Momentum Flux Research Articles

First results of a newly-built hard-X-ray/soft-Gamma spectrometer imaging system: on the aspect of plasma disruptions

Abstract A new Hard X-ray and soft gamma-ray spectrometer imaging System (HXS) has been built for the 2-Dimensional measurements of plasma emitted photons on the Experimental Advanced Superconducting Tokamak (EAST). The system uses a 2-D Cadmium Zinc Telluride (CZT) detector and an integrated electronics, which is as a whole shielded by a tungsten box with a pinhole and is tangential to the toroidal field. Three classes of typical energy spectra have been summarized in differently experimental scenarios over the past campaigns. After performing tomography calculations, the local emissivity contours have been obtained in different energy ranges which obviously show the asymmetry on the plasma cross section. The spatial perturbation structure is similar to the magnetohydrodynamics (MHD) modes with low mode numbers. In particular, the runaway island found by an infrared camera [R. Jaspers et al, Phys. Rev. Lett. 72, 4093 (1994)] is also measured by the HXS. There exists a reversal population on the energy spectra in both slide-away and strong neutral beam injection (NBI) shots. It is consistently observed that the count rate is increased in the low energy range before the plasma disruptions. Calculations in phase space indicate that the accelerated momentum flux can be deflected back to the low energy region by the large pitch-angle scattering. In the post-disruption phase the plasma current is not replaced by runaway electrons due to tearing modes or transiently bursting instabilities. This paper constructs the basics for the proper use of HXS for Hard X-ray and Soft Gamma-ray measurements in future investigations of plasma disruptions.

A comparative study on the performance characteristics of buffer blocks configurations as energy dissipators

This study examines the effectiveness of buffer blocks in dissipating the flow due to extreme events along the coasts using the numerical modelling approach. Initially, the study explores the effect of the number of rows of buffer blocks on the reduction of momentum flux. After establishing that the three rows configuration are the most efficient, subsequent analysis were carried out which include the understanding in the variations of block heights, including adjustments in height ratios between rows and by arranging blocks in increasing or decreasing height within the rows. Through a systematic examination of these configurations, the study aims to determine the most effective setup for maximizing energy dissipation of flow characteristics during extreme events such as tsunamis and storm surges.

Mean-motion resonances with interfering density waves

ABSTRACT In this work, we study the dynamics of two less massive objects moving around a central massive object, which are all embedded within a thin accretion disc. In addition to the gravitational interaction between these objects, the disc–object interaction is also crucial for describing the long-term dynamics of the multibody system, especially in the regime of mean-motion resonances. We point out that near the resonance the density waves generated by the two moving objects generally coherently interfere with each other, giving rise to extra angular momentum fluxes. The resulting backreaction on the objects is derived within the thin-disc scenario, which explicitly depends on the resonant angle and sensitively depends on the smoothing scheme used in the two-dimensional theory. We have performed hydrodynamical simulations with planets embedded within a thin accretion disc and have found qualitatively agreement on the signatures of interfering density waves by measuring the torques on the embedded objects, for the cases of $2:1$ and $3:2$ resonance. By including in interference torque and the migration torques in the evolution of a pair of planets, we show that the chance of resonance trapping depends on the sign of the interference torque. For negative interference torques the pairs are more likely located at off-resonance regimes. The negative interference torques may also explain the $1~{{\ \rm per\ cent}}-2~{{\ \rm per\ cent}}$ offset (for the period ratios) from the exact resonance values as observed in Kepler multiplanet systems.

