Spontaneous inertia-gravity wave generation from mesoscale eddies

2021 ◽  
Author(s):  
Bo Zhao ◽  
Zhenhua Xu ◽  
Qun Li ◽  
Yang Wang ◽  
Baoshu Yin
Keyword(s):  
Mesoscale Eddy ◽  
Vertical Direction ◽  
Mesoscale Eddies ◽  
Forced Response ◽  
Rossby Number ◽  
Generation Process ◽  
Inertial Oscillations ◽  
Long Distance ◽  
High Frequency Oscillations ◽  
Geostrophic Vortex

<p>An exact geostrophic vortex generate spontaneously inertia-gravity waves (IGWs) with spiral patterns via singularity instability mechanism. In the vertical direction, the energy of the IGWs is dominated by mode-1 in the generation and propagation processes, leading to weak dissipation and long-distance propagation. The amplitude of the IGWs increases linearly with the Rossby number in the range 0.04–0.1. Additionally, the IGWs emitted from an anticyclonic vortex are stronger than those radiated from the cyclonic vortex. Anticyclonic and cyclonic geostrophic vortices transfer roughly 0.54% and 0.41% of their kinetic energy to IGWs in this transient generation process, respectively. However, quasi-geostrophic mesoscale eddies are decomposed to balanced geostrophic component and unbalanced near-inertial oscillations with different timescales. Near-inertial waves (NIWs) also can be generated as a forced response to the nonlinear coupling of the geostrophic component and high-frequency oscillations of the quasi-geostrophic eddies. Afterwards, the NIWs resonate with the near-inertial oscillations and share the same horizontal wavenumbers with the eddy. Generally, an anticyclonic mesoscale eddy can emit much stronger NIWs than does a cyclonic eddy. The NIW intensity strengthens exponentially with the Rossby number. The spontaneous generated NIWs represent an effective pathway for mesoscale eddy energy skin and non-negligible contribution to the global NIW energy.</p>

Hierarchical Concept-Driven Language Model

2021 ◽  
Vol 15 (6) ◽  
pp. 1-22
Author(s):  
Yashen Wang ◽  
Huanhuan Zhang ◽  
Zhirun Liu ◽  
Qiang Zhou
Keyword(s):  
Language Model ◽  
Generation Process ◽  
Data Generation ◽  
Modeling Framework ◽  
Long Distance ◽  
Short Text ◽  
Proposed Model ◽  
Scalable Inference ◽  
End To End ◽  
Hidden Layer

For guiding natural language generation, many semantic-driven methods have been proposed. While clearly improving the performance of the end-to-end training task, these existing semantic-driven methods still have clear limitations: for example, (i) they only utilize shallow semantic signals (e.g., from topic models) with only a single stochastic hidden layer in their data generation process, which suffer easily from noise (especially adapted for short-text etc.) and lack of interpretation; (ii) they ignore the sentence order and document context, as they treat each document as a bag of sentences, and fail to capture the long-distance dependencies and global semantic meaning of a document. To overcome these problems, we propose a novel semantic-driven language modeling framework, which is a method to learn a Hierarchical Language Model and a Recurrent Conceptualization-enhanced Gamma Belief Network, simultaneously. For scalable inference, we develop the auto-encoding Variational Recurrent Inference, allowing efficient end-to-end training and simultaneously capturing global semantics from a text corpus. Especially, this article introduces concept information derived from high-quality lexical knowledge graph Probase, which leverages strong interpretability and anti-nose capability for the proposed model. Moreover, the proposed model captures not only intra-sentence word dependencies, but also temporal transitions between sentences and inter-sentence concept dependence. Experiments conducted on several NLP tasks validate the superiority of the proposed approach, which could effectively infer meaningful hierarchical concept structure of document and hierarchical multi-scale structures of sequences, even compared with latest state-of-the-art Transformer-based models.

scholarly journals The fully nonlinear stratified geostrophic adjustment problem

2017 ◽  
Vol 24 (1) ◽  
pp. 61-75 ◽  
Author(s):  
Aaron Coutino ◽  
Marek Stastna
Keyword(s):  
Stokes Equations ◽  
Wave Train ◽  
Shallow Water Equation ◽  
Classical Problem ◽  
Point Of View ◽  
Rossby Number ◽  
Adjustment Problem ◽  
Inertial Oscillations ◽  
Dispersive Waves ◽  
Fully Nonlinear

