scholarly journals Generation Mechanism of Tidally-driven Whirlpools at A Narrow Strait in An Estuary

2021 ◽  
Vol 945 (1) ◽  
pp. 012028
Author(s):  
Yusuke Uchiyama ◽  
Xu Zhang ◽  
Shota Yanase
Keyword(s):  
Ocean Circulation ◽  
Local Governments ◽  
Tidal Currents ◽  
Generation Mechanism ◽  
Shear Instability ◽  
Gradient Force ◽  
Pressure Gradient Force ◽  
Horizontal Shear ◽  
Tidal Waves ◽  
Kii Channel

Abstract This study investigates the generation mechanism and influence of the whirlpools in the Naruto Strait on the surrounding marine environment using state-of-the-art high-resolution numerical ocean circulation modeling in a quadruple nested configuration. The Naruto whirlpools is recognized as an extraordinary seascape that the local governments and the citizens seek to register as a world natural heritage site. We found that the pronounced pressure gradient force associated with the meridional surface elevation difference was induced by a phase difference of two bifurcating major tidal waves. These waves originate from the Kitan Strait, and ultimately produce intense tidal currents at the Naruto Strait. One branch of the tidal waves propagates counter-clockwise along Awaji Island through the Akashi Strait, while the other occurs directly from the Kii Channel. As such, the whirlpool emerges as a large number of sub-mesoscale eddies, primarily due to the horizontal shear instability of tidal currents energized at the narrow topography between two headlands that extend into the strait. A dipole of overturning vertical circulations appears underneath the whirlpools with convergent downward transport at the strongest tidal current near the center of the strait; this causes efficient vertical mixing. This three-dimensional non-linear mixing promotes a time-averaged southeastward mass transport that extracts water and materials from the Harima-nada Sea into the Kii Channel.

scholarly journals Jet–Topography Interactions Affect Energy Pathways to the Deep Southern Ocean

2017 ◽  
Vol 47 (7) ◽  
pp. 1799-1816 ◽  
Author(s):  
Alice Barthel ◽  
Andrew McC. Hogg ◽  
Stephanie Waterman ◽  
Shane Keating
Keyword(s):  
Southern Ocean ◽  
Ocean Circulation ◽  
Baroclinic Instability ◽  
Deep Ocean ◽  
Ocean Model ◽  
Shear Instability ◽  
Horizontal Shear ◽  
Mean Flow ◽  
Flat Bottom ◽  
Turbulent Dissipation

AbstractIn the Southern Ocean, strong eastward ocean jets interact with large topographic features, generating eddies that feed back onto the mean flow. Deep-reaching eddies interact with topography, where turbulent dissipation and generation of internal lee waves play an important role in the ocean’s energy budget. However, eddy effects in the deep ocean are difficult to observe and poorly characterized. This study investigates the energy contained in eddies at depth, when an ocean jet encounters topography. This study uses a two-layer ocean model in which an imposed unstable jet encounters a topographic obstacle (either a seamount or a meridional ridge) in a configuration relevant to an Antarctic Circumpolar Current frontal jet. The authors find that the presence of topography increases the eddy kinetic energy (EKE) at depth but that the dominant processes generating this deep EKE depend on the shape and height of the obstacle as well as on the baroclinicity of the jet before it encounters topography. In cases with high topography, horizontal shear instability is the dominant source of deep EKE, while a flat bottom or a strongly sheared inflow leads to deep EKE being generated primarily through baroclinic instability. These results suggest that the deep EKE is set by an interplay between the inflowing jet properties and topography and imply that the response of deep EKE to changes in the Southern Ocean circulation is likely to vary across locations depending on the topography characteristics.