Influence of atmospheric stability conditions on wind energy density in Ali Al-Gharbi region of Iraq

Atmospheric stability is considered as one of the most important factors affecting the increase or decrease in wind speed in the atmosphere and thus affects the wind energy density. This study aims to analyze the stability of the atmospheric conditions in southern part of Iraq, specifically in the Ali Al-Gharbi region, using one of methods to determine atmospheric stability called Monin-Obukhov length . Field data of horizontal and vertical wind speed and air temperature collected at three heights (10m, 30m, and 50m) in 2017 from tower installed in Ali Al-Gharbi region. The results show that the vertical wind speed increases with height up to 30 m and decreases at 50 m, while the horizontal wind speed increases as the height increases. The friction velocity , surface heat flux , momentum flux and shear stress were calculated and the stability conditions were determined. Results revealed that stable atmospheric condition was the most frequent with about 59% occasions occurring during the year followed by unstable (40%) and neutral (1%) conditions. The highest wind energy density was in stable conditions (0 ≤ L< 200), with percentage (58% - 57%) in spring season at both heights 10m and 50m, respectively, followed by unstable conditions (-200 < L ≤ 0), while the lowest wind energy density was in neutral conditions (-200 ≤ L ≥ 200) with percentage (1.3% - 0.8%) in autumn season.Atmospheric stability is considered as one of the most important factors affecting the increase or decrease in wind speed in the atmosphere and thus affects the wind energy density. This study aims to analyze the stability of the atmospheric conditions in southern part of Iraq, specifically in the Ali Al-Gharbi region, using one of methods to determine atmospheric stability called Monin-Obukhov length . Field data of horizontal and vertical wind speed and air temperature collected at three heights (10m, 30m, and 50m) in 2017 from tower installed in Ali Al-Gharbi region. The results show that the vertical wind speed increases with height up to 30 m and decreases at 50 m, while the horizontal wind speed increases as the height increases. The friction velocity , surface heat flux , momentum flux and shear stress were calculated and the stability conditions were determined. Results revealed that stable atmospheric condition was the most frequent with about 59% occasions occurring during the year followed by unstable (40%) and neutral (1%) conditions. The highest wind energy density was in stable conditions (0 ≤ L< 200), with percentage (58% - 57%) in spring season at both heights 10m and 50m, respectively, followed by unstable conditions (-200 < L ≤ 0), while the lowest wind energy density was in neutral conditions (-200 ≤ L ≥ 200) with percentage (1.3% - 0.8%) in autumn season.

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.

The XMM-Newton and NuSTAR view of IRASF11119+3257

Context. IRASF11119+3257 is an ultra-luminous infrared galaxy with a post-merger morphology, hosting a type-1 quasar at z = 0.189. It shows a prominent ultra-fast outflow (UFO) absorption feature (vout ∼ 0.25c) in its 2013 Suzaku spectrum. This is the first system in which the energy released by the UFO was compared to that of the known galaxy-scale molecular outflow to investigate the mechanism driving active galactic nuclei (AGN) feedback. Aims. In 2021, we obtained the first XMM-Newton long look of the target, coordinated with a simultaneous NuSTAR observation, with the goal of constraining the broad band continuum and the nuclear wind physical properties and energetics with an unprecedented accuracy. Methods. The new high-quality data allowed us to clearly detect at a confidence level P > 99.8% multiple absorption features associated with the known UFO at the 9.1 and 11.0 keV rest frames. Furthermore, an emission plus absorption feature at 1.1 − 1.3 keV reveals the presence of a blueshifted P-Cygni profile in the soft band. Results. We associate the two hard band features with blends of FeXXV and FeXXVI Heα-Lyα and Heβ-Lyβ line pairs and infer a large column (NH ∼ 1024 cm−2) of highly ionized (log ξ ∼ 5) gas outflowing at vout = 0.27 ± 0.01c. The 1.3 keV absorption line can be associated with a blend of Fe and Ne transitions, produced by a lower column (NH ∼ 3 × 1021 cm−2) and ionization (log ξ ∼ 2.6) gas component outflowing at the same speed. Using a radiative-transfer disk wind model to fit the highly ionized UFO, we derive a mass outflow rate comparable with the mass accretion rate and the Eddington limit (Ṁout = 4.25−0.73+1.11 M⊙/yr, ∼1.6 Ṁacc and ∼1.0 ṀEdd), and kinetic energy (Ėkin = 1.21−0.20+0.32 Lbol and ∼0.7LEdd) and momentum flux (Ṗout = 6.37−1.09+1.67 Lbol/c) among the highest reported in the literature. We measured an extremely low high-energy cutoff (Ecut ∼ 25 − 30 keV). This and several other cases in the literature suggest that a steep X-ray continuum may be related to the formation of powerful winds. We also analyzed the ionized [OIII] component of the large-scale outflow through optical spectroscopy and derived a large outflow velocity (vout ∼ 3000 km/s) and energetics comparable with the large-scale molecular outflows. Finally, we observe a trend of decreasing outflow velocity from forbidden optical emission lines of decreasing ionization levels, interpreted as the outflow decelerating at large distances from the ionizing source. Conclusions. The lack of a significant momentum boost between the nuclear UFO and the different phases of the large-scale outflow, observed in IRASF11119 and in a growing number of similar sources, can be explained by (i) a momentum-driven expansion, (ii) an inefficient coupling of the UFO with the host interstellar medium, or (iii) by repeated energy-driven expansion episodes with a low duty cycle, that average out on long timescales to produce the observed large-scale outflow.