Abstract. The study of the adjustment to equilibrium by a stratified fluid in a rotating reference frame is a classical problem in geophysical fluid dynamics. We consider the fully nonlinear, stratified adjustment problem from a numerical point of view. We present results of smoothed dam break simulations based on experiments in the published literature, with a focus on both the wave trains that propagate away from the nascent geostrophic state and the geostrophic state itself. We demonstrate that for Rossby numbers in excess of roughly 2 the wave train cannot be interpreted in terms of linear theory. This wave train consists of a leading solitary-like packet and a trailing tail of dispersive waves. However, it is found that the leading wave packet never completely separates from the trailing tail. Somewhat surprisingly, the inertial oscillations associated with the geostrophic state exhibit evidence of nonlinearity even when the Rossby number falls below 1. We vary the width of the initial disturbance and the rotation rate so as to keep the Rossby number fixed, and find that while the qualitative response remains consistent, the Froude number varies, and these variations are manifested in the form of the emanating wave train. For wider initial disturbances we find clear evidence of a wave train that initially propagates toward the near wall, reflects, and propagates away from the geostrophic state behind the leading wave train. We compare kinetic energy inside and outside of the geostrophic state, finding that for long times a Rossby number of around one-quarter yields an equal split between the two, with lower (higher) Rossby numbers yielding more energy in the geostrophic state (wave train). Finally we compare the energetics of the geostrophic state as the Rossby number varies, finding long-lived inertial oscillations in the majority of the cases and a general agreement with the past literature that employed either hydrostatic, shallow-water equation-based theory or stratified Navier–Stokes equations with a linear stratification.

scholarly journals Can We Detect Submesoscale Motions in Drifter Pair Dispersion?

2019 ◽  
Vol 49 (9) ◽  
pp. 2237-2254 ◽  
Author(s):  
Sebastian Essink ◽  
Verena Hormann ◽  
Luca R. Centurioni ◽  
Amala Mahadevan
Keyword(s):  
Bay Of Bengal ◽  
Velocity Structure ◽  
Mesoscale Eddies ◽  
Structure Functions ◽  
Second Order ◽  
Helmholtz Decomposition ◽  
Impact Structure ◽  
Inertial Oscillations ◽  
Geostrophic Velocity ◽  
Local Dispersion

AbstractA cluster of 45 drifters deployed in the Bay of Bengal is tracked for a period of four months. Pair dispersion statistics, from observed drifter trajectories and simulated trajectories based on surface geostrophic velocity, are analyzed as a function of drifter separation and time. Pair dispersion suggests nonlocal dynamics at submesoscales of 1–20 km, likely controlled by the energetic mesoscale eddies present during the observations. Second-order velocity structure functions and their Helmholtz decomposition, however, suggest local dispersion and divergent horizontal flow at scales below 20 km. This inconsistency cannot be explained by inertial oscillations alone, as has been reported in recent studies, and is likely related to other nondispersive processes that impact structure functions but do not enter pair dispersion statistics. At scales comparable to the deformation radius LD, which is approximately 60 km, we find dynamics in agreement with Richardson’s law and observe local dispersion in both pair dispersion statistics and second-order velocity structure functions.

scholarly journals The impact of the planetary β-effect on the tilting vertical structure of a mesoscale eddy

2018 ◽  
Author(s):  
Shengmu Yang ◽  
Jiuxing Xing ◽  
Shengli Chen ◽  
Jiwei Tian ◽  
Daoyi Chen
Keyword(s):  
South China Sea ◽  
South China ◽  
General Circulation ◽  
Vertical Structure ◽  
Mesoscale Eddy ◽  
Maximum Velocity ◽  
Circulation Model ◽  
Mesoscale Eddies ◽  
China Sea ◽  
The Impact

Abstract. Tilting mesoscale eddies in the South China Sea have been reported recently from observed field data. The mechanism of the dynamic process of the tilt, however, is not well understood. In this study, the influence of planetary β on the vertical structure of mesoscale eddies and its mechanism is investigated using theoretical analysis and numerical model experiments based on the MIT General Circulation Model (MITgcm). The results of the both approaches show that vertical motion due to the planetary β effect and nonlinear dynamics causes a pressure anomaly in the horizontal domain which triggers the tilt of the eddy axis. The tilting distance extends to be the radius of the eddy maximum velocity. In addition, the vertical stratification is another key factor in controlling the tilt of a mesoscale eddy. External forcings such as wind and inflow current are not considered in this study, and topography is included only in a realistic South China Sea model. Therefore, mesoscale eddies with large vertical depth should have the similar axis tilt character in open oceans under the β-effect.

scholarly journals Extraction of spatial-temporal rules from mesoscale eddies in the South China Sea based on rough set theory

