Gravity-driven flows, driven by density differences, due to temperature (e.g. katabatic winds) and/or salinity (e.g. density currents) differences, and/or the presence of particles (e.g. snow avalanches, debris-flows turbidites, pyroclastic flows) are an ubiquitous geophysical phenomenon involving stratified turbulent effects. These effects are coupled with entrainment, particle–fluid interactions, non-Newtonian rheologies, and interactions with ambient stratified environments. Although occurring in various planetary environments and similar physical processes governing their dynamics, a universal description of gravity-driven flows remains elusive, as the feedback on the aforementioned flow processes is particularly difficult to predict.
This session aims to bring together the recent advancements in stratified turbulence and gravity-driven flows in geophysical, planetary, and astrophysical flows. We welcome fundamental and applied contributions from theoretical, numerical, and modelling perspectives, as well as complementary approaches based on field observations, laboratory and analogue experiments, and numerical simulations (including data-driven and IA-based methods). Topics include, but are not limited to:
— turbulent fluxes and transports; turbulent decay, mixing, and dissipation
— stable atmospheric boundary layer flows and intermittent turbulence
— wave turbulence and wave-vortex dynamics in various turbulent regimes
— turbulence in weakly and strongly stratified flows and stratified shear flows
— snow avalanches, dust storms, landslides, turbidity currents
— river, volcanic and oceanic plumes, mud, debris and pyroclastic flows
— katabatic winds, oceanic density currents
We particularly encourage participation from early career researchers.
Orals: Fri, 8 May, 14:00–15:45 | Room -2.33
Turbulence in the stably stratified boundary layer is generated by shear, while its development is inhibited by buoyant forces. Due to this interplay, flow regimes with different physical and dynamical characteristics exist. Fully turbulent stable boundary layers, also coined as weakly stable boundary layers, are rather well described by turbulence theory, but the very stable boundary layer is home to unsteady and intermittent turbulence that is less well understood. At high stability in the atmospheric boundary layer, non-turbulent processes on sub-mesoscales (such as dirty waves, drainage flows, etc) become more important, and the flow becomes highly non-stationary. Multiscale data analyses based on different field measurement campaigns show signs of direct energy transfers between sub-mesoscales and turbulent scales, with impacts on the turbulence characteristics. On the one hand, the scale interactions are linked to anisotropic turbulence; on the other hand, turbulence intermittency becomes important when the energy content of the sub-mesoscales becomes an important percentage of the mean kinetic energy.
How to cite: Vercauteren, N., Gucci, F., and Kuttikulangara, A.: Scale interactions in the stably stratified atmospheric boundary layer and impacts on the anisotropy and intermittency of turbulence, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22015, https://doi.org/10.5194/egusphere-egu26-22015, 2026.
The circulation of the Earth’s atmosphere and those of many other planets is dominated by turbulent interactions in a baroclinically unstable, rotating, stratified flow. Even for the Earth, which has been well observed for many years, the energy spectrum and complex properties of the anisotropic and inhomogeneous turbulent cascades of energy and enstrophy remain poorly understood and difficult to model accurately. Here we measure geostrophic turbulence energised by baroclinic instability in a rotating, differentially heated fluid annulus in the laboratory, which is bounded by convectively-driven warm and cold flows at the outer and inner boundaries, respectively (see Fig. 1a). Horizontal velocity fields (Fig. 1b-c) are obtained via particle image velocimetry of neutrally buoyant particles suspended in the flow, while the temperature structure is sampled using a vertical array of thermocouples located in the middle of the channel. The horizontal kinetic energy spectra exhibit a wavenumber range at relatively large length scales which scales as k−3, where k denotes the horizontal wavenumber (see Fig. 1d-e). Moreover, the spectral amplitude is found to correlate with the square of the Brunt–Vaisala frequency N at the same heights as the velocity measurements. The observed turbulent state exhibits a net forward enstrophy cascade across all scales, along with bidirectional kinetic energy transfer, which is indicated by a reversal in the sign of the spectral energy flux. The change of sign of the kinetic energy cascade occurs at a scale proportional to the internal Rossby radius of deformation Ld. These findings highlight the role of baroclinic instability in shaping the distribution of energy across scales with implications for synoptic- and meso-scale turbulent flows in the atmospheres of the Earth and other terrestrial planet atmospheres and oceans.
FIG. 1. (a) Schematic plot of the convective tank. Snapshots of vorticity ζ for thermal Rossby number RoT = 5.41 (b) and RoT = 0.03 (c). On the scale bar, Lid = 2.4 cm and Liid = 22.6 cm are the Rossby radius of deformation for (c) and (b), respectively. (d) Kinetic energy spectra, E(k), for various values of RoT. The arrow indicates the wave number kp corresponding to the peak of E(k) when RoT = 0.03. Inset: radial profiles of temporal- and zonal-averaged azimuthal velocity, Uθ. (e) Kinetic energy spectra compensated by k−3 and normalised by N2 versus LRk. The dashed line indicates the plateau segment for LRk ∈ [2, 10] and has a magnitude of ∼ 0.5. Data are for height h = 0.18 m.
How to cite: Read, P., Ding, S., Bobas, H., Scolan, H., and Young, R.: A Stratification-Dependent, Enstrophy-Controlled Regime in Baroclinic Turbulence Experiments in the Laboratory, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18700, https://doi.org/10.5194/egusphere-egu26-18700, 2026.
Fluctuation-dissipation relation (FDR)—a well-known theorem in statistical mechanics—comes in various versions. In an early version (Nyquist 1928, Callen and Welton, 1951), a FDR is thought to be responsible for the emergence of dynamical equilibrium, characterized by well-defined statistics such as variances and spectra. A later version, proposed by Kubo (1957) and introduced to climate research by Leith (1975) and further extended by Lucarini et al. (2017), focuses on the response of a system to an external forcing perturbation and relates this response to the system’s restoring behavior found in the absence of perturbation. Geophysical turbulence—generated by dissipative systems under constant external forcing and characterized by variances and spectra conform with the given external forcing—represents fluctuations in a dynamical equilibrium. As such, it should be governed by Nyquist’s FDR.