The Wave-Coherent Stress and Turbulent Structure over Swell Waves

Abstract The generation of ocean surface waves by wind has been studied for a century, giving rise to wave forecasting and other crucial applications. However, the reacting force of swell waves on the turbulence in the marine atmospheric boundary layer (ABL) remains unknown partly due to the unclear magnitude and profile of wave-coherent (WC) stress. In this study, the intersection frequency between the energy-containing range and inertial subrange range in the turbulent spectra is identified based on the attached eddy model (AEM), as the intersection modulated by swell wave could help to comprehend the physical process between the ocean surface wave and the marine ABL. Using observations from a fixed platform located in the South China Sea, this study shows that the intersection when the WC stress accounts for a lower proportion of the total wind stress (<10%) follows U/(2πz) given by AEM, where U is the wind speed and z is the height. While the intersection depends on the drag coefficient of WC stress for the case, WC stress accounts for a large part of the total wind stress (>10%). Considering the unclear magnitude and profile of WC stress, this study derives a new function to depict the WC stress. Significance Statement Turbulence located in the energy-containing range of the spectra is the primary source of momentum, heat, and water vapor fluxes between the ocean and marine atmospheric boundary layer (ABL). Thus, a better understanding of the turbulent structure within the wave boundary layer can help us accurately parameterize those fluxes. In addition to absorbing energy from the marine ABL, waves, especially swell waves, influence the turbulent structure. However, until now, the turbulent structure is unclear due to the unclear wave-coherent stress size and profile. In this study, a function that can depict the wave-coherent stress is proposed. We found that the wave-coherent stress can modulate the intersection between the energy-containing range and the inertial subrange range in the turbulent spectra.

Parameterization of Wave‐Induced Stress in Large‐Eddy Simulations of the Marine Atmospheric Boundary Layer

AbstractLarge‐eddy simulations (LES) of the Marine Atmospheric Boundary Layer (MABL) commonly utilize roughness length to parameterize wave effects on the sea surface. However, this method might not adequately capture the intricacies of wind‐wave interactions, especially in swell‐dominated conditions. In this study, we integrated a wave‐induced stress parameterization method into the open‐source LES code, PArallel Large‐eddy simulation Model (PALM), and assessed its performance under low wind conditions with varying wave ages and directions. Our method treats windsea effects as surface friction while employing an exponentially decaying profile to represent swell‐induced stress. We examined the model's sensitivity to wind and wave parameters and calibrated the wave damping rate values across various scenarios, leveraging data from wave‐phase‐resolved simulations and field measurements. The enhanced LES model with the proposed wave parameterization effectively reproduces wave‐influenced wind characteristics such as upward momentum flux, low‐level wind maximum, and negative wind gradients, showing good agreement with previous numerical and observational data. Moreover, our model accounts for wind‐wave misalignment scenarios by calculating each directional and spectral wave stress component individually and integrating them over the wave spectrum. We found that the swell‐induced stress is the dominant force in the wave boundary layer (WBL) with low wind speed, with its magnitude significantly varying with the wave direction relative to the wind. This variation influences the dynamic equilibrium within the WBL, modifying both wind shear and wind veer, and these effects persist up to the top of the boundary layer flow.

