Vertical Velocity Research Articles

Temperature-dependent akinete formation strategies of the harmful cyanobacterium Dolichospermum circinale

Cyanobacteria from the orders Nostocales and certain Stigonematales form akinetes, spore-like dormant cells that allow them to survive adverse environmental conditions. Temperature is known to be one of the key factors affecting akinete formation, but there is currently little known about akinete formation during cell growth over a wide range of temperature conditions and its relation to the overall survival strategy of cyanobacteria. Therefore, in the current study, we conducted a temperature-controlled experiment to analyze the akinete formation of a harmful cyanobacterium Dolichospurmum circinale using a growth chamber. We measured the concentration and size of both vegetative cells and different types of akinetes (free, attached, and empty type) under varying temperatures (5–25 °C). We also analyzed the buoyant ability and vertical migration velocity of trichomes along with changes in the volume of vegetative cells and akinetes. The total akinete concentration and ratio (number of akinetes to total number of cells) were both found to be higher at high temperatures (20–25°C) than they were at low temperatures (5–10°C) (p<0.05). Meanwhile, the rate of formation of akinetes (both free and attached akinetes) was highest at low temperature (10 °C) and decreased with increasing temperature. The rate of empty akinete formation increased with increasing temperature and was highest at 25°C, indicating that most of the akinetes produced under high temperature conditions germinated. The change in vegetative cell size was proportional to the increase in the growth rate in response to increasing temperature (p<0.05). At high temperature, vegetative cells exhibited positive buoyancy and higher vertical migration velocity, while at low temperature, they exhibited negative buoyancy and relatively low migration velocity. Akinete size was larger at low temperature than it was at high temperature. These findings suggest that akinetes play an important role in maintaining populations in the water column, with a link between akinete formation and germination during summer cyanobacteria blooms. This information is expected to contribute to a deeper understanding of the D. circinale life cycle.

A kinematic analysis of the two types of soccer throw-in techniques

This study aimed to identify kinematic variables in two soccer throw-in techniques, examine their relationship to throw distance, and explore differences based on technique. A descriptive approach was used, with a purposive sample of 15 first-grade players from the Hussein Youth Club. Each player performed both types of throw-in techniques, recorded at 60 f/s using a Nikon D3400 camera placed laterally. A total of 30 successful attempts were analyzed using Kinovea 0.8.27 x64. Variables studied included foot distance, skill duration, release velocity and angle, and ball release height. Data were analyzed with SPSS. The results revealed weaknesses in the side throw-in technique, such as a low release angle, though better distances were achieved with the second technique. Significant correlations were found between foot distance, release angle, release velocity, vertical velocity, and throw distance (p&lt;0.05). There were also statistically significant differences in knee angle, moment of throw, and throw distance, favoring the second technique (p&lt;0.05). The sample's technique shows several weaknesses impacting performance. Projectile variables strongly influence throw distance, closely linked to various kinematic factors. Moreover, the throw-in method is crucial in determining the overall distance.

A Numerical Investigation on the Sinkage of the Deep-Sea Mining Vehicle Based on a Modified Constitutive Soil Model

Abstract The seabed soil of the polymetallic nodule mining area is relatively thin, soft, and fluid, which will produce large deformation under external disturbance. Its undrained shear strength is related to strain-rate and strain-softening effect. It is an important engineering safety problem for the deep-sea mining vehicle (DSMV) to travel in the soft seabed, and its sinkage is a vital index affecting the traction performance. It is necessary to study the sinkage performance of the DSMV under the characteristics of large soil deformation, but there are only few existing studies. This study established a numerical model of seabed soft soil with Tresca constitutive considering strain-rate and strain-softening effects. First, a numerical simulation study was carried out on the interaction between the DSMV track plate and the seabed soil, and the influence of track plate structures on the pressure–sinkage characteristic was obtained. Then, a simplified three-dimensional model of the “PIONEER-I” DSMV was established. Under the condition of wet weight and initial vertical velocity, the influence of different initial bottoming velocities, weight, and soil parameters on the sinkage of the DSMV was obtained. An empirical prediction model of the DSMV sinkage was established based on the energy method and numerical calculation results.