Ocean Science ◽  
2011 ◽  
Vol 7 (6) ◽  
pp. 835-849 ◽  
Author(s):  
Y. Du ◽  
X. Fan ◽  
Z. He ◽  
F. Su ◽  
C. Zhou ◽  
...  
Keyword(s):  
South China Sea ◽  
Set Theory ◽  
Rough Set ◽  
South China ◽  
Rough Set Theory ◽  
Mesoscale Eddy ◽  
The South China Sea ◽  
The South ◽  
Long Distance ◽  
China Sea

Abstract. In this paper, a rough set theory is introduced to represent spatial-temporal relationships and extract the corresponding rules from typical mesoscale-eddy states in the South China Sea (SCS). Three decision attributes are adopted in this study, which make the approach flexible in retrieving spatial-temporal rules with different features. The results demonstrate that this approach is effective, and therefore provides a powerful approach to forecasts in the future studies. Spatial-temporal rules in the SCS indicate that warm eddies following the rules are generally in the southeastern and central SCS around 2000 m isobaths in winter. Their intensity and vorticity are weaker than those of cold eddies. They usually move a shorter distance. By contrast, cold eddies are in 2000 m and deeper regions of the southwestern and northeastern SCS in spring and fall. Their intensity and vorticity are strong. Usually they move a long distance. In winter, a few rules are followed by cold eddies in the northern tip of the basin and southwest of Taiwan Island rather than warm eddies, indicating cold eddies may be well-regulated in the region. Several warm-eddy rules are achieved west of Luzon Island, indicating warm eddies may be well-regulated in the region as well. Otherwise, warm and cold eddies are distributed not only in the jet flow off southern Vietnam induced by intraseasonal wind stress in summer-fall, but also in the northern shallow water, which should be a focus of a future study.

scholarly journals Extraction of Revolving Channels of Drifters around Mesoscale Eddy Centers Based on Spatiotemporal Trajectory Clustering

2019 ◽  
Vol 36 (9) ◽  
pp. 1903-1916
Author(s):  
Chunyong Ma ◽  
Siqing Li ◽  
Yang Yang ◽  
Jie Yang ◽  
Ge Chen
Keyword(s):  
Clustering Algorithm ◽  
Spatial Clustering ◽  
Mesoscale Eddy ◽  
Mesoscale Eddies ◽  
Trajectory Clustering ◽  
Satellite Altimeter ◽  
Principal Mode ◽  
In Situ Data ◽  
Anticyclonic Eddies

The global oceanic transports of energy, plankton, and other tracers by mesoscale eddies can be estimated by combining satellite altimetry and in situ data. However, the revolving channels of particles entrained by mesoscale eddies, which could help explain the dynamic process of eddies entraining materials, are still unknown. In this study, satellite altimeter and drifter data from 1993 to 2016 are adopted, and the normalized trajectory clustering algorithm (N-TRACLUS) is proposed to extract the revolving channels of drifters. First, the trajectories of drifters are normalized and clustered by using the density-based spatial clustering of applications with noise (DBSCAN) algorithm. Next, the revolving channels of drifters around the eddy center are extracted. The ring or arc pattern in the middle of a normalized eddy appears when drifters are uninterruptedly entrained by eddies for more than 30 days. Moreover, the revolving channels of drifters in cyclonic eddies are relatively closer to the eddy center than those in anticyclonic eddies. These revolving channels suggest the principal mode of materials’ continuous motion processes that are inside eddies.

scholarly journals Mesoscale Eddy Energy Locality in an Idealized Ocean Model

2013 ◽  
Vol 43 (9) ◽  
pp. 1911-1923 ◽  
Author(s):  
Ian Grooms ◽  
Louis-Philippe Nadeau ◽  
K. Shafer Smith
Keyword(s):  
Energy Budget ◽  
Mesoscale Eddy ◽  
Mesoscale Eddies ◽  
Spatial Filter ◽  
Ocean Model ◽  
Energy Budgets ◽  
Subgrid Scale ◽  
Common Time ◽  
Local Functions ◽  
The Mean

Abstract This paper investigates the energy budget of mesoscale eddies in wind-driven two-layer quasigeostrophic simulations. Intuitively, eddy energy can be generated, dissipated, and fluxed from place to place; regions where the budget balances generation and dissipation are “local” and regions that export or import large amounts of eddy energy are “nonlocal.” Many mesoscale parameterizations assume that statistics of the unresolved eddies behave as local functions of the resolved large scales, and studies that relate doubly periodic simulations to ocean patches must assume that the ocean patches have local energetics. This study derives and diagnoses the eddy energy budget in simulations of wind-driven gyres. To more closely approximate the ideas of subgrid-scale parameterization, the authors define the mean and eddies using a spatial filter rather than the more common time average. The eddy energy budget is strongly nonlocal over nearly half the domain in the simulations. In particular, in the intergyre region the eddies lose energy through interactions with the mean, and this energy loss can only be compensated by nonlocal flux of energy from elsewhere in the domain. This study also runs doubly periodic simulations corresponding to ocean patches from basin simulations. The eddy energy level of ocean patches in the basin simulations matches the level in the periodic simulations only in regions with local eddy energy budgets.