Ammonia adiabatic two-phase flow patterns in the horizontal tube

The manuscript reports the experimental study results dealing with the ammonia two-phase flow pattern observations in the transparent horizontal tube of ID 7.5 mm with a saturation temperature of 15 to 65°C, mass velocity of 50 to 160 kg·m−2s−1 and vapour quality of 0.1 to 0.8. Stratified-wavy, annular-wave and annular smooth patterns have been identified based on analyses of camera images. The annular-wavy pattern was not distinguished in the previous ammonia studies at low saturation temperatures (Lima et al., 2009; Gao et al., 2021). Transitions between stratified-wavy and annular-wavy and between annular-wavy and smooth annular patterns occur at constant interfacial vapour momentum flux. This observation aligns with Hewitt and Roberts's (1969) suggestions for vertical steam-water flows. It does not match the existing iterations of Taitel and Dukler's (1976) map, which accurately predicts the transition of HFC fluids and partly the low-temperature ammonia tests. Implementing newly developed transitions between the two-phase ammonia flow patterns in the horizontal tubes updated and validated the existing hydraulic and heat transfer correlations. The most significant among them is an update to the Müller-Steinhagen and Heck's (1986) model in predicting adequately the ammonia frictional pressure losses in the horizontal tube for the broad range of boundary conditions.

Transfer Efficiency and Organization in Turbulent Transport over Alpine Tundra

The exchange of momentum, heat and trace gases between atmosphere and surface is mainly controlled by turbulent fluxes. Turbulent mixing is usually parametrized using Monin–Obukhov similarity theory (MOST), which was derived for steady turbulence over homogeneous and flat surfaces, but is nevertheless routinely applied to unsteady turbulence over non-homogeneous surfaces. We study four years of eddy-covariance measurements at a highly heterogeneous alpine valley site in Finse, Norway, to gain insights into the validity of MOST, the turbulent transport mechanisms and the contributing coherent structures. The site exhibits a bimodal topography-following flux footprint, with the two dominant wind sectors characterized by organized and strongly negative momentum flux, but different anisotropy and contributions of submeso-scale motions, leading to a failure of eddy-diffusivity closures and different transfer efficiencies for different scalars. The quadrant analysis of the momentum flux reveals that under stable conditions sweeps transport more momentum than the more frequently occurring ejections, while the opposite is observed under unstable stratification. From quadrant analysis, we derive the ratio of the amount of disorganized to organized structures, that we refer to as organization ratio (OR). We find an invertible relation between transfer efficiency and corresponding organization ratio with an algebraic sigmoid function. The organization ratio further explains the scatter around scaling functions used in MOST and thus indicates that coherent structures modify MOST. Our results highlight the critical role of coherent structures in turbulent transport in heterogeneous tundra environments and may help to find new parametrizations for numerical weather prediction or climate models.

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.