Surface Quasi Geostrophic Reconstruction of Vertical Velocities and Vertical Heat Fluxes in the Southern Ocean: Perspectives for SWOT

AbstractMesoscale currents account for 80% of the ocean's kinetic energy, whereas submesoscale currents capture 50% of the vertical velocity variance. SWOT's first sea surface height (SSH) observations have a spatial resolution an order of magnitude greater than traditional nadir‐looking altimeters and capture mesoscale and submesoscale features. This enables the derivation of submesoscale vertical velocities, crucial for the vertical transport of heat, carbon and nutrients between the ocean interior and the surface. This work focuses on a mesoscale energetic region south of Tasmania using a coupled ocean‐atmosphere simulation at km‐scale resolution and preliminary SWOT SSH observations. Vertical velocities (w), temperature anomalies and vertical heat fluxes (VHF) from the surface down to 1,000 m are reconstructed using effective surface Quasi‐Geostrophic (sQG) theory. An independent method for reconstructing temperature anomalies, mimicking an operational gridded product, is also developed. Results show that sQG reconstructs 90% of the modeled w and VHF rms at scales down to 30 km just below the mixed layer and 50%–70% of the rms for scales larger than 70 km at greater depth, with a spatial correlation of 0.6. The reconstruction is spectrally coherent for scales larger than 30–40 km at the surface, slightly degrading ( 0.55) at depth. Two temperature anomaly data sets yield similar results, indicating the dominance of w on VHF. The RMS of sQG and VHF derived from SWOT are twice as large as those derived from conventional altimetry, highlighting the potential of SWOT for reconstructing energetic meso and submesoscale dynamics in the ocean interior.

Outer spiral drill rod lunar soil sampling resistance moment simulation study

Abstract The task of unmanned automated sampling of China’s lunar exploration is to bring back lunar soil samples with a certain depth, and sampling of external auger drill pipe is the best way. The power and moment size of the lunar surface is limited, so a special design is required. In this paper, a unique structural model of a double-auger drilling tool is designed. It is a movement analysis of lunar soil and drill pipe. We use simulated lunar soil simulations and experiments. The Hertz-Mindlin slip-free model in the discrete element software EDEM was used for numerical simulation. Given the disadvantage of the large amount of computation of discrete elements, the “embedding simulation method” proposed in this paper reduces the amount of computation. When drilling 0.4m and 1m under lunar and earth gravity, the magnitude and influence of drill pipe rotation and vertical velocity on the drag moment were analyzed. We provide the relevant technical parameters of the real unmanned drilling activities on the lunar surface. Through simulation, the rationality parameters of several groups of drill pipe drilling are obtained to ensure the smooth progress of drilling.

On the Role of Physical Processes in Controlling Equatorial Plasma Bubble Morphology

AbstractIn this study, we present the results of an analysis of the morphological features of Equatorial Plasma Bubbles (EPBs) over South America. In this context, we analyzed data from the Disturbance Ionosphere indeX (DIX) maps calculated using around 450 Global Navigation Satellite System (GNSS) stations. To mitigate the influence of magnetic disturbances on bubble development, only data from geomagnetically quiet days were utilized. This study covered the period from the post‐peak of solar cycle 24 (2015) to the pre‐peak of solar cycle 25 (2023), totaling 1321 nights with EPB occurrences, representing the largest data set of EPBs ever compiled for South America. Our analysis unveiled several key findings regarding EPBs and their behavior over the South American region. First, we observed that the amplitude of plasma depletions, as reflected in the DIX values, and the EPB latitudinal development follow an approximately 11‐year cycle driven by solar radiation levels. Furthermore, our analysis highlights the significant influence of factors such as the angle between the solar terminator and the magnetic meridian (T‐M angle), which varies inversely with the vertical plasma drift velocity during the pre‐reversal enhancement (PRE). Additionally, we discuss the longitudinal variations associated with magnetic declination, as well as the saturation behavior of EPB development with extreme solar flux.