However, it is not clear how such a FDR is related to the differential equations that govern the evolution of turbulent flows, not mentioning the way dissipation operates and controls the statistics of turbulent flows. The integral fluctuation-dissipation relation (IFDR) (von Storch 2026) generalizes and extends Nyquist’s FDR. It postulates that the IFDR resides in integrals of differential forcings that define the governing differential equations, and represents a principle that is complementary to but distinct from these differential equations. It is complementary in the sense that turbulent flows are described not only by solutions of the differential equations but also by statistics, such as variance and spectra, which only emerge due to the IFDR. It is distinct in the sense that IFDR does not exist as a time rate of change and hence cannot be included in the governing differential equations. This situation is a manifestation of the fact that in a dynamical equilibrium, the differential forcing of a component x of the full state vector is effectively non-dissipative and acts as a driver of x, while dissipation of x arises from dissipative processes implemented in equations of all components that interact with x. Such a dissipation only unfolds when the system is integrated forward in time and reaches its maximum strength for sufficiently long integration period. The IFDR is exemplified using the Lorenz 1963 model. The identification of IFDR opens a new perspective for understanding the macroscopic behaviors of turbulent flows characterized by well-defined variances and spectra.
von Storch 2026: https://doi.org/10.1016/j.physa.2025.131218
How to cite: von Storch, J.-S.: Integral fluctuation-dissipation relation and turbulence as equilibrium fluctuations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2832, https://doi.org/10.5194/egusphere-egu26-2832, 2026.
Kinetic energy exchanges between resolved and sub-grid motions in geophysical turbulence simulations can act in both directions: downscale transfer contributes to dissipation of the resolved kinetic energy, while upscale transfer, known as backscatter, can energize the resolved scales. Backscatter can be significant in real turbulence but is not included in many sub-grid models. This talk will discuss properties and modelling of backscatter in numerical simulations of decaying homogeneous stratified turbulence. In direct numerical simulations (DNS), we measure backscatter by filtering the solution and explicitly calculating the sub-filter energy transfers. In large eddy simulations, we include backscatter following the Leith stochastic backscatter model along with Smagorinsky eddy viscosity. Different values of the Leith coefficient are considered, and the modelled backscatter is compared to that measured in the DNS. Overall, the Leith model is capable of generating realistic levels of backscatter if the Leith coefficient is not too large. Strong backscatter forcing also changes the resolved turbulent energy transfer and leads to a reduction of kinetic energy in the inertial range. Dependence on stratification will also be discussed.
How to cite: Waite, M. and Lawrence, J.: Backscatter in stratified turbulence, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13923, https://doi.org/10.5194/egusphere-egu26-13923, 2026.
The Strato-Rotational Instability (SRI) is a hydrodynamic instability, proposed as a possible mechanism for angular-momentum transport in stratified astrophysical accretion disks. It is also a laboratory analogue for rotating stratified shear flows relevant to geophysical and planetary systems, such as atmospheric dynamics. In Taylor–Couette flows with stable density stratification in the axial direction, the SRI generates spiral patterns that propagate alternately upward and downward along the rotation axis. While such axial reversals have been observed in experiments and numerical simulations in [1, 2], their physical origin and connection to mean-flow dynamics remain to be investigated. Here, we combine numerical simulations consistent with laboratory measurements and reduced (toy) models to investigate the mechanisms driving axial spiral propagation and low-frequency modulation in SRI. Using a Radon Transform decomposition, we isolate upward- and downward-traveling spiral components and show that each exhibits a distinct, slowly varying amplitude modulation. These modulations are phase-shifted and interact through the mean flow, leading to transitions in the direction of the axial spiral propagation. The changes also lead to changes in the axial mean flow velocity. Motivated by these observations, we introduce a reduced toy model consisting of two counter-propagating, modulated wave-like spirals. Despite its simplicity, the model clearly reproduces the observed pattern transitions, demonstrating that linear superposition of individually modulated spirals is sufficient to explain the dynamics. To interpret the simultaneous occurrence of low-frequency spiral and axial mean flow modulations, we propose a quasi-biennial oscillation (QBO)–like mechanism, inspired by several dynamical similarities of the SRI reversals with the atmospheric QBO, where the wave–mean flow interactions drive periodic reversals of the zonal flow [3, 4]. Adapting this framework to rotating stratified shear flows, we derive a reduced inertial-wave model for the axial mean flow. The model predicts periodic reversals and amplitude modulation consistent with SRI observations. Our results suggest that SRI spiral reversals arise from a weak nonlinear coupling between counter-propagating inertial waves and the mean flow, providing an interpretation linking laboratory SRI to the geophysical wave–mean flow interactions.
References [1] Meletti, G., Abide, S., Viazzo, S., Krebs, A., and Harlander, U., Experiments and long-term high-performance computations on amplitude modulations of Strato-Rotational flows, Geophysical & Astro-physical Fluid Dynamics, pp. 1–25, 2020. [2] Meletti, G., Abide, S., Viazzo, S., and Harlander, U., A parameter study of strato-rotational low-frequency modulations: impacts on momentum transfer and energy distribution, Philosophical transactions of the Royal Society A, 381, pp. 20220297, 2023. [3] Holton, J. R. & Lindzen, R. S. An updated theory for the quasi-biennial cycle of the tropical stratosphere, Journal of Atmospheric Sciences, 29(6), pp. 1076–1080, 1972. [4] Plumb, R. A. The interaction of two internal waves with the mean flow: Implications for the theory of the quasi-biennial oscillation, Journal of Atmospheric Sciences, 34(12), pp. 1847–1858, 1977.
How to cite: Meletti, G., Curbelo, J., Adibe, S., Viazzo, S., and Harlander, U.: Wave–Mean Flow Interactions and QBO-Like Modulations in Strato-Rotational Instabilities, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3006, https://doi.org/10.5194/egusphere-egu26-3006, 2026.
Submarine canyons are major conduits for density currents that transport water and sediment to the deep sea. To date, most in-situ studies and observations of these currents have been conducted in large submarine canyons that either incise the shelf, are adjacent to major perennial rivers, or a combination of both features. Little, if any, observational data exist from the more globally common small submarine canyons, that may be confined to the continental slope (headless) and located far offshore from smaller, ephemeral streams. In Israel- Eastern Mediterranean, submarine canyons are found only along the northern shore. These canyons are generally small (5–20 km long) and are not connected to major coastal rivers. Whether and how these canyons serve as pathways for density currents that transport sediment to the deep Levantine Basin was unknown. To address these questions, two moored stations (landers) equipped with instrument arrays were deployed at depths of 350 m and 710m along the thalweg of the “Bat-Galim” submarine canyon, offshore Haifa. The landers operated from October 2019 to June 2020 and from September 2020 to May 2021. In both deployments, winter density currents were recorded, characterized by turbid water moving rapidly down the canyon near the seabed, with velocities comparable to those reported in larger submarine canyons. During these events, sediment-laden warm and saline shelf water plunged beneath the colder, denser canyon water, leading to temperature inversions. This inversion may cause sediment lofting and upward convection through the water column once sediment settling relieves the otherwise buoyant warm water of its ballast. Mean sediment fluxes in the canyon during these deployments were extraordinarily high compared to both the adjacent shelf and the deep sea, suggesting substantial sediment transport. These results demonstrate that the Bat-Galim canyon, and likely other submarine canyons in northern Israel, serve as active pathways for annually occurring density flows. Additionally, the findings suggest a novel turbidity flow-driven mechanism for water column convection. These unique observations highlight the need for further investigation into the possibly significant role of small submarine canyons worldwide as key conduits for water and sediment transport to the deep sea, via density currents.