Frontogenesis and frontal arrest of a dense filament in the oceanic surface boundary layer

2017 ◽  
Vol 837 ◽  
pp. 341-380 ◽  
Author(s):  
Peter P. Sullivan ◽  
James C. McWilliams
Keyword(s):  
Boundary Layer ◽  
Turbulent Mixing ◽  
Shear Instability ◽  
Upper Ocean ◽  
Surface Boundary ◽  
Horizontal Shear ◽  
Boundary Layer Turbulence ◽  
Filament Axis ◽  
Small Width ◽  
The Cross

The evolution of upper ocean currents involves a set of complex, poorly understood interactions between submesoscale turbulence (e.g. density fronts and filaments and coherent vortices) and smaller-scale boundary-layer turbulence. Here we simulate the lifecycle of a cold (dense) filament undergoing frontogenesis in the presence of turbulence generated by surface stress and/or buoyancy loss. This phenomenon is examined in large-eddy simulations with resolved turbulent motions in large horizontal domains using${\sim}10^{10}$grid points. Steady winds are oriented in directions perpendicular or parallel to the filament axis. Due to turbulent vertical momentum mixing, cold filaments generate a potent two-celled secondary circulation in the cross-filament plane that is frontogenetic, sharpens the cross-filament buoyancy and horizontal velocity gradients and blocks Ekman buoyancy flux across the cold filament core towards the warm filament edge. Within less than a day, the frontogenesis is arrested at a small width,${\approx}100~\text{m}$, primarily by an enhancement of the turbulence through a small submesoscale, horizontal shear instability of the sharpened filament, followed by a subsequent slow decay of the filament by further turbulent mixing. The boundary-layer turbulence is inhomogeneous and non-stationary in relation to the evolving submesoscale currents and density stratification. The occurrence of frontogenesis and arrest are qualitatively similar with varying stress direction or with convective cooling, but the detailed evolution and flow structure differ among the cases. Thus submesoscale filament frontogenesis caused by boundary-layer turbulence, frontal arrest by frontal instability and frontal decay by forward energy cascade, and turbulent mixing are generic processes in the upper ocean.

scholarly journals Sensitivity of Hurricane Intensity Forecast to Convective Momentum Transport Parameterization

2006 ◽  
Vol 134 (2) ◽  
pp. 664-674 ◽  
Author(s):  
Jongil Han ◽  
Hua-Lu Pan
Keyword(s):  
Wind Shear ◽  
Vertical Wind Shear ◽  
Momentum Transport ◽  
Gradient Force ◽  
Pressure Gradient Force ◽  
Momentum Exchange ◽  
Forecast System ◽  
Hurricane Intensity ◽  
Convective Momentum Transport ◽  
The Many

Abstract A parameterization of the convection-induced pressure gradient force (PGF) in convective momentum transport (CMT) is tested for hurricane intensity forecasting using NCEP's operational Global Forecast System (GFS) and its nested Regional Spectral Model (RSM). In the parameterization the PGF is assumed to be proportional to the product of the cloud mass flux and vertical wind shear. Compared to control forecasts using the present operational GFS and RSM where the PGF effect in CMT is taken into account empirically, the new PGF parameterization helps increase hurricane intensity by reducing the vertical momentum exchange, giving rise to a closer comparison to the observations. In addition, the new PGF parameterization forecasts not only show more realistically organized precipitation patterns with enhanced hurricane intensity but also reduce the forecast track error. Nevertheless, the model forecasts with the new PGF parameterization still largely underpredict the observed intensity. One of the many possible reasons for the large underprediction may be the absence of hurricane initialization in the models.

scholarly journals Temporal evolution of the momentum balance terms and frictional adjustment observed over the inner shelf during a storm

Ocean Science ◽  
2016 ◽  
Vol 12 (1) ◽  
pp. 137-151 ◽  
Author(s):  
M. Grifoll ◽  
A. L. Aretxabaleta ◽  
J. L. Pelegrí ◽  
M. Espino
Keyword(s):  
Coriolis Force ◽  
Wind Stress ◽  
Water Depth ◽  
Momentum Balance ◽  
Wave Radiation ◽  
Gradient Force ◽  
Pressure Gradient Force ◽  
Inner Shelf ◽  
Coastal Waves ◽  
Nw Mediterranean