Characteristics of Gravity Waves in Opposing Phases of the QBO: A Reanalysis Perspective with ERA5

Abstract Gravity waves dispersing upward through the tropical stratosphere during opposing phases of the QBO are investigated using ERA5 data for 1979–2019. Log–log plots of two-sided zonal wavenumber–frequency spectra of vertical velocity, and cospectra representing the vertical flux of zonal momentum in the tropical lower stratosphere, exhibit distinctive gravity wave signatures across space and time scales ranging over two orders of magnitude. Spectra of the vertical flux of momentum are indicative of a strong dissipation of westward-propagating gravity waves during the easterly phase and vice versa. This selective “wind filtering” of the waves as they disperse upward imprints the vertical structure of the zonal flow on the resolved wave spectra, characteristic of (re)analysis and/or free-running models. The three-dimensional structures of the gravity waves are documented in composites of the vertical velocity field relative to grid-resolved tropospheric downwelling events at individual reference grid points along the equator. In the absence of a background zonal flow, the waves radiate outward and upward from their respective reference grid points in concentric rings. When a zonal flow is present, the rings are displaced downstream relative to the source and they are amplified upstream of the source and attenuated downstream of it, such that instead of rings, they assume the form of arcs. The log–log spectral representation of wind filtering of equatorial waves by the zonal flow in this paper can be used to diagnose the performance of high-resolution models designed to simulate the circulation of the tropical stratosphere.

Evolution of Turbulent Boundary Conditions on the Surface of Large Barchan Dunes: Anomalies in Aerodynamic Roughness and Shear Velocity, Aeolian Threshold, and the Role of Dune Skewness

AbstractWe recorded aerodynamic roughness and shear velocity along transects on and around mature crescent‐shaped barchan dunes of and height above the horizontal rock‐covered Qatar desert by fitting to the log‐law time‐averaged vertical velocity profiles acquired from triads of ultrasonic anemometers penetrating the inner turbulent boundary layer. Shear velocity first decreased, then recovered as air climbed on the dune, with a local maximum ahead of the crest as predicted by the Jackson and Hunt (1975, https://doi.org/10.1002/qj.49710143015) theory. Unlike flows over gentler bedforms without a slope discontinuity, an anomalous peak of shear velocity also arose on the dune centerline at the brink, which the theory attributed to skewness in the dune transect profile. The onset of aeolian transport produced a log‐law passing through the Bagnold (1941, https://doi.org/10.1007/978‐94‐009‐5682‐7) focal point. It was bracketed by noticeable hysteretic peaks in the correlation between wind speed and entrained sand flux. The dunes' rocky surroundings and topography produced an aerodynamic roughness at odds with the Nikuradse (1933, https://ntrs.nasa.gov/citations/19930093938) data for fully developed turbulent boundary layers. Large‐eddy numerical simulations illustrated the sensitivity of shear velocity to wide changes in aerodynamic roughness from desert floor to dune surface.

Dynamics of the air bubble on the upper surface of a plate: Influences of the cavitation bubble

The interaction of laser-induced cavitation bubbles with air bubbles attached to the upper surface of a horizontal plate was studied with high-speed photography. On the cavitation bubble side, the dimensionless distance parameter, γ=4.5 for vertical jets from cavitation bubbles as proposed in previous research and the dimensionless parameter, γ=5.8 for oblique upward jets have been established. On the attached air bubble side, the relationship between the dimensionless distance parameter, γa and the four types of morphology (Omega, hemisphere, hemisphere to hat with split, and hemisphere to hat without split) of attached air bubbles, as well as the three modes of jets (initial, multiple, and delay), has been demonstrated. The split of the small bubble from the attached bubble is primarily due to the vertical velocity differences brought about by the multiple collapses of cavitation bubbles and the pulsation of attached bubbles. Subsequent studies on the detachment behavior of attached bubbles determined the ideal dimensionless distance, γa=3.4 for detachment. The surface ripples play a dominant role in promoting the detachment of attached bubbles at greater distances.