How to cite: Jaijel, R., Biton, E., Weinstein, Y., Ozer, T., and Katz, T.: In situ observations of density currents in a small submarine canyon in the eastern mediterranean , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-290, https://doi.org/10.5194/egusphere-egu26-290, 2026.
Freshwater plumes generated by small rivers play a signficant role in coastal processes. In glacially fed systems, such as those found in Patagonia, strong buoyancy forcing and turbulence produce sharp density interfaces and complex flow structures that regulate plume spreading and vertical exchange. Understanding the physical mechanisms controlling mixing and sediment transport in these environments is essential for linking small-scale turbulence to larger-scale coastal processes.
We present results from direct numerical simulations (DNS) of freshwater plumes discharging into denser ambient fluid under subcritical and supercritical conditions. The simulations resolve the 3D coherent structures, capturing the development of interfacial instabilities and vortical motions that control entrainment and mixing efficiency. We show that plume dynamics transition between regimes dominated by shear-driven instabilities and large-scale overturning, with distinct implications for vertical density fluxes and plume thickness.
We also explore the influence of suspended sediment on plume dynamics, focusing on how particle settling modifies turbulence, alters effective vertical transport, and feeds back on interfacial structure. The interactions of sediment transport with stratified turbulence significantly affect near-field plume evolution. These results provide new physical insights into mixing and transport in buoyancy-driven flows and help bridge idealized turbulence studies with the behavior of natural glacial river plumes in coastal environments.
This work has been supported by ONR-Global grant N62909-23-1-2004.
How to cite: Escauriaza, C., Williams, M., and Fringer, O.: Dynamics, Mixing, and Sediment Transport in the Near -Field of Freshwater Plumes, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15874, https://doi.org/10.5194/egusphere-egu26-15874, 2026.
Gravity currents are buoyancy-driven flows generated by horizontal density gradients and govern the transport of mass, momentum, and scalars in both natural and engineered systems. A detailed understanding of their near-wall behavior is essential for accurately describing the turbulent mechanisms developing in this region, which is characterized by strong spatial variability, particularly at increasing Reynolds numbers (Re=UbH/ν, with H the initial height of the dense fluid, ν the cinematic viscosity, Ub=(g’H)0.5 a velocity scale related to the reduced gravity g’=g(ρ1- ρ0)/ ρ0, where g is the gravitational acceleration, ρ1 the density of the heavier fluid and ρ0 the ambient density).
Several numerical simulations were performed in straight channels under a lock-exchange configuration using a wall-resolved Large Eddy Simulation. The analyzed cases differ in terms of Reynolds number (in the range 34000-136000), both by increasing the height of the domain and by modifying the density difference.
The analysis of the near-wall behavior focused on the head of the current, identified through mean density values. Subsequently, streamwise velocity profiles in the wall-normal direction were extracted, first averaged in the spanwise direction and then also along the streamwise direction. Although the latter direction is not homogeneous, this procedure provides an overall view of the behavior of the current head during its temporal evolution.
The gradient of the streamwise velocity in the wall-normal direction was used to define the boundary-layer thickness δ. It was observed that the temporal evolution of the normalized thickness δ* = δ/H is similar for all the cases analyzed; moreover, after an initial increase, it tends to approach an asymptotic value during the self-similar phase. In accordance with the characteristics of this phase, it is also observed that the mean velocity profile tends to remain invariant over time during the evolution of the current. Moreover, the presence of a logarithmic region is identified, of the form u+=a(lny+)+bu+=alny++b (where u+=u/u𝜏, and y+=yu𝜏/νy+=yu𝜏/𝜈, u𝜏 denoting the friction velocity), with an increase in the slope A (in a logarithmic plot) relative to the canonical value (A=2.44), consistent with the local presence of stable stratification.
The results obtained may have important implications for the parameterization of simplified large-scale circulation models, particularly with regard to the definition of appropriate boundary conditions.
How to cite: Ammendola, A., Rebesco, M., Salon, S., Falcini, F., and Roman, F.: Boundaries behaviour of gravity currents, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21559, https://doi.org/10.5194/egusphere-egu26-21559, 2026.
Posters on site: Fri, 8 May, 08:30–10:15 | Hall X4
The Ekman boundary layer is driven by the triadic balance of pressure gradient, Coriolis, and friction force. Under strongly stable stratification, the flow can become globally intermittent, with large-scale motions controlling the spatial organisation of quasi-laminar patches of fluid that extend from the outer layer down to the surface layer. Stable stratification additionally affects the Ekman spiral, making it shallower and characterized by a faster veering of the wind vector compared to neutral stratification, resulting in stronger directional wind shear.
In the present contribution, a dataset from direct numerical simulations (DNS) of a turbulent Ekman flow over a smooth and flat wall is used to investigate how the spatial organization of a globally intermittent flow and the modified Ekman spiral shape the anisotropy of the stress tensor. Multiple studies have shown that small-scale turbulence becomes more anisotropic with increasing stratification, with frequent occurrence of one-component anisotropic stress tensors (i.e. kinetic energy distributed along one dominant direction) that also characterizes the large scales. Previous analyses of small-scale coherent vortical structures in these DNS revealed that hairpin vortices within a turbulent patch of a globally intermittent flow are aligned along the same direction, which may contribute to shaping the anisotropy of the stress tensor at the large and small scales.
Scale-wise analyses of the flow and its stress anisotropy under strongly stable stratification and neutral stratification are performed to investigate these features. Results show that large-scale motions found in the outer layer are associated with a dominant energy-containing length scale that extends down to the inner layer. As a result, the energy spectrum in the inner layer has two dominant length scales, with shear-driven turbulence associated with the smaller length scale. Directional wind shear contributes to large-scale anisotropy as the surface is approached. Due to the strong coupling arising from global intermittency, information on anisotropy is transferred from the outer layer down to the surface layer.
How to cite: Gucci, F., Vercauteren, N., and Harikrishnan, A. P.: Anisotropic turbulence in the Ekman boundary Layer, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22097, https://doi.org/10.5194/egusphere-egu26-22097, 2026.