Abstract. We investigate the rapidly changing equilibrium between the momentum sources and sinks during the passage of a single two-peak storm over the Catalan inner shelf (NW Mediterranean Sea). Velocity measurements at 24 m water depth are taken as representative of the inner shelf, and the cross-shelf variability is explored with measurements at 50 m water depth. During both wind pulses, the flow accelerated at 24 m until shortly after the wind maxima, when the bottom stress was able to compensate for the wind stress. Concurrently, the sea level also responded, with the pressure-gradient force opposing the wind stress. Before, during and after the second wind pulse, there were velocity fluctuations with both super- and sub-inertial periods likely associated with transient coastal waves. Throughout the storm, the Coriolis force and wave radiation stresses were relatively unimportant in the along-shelf momentum balance. The frictional adjustment timescale was around 10 h, consistent with the e-folding time obtained from bottom drag parameterizations. The momentum evolution at 50 m showed a larger influence of the Coriolis force at the expense of a decreased frictional relevance, typical in the transition from the inner to the mid-shelf.

scholarly journals Peran TNI dalam Penanggulangan Bencana Alam (Studi Kasus Peran Korem 043/Gatam dalam Penanggulangan Bencana Alam di Provinsi Lampung)

2020 ◽  
Vol 3 (1) ◽  
Author(s):  
Nrangwesthi Widyaningrum ◽  
Muhammad Sarip Kodar ◽  
Risma Suryani Purwanto ◽  
Agung Priambodo
Keyword(s):  
Natural Disasters ◽  
Disaster Management ◽  
Local Governments ◽  
Disaster Response ◽  
Volcanic Eruptions ◽  
Literature Study ◽  
Tidal Waves ◽  
Study Approach ◽  
Natural Disaster Management

Indonesia has the most complete types of disasters in the world such as floods, landslides, tidal waves, tornadoes, drought, forest and land fires, earthquakes, tsunamis, volcanic eruptions, liquefaction and many more. Natural disasters that occur in Indonesia often just happen and it is not predictable when it will happen. This causes problems in handling natural disasters. Natural disaster management is not a matter of BNPB or BPBD, one important element is the involvement of the Indonesian National Army (TNI). One of Indonesia's regions that are vulnerable to natural disasters is Lampung Province. This research will describe how the role of the TNI in the case study in Korem 043 / Gatam in helping to overcome natural disasters in Lampung Province. The research method used in this research is qualitative research with a literature study approach. The role of the TNI in disaster management in Lampung Province is inseparable from the duties and functions of the TNI that have been mandated in Law Number 34 of 2004. Korem 043 / Gatam has taken strategic steps both from the pre-disaster, disaster response, and post-disaster phases . TNI involvement in the process of disaster management does not stand alone, but cooperates and synergizes with local governments.

scholarly journals On the fine vertical structure of the low troposphere over the coastal margins of East Antarctica

2019 ◽  
Author(s):  
Étienne Vignon ◽  
Olivier Traullé ◽  
Alexis Berne
Keyword(s):  
Pressure Gradient ◽  
Vertical Structure ◽  
East Antarctica ◽  
Radiosonde Data ◽  
Gradient Force ◽  
Pressure Gradient Force ◽  
Near Surface ◽  
Ice Shelves ◽  
Low Level ◽  
Humidity Profiles

Abstract. Eight years of high-resolution radiosonde data at nine Antarctic stations are analysed to provide the first large scale characterization of the fine scale vertical structure of the low troposphere up to 3 km of altitude over the coastal margins of East Antarctica. Radiosonde data show a large spatial variability of wind, temperature and humidity profiles, with different features between stations in katabatic regions (e.g., Dumont d'Urville and Mawson stations), stations over two ice shelves (Neumayer and Halley stations) and regions with complex orography (e.g., Mc Murdo). At Dumont d'Urville, Mawson and Davis stations, the yearly median wind speed profiles exhibit a clear low-level katabatic jet. During precipitation events, the low-level flow generally remains of continental origin and its speed is even reinforced due to the increase in the continent- ocean pressure gradient. Meanwhile, the relative humidity profiles show a dry low troposphere, suggesting the occurence of low-level sublimation of precipitation in katabatic regions but such a phenomenon does not appreciably occur over the ice-shelves near Halley and Neumayer. Although ERA-Interim and ERA5 reanalyses assimilate radiosoundings at most stations considered here, substantial – and sometimes large – low-level wind and humidity biases are revealed but ERA