Vertical Velocity Dynamics in the North Atlantic and Implications for AMOC

Abstract The Atlantic meridional overturning circulation (MOC) is traditionally monitored in terms of zonally integrated transport either in depth space or in density space. While this view has the advantage of simplicity, it obscures the rich and complex three-dimensional structure, so that the exact physics of the downwelling and upwelling branch remains poorly understood. The near-equivalence of the depth- and density-space MOC in the subtropics suggests that vertical and diapycnal volumes transports are intimately coupled, whereas the divergence of these two metrics at higher latitudes indicates that any such coupling is neither instantaneous nor local. Previous work has characterized the surface buoyancy forcing and mixing processes which drive diapycnal volume transport. Here, we develop a new analytical decomposition of vertical volume transport based on the vorticity budget. We show that most terms can be estimated from observations and provide additional insights from a high-resolution numerical simulation of the North Atlantic. Our analysis highlights the roles of 1) relative vorticity advection for the sinking of overflow water at the northern subpolar North Atlantic boundaries and 2) the geostrophic β effect for the sinking of dense waters in the intergyre region. These results provide insights into the coupling between density- and depth-space overturning circulations. Significance Statement The purpose of this study is to better understand where and why dense water sinks in the North Atlantic. This is important because dense water sinking in the North Atlantic is a crucial component of the global thermohaline circulation. Our results reveal the primary controls on dense water sinking at a regional level and highlight the importance of mesoscale processes at high latitudes in shaping the circulation and heat distribution throughout the Atlantic Ocean.

Tropical Cyclones in the GEOS-S2S-2 Subseasonal Forecasts

Abstract This paper analyzes the climatology, prediction skill, and predictability of tropical cyclones (TCs) in NASA’s Goddard Earth Observing System Subseasonal to Seasonal (GEOS-S2S) forecast system version 2. GEOS reasonably simulates the number and spatial distribution of TCs compared to observations except in the Atlantic where the model simulates too few TCs due to low genesis rates in the Caribbean Sea and Gulf of Mexico. The environmental conditions, diagnosed through a genesis potential index, do not clearly explain model biases in the genesis rates, especially in the Atlantic. At the storm scale, GEOS reforecasts replicate several key aspects of the thermodynamic and dynamic structures of observed TCs, such as a warm core and the secondary circulation. The model, however, fails to simulate an off-center eyewall when evaluating vertical velocity, precipitation, and moisture. The analysis of the prediction skill of TC genesis and occurrence shows that GEOS has comparable skill to other global models in WMO S2S archive and that its skill could be further improved by increasing the ensemble size. After calibration, GEOS forecasts are skillful in the western North Pacific and southern Indian Ocean up to 20 days in advance. A model-based predictability analysis demonstrates the importance of the Madden–Julian oscillation (MJO) as a source of predictability of TC occurrence beyond the 14-day lead time. Forecasts initialized under strong MJO conditions show evidence of predictability beyond week 3. However, due to model biases in the forecast distribution, there are notable gaps between the MJO-related prediction skill and predictability, which require further study.

A Review on the Vertical Coordinate Systems used in Oceanic and Atmospheric Circulation Numerical Model

In a numerical method for the study of the circulation model, various vertical coordinate systems are used to simulate the physical response of the ocean and atmosphere to the increasing greenhouse gas emission. In this study, four types of vertical coordinate systems frequently used in oceanic and atmospheric circulation numerical models, i.e., height, general, pressure, and normalized vertical coordinate systems, respectively are introduced. Finally, the hydrostatic pressure equation, vertical velocity, equation of horizontal motion, and continuity equation expressed in a vertical coordinate system were introduced, and the pros and cons of the vertical coordinate system were summarized to promote the accuracy of numerical model development.

DEM investigation on the dynamic characteristics of wall normal stress and particle flow during silo discharge

Violent fluctuations of wall normal stress and particle velocity during silo discharge have been frequently reported by researchers, yet a detailed particle-scale description of these phenomena is still lacking. In this work, the discharge of granular assembly from a flat-bottomed silo was investigated by performing three-dimensional (3D) Discrete Element Method (DEM) simulations. It is found that arc-shaped rupture surfaces, characterized by the lower solid volume fraction, stronger shear interaction between particles and higher particle rotating velocity, developed continuously in the bottom converging part of flowing zone. And the temporal evolution of particle velocity field in this converging part presented a swinging feature manifested by the alternate appearance of large particle velocity magnitude in the right- and left- side regions. Discrete Fourier transform results showed that the fluctuation of wall normal stress at the transition point contained two dominate frequencies. The lower frequency matched well with the dynamic evolution of the rupture surface joining the transition point, and the higher frequency was nearly the same as the fluctuating frequency of particle vertical velocity. Thus, our DEM simulation results suggested that for the silo discharge considered in this work, the periodic fluctuation of wall normal stress at the transition point was contributed by both the alternating flow pattern mechanism and the free-fall arch mechanism.