The increase in greenhouse gas emissions from human activities are driving a continuous rise in Earth’s temperature. The atmosphere is a highly complex system: it is vertically stratified, composed of layers with distinct flow characteristics, involves energy exchanges in both horizontal and vertical directions, exhibits heterogeneous composition, and is turbulent over a wide range of spatial and temporal scales. A detailed understanding of stratified turbulence and its role in climate dynamics is therefore essential.
Climate models necessarily rely on assumptions, either by explicitly resolving large-scale dynamics while parameterizing small-scale processes, or by focusing on small-scale turbulence with simplified representations of large-scale flows. To better understand the interactions across scales, we perform a scale-by-scale analysis based on structure functions for idealized Direct Numerical Simulation (DNS) and for Weather Research and Forecasting (WRF) model outputs.
While deriving the governing equations from both DNS and WRF datasets, second-, third- and fourth-order structure functions are computed in two-dimensions. Firstly, along the z-axis for DNS and WRF, in the direction of stratification, and secondly, in the plain perpendicular to z-axis (perpendicular to the surface). Despite differences in model complexity and scales, both datasets exhibit similar statistical behavior across orders.
The two-dimensional structure functions shows: a 90° reflection symmetry when averaging over space and time, while a 180° rotational symmetry is observed when averaging over space at each time step. Furthermore, the third-order structure function reveals a direct energy cascade aligned with the mean flow direction and an inverse energy cascade in the direction perpendicular to the mean flow. These features are consistent across both datasets and are in agreement with previous experimental observations from academic flows.
Future work will focus on separating wave-like motions, such as gravity waves, from the turbulent component in DNS and WRF outputs. This decomposition will give a clearer assessment of the respective roles of waves and turbulence in scale-by-scale energy transfers, and will help the interpretation of structure function analyses in stratified atmospheric flows.
How to cite: Rodriguez, F., Sayeed, K., Fossa, M., Massei, N., and Danaila, L.: Scale-by-scale analysis of stratified turbulence using DNS and WRF simulations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7804, https://doi.org/10.5194/egusphere-egu26-7804, 2026.
One of the main factors characterizing the dynamics in the atmosphere is its vertical density stratification. Gravity waves propagation upwards and breaking in the middle atmosphere play an essential role in large-scale energy transport, planetary-scale circulation and the generation of stratified turbulence, manifesting in phenomena such as the cold summer mesopause in the mesosphere. Direct observation or numerical simulation of these processes with high resolution proves difficult however due to the remoteness of the region combined with horizontal scales of 10-100km and vertical scales of 10-100m that have to be resolved for a detailed analysis of the underlying stratified turbulence.
To tackle these limitations and further our knowledge on turbulence activity in the middle atmosphere, we combine the physics-informed machine learning method HYPER (Hydrodynamic Point‐wise Environment Reconstructor) with state-of-the-art radar observations from MAARSY (Middle Atmosphere Alomar Radar System) and SIMONe (Spread-spectrum Interferometric Multistatic Meteor Radar Observing Network). The method allows reconstruction of complete 4D wind fields (spatial+temporal) based on line-of-sight measurements while adhering to Navier-Stokes-based physics constraints and has been successfully deployed previously to extract winds on 10km-scales from inputs of SIMONe.
In our work we extend the procedure to combine the input of MAARSY and SIMONe and predict complete 4D wind fields at unprecedented horizontal and vertical resolution. Using DNS of stratified turbulence with virtual radars as a validation case, we show that our improved method is able to produce accurate results in the entire prediction domain beyond the provided measurement points, while respecting the given physics constraints. Building on this, we aim to provide a first machine learning supported analysis of stratified turbulence in the mesopause region based on radar observations.
How to cite: Peterhans, V. J., Urco, J. M., Huyghebaert, D., Chau, J., and Avsarkisov, V.: Reconstructing 4D Wind Fields from Radar Observations using Machine Learning, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3468, https://doi.org/10.5194/egusphere-egu26-3468, 2026.
The midlatitude atmospheres of gas giant planets are characteristic of strong and persistent zonal jets; however, the processes governing their formation and the associated energy pathways remain less understood. To investigate these mechanisms, we conducted a laboratory study of zonal jets driven by thermal forcing in an annular cylindrical tank partially filled with distilled water as the working fluid. Heating is applied at the outer boundary, cooling at the inner boundary, the bottom is thermally insulated, and the top is a free surface. An array of laser diodes embedded in the inner cylinder generates an annular laser sheet, enabling the measurement of velocity fields at a fixed height using particle image velocimetry. By systematically varying the rotation rate and the imposed temperature contrast, we adjusted the steepness of the free surface, thus the topographic β effect, and the thermal forcing strength, respectively. The non-dimensional controlling parameter, thermal Rossby number, RoT, ranges from 0.0012 to 0.01 and Taylor number, Ta, from 2.3 × 1010 to1.7 × 1011. We discerned the emergence of robust zonal jets, of which the zonal-mean kinetic energy accounts for up to 70% of the total kinetic energy, corresponding to a zonostrophic index of 2.7. In this regime, two coherent and persistent prograde jets form near the inner and outer boundaries. The radial profile of the potential vorticity develops toward a pronounced staircase-like structure, consistent with previous numerical studies (Scott and Dritschel, J. Fluid Mech., 2012). Analysis of the inter-scale energy transfer reveals a dominant interaction between the zonal-mean flow and eddies, while the kinetic energy spectrum of the zonal-mean component exhibits k−5 (where k denotes the wavenumber), in agreement with the theory of zonostrophic turbulence (Sukoriansky and Galperin, PRL, 2002).
Figure 1: A snapshot of azimuthal velocity contour for RoT = 7.1 × 10−3, Ta = 1.44 × 1011 and β =49.7 m−1 s−1.
How to cite: Ding, S. and Read, P.: Emergence of Robust Zonal Jets in a Differentially Heated Rotating Annulus, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19406, https://doi.org/10.5194/egusphere-egu26-19406, 2026.
High-frequency internal gravity waves are ubiquitous features in rotating stratified flows, and interact nonlinearly with balanced vortices as well as other waves, resulting in energy transfers across multiple scales. Understanding these multiscale exchanges rests on a precise disentangling of internal waves from the balanced flow in a fully nonlinear flow system. This is the focus of this work, which facilitates the understanding of complex nonlinear mechanisms of internal gravity wave generation, such as spontaneous loss of balance, associated with the notion of the 'slow manifold'.
