratified turbulence.

Isotropic and anisotropic velocity model building for subsalt seismic imaging

The effectiveness of basin simulators for deriving subsalt velocity models has been previously shown through the use of a correlation to relate effective stress to velocity. We build on this and others’ work by using physical models to relate porosity to velocity. This process yields a physically realizable isotropic velocity model that is consistent with the geologic model and matches the tomographic velocity model above salt and in regions where the tomographic velocity estimate is accurate. We then use a geomechanical simulator to model the stress distribution in and around allochthonous salt in which material properties between salt and sediment change. Our stress model is the basis for an anisotropic velocity model using Murnaghan’s theory for finite elastic deformation. This formulation, with bounds placed on the elastic coefficients, leads to significant imaging improvements adjacent to salt.

A Simple and Robust Sliding Mode Velocity Observer for Moving Coil Actuators in Digital Hydraulic Valves

This paper focuses on estimating the velocity and position of fast switching digital hydraulic valves actuated by electromagnetic moving coil actuators, based on measurements of the coil current and voltage. The velocity is estimated by a simple first-order sliding mode observer architecture and the position is estimated by integrating the estimated velocity. The binary operation of digi-valves enables limiting and resetting the position estimate since the moving member is switched between the mechanical end-stops of the valve. This enables accurate tracking since drifting effects due to measurement noise and integration of errors in the velocity estimate may be circumvented. The proposed observer architecture is presented along with stability proofs and initial experimental results. To reveal the optimal observer performance, an optimization of the observer parameters is carried out. Subsequently, the found observer parameters are perturbed to assess the robustness of the observer to parameter estimation errors. The proposed observer demonstrates accurate tracking of the valve movement when using experimentally obtained data from a moving coil actuated digi-valve prototype and observer parameters estimates in the vicinity of the optimized parameter values.

Analysis of the Improvement in Accuracy Using Multiple Gyros

The possibility to improve the accuracy of angular velocity estimate by optimally combining multiple individual micro electromechanical systems (MEMS) gyroscopes is analyzed in this paper. Kalman filter (KF) is used to fuse the numerous measurements into a single improved rate estimate. Based on the virtual gyro idea, a revised approach can give an unbiased estimator regardless of the true angular velocity signal. Numerical simulations are performed to demonstrate the desirable performance, reducing the bias drift and noise.

Enhanced Signal Processing Algorithms for the ASR-9 Weather Systems Processor

New signal processing algorithms for the Airport Surveillance Radar-9 (ASR-9) Weather Systems Processor (WSP) are introduced. The Moving Clutter Spectral Processing for Uneven-Sampled Data with Dealiasing (MCSPUDD) algorithm suite removes isolated moving clutter targets and corrects aliased velocity values on a per-range-gate basis. The spectral differencing technique is applied to the low- and high-beam data to produce a dual-beam velocity estimate that is more accurate than the current autocorrelation-lag-1-based approach. Comparisons with Terminal Doppler Weather Radar (TDWR) data show that estimate errors are reduced by 8%, 15%, and 15% for the low-, high-, and dual-beam velocities, respectively.