Over 100-fold improvement in the accuracy of relaxed eddy accumulation flux estimates through error diffusion

Measurements of atmosphere-surface exchange are largely limited by the availability of fast-response gas analyzers; this limitation hampers our understanding of the role of terrestrial ecosystems in atmospheric chemistry and global change. Current micrometeorological methods, compatible with slow-response gas analyzers, are difficult to implement, or rely on empirical parameters that introduce large systematic errors.Here, we develop a new micrometeorological method, optimized for slow-response gas analyzers, that directly measures exchange rates of different atmospheric constituents, with minimal requirements. The new method requires only the sampling of air at a constant rate and directing it into one of two reservoirs, depending on the direction of the vertical wind velocity. An integral component of the new technique is an error diffusion algorithm that minimizes the biases in the measured fluxes and achieves direct flux estimates.We demonstrate that the new method provides an unbiased estimate of the flux, with accuracy within 0.1% of the reference eddy covariance flux, and importantly, allows for significant enhancements in the signal-to-noise ratio of measured scalars without compromising accuracy. Our new method provides a simple and reliable way to address complex environmental questions and offers a promising avenue for advancing our understanding of ecological systems and atmospheric chemistry.

A statistical analysis of atmospheric parameters for cataloged astronomical observatory sites

Astronomical sites have to be selected according to many factors whereas the geographic location of the site and the quality of the atmosphere above the site play an important role in the decision process. The following factors were chosen to create layers 1907 northern and 235 southern observatories: CC (cloud coverage), PWV (precipitable water vapor), AOD (aerosol optical depth), VWV (vertical wind velocity), and HWV (horizontal wind velocity). To estimate the astronomical importance of the sites, DEM (digital elevation model) and LAT (latitude of observatory location) layers were also included. In addition to the variations or trends, a complete statistical analysis was carried out for all factors to investigate the potential correlations between the factors. There is a clear difference between the northern and southern hemispheres. The exchange of meteorological seasons between hemispheres is also compliant with factors. The geographical locations of most of the observatories were found to be “not suitable”. There seem to be no apparent long-term variations and/or patterns in all factors.

Comparative Analysis of the Kinematic Characteristics of Lunge-Style and Squat-Style Jerk Techniques in Elite Weightlifters.

This study aimed to discuss the differences in technical characteristics between the lunge-style and squat-style jerk techniques and to reveal the adaptability of these techniques for individual weightlifters. A total of 52 attempts by 32 male weightlifters were selected, and the video data were digitized manually using the SIMI Motion 7.50 three-dimensional analysis system. The technical characteristics of the lunge split and squat jerk were fundamentally consistent during the pre-squat, force exertion, and inertia ascent phases. The primary differences between the lunge split and squat jerk techniques were observed during the squatting and support phases, including the vertical descent velocity of the barbell at the end of the squat shoulder-locking phase and the stability angles in the sagittal and coronal axes. The vertical velocity of the barbell at the end of the squat shoulder-locking phase was significantly greater in the squat style (-0.41 ± 0.17 vs. -0.88 ± 0.14) compared to the lunge style (t = 6.393, p < 0.05). The stability angle on the sagittal axis at the end of the squat-supporting phase in the lunge style was significantly greater (46.99 ± 3.23 vs. 13.64 ± 0.51) than that of the squat style (t = 45.639, p < 0.05).

Seasonal Tracer Subduction in the Subpolar North Atlantic Driven by Submesoscale Fronts

AbstractSubmesoscale flows (0.1–10 km) are often associated with large vertical velocities, which can have a significant impact on the transport of surface tracers, such as carbon. However, global models do not adequately account for these small‐scale effects, which still require a proper parameterization. In this study, we introduced a passive tracer into the surface mixed layer (ML) of a northern Atlantic Ocean simulation based on the primitive‐equation model CROCO, with a horizontal resolution of Δx = 800 m, aiming to investigate the seasonal submesoscale effects on vertical transport. Using surface vorticity and strain rate criteria, we identified regions with submesoscale fronts and quantified the associated subduction, that is the export of tracer below the ML depth. The results suggest that the tracer vertical distribution and the contribution of frontal subduction can be estimated from surface strain and vorticity. Notably, we observed significant seasonal variations. In winter, the submesoscale fronts contribute up to 40% of the total vertical advective transport of tracer below the ML, while representing only 5% of the domain. Conversely, in summer, fronts account for less than 1% of the domain and do not contribute significantly to the transport below the ML. The findings of this study contribute to a better understanding of the seasonal water subduction due to fronts in the region.

