NP7.1

Simulations of internal solitary waves (ISW) of the first mode over the isolated obstacles of various shapes:  triangles, semicircle and rectangles of different lengths are presented.  The influence of height, length and shape of the obstacle on the transformation of ISW and energy dissipation was investigated. A two-layer free surface water system with upper and bottom layer thicknesses h₁ and h₂ and densities ρ₁ and ρ₂, respectively, and water depth H was considered.  It was carried out set of 42 numerical experiments with both ISW of elevation and depression types. The results of simulation were compared with the results of laboratory experiments. It is shown that the blocking parameter B  [1] (that is a dimensionless parameter equal to the ratio of the lower layer above the obstacle to the wave amplitude) is useful for describing the type of interaction and estimation of energy loss.  The transformation of large amplitude ISW over a triangular obstacle differs from the corresponding interaction with the semicircle obstacle. Internal boluses formed in the case of semicircle or rectangle obstacle are 1.5 - 2 times larger than in the case of a triangular obstacle. As a result, energy dissipation and corresponding mixing in the case of ISW transformation over semicircle and a rectangular obstacle is greater than in the case of a triangular ones. Maximum energy losses can reach 42% in the case of a rectangular obstacle. Energy losses increase with increasing length of the obstacle. Thus, we can conclude that topographic effects, namely the influence of shape and geometric characteristics of underwater obstacles have a significant impact on the dissipation of mechanical energy. 

[1]  T. Talipova , K. Terletska, V. Maderich, I. Brovchenko, K. T. Jung, E. Pelinovsky and R. Grimshaw  Internal solitary wave transformation over the bottom step: loss of energy. // Phys. Fluids, 2013, 25, 032110

How to cite: Terletska, K. and Maderich, V.: Estimation of energy loss of internal solitary waves over an isolated obstacle, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4274, https://doi.org/10.5194/egusphere-egu22-4274, 2022.

In late winter/early spring temperate and northern lakes often experience a so-called weak, inverse stratification.  This occurs since: i) fresh water experiences a maximum density at around four degrees Centigrade, ii) the lake is iced over and thus mechanically isolated from the overlying atmosphere, iii) the increasing solar insolation heats the water column according to the Beer-Lambert-Bouguer law; thereby producing a region of instability that mixes a portion of the water column.  This classical scenario fits some lakes, but the small density differences due to the thermal forcing also imply that very small amounts of dissolved salts could create a more complex, combined solute-thermal stratification.  We explore the behaviour of nonlinear internal waves for one such measured stratification. For mode-1 we find well defined internal solitary waves. For mode-2 the coupling between pycnoclines is weaker leading to a more complex dynamics that we quantify in detail. 

How to cite: Stastna, M.: Mode-2 internal waves and inter-mode resonance in late winter lakes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1228, https://doi.org/10.5194/egusphere-egu22-1228, 2022.

Fronts and near-inertial waves (NIWs) are energetic motions in the upper ocean that are thought to interact and provide a possible route for kinetic energy dissipation of mesoscale balanced flows. To date, the theoretical explanations for such interactions rely on the fronts being geostrophic, with a weak ageostrophic secondary circulation (ASC) and a small Rossby number. We develop a quasilinear model to study the interactions between NIW vertical modes and a 2D front undergoing semigeostrophic frontogenesis. In our model, frontal sharpening is divided into two stages: an exponential stage, that is characterized by a low Rossby number and is driven by geostrophic strain; and a super-exponential stage, that is characterized by an O(1) Rossby number and is driven by the convergence of the ASC. We identify a new mechanism, the convergence production, through which NIWs can efficiently extract energy from the front during the super-exponential stage. It is shown that the convergence production can dominate the known mechanism of energy extraction during the exponential stage, the deformation shear production, for a relatively strong geostrophic strain field.

How to cite: Kar, S. and Barkan, R.: Energy exchanges between two-dimensional front and internal waves., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7582, https://doi.org/10.5194/egusphere-egu22-7582, 2022.

Ocean circulation strongly influences how internal tides radiate and break and stimulates the spatial inhomogeneity and temporal variation of internal tidal mixing. Qualitative and quantitative characterizations of interactions between internal tides and general circulation are critical to multi-scale circulation dynamics. Based on significant progress in regional circulation simulation, we obtain an observation-supported internal tide energy field around Luzon Strait by deterministically resolving the dynamics of the radiating paths of the internal tide energy. These paths are created when the known most powerful internal tide of Luzon Strait interacts with the Kuroshio Current. We found that the radiating tidal pattern, local dissipation efficiency, and energy field respond differently to the leaping, looping, and leaking Kuroshio paths within Luzon Strait. Our new insights into the dynamics and our clarifying the controlling refraction mechanism within the general circulation create the potential for internal tides to be represented better in climate models. 