Here I discuss the generation of internal waves by nonlinear processes: spontaneous emission, symmetric instability, and stimulated emission; through different nonlinear flow decomposition methods: nonlinear normal-mode initialization and nonlinear decomposition at higher orders with asymptotic expansion in Rossby number. Wave generation diagnosed with a different approach, namely optimal balance with and without time-averaging is also compared and discussed. An important result is that wave generation by spontaneous emission is generally weak to negligible, becoming significant only at higher orders and high Rossby numbers. Symmetric instability is more effective in wave generation, also at moderate Rossby numbers. Stimulated emission represents a more realistic scenario of wave emission that might be at play in the real ocean conditions, and is expected to be effective even at low Rossby numbers. The results present a new perspective on internal wave energetics in geophysical flows, and call for reevaluation of the energy transfers in and out of the internal gravity wave compartment.
How to cite: Chouksey, M. and Peringampurath, A. H.: Fast Gravity Waves and Slow Manifolds, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21329, https://doi.org/10.5194/egusphere-egu26-21329, 2026.
The energy cascade in ocean mixing caused by stratified turbulence remains poorly understood due to the wide separation of scales at very high Reynolds numbers Re. We present a new conceptual model for this cascade, grounded in high-resolution multibeam echo-sounding observations from the mouth of the Connecticut River, a shallow salt-wedge estuary with intense interfacial mixing. During flood tide, large-scale topography and hydraulics slope the pycnocline, generating interfacial shear and Kelvin-Helmholtz billows on a vertical scale of ~1-2 m. The multibeam captures instantaneous two-dimensional images that resolve the true slopes and geometry of these instabilities, revealing the structure and evolution of turbulent mixing using acoustic backscatter as a proxy for salinity microstructure dissipation. At Re ~ 10^6, we find that mixing is dominated not by the slowly evolving billow cores, which rarely overturn, but by fast, sustained turbulence within the braids that connect them, energized by baroclinic shear within their slopes. Secondary shear instabilities within the braid are predicted by two-dimensional direct numerical simulation with parameters matching the field values. Braid dissipation and mixing is quantified by scaling arguments derived from laboratory experiments in an inclined channel, and may explain why the primary billows do not overturn. This braid-dominated mixing contrasts with the core-dominated mixing seen in transient simulations at Re ~ 10^3-10^4. We conclude that high-Re mixing hotspots continuously driven by large-scale shear – including in estuaries, wind-driven surface currents, and deep overflows – operate through fundamentally different cascade physics than implied by existing low-Re paradigms.
How to cite: Lefauve, A., Bassett, C., Plotnick, D., Lavery, A., and Geyer, R.: The structure and lifecycle of stratified mixing by shear instability in continuously forced shear flows, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5778, https://doi.org/10.5194/egusphere-egu26-5778, 2026.
In stratified fluids, turbulent patches can arise due to breaking internal gravity waves (GWs). One important breaking mechanism is associated with the presence of a critical level, which occurs when the phase speed of the GW matches the background flow velocity in the direction of propagation. Linear theory predicts a diverging amplitude and energy density as the wave approaches the critical level, ultimately leading to wave breaking and the eventual onset of turbulence. However, the precise physics of the turbulent state after the wave breaking and during GW dissipation have received limited attention in the past and remains less understood. This lack in research renders a challenge for the physical representation of GW breaking in contemporary weather and climate models.
To address this issue, we perform idealized direct numerical simulations (DNS) of a GW approaching its critical level and analyze the resulting turbulent flow. We present our simulation framework and investigation results regarding different background flow configurations and obtain the scaling of the turbulent kinetic energy (TKE) dissipation with the wavelength and the background buoyancy frequency. Furthermore, Reynolds number similarity as well as the generation of secondary GWs is observed. Numerical results regarding TKE dissipation are also compared to atmospheric observations. This comparison suggests that the DNS are able to represent the physics we want to address despite their idealized nature. Additionally, the observation of secondary emissions by the turbulent layer indicates that turbulent wave breaking enables tunneling of energy across the critical level, which is a phenomenon not permitted in linear theory.
How to cite: Vandamme, T., Mellado, J. P., and Avsarkisov, V.: Numerical investigation of the turbulent gravity wave break-up near a critical level, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5598, https://doi.org/10.5194/egusphere-egu26-5598, 2026.
Numerical simulations are performed to investigate the propagation, flow structure, and runout of turbidity currents in regimes where buoyancy-driven dynamics interact with finite settling effects. A Lagrangian particle-tracking framework is used to represent the evolving density field and its coupling with the carrier flow, enabling detailed analysis of current dynamics across multiple flow regimes.
We first examine the temporal evolution of turbidity currents, which exhibit distinct slumping, propagation, and dissipation stages. The role of finite settling is shown to modulate density stratification and, in turn, the efficiency of momentum transfer within the current. We then analyse flow structure and deposition-induced feedbacks on the current dynamics. Transverse variations in the flow and deposition pattern are associated with lobe-and-cleft structures, while longitudinal variations arise from vortex detachment and decay. Finally, we propose a new scaling law for turbidity-current propagation speed and runout length that incorporates the combined effects of buoyancy forcing and settling-induced density evolution. The numerical results show close agreement with the proposed scaling, supporting its applicability to a wide class of particle-laden density currents. These results provide new insight into the dynamics of turbidity currents as geophysical density currents and contribute to improved predictive frameworks for buoyancy-driven flows in natural environments.
How to cite: Chou, Y.-J. and Yeh, Y.-C.: Propagation and flow structure of turbidity currents in settling regimes: A Lagrangian particle-tracking study, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21650, https://doi.org/10.5194/egusphere-egu26-21650, 2026.
Turbulence in deep ocean environments, particularly bottom mixing, plays a critical role in multiple disciplines such as regulating energy transport, sediment resuspension, and biogeochemical exchanges. Despite its importance, bottom turbulence remains one of the least understood components of oceanography, largely due to observational challenges and the inherent complexity of seabed environments. Meanwhile, the Luzon Strait, which connects the northern South China Sea and the western Pacific Ocean, is recognized as a global hotspot for internal wave generation to the South China Sea from the Pacific Ocean. Therefore, this study investigates the structure and variability of the bottom mixed layer (BML) and its associated turbulence mechanisms across the Luzon Strait. Specifically, we aim to characterize the height of the bottom mixed layer (HBML), identify dominant physical drivers of bottom turbulence mixing, and compare mixing regimes between the northen South China Sea and the western Pacific Ocean.
Between July 27 and August 22, 2022, an oceanographic survey was conducted along both sides of the Luzon Strait. A total of 23 temperature profiles were successfully collected from two sections, 10 from the western Pacific Ocean and 13 from the northern South China Sea. The results reveal significant spatial inhomogeneity in BML characteristics across the strait. Preliminary analysis reveals that HBML is modified by a distinct mechanism on either side of the strait. In the western Pacific Ocean, HBML is positively correlated with ocean depth, suggesting that deeper regions support thicker BMLs due to weaker stratification. In the norther South China Sea, HBML appears more sensitive to seabed roughness, with thicker layers observed over complex topography. A more detailed examination of turbulence intensity and mixing efficiency is planned to further investigate these mechanisms.
