Explore the vast range of titles available.

Submesoscale dynamics play a crucial role in energy redistribution in the upper ocean but remain challenging to observe due to their small spatial and temporal scales. We use ship‐based observations of an oceanic submesoscale front sampled at high resolution while repeatedly traversed to observe deformation and splitting of an embedded cyclonic eddy. The velocity field from a shipboard acoustic Doppler current profiler was analyzed with spectral Helmholtz techniques and structure functions to examine the partitioning of kinetic energy into rotational and divergent components and energy transfer between mesoscales and submesoscales. During the eddy splitting, intensified mesoscale strain enhances the divergent component of kinetic energy in the mixed layer, where Rossby numbers are O(1)$\\mathcal{O}(1)$ . This coincides with a transient forward energy cascade from mesoscales to submesoscales. The wave‐vortex decomposition reveals enhanced wave‐like energy during and after splitting, with subsurface maxima indicative of near‐inertial wave activity and downward energy propagation.

Electromagnetic vortex waves have received widespread attention in many fields due to their unique physical characteristics. The information dimension provided by vortex electromagnetic waves brings possibilities for future breakthroughs in radar detection and imaging. This article proposes a multi-modal aggregated electromagnetic vortex wave generation method for the first time. Moreover, it conducts vehicle imaging experiments to verify the method’s practicality. The core element of the experiment is to simultaneously generate multiple-mode electromagnetic vortex wave signals with energy accumulation and perform fusion processing. Firstly, multiple orbital angular momentum (OAM) modes are superimposed to generate a mode group, and the initial phase of the modes in the mode group is further controlled to synthesize aggregated electromagnetic vortex waves. Based on the generation of aggregated vortex waves, imaging experiments were conducted using a vehicle-mounted setup. The experimental procedure and multi-modal fusion results were presented. It has been shown that the energy of the main lobe signal of the image target is enhanced by utilizing multi-modal vortex radar information fusion, which can improve the signal-to-noise ratio of the target imaging.

The decomposition of oceanic flow into its geostrophically balanced and unbalanced motions carries theoretical and practical significance for the oceanographic community. These two motions have distinct dynamical characteristics and affect the transport of tracers differently from one another. The launch of the Surface Water and Ocean Topography (SWOT) satellite provides a prime opportunity to diagnose the surface balanced and unbalanced motions on a global scale at an unprecedented spatial resolution. Here, we apply dynamic‐mode decomposition (DMD), a linear‐algebraic data‐driven method, to tidally‐forced idealized and realistic numerical simulations at submesoscale‐permitting resolution and one‐day‐repeat SWOT observations of sea‐surface height (SSH) in the Gulf Stream downstream of Cape Hatteras, a region commonly referred to as the separated Gulf Stream. DMD is able to separate out the spatial modes associated with sub‐inertial periods from super‐inertial periods. The sub‐inertial modes of DMD can be used to extract geostrophically balanced motions from SSH fields, which have an imprint of internal gravity waves, so long as the data extends long enough in time. We utilize the statistical relation between relative vorticity and strain rate as the metric to gauge the extraction of geostrophy. Plain Language Summary Observations of the global ocean surface are now done routinely by satellites. One of the key variables in describing the oceanic state is sea‐surface height (SSH), that is, elevations of the sea surface. For mariners and those who enjoy marine sports, it is well appreciated that the ocean surface is teeming with waves and currents. Similar to the density interface between the ocean and atmosphere, there are waves beneath the surface at density interfaces within the ocean. Waves at the ocean surface are called surface waves and in the interior are called internal waves. Both surface‐ and internal‐wave signals imprint onto SSH. In order to extract information on oceanic currents (e.g., flow direction and speed) from SSH, it is necessary to remove the signal of surface and internal waves since waves and currents not associated with waves are generally not physically related to each other on the same scales in space and time. Namely, waves tend to move much faster and have smaller spatial scales than the currents. Here, we implement a method based on linear algebra, which is able to capture the slowly varying residual signals from the waves. Key Points Dynamic‐mode decomposition (DMD) is applied to sea‐surface height (SSH) fields DMD extracts the sub‐inertial signals from SSH fields that have an imprint of internal gravity waves (IGWs) Slowly varying DMD spatial modes can be used to isolate geostrophically balanced motions

The interaction between submesoscale baroclinic vortical structures and large amplitude inertia‐gravity waves (IGWs), with emphasis on the vertical velocity, is numerically investigated using a high‐resolution three‐dimensional non‐hydrostatic model. A rich variety of vortex‐wave interactions are possible depending on the potential vorticity (PV) content and length scale of the submesoscale monopoles or dipoles, and on the amplitude and wave number of the IGWs. On the one hand, large amplitude IGWs cause horizontal and vertical advection of the vortices, which conserve their stability though their geometry is largely modified by the wave motion. On the other hand, the horizontal vortical motion Doppler shifts the local frequency of IGWs. The vortical angular velocity and vortex density stratification lead to a wave dispersion relation involving the effective Coriolis frequency (Coriolis frequency plus the vortical angular velocity) and the total Brunt‐Väisälä frequency. This inhomogeneous change in the local wave frequency causes IGWs to depart from their initial plane geometry. In the particular case of inertial waves, the nonlinear vortex‐wave interaction generates spiral IGWs, having vertical velocities one order of magnitude larger than the submesoscale vortical flow in the absence of waves.