Study on the fuel/air mixing process in a compact combustor with uneven flame stabilizer wall

Close-coupled injection is an important fuel injection method for future compact design combustors, and improving the mixing of fuel and gas is an important challenge for a wide operating range of the engine. By arranging uneven flame stabilizer walls behind the injection nozzles, the fuel penetration depth and fuel/air mixing of the close-coupled injection can be effectively improved at a low thrust state. In this paper, two kinds of uneven flame stabilizer wall structures were proposed, namely, the forked tail type and the lug-shaped type. The flow characteristics of different uneven flame stabilizer wall structures were investigated by combining numerical simulation and atomization experiments, and the differences in fuel distribution, jet trajectory, and combustion performance between the strut with uneven flame stabilizer wall structures and the U-shaped strut were qualitatively assessed. The results show that both proposed strut structures had a larger low-speed flame stabilization region, a greater jet penetration depth, and better combustion performance than did the common U-shaped strut, but with a greater flow resistance loss. The strut with a forked tail caused the airflow to deflect at the trailing edge of the strut, which in turn deflected the fuel, resulting in a larger recirculation zone and greater jet penetration depth. The lug-shaped strut produced a small recirculation zone behind the lug-shaped structure, and the fuel with a low fuel/air jet momentum flux ratio collided with the lug-shaped structure, thereby increasing the fuel jet penetration depth. The gap lug-shaped structure enhanced fuel diffusion and fuel/air mixing in the radial direction. Numerical studies under real operating conditions showed that the two types of uneven flame stabilizer wall structures were promising for improving the compactness of the combustor. Overall, two types of uneven flame stabilizer wall structures can promote fuel/air mixing during low engine operating states, which is conducive to widening the engine operating range and providing design solutions for the next generation of engine combustor designs with wide operating ranges.

Tangential artificial viscosity to alleviate the carbuncle phenomenon, with applications to single-component and multi-material flows

This paper describes a novel approach to alleviate the carbuncle phenomenon which consists in adding to any carbuncle prone Riemann solver an extra viscosity term in tangential momentum flux and its contribution to the energy conservation equation. This term contains one numerical parameter only, a scalar viscosity, which is reduced using a face-based shear detector to preserve shear waves.The idea stems from the investigation of some of the existing Riemann solvers, also presented in the paper. Indeed, when splitting the numerical flux into the face normal and tangential components, we observe that all the carbuncle free Riemann solvers present in the tangential part a numerical viscosity which scales with the sound speed when the normal flow velocity becomes zero. Opposite, in the carbuncle prone solvers this viscosity scales with the normal flow velocity. In particular the carbuncle free HLLCM scheme proposed by Shen et al. can be written by adding to the carbuncle prone HLLC scheme a tangential artificial viscosity term. Then the same can be done for any other Riemann solver, which renders the approach easy to implement in CFD codes for compressible flows.Numerical experiments shows the efficiency of the approach in computing carbuncle free single-component and multi-material flows.

Gravity Wave Momentum Fluxes from 1 km Global ECMWF Integrated Forecast System

Progress in understanding the impact of mesoscale variability, including gravity waves (GWs), on atmospheric circulation is often limited by the availability of global fine-resolution observations and simulated data. This study presents momentum fluxes due to atmospheric GWs extracted from four months of an experimental “nature run", integrated at a 1 km resolution (XNR1K) using the Integrated Forecast System (IFS) model. Helmholtz decomposition is used to compute zonal and meridional flux of vertical momentum from ~1.5 petabytes of data; quantities often emulated by climate model parameterization of GWs. The fluxes are validated using ERA5 reanalysis, both during the first week after initialization and over the boreal winter period from November 2018 to February 2019. The agreement between reanalysis and IFS demonstrates its capability to generate reliable flux distributions and capture mesoscale dynamic variability in the atmosphere. The dataset could be valuable in advancing our understanding of GW-planetary wave interactions, GW evolution around atmospheric extremes, and as high-quality training data for machine learning (ML) simulation of GWs.