In summary, by comparing mixing behavior across the norther South China Sea and western Pacific Ocean, this study advances our understanding of bottom mixed layer dynamics and contributes to the development of more accurate models for ocean circulation, which is important to improve the understanding of turbulent mixing in the deep ocean.
How to cite: Zhou, J., Huang, P., Lai, Y., and Guo, S.: Decoding Deep Ocean Turbulence: Bottom Mixed Layer Dynamics in the South China Sea and Western Pacific, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-270, https://doi.org/10.5194/egusphere-egu26-270, 2026.
The interaction between small-scale waves and a larger-scale flow can be described by a multi-scale theory that forms the basis for parameterizations of subgrid-scale gravity waves (GWs) in weather and climate models (e.g., Achatz et al., 2023). These parameterizations have recently been extended to include transient GW–mean-flow interactions and oblique GW propagation. Existing gravity-wave parameterizations include only rudimentary descriptions of the coupling between the dynamics of unresolved GWs and turbulence, but recent studies (Banerjee et al., 2025) have shown that this interaction is non-negligible. Energetic consistency therefore necessitates an extension of the multi-scale theory to include a more accurate representation of this interaction.
We propose an extension of this multi-scale theory that incorporates an additional turbulence formulation, allowing for a more robust bidirectional coupling between GWs and turbulence. Key results include a well-defined organization of turbulence along the phase structure of individual GWs and a correspondingly structured feedback on turbulent GW damping. We plan to present initial results from the validation of this extended theory by comparing idealized simulations with parameterized GWs to wave-resolving reference simulations.
How to cite: Suresh, D., Steiger, I., Dolaptchiev, S., Klein, R., and Achatz, U.: A Multi-Scale Theory for Gravity-Wave Interaction with Turbulence, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16697, https://doi.org/10.5194/egusphere-egu26-16697, 2026.
Observations and numerical simulations consistently show that the horizontal kinetic energy spectrum follows a -5/3 slope at mesoscales from the troposphere to the lower stratosphere. Various fundamentally different theories have been proposed to explain this mesoscale spectral slope, including gravity waves, stratified turbulence, and wave-vortex interactions. To investigate the underlying mesoscale mechanism, we implement a combined diagnostic framework consisting of two complementary approaches: a non-hydrostatic, Fourier-based spectral energy budget and a scale-dependent energy transfer in physical space, used to diagnose the instantaneous, local structure of energy transfers in regional atmospheric domains, with particular emphasis on the mesosphere and lower thermosphere (MLT).
The methodology is validated using idealized mountain-wave simulations, where the dominant dynamical mechanisms are well understood. The framework is then applied to high-resolution nested UA-ICON simulations from the NASA Vorticity Experiment (VortEx) over Andøya, Norway, a dynamically active region. The results reveal pronounced spatial and scale-dependent variability in energy transfers that is not captured by domain-averaged spectral diagnostics alone. The scale-dependent energy transfers are consistent with independent turbulence indicators, including the Richardson number and parameterized turbulent kinetic energy (TKE). Regions characterized by low Richardson numbers and elevated TKE exhibit significantly stronger downscale energy cascades than those in more stable, high Richardson number regimes. This study provides insight into mesoscale dynamics by extending energy transfer analyses into the MLT and offers a robust framework for investigating energy transfer across different atmospheric regimes.
How to cite: Krishnan, B., Morfa Avalos, Y., Zülicke, C., and Stephan, C.: Mesoscale Energy Transfers in Regional domains: Spectral and Physical Space diagnostics., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9959, https://doi.org/10.5194/egusphere-egu26-9959, 2026.
Gravity-driven flows are controlled by density contrasts that can be induced, among other factors, by temperature variations. In laboratory experiments, accurately measuring temperature fields is therefore helpful to better understand the mixing mechanisms governing such flows. Optical, non-intrusive techniques are particularly valuable in this context, as they allow spatially and temporally resolved measurements without disturbing the flow.
In this study, we focus on optimizing thermal field imaging obtained using temperature-sensitive lifetime of luminescent materials. The method relies on multi-exposure accumulation within a single frame using a CMOS camera on a custom-built platform that we previously demonstrated to be significantly lower in cost while maintaining precision and sampling rates compared to specialized systems [1]. Measurements can be performed directly in the fluid, using a laser sheet to illuminate dispersed luminescent particles, or at solid boundaries when the sensing materials are coated on the container walls. Despite its proven capabilities, the method has significant optimization potential through independent refinement of both exposure and illumination durations. The main purpose of this investigation is to optimize the technique by minimizing uncertainty. To achieve this, we model uncertainty to predict a theoretically optimized timing scheme and compare it to an empirically optimized scheme. Preliminary results will be presented to assess the correspondence between theoretical and empirical uncertainty minimization, with implications for practical implementation of optimized measurement protocols. The optimized method presented here was developed using YAl3(BO3)4:Cr3+, Y3Al5O12:Cr3+ or ruby but can be applied to different luminescent material with lifetime sensitive to temperature or other quantities (i.e. pH, Oxygen, CO2, etc.).
References:
[1] Rousseau, G., Pons, M., Adelerhof, H., Pellerin, N., Giesbergen, M., Carde, B., Wolf M., Blanckaert K., Borisov S. M., & Fond, B. (2025). Low-cost CMOS-based luminescence lifetime imaging with oxygen, temperature and pH sensors. Sensors and Actuators B: Chemical, 138849, https://doi.org/10.1016/j.snb.2025.138849
How to cite: Pons, M., Rousseau, G., Carde, B., Borisov, S., Fond, B., and Blanckaert, K.: Optimizing a luminescence lifetime measurement technique for non-intrusive temperature imaging in laboratory flows , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9841, https://doi.org/10.5194/egusphere-egu26-9841, 2026.
Gravity currents, driven by density variations caused by gradients in temperature, salinity, or sediment concentration, arise due to hydrostatic imbalances between adjacent fluids. These flows play a pivotal role in a wide range of geophysical and engineering applications, shaping atmospheric, terrestrial, and subaqueous environments. In natural settings, the propagation of gravity currents often encounters uneven topographies, where the dynamics of the dense flow are significantly influenced by topographic features. Recent research has increasingly focused on understanding gravity currents moving through channels obstructed by finite-size patches of obstacles, which adds complexity to their behavior and mixing processes. This experimental study investigates the interaction mechanisms between gravity currents and such obstructions, providing insights into their dynamics and mixing implications through a non-intrusive image analysis technique based on light reflection to evaluate instantaneous density fields.