Investigation of Improved Energy Dissipation in Stepped Spillways Applying Bubble Image Velocimetry

This study investigates skimming flow regimes, two-phase air–water flow conditions, and simple measures to improve energy dissipation in stepped spillways. Experiments were conducted using two different scale physical models, 1:50 and 1:17, within separate rectangular flumes to define scale effects. Flow patterns were analyzed using the Bubble Image Velocimetry (BIV) technique, which tracks air bubbles. The introduction of splitters resulted in a 7% increase in relative energy dissipation. Additionally, the length of inception was reduced to Li/ks = 10, thereby decreasing the potential for subsequent cavitation. Beyond the BIV experiments, two experiments were conducted on the large-scale model using Acoustic Doppler Velocimetry (ADV), with and without splitters, to examine the impact of splitters on the velocity profile above the crest. In the experiment with splitters, the vertical velocity vector (v) contributed to turbulence by changing direction, thereby reducing average velocities both in front of and behind the ogee crest. This led to a reduction in energy on the downstream side of the spillway. Although the small-scale model appears unsuitable for studying two-phase flow, the change in relative energy dissipation from the baseline to the splitter configuration was practically identical for both scale models, thereby supporting the findings of the large-scale model.

Smartphone-Based Sit-to-Stand Analysis for Mobility Assessment in Middle Age.

Mobility can decline in middle age and growing evidence highlights the importance of assessing mobility at this stage of life. Smartphone-based accelerometry during sit-to-stand has been shown to identify mobility impairments, but its utility in detecting subtle mobility deterioration in middle age has not been tested. This study aimed to examine whether smartphone-based accelerometry data measured during sit-to-stand tests performed on a regular chair and a cushioned sofa could be useful for detecting subtle changes in mobility in middle age. Twenty-three young (25.0±2.5 years), 25 middle-aged (52.0±5.2 years), and 17 older adults (70.0±4.1 years) performed the 5-times sit-to-stand test on both a standard chair and a sofa. A smartphone attached to the participants' lower back was used to measure lower-limb muscle power, maximal vertical velocity (MVV) during rising, the duration of the total task and the subphase of transition from sitting to standing (SiToSt), and repetition variability using the dynamic time warping method. Middle-aged adults had reduced lower-limb muscle power compared to young adults (5.25 ± 1.08 vs 6.19 ± 1.38 W/kg, p = .034), being more pronounced on the sofa (6.23 ± 1.61 vs 8.08 ± 2.17 W/kg, p = .004). Differences between middle-aged and young adults in terms of MVV (p = .011) and SiToSt duration (p = .038) were only detected on the sofa, and the middle-aged adults showed less variability compared to the older adults on the chair (p = .018). There was no difference in total task duration between the middle-aged group and the young or older adults in either condition. Most common tests are limited in their ability to detect early mobility deterioration in midlife due to a ceiling effect. Our results, which show the potential of smartphone-based sit-to-stand assessment in detecting subtle mobility decline in midlife, could serve as a screening tool for this purpose.

Numerical solution of the boundary value problem for inertia-gravity internal waves

This paper presents a numerical calculation of the boundary value problem for the equation of free internal inertia-gravity waves in an unbounded basin of constant depth in the Boussinesq approximation and the presence of a two-dimensional vertically inhomogeneous flow. The boundary value problem for the vertical velocity amplitude has complex coefficients and is solved both numerically and by perturbation theory. Using the example of calculating the decrement of attenuation of internal waves and momentum wave flows, it is shown that the exact numerical calculation gives significantly better estimates in comparison with the perturbation method. In particular, at minimum divergence in the dispersion curves for both calculation methods, the imaginary part of the wave frequency, interpreted as the decrement of attenuation, can differ by two or three orders of magnitude. Vertical wave momentum fluxes are comparable to turbulent ones and may exceed them, with results obtained by the numerical method being almost an order of magnitude smaller than those calculated by the perturbation theory method.