Effects of injector spacing and momentum flux ratio on combustion instability in a model chamber with gas-centered swirl coaxial injectors

This study investigates the effects of injector spacing and momentum flux ratio on combustion instability in a model chamber with single and two injectors, both experimentally and numerically. For the experiments, injectors similar to those used in actual rocket engines were installed in a laboratory-constructed model chamber. Numerical simulations were conducted using ANSYS Fluent, employing a detailed combustion model to complement the experimental data. Flow conditions were categorized as fuel-lean and fuel-rich based on the fuel mass flow rate. The injector spacing varied from 15 to 45 mm, and the momentum flux ratio was adjusted from 6.4 to 139.8 by manipulating the fuel and oxidizer flow rates. Both experimental and numerical results consistently revealed distinct trends in combustion instability for lean and rich conditions, influenced by injector spacing and momentum flux ratio. Combustion stabilization was consistently more effective under fuel-rich conditions. Increasing the momentum flux ratio intensified combustion instability regardless of the fuel condition. For fuel-lean conditions, a rapid transition in combustion stability was observed, with the specific transition point varying depending on the injector spacing. Considering the trade-off between instability and injector number density, a spacing of 30 mm between injectors is recommended. Additionally, for both single and two injectors with various spacings under both lean and rich conditions, combustion stability was generally better when the momentum flux ratio was less than 48.8. These findings provide valuable insights into the control and management of combustion instability, aiding in the design of rocket engine combustors.

Ammonia two-phase flow patterns and condensation in the inclined smooth tubes

The paper reports the experimental study of the two-phase ammonia flow patterns and condensation in the upward and downward inclined tubes. The two-phase patterns have been studied by the photography method in the transparent quartz tube of ID 7.5 mm at the inclination of −90 to 90°, saturation temperature of 35–65 °C, mass velocity of 40–160 kg m−2 s−1 and vapour quality of 0.1–0.8. The Hewitt and Roberts (1969) [19] upward pattern map in interfacial momentum flux coordinates compiled for the high-pressure steam water flows was compared with the obtained ammonia patterns, showing satisfactory qualitative correspondence. However, the transition lines quantitatively are not accurate for ammonia, especially in churn-to-slug cases. Matching the two-phase patterns and ammonia condensation HTC identified in the prior study for the smooth tubes of ID 8 and 11 mm, a so-called forced convective condensation (flow velocity dependent) domination line has been clearly shown for the upward and downward flows. This line splits the boundary conditions, providing similar condensation HTC for the horizontal and upward/downward flows independently on the expected pattern and with the essentially reduced HTC at the upward/downward configuration. The existence of the HTC maximum for the ammonia flow at the inclination of −30° was proved and quantified experimentally for the broad range of boundary conditions in the ID 8 and 11 mm tubes. Matching the identified condensation HTC and the observed flow patterns allows us to conclude that the condensation HTC maximum is mainly determined by the change of stratified-wavy pattern on a smooth stratified one.

Vulnerability of Physical Infrastructure Network Components to Damage from the 2015 Illapel Tsunami, Coquimbo, Chile

AbstractThis study assesses physical infrastructure vulnerability for infrastructure network components exposed during the 2015 Illapel tsunami in Coquimbo, Chile. We analyse road and utility pole vulnerability to damage, based on interpolated and simulated tsunami hazard intensity (flow depth, flow velocity, hydrodynamic force and momentum flux) and network component characteristics. A Random Forest Model and Spearman’s Rank correlation test are applied to analyse variable importance and monotonic relationships, with respect to damage, between tsunami hazards and network component attributes. These models and tests reveal that flow depth correlates higher with damage, relative to flow velocity, hydrodynamic force and momentum flux. Scour (for roads and utility poles) and debris strikes (for utility poles) are strongly correlated with damage. A cumulative link model methodology is used to fit fragility curves. These fragility curves reveal that, in response to flow depth, Coquimbo roads have higher vulnerability than those analysed in previous tsunami event studies, while utility poles demonstrate lower vulnerability than with previous studies. Although we identify tsunami flow depth as the most important hydrodynamic hazard intensity metric, for causing road and utility pole damage, multiple characteristics correlate with damage and should also be considered when classifying infrastructure damage levels.