How to cite: Xu, Z.: Dynamics Insight of  Internal Tide Radiation in the Kuroshio, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3255, https://doi.org/10.5194/egusphere-egu22-3255, 2022.

Oceanic nonlinear internal waves (NLIWs) play an important role in regional circulation, marine biogeochemistry, energetics, vertical mixing, underwater acoustics, marine engineering, and submarine navigation, most commonly generated by the interaction between barotropic tides and bathymetry. However, our understanding of their characteristics, generation, and propagation is still far from complete in many water bodies. Here, we present the characteristics of NLIWs observed from moored and underway observation in the northern East China Sea during May 15-28, 2015 and discuss their generation and propagation. The NLIWs observed during the experiment were characterized by an amplitude ranging from 4 to 16 m, width ranging from 380 to 600 m, and propagated southwestward at a speed of 0.64–0.72 m s⁻¹. Groups of NLIWs were predominantly observed during, or a couple of days after, the period of spring tides, with a time interval 24–96 min shorter than the canonical semidiurnal period (12.42 h; M₂); this is in contrast to those found in many other regions that have a phase-locking to the barotropic semidiurnal tides. The remote generation and propagation of the NLIWs from potential generation sites into the study area under time-varying stratification support the fact that the time interval departed from the semidiurnal period. Our results have substantial implications for turbulent mixing and ocean circulation in regions where the shelf is broad and shallow. The NLIWs generated from multiple sources propagate in multiple directions with propagating speeds varying over days depending on stratification. 

How to cite: Lee, S.-W. and Nam, S.: Characteristics, Generation, and Propagation of Nonlinear Internal Waves Observed in the Northern East China Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8974, https://doi.org/10.5194/egusphere-egu22-8974, 2022.

  Internal tides are energetic in the Mariana arc, but their three-dimensional radiation and dissipation remain unexplored, particularly the trench-arc-basin impacts. Here, the generation, propagation and dissipation of M₂ internal tides over the Mariana area are examined using a series of observation-supported high-resolution simulations. The M₂ barotropic to baroclinic conversion rate amounts to 8.35 GW, of which two arc-shaped ridges contribute ~81% of the generated energy. The contributions to generation by the Mariana basin and deep trench are weak. Nevertheless, they are important in modulating the energy radiation and dissipation, since tidal beams can spread to these areas. The Mariana ridges radiate the westward-focused and eastward-spreading tidal beams. This is very consistent with the altimetric measurements. The resonance in the ridge center enhances the westward converging beam, which can travel across the Palau Ridge, 800 km away. In contrast, the eastward beams propagate over a limited lateral range, but can radiate and dissipate significant energy in the deep water column, reaching even to the abyssal Mariana trench. The direct estimation from the model results reveals the dissipation’s multilayer vertical profile in the entire water column, and is well consistent with the finescale parameterization estimate based on vertical strain. However, the estimate of an oft-used energy balance method, which typically assumes an exponentially decaying vertical structure function for the dissipation rate based on distance above the seafloor, is largely inconsistent with the measurements. Our findings highlight the complexity of three-dimensional radiation paths and dissipation map of internal tides in the Mariana area.

How to cite: Zhao, C., Xu, Z., Robertson, R., Li, Q., Wang, Y., and Yin, B.: The Three-Dimensional Internal Tide Radiation andDissipation in the Mariana Arc-Trench System, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3451, https://doi.org/10.5194/egusphere-egu22-3451, 2022.

Internal tide variations and mixing properties are important to shelf dynamics and mass exchange. In the present study, spatiotemporal variability of internal tides and their modulation factors on the southern East China Sea (ECS) shelf are examined using a three-month mooring observation. Semidiurnal and diurnal internal tides are found to exhibit distinct varying trends. Specifically, the semidiurnal internal tides are quite weak at the early stage, but greatly enhanced in the last three spring-neap cycles. In contrast, the diurnal internal tides follow quasi spring-neap variability except for the strengthening in two specific periods. The enhancement of semidiurnal internal tides in late July and August can be attributed to the strengthened stratifications shelf-slope area northeast of Taiwan Island, which is identified as the generation source. While the diurnal internal tides are modulated by background circulation through the effective critical latitude. The weak critical latitude effect corresponds to the intermittent enhancement of diurnal internal tides in two specific periods. In addition, the circulation also affects the vertical modal structures of the internal tides. The proportion of higher modes internal tides increases during robust eddy activities.  The high-frequency and high-mode internal tides are of crucial significance for turbulent mixing on the shelf region.