Colder and smaller : 10 years of observations of surface salinity by SMOS, Aquarius and SMAP to study mesoscale eddies in the Southern Ocean

2020 ◽  
Author(s):  
Audrey Hasson ◽  
Cori Pegliasco ◽  
Jacqueline Boutin ◽  
Rosemary Morrow
Keyword(s):  
Soil Moisture ◽  
Southern Ocean ◽  
European Space Agency ◽  
Mesoscale Eddy ◽  
Mesoscale Eddies ◽  
Sea Surface ◽  
Sea Surface Salinity ◽  
Global Ocean ◽  
Surface Salinity ◽  
Sst Anomalies

<p>Since 2010, space missions dedicated to Sea Surface Salinity (SSS) have been providing observations with almost complete coverage of the global ocean and a resolution of about 45 km every 3 days. The European Space Agency (ESA) Soil Moisture and Ocean Salinity (SMOS) mission was the first orbiting radiometer to collect regular SSS observations from space. The Aquarius and SMAP (Soil Moisture Active-Passive) missions of the National Aeronautics and Space Administration (NASA) then reinforced the SSS observing system between mid-2011 and mid-2015 and since mid-2015, respectively.</p><p>Using the most recent SSS Climate Change Initiative project dataset merging data from the 3 missions, this study investigates the SSS signal associated with mesoscale eddies in the Southern Ocean. Eddies location and characteristics are obtained from the daily v3 mesoscale eddy trajectory atlas produced by CLS. SSS anomalies along the eddies journey are computed and compared to Sea Surface Temperature (SST) anomalies (v4 Remote Sensing Systems) as well as the SubAntarctic Front (SAF) position (CTOH, LEGOS). The vertical structure of the eddies is further investigated using profiles from colocated Argo autonomous floats.<span> </span></p><p>This study highlights a robust signal in SSS depending on both the eddies rotation (cyclone/anticyclone) and latitudinal position with respect to the SAF. Moreover, this dependence is not found in SST. These observations reveal oceanic the interaction of eddies with the larger scale ocean water masses. SSS and SST anomalies composites indeed show different patterns either bi-poles linked with horizontal stirring of fronts, mono-poles from trapping water or vertical mixing changes, or a mix of the two.</p><p>This analysis gives strong hints for the erosion of subsurface waters, such as mode waters, induced by enhanced mixing caused by the deep-reaching eddies of the southern ocean.</p>

scholarly journals Random movement of mesoscale eddies in the global ocean

2020 ◽  
Author(s):  
Xiaoming Zhai ◽  
Qinbiao Ni ◽  
Guihua Wang ◽  
David Marshall
Keyword(s):  
Isotropic Turbulence ◽  
Mesoscale Eddy ◽  
Lateral Diffusion ◽  
Mesoscale Eddies ◽  
Global Ocean ◽  
Altimeter Data ◽  
High Latitudes ◽  
Turbulence Regime ◽  
Low Latitudes ◽  
Baroclinic Rossby Wave

<p>In this study we track and analyze eddy movement in the global ocean using 20 years of altimeter data and show that, in addition to the well-known westward propagation and slight polarity-based meridional deflections, mesoscale eddies also move randomly in all directions at all latitudes as a result of eddy-eddy interaction. The speed of this random eddy movement decreases with latitude and equals the baroclinic Rossby wave speed at about 25° of latitude. The tracked eddies are on average isotropic at mid and high latitudes, but become noticeably more elongated in the zonal direction at low latitudes. Our analyses suggest a critical latitude of approximately 25° that separates the global ocean into a low-latitude anisotropic wavelike regime and a high-latitude isotropic turbulence regime. One important consequence of random eddy movement is that it results in lateral diffusion of eddy energy. The associated eddy energy diffusivity, estimated using two different methods, is found to be a function of latitude. The zonal-mean eddy energy diffusivity varies from over 1500 m<sup>2</sup> s<sup>-1</sup> at low latitudes to around 500 m<sup>2</sup> s<sup>-1</sup> at high latitudes, but significantly larger values are found in the eddy energy hotspots at all latitudes, in excess of 5000 m<sup>2</sup> s<sup>-1</sup>. Results from this study have important implications for recently-developed energetically-consistent mesoscale eddy parameterization schemes which require solving the eddy energy budget.  </p>

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