Laboratory experiments were conducted in a Perspex tank with dimensions of 3 m in length, 0.3 m in height, and 0.2 m in width. An array of rigid plastic cylinders, each with a diameter of 2.5 cm, was placed at the bottom of the tank spanning its entire width. The gravity current was reproduced using the lock-release technique with a density difference ∆ρ=6 kg/m³. A total of 15 full-depth lock-exchange experiments were performed to analyze the submergence ratio, i.e. the ratio between the initial current depth and the obstacle height, and the gap-spacing ratio, i.e. the ratio between the spacing of the bottom obstacles and the obstacle height.
The analysis of instantaneous density fields provides valuable insights into the complex dynamics of gravity currents. During the initial slumping phase, the front of the dense current advances at a constant velocity. However, upon reaching the obstacles, the gravity current slows down, leading to the emergence of distinct flow regimes. High-resolution density measurements reveal that the submergence ratio plays a critical role in controlling current diversion, while obstacle spacing governs the flow pathway. An increase in the submergence ratio enhances the interactions between the current and the roughness elements, resulting in marked fluctuations in potential energy and mixing intensity that significantly affect the current evolution. Although bottom roughness generally reduces the front velocity and alters entrainment behavior, the effect of obstacle spacing is less important, particularly for low submergence ratio. For large submergence ratio, the current exhibits a shift in mixing dynamics, deviating from the near-linear growth of background potential energy observed in smoother cases.
How to cite: Adduce, C., Maggi, M., and Di Lollo, G.: Mixing in gravity currents over an array of cylindrical obstacles, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13310, https://doi.org/10.5194/egusphere-egu26-13310, 2026.
This study uses large eddy simulations with a mixture model to investigate how secondary flows (SFs) in gravity currents (GCs), which are triggered by spanwise heterogeneous roughness or unstable buoyancy convection, influence their layer structures. These processes are analogous to those governing density-driven flows in stratified river and estuary systems. We introduce a double-averaged methodology to separate the contributions of SFs and bed roughness to the spatial fluctuations within GCs. Our results show that the spanwise locations of low and high momentum paths for GCs are locked at the crests and valleys of a rough impermeable bed, respectively, while a rough permeable boundary reverses these locations. Strong Rayleigh-Taylor instabilities developing in bed pores can eliminate the roughness-triggered SFs within GCs and generate new buoyancy-driven ones with an opposite rotation. Asymmetric boundary shear creates a barrier layer of GCs that prevents the SFs from penetrating their jet region, which continuously intensifies the rolls but restricts their vertical growth. On rough impermeable beds, these SFs sustain as a coexistence of the first and second kinds, with the first kind generated by streamwise vortex stretching. On rough permeable beds, the second kind dominates as unsteady buoyancy convection breaks the skewing of the mean shear induced by the spanwise pressure gradient. In the mean flow field, energy-transfer terms related to the SFs and bed roughness alleviate and exacerbate the uneven distribution of mean kinetic energy, respectively. In the dispersive field, the SFs-related component transfers dispersive kinetic energy from the lower part of SFs to their upper part, while the bed-roughness-related one makes an inverted transfer with a relatively small contribution. In the turbulent field, transfer terms related to the SFs and bed roughness both tend to suppress the homogenization of turbulent distribution within GCs. These findings provide insight into complex flow-bed interactions relevant to component transport and mixing processes in estuaries and oceans.
How to cite: Han, D., He, Z., Guo, Y., and Lin, Y.: Roughness- and buoyancy-triggered secondary flows in gravity currents , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4493, https://doi.org/10.5194/egusphere-egu26-4493, 2026.
Highly concentrated geogenic CO2 emissions are frequently observed in volcanic and tectonic areas. Specific topographic and meteorological conditions can lead to surface accumulation in the form of buoyancy-driven “CO2 rivers.” While history records catastrophic events, such as the deadly limnic eruption of Lake Nyos in 1986, the dynamics of these CO2 rivers are not well understood. Current modeling efforts are often limited by a lack of controlled empirical data, hindering the development of robust hazard assessment and mitigation strategies. To address this issue, we simulate CO2 rivers in scaled analog laboratory experiments by turbulently injecting high-density saline water into a tank of lower-density fresh water over a rough, inclined surface. We vary the volume flow rate, slope angle, and surface roughness between experiments. We characterize the flow dynamics by measuring the front and lateral spreading velocities as a function of time. The acquired experimental datasets are then used to calibrate TWODEE, a depth-averaged, shallow-layer numerical model for buoyancy-driven flows that relies on several empirical parameters to describe entrainment. To test the new range of parameters, we apply the calibrated model to our field data on airborne concentration and surface flux of CO2 collected at the Ribeira Grande CO2 degassing zone on São Miguel, Azores, Portugal. The results validate the experimentally calibrated model and demonstrate that our refined set of model parameters significantly improves the modeling of turbulent dense-gas flows, enabling more robust predictions of the behavior of hazardous CO2 rivers in volcanically and tectonically active regions.
How to cite: Girault, F., Robert, M.-M., Carazzo, G., Viveiros, F., and Silva, C.: Laboratory experiments of turbulent density currents and implications for near-surface CO2 rivers dispersion, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6915, https://doi.org/10.5194/egusphere-egu26-6915, 2026.
Scalar transport models derived from the two-dimensional depth averaged shallow water equations are frequently applied to a wide range of environmental flow conditions. A scalar may represent a dissolved solute, a pollutant, or fine sediment transported in river channels, estuaries, or ocean waters. However, these depth-averaged scalar transport models do not provide detailed information about the vertical distribution of the solute. The vertical distribution of a scalar could be computed from the 3D shallow water equations but is complex to compute numerically. One possible approach is to implement a multi-layer transport system, in which exchanges between layers determine the vertical concentration distribution of the transported scalar depending on the velocity of deposition, vertical eddy viscosity, and flow velocity.
The model presented is a GPU-based multi-layer scalar transport model implemented in C++/CUDA and coupled with an existing two-dimensional shallow water (SWE-2D) model. The SWE-2D framework is designed to handle three types of mesh topology: structured quadrilateral meshes, structured triangular meshes, and unstructured triangular meshes. The multi-layer system is implemented using an implicit scheme that accounts for interlayer exchanges. The layers are uniformly distributed in the vertical direction, with the total water depth divided by the number of layers, however, layer thickness varies in time and space with the water depth. Flux exchanges between layers depend on the vertical eddy viscosity, flow velocity, and the scalar deposition (settling) velocity. Different types of vertical eddy viscosity models have been developed (linear and constant), and the vertical flow velocity model implemented is a simple logarithmic wall low model.