Key word: Internal Tides; Mooring Observation; Spatiotemporal variation; Shelf dynamics

How to cite: Wang, W., Robertson, R., Wang, Y., Zhao, C., You, J., Xu, Z., and Yin, B.: Temporal variability of Multimodal Internal Tides at the East China Sea Shelf, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3460, https://doi.org/10.5194/egusphere-egu22-3460, 2022.

The diurnal internal tides contribute nearly a quarter of global baroclinic tidal energy, while their roles in shaping spatiotemporal inhomogeneity of tidal energy field are not well known. Here, based on a combination of observation-supported numerical simulation and theoretical analyses, we clarify the combined and relative contributions of β refraction, subtidal circulation refraction and multi-wave interference to the long-range radiation and dissipation maps of diurnal internal tides in the northwestern Pacific. The diurnal tidal beams are primarily emanated from the Luzon Strait (LS) and Talaud-Halmahera Passage (THP). The β refraction effect, which is more pronounced at higher latitudes, refracts the mean path of LS tidal beam equatorward by ~40° when it arrives at the deep basin, consistent with previous altimeter observations. A second refraction effect by subtidal circulation with seasonal variability deflects the mean beam path by ~10°. Multi-wave interference of tidal beams from the LS and THP further enhances the inhomogeneous pattern, resulting in enhanced and reduced energy flux beam branches with distinct vertical structures in the west Mariana basin. A modified line-source model and theoretical ray-tracing analysis can well explain the effects of refraction and interference. Internal tidal dissipation map in the deep basin coincides well with the inhomogeneous and spreading radiation paths. The mechanism characterization of the world’s most energetic diurnal internal tides in the northwestern Pacific could improve our understanding of global baroclinic tidal energy redistribution and associated tidal mixing parameterization in climate-scale ocean models.

How to cite: Wang, Y., Xu, Z., Hibiya, T., Yin, B., and Wang, F.: Radiation Path of Diurnal Internal Tide in the Northwestern Pacific Controlled by Refraction and Interference, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8278, https://doi.org/10.5194/egusphere-egu22-8278, 2022.

As it is known, the canonical Korteweg-de Vries equation is applied to describe nonlinear long internal waves in the first approximation on parameters of nonlinearity and dispersion. To compare with surface gravity waves, the coefficient of quadratic nonlinearity can have either sign and to be zero. In this case, the asymptotic procedure should take into account higher terms of nonlinearity. Generalized Korteweg-de Vries equation called the Gardner equation is now a popular model to analyze nonlinear internal waves in the ocean with complicated density and shear flow stratification. If the density stratification is almost linear, the number of nonlinear terms is increased. The family of the Korteweg-de Vries-like equations for internal waves in the form u_t+ [F(u)]_x + u_xxx = 0 is discussed in this presentation. In leading order the nonlinear term is F(u) ~ qu^b  with b > 0. The steady-state travelling solitary waves is analyzed.

            For q > 0 and b > 1 the analysis re-confirmed that all travelling solitons have “light” exponentially decaying tails and propagate to the right. If q < 0 and b < 1, the travelling solitons (so called compactons) have a compact support (and thus vanishing tails) and propagate to the left. For more complicated F(u) and b > 1 (e.g., the Gardner equation and higher-order generalizations) standing algebraic solitons with “heavy” power-law tails may appear. If the leading term of F(u) is negative, the set of solutions may include wide or table-top solitons (similar to the solutions of the Gardner equation), including algebraic solitons and compactons with any of the three types of tails. The solutions usually have a single-hump structure but if F(u) represents a higher-order polynomial, the generalized KdV equation may support multi-humped pyramidal solitons.

Study is supported by RFBR Grant No 21-55-15008.

How to cite: Talipova, T. and Pelinovsky, E.: Korteweg-de Vries equation family in the theory of nonlinear internal waves, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3184, https://doi.org/10.5194/egusphere-egu22-3184, 2022.