Turbulent Exchange in Unsteady Air-Sea Interaction at Small and Submesoscales

An adequate description of the interaction between the atmosphere and ocean remains one of the most important problems of modern oceanology and climatology. An extremely wide variety of physical processes occurring in the coupled layers, a large range of scales, a moving boundary, all this factors significantly complicates the creation of models that would allow calculating the physical characteristics in both media with the necessary accuracy. In this paper the temporal variability of dynamic parameters in the driving layer of the atmosphere and in the near-surface layer of the sea on small and sub-mesoscales from one to several tens of hours is considered. The collected experimental data show a very high correlation between the dynamic wind speed and turbulence intensity in the upper sea layer on all scales recorded. An important distinguishing feature of all measured physical quantities in both media is the presence of quasi-periodic oscillations with different periods. For a more accurate description of momentum and energy fluxes from the atmosphere a non-stationary model of turbulent exchange in the near-surface layer of the sea is proposed. The model takes into account quasi-periodicity in the intensity of dynamic interaction between the atmosphere and the sea at these scales. In the model we use the equations of momentum and turbulent energy balance, the system of equations is solved numerically, the calculation results are compared with other models and with experimental data. It is shown that taking into account the non-stationarity of the wind strain improves the correspondence between the calculations and the experimental data. It is noted that in the nonstationary case, the energy and momentum flux from the atmosphere and the turbulence intensity increases compared to the action of a constant average wind of the same duration. Therefore, the strong averaging often used in global models may markedly underestimate the intensity of the dynamic interaction between the atmosphere and ocean.

The Climatology of Gravity Waves over the Low-Latitude Region Estimated by Multiple Meteor Radars

Atmospheric gravity waves (GWs) can strongly modulate middle atmospheric circulation and can be a significant factor for the coupling between the lower atmosphere and the middle atmosphere. GWs are difficult to resolve in global atmospheric models due to their small scale; thus, GW observations play an important role in middle atmospheric studies. The climatology of GW variance and momentum in the low-latitude mesosphere and lower thermosphere (MLT) region are revealed using multiple meteor radars, which are located at Kunming (25.6°N, 103.8°E), Sanya (18.4°N, 109.6°E), and Fuke (19.5°N, 109.1°E). The climatology and longitudinal variations in GW momentum fluxes and variance over the low-latitude region are reported. The GWs show strong seasonal variations and can greatly control the mesospheric horizontal winds via modulation of the quasi-geostrophic balance and momentum deposition. The different GW activities between Kunming and Sanya/Fuke are possibly consistent with the unique prevailing surface winds over Kunming and the convective system over the Tibetan Plateau according to the European Centre for Medium-Range Weather Forecasts (ECMWF), Reanalysis v5 (ERA5) data, and outgoing longwave radiation (OLR) data. These findings provide insight for better understanding the coupling between the troposphere and mesosphere.

Evolution of liquid film in a crossflow tunnel: liquid film thickness measurement and effect of droplet impingement on film breakup

Abstract Liquid jet in crossflow tunnel has widespread applications in various industrial devices,
with the measurements of liquid film on the bottom surface pivotal in exploring relevant mechanisms
such as heat transfer and film breakup. This work reports the measurements of liquid film on the
bottom surface of a crossflow tunnel using the brightness-based laser induced fluorescence (LIF)
method under different flow conditions at ambient pressure and temperature. Film breakup
phenomena are observed downstream within the tunnel. Employing the shadowgraph method, two
distinct patterns of film breakup associated with the droplet impingement positions on the film wave
are identified, i.e., bag breakup and membrane breakup. The film thickness is subsequently calculated,
and jet impingement and spray impingement of injected liquid on tunnel bottom surface are classified
based on the centerline film thickness. A critical jet-to-crossflow momentum flux ratio (q) is determined to be proportional to the square of tunnel height. The averaged film thickness across the entire cross-section downstream at a distance of 50 mm from the nozzle is found to increase with the logarithm of q. Besides, the film boundaries are also identified under different flow conditions, which can be well predicted by a quadratic fit with the fitting parameters also correlated to the logarithm of q.