To assess the viability of the multi-layer model, a series of synthetic channel test cases are implemented, in which the vertical eddy viscosity and the settling velocity are systematically varied but the vertical velocity considered as constant in depth. In addition, an experimental study by García J.A, Latorre B. et al., investigating the vertical concentration distribution of a passive solute in unsteady laboratory channel flow, is reproduced using the multi-layer framework. Results from the laboratory experiments and the numerical model are first compared using depth-averaged concentrations and, secondly, using the multi-layer system with a depth-varying vertical velocity profile. The model demonstrates a good representation of the horizontal solute distribution. Vertically, when the flow velocity varies with depth, the multi-layer system captures the solute global distribution, however , the lack of precision is due to the flow velocity and eddy viscosity vertical models that must be adapted to the specific flow conditions and environmental context.
How to cite: Sicard, L., Garcia Navarro, P., Martinez Aranda, S., and Latorre, B.: A GPU based model for multi-layer scalar transport in open channels, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13374, https://doi.org/10.5194/egusphere-egu26-13374, 2026.
Accurate quantification of melt rates of marine-terminating glaciers is one of the most critical challenges in contemporary glaciology (Straneo & Cenedese, 2015), where small-scale ice-ocean interactions play an important role (Mamer et al., 2024). However, large-scale coupled models often misrepresent the processes that mediate these interactions, which increases uncertainty in future projections. These systems discharge substantial volumes of cold freshwater into the open ocean through subglacial plumes. The dynamics of these buoyant plumes are crucial for heat transfer, mixing, and melting processes at the ice-ocean boundary. Previous studies have demonstrated that, under specific conditions influenced by discharge, system density, and ambient turbulence, seawater may enter the subglacial cavity as a wedge-shaped density front (Wilson et al., 2020). The mechanisms that promote or inhibit seawater intrusion and mixing remain poorly understood. To address this, we carried out direct numerical simulations (DNS) of a subglacial channel discharging into the open ocean, following the laboratory experiments of Wilson et al. (2020), and evaluated the impact of different densimetric Froude numbers on seawater intrusion and the resulting buoyant plume. Our findings provide new insights into the role of subglacial plumes in heat and salt transport, thereby clarifying the mechanisms that drive melting at the ice-ocean interface.
How to cite: Redel, T., Barros, M. M., and Escauriaza, C.: Dynamics of Subglacial Plumes and Seawater Intrusion at the Ice-Ocean Interface, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15439, https://doi.org/10.5194/egusphere-egu26-15439, 2026.
Posters virtual: Thu, 7 May, 14:00–18:00 | vPoster spot 1b
EGU26-4129 | ECS | Posters virtual | VPS23
Rapid Turbulence Evolution Resulting from Stable Shear layer and Atmospheric Gravity Wave InteractionsThu, 07 May, 14:18–14:21 (CEST) vPoster spot 1b
Early laboratory experiments of shear flow by Thorpe (Thorpe, 2002) provided evidence of Kelvin-Helmholtz Instability (KHI) billow interactions either due to misaligned adjacent billow cores or varying phases along the adjacent billow axes. Similar evidence has been found in the observations of tropospheric clouds, airglow, and Polar Mesospheric Clouds (PMC) imagery data in the mesosphere. Initial High-Resolution Direct Numerical Simulations (DNS) studies performed at Reynolds Number of 5000 (Fritts et al., 2021a, Fritts et al., 2021b) have demonstrated the that misaligned KH billow cores exhibit strong and complex vortex interactions inducing ‘Tubes and Knots’ (T&K) structures (Thorpe, 2002). These T&K structures were observed to accelerate transition to small-scale turbulence in contrast to previously known notable transitional mechanisms such as secondary KHI and convective instabilities emerging in individual KH billows. Also, the KHI T&K dynamics evidently yield intense turbulence dissipation rates contrasting that of secondary KHI and convective instabilities in billow cores.
More recent high-resolution imaging of OH airglow (Hecht et al., 2021) provide concrete evidence of KHI billows with wavelength ranging between 7-10 km modulated by atmospheric Gravity Waves (GWs) of dominant horizontal wavelengths ∼ 30km and oriented orthogonal to KH billow axes and propagate along the billow cores which result in apparent T&K dynamics rapidly driving KH billow breakdown. Similar evidence has been found in recent PMC imaging. This is the central theme of the idealized DNS discussed in this talk.
We conducted DNS studies to demonstrate the turbulence energetics of KHI billow interactions when subject to modulations due to monochromatic atmospheric gravity waves of small perturbation amplitudes and intrinsic frequency of N/5 (where N is the background Brunt-Vaisala Frequency). Preliminary analyses of our DNS results indicate that GW modes with modest amplitudes promote KHI billow misalignments resulting in complex multi-scale T&K dynamics fixed at specific GW phases. An increase in the GW amplitude resulted in noticeable reduction of KHI billow wavelengths further promoting KH billow misalignments. The resulting turbulence is expected to consist of broader scale ranges of intense turbulence dissipation rate and diffusivity.
References
[Fritts et al., 2021a] Fritts, D. C., Wang, L., Lund, T. S., and Thorpe, S. A. (2021a). Multi-Scale Dynamics of Kelvin-Helmholtz Instabilities . Part 1 : Secondary Instabilities and the Dynamics of Tubes and Knots. pages 1–27.
[Fritts et al., 2021b] Fritts, D. C., Wang, L., Thorpe, S. A., and Lund, T. S. (2021b). Multi-Scale Dynamics of Kelvin-Helmholtz Instabilities . Part 2 : Energy Dissipation Rates , Evolutions , and Statistics. pages 1–39.
[Hecht et al., 2021] Hecht, J. H., Fritts, D. C., Gelinas, L. J., Rudy, R. J., Walterscheid, R. L., and Liu, A. Z. (2021). Kelvin-Helmholtz Billow Interactions and Instabilities in the Mesosphere Over the Andes Lidar Observatory: 1. Observations. Journal of Geophysical Research: Atmospheres, 126(1):e2020JD033414. Publisher: John Wiley & Sons, Ltd.
[Thorpe, 2002] Thorpe, S. A. (2002). The axial coherence of Kelvin–Helmholtz billows. Quarterly Journal of the Royal Meteorological Society, 128(583):1529–1542. Publisher: John Wiley & Sons, Ltd.
How to cite: Doddi, A., Fritts, D., and Lund, T.: Rapid Turbulence Evolution Resulting from Stable Shear layer and Atmospheric Gravity Wave Interactions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4129, https://doi.org/10.5194/egusphere-egu26-4129, 2026.