Vortex wave and plane wave, as two most fundamental forms of wave propagation, are widely applied in various research fields. However, there is currently a lack of basic mechanism to enable arbitrary conversion between them. In this paper, we propose a new paradigm of extremely anisotropic acoustic metasurface (AM) to achieve the efficient conversion from 2D vortex waves with arbitrary orbital angular momentum (OAM) to plane waves. The underlying physics of this conversion process is ensured by the symmetry shift of AM medium parameters and the directional compensation of phase. Moreover, this novel phenomenon is further verified by analytical calculations, numerical demonstrations, and acoustic experiments, and the deflection angle and direction of the converted plane waves are qualitatively and quantitatively confirmed by a simple formula. Our work provides new possibilities for arbitrary manipulation of acoustic vortex, and holds potential applications in acoustic communication and OAM-based devices.

In theoretical research framework of acoustics or optics, how to provide stable and efficient experimental vortex sources with arbitrary orbital angular momentum (OAM) (especially with larger OAM) is a highly challenging research topic. Here, we propose and demonstrate the general principle of two different methods to generate vortex sources with arbitrary OAM, based on the point-sources array and acoustic metamaterials, respectively. Specifically, the general synthetic law is summarized from the analytical perspective behind generating two-dimensional vortex waves using different point sources with different phases, and the design flexibility of acoustic metamaterials is also utilized to provide an ideal solution for generating vortex sources with larger OAM. Besides, we qualitatively and quantitatively determine the OAM of generated vortex waves through simple formulas, and briefly discuss the applicability and stability of two different methods with complementary advantages. The principles of vortex sources generation revealed in this work provide direct theoretical support for the experimental exploration of interactions between multiphysics fields and complex media, with potential applications in vortex fields manipulation and OAM detection.

Electrogenic vortex wave refer to the wave that carry orbital angular momentum (OAM) in the radio frequency (RF) domain. The OAM mode is expected to be initially explored and applied as a full novel spatial dimension resource. However, the radiation energy distribution pattern of electromagnetic vortex wave exhibits a central hollow. The energy hollow phenomenon has become one of the major drawbacks limiting the popularization of electromagnetic vortex wave. In this article, a generation scheme of convergent vortex wave is proposed and research generated by uniform circular array (UCA). Orthogonal waveforms are introduced into the antenna to change the phase relationship between the original signals so that the energy remains in the wave center region. The numerical results validate the effectiveness of the proposed scheme. The circular intensity disappears, while the spiral phase wavefront features can still be maintained.

We study a reduced electrostatic fluid model for the tokamak scrape-off layer, which incorporates temperature gradient and vorticity gradient as two free energy fields. Two scenarios of field coupling are addressed: (1) sheath condition; (2) vortex wave coupling. For the sheath condition induced field coupling, the poloidal E×B flow shear is coupled with the temperature gradient. Combining an eigenmode analysis and the nonlinear phase dynamics approach, our findings indicate that in the absence of a vorticity gradient, the overall effect of the sheath condition induced flow shear can either stabilize or destabilize the interchange mode, depending on the competition between the flow shear suppression and the temperature gradient driving. This is different from the case where the gradient drive and shear damping are decoupled. When the field coupling is mediated by wave interactions, by setting an idealized step-like temperature and vorticity profiles, a joint mode forms through resonant interaction between the interfacial waves driven by the temperature and vorticity gradients, respectively. Near the phase locking condition, the joint mode can be more unstable than pure temperature gradient driven mode.

The resolution and accuracy of airborne/spaceborne SAR are continuously improving, making it an effective means for observing ocean dynamic processes and detecting marine targets. In contrast, utilizing its unique orbital angular momentum (OAM) mode, vortex radar does not require temporal accumulation to achieve azimuthal resolution, making it particularly suitable for observing moving sea surfaces. This capability enables stable and continuous monitoring of dynamic ocean scenes. This paper proposes a vortex radar imaging method based on three-dimensional sea surface scattering characteristics: first, a three-dimensional wind-driven sea surface geometric model is established based on the Elfouhaily sea spectrum, and its scattering characteristics under different incident angles, wind speeds, and wind directions are analyzed using the semi-deterministic facet-based two-scale method; then, two-dimensional range-azimuth imaging is achieved through coordinate transformation, echo modeling, pulse compression, and fast Fourier transform (FFT) in OAM mode domain, with the correctness of the imaging algorithm verified through multiple point target imaging results. Finally, simulation results of two-dimensional sea surface vortex imaging under different incident angles are presented, and the influence of wind speed and direction on sea surface vortex imaging is analyzed. The study shows that the vortex imaging system can effectively reflect wave fluctuations and wind direction characteristics, demonstrating the feasibility and potential of vortex radar imaging in oceanographic applications.

Developing electromagnetic metamaterials that simultaneously offer broadband response, a thin profile, and multifunctional capabilities remains a key challenge in stealth technology. Based on the Pancharatnam–Berry (PB) phase principle, this study proposes a multilayer cascaded geometric phase metasurface. By rotating the meta-atoms to introduce a controllable phase gradient, the metasurface efficiently converts incident circularly polarized waves into co-polarized reflected vortex waves, while leveraging electromagnetic coupling and resonance characteristics between the multilayer structures to achieve broadband energy dissipation. Experimental results demonstrate that this merely 2.72 mm thick multilayer cascaded structure achieves an effective absorption bandwidth of 7.9 GHz (8.1–16.0 GHz), representing a threefold increase over a single-layer design, and exhibits excellent radar cross-section (RCS) reduction performance. Near field and scattering confirm vortex wave generation with specific topological charges, revealing the intrinsic physical mechanism underlying broadband absorption and stealth through energy scattering across a wide angular domain. This study provides new insights for addressing the technical challenges of broadband and multifunctional absorption materials, laying an important foundation for the development of next-generation intelligent stealth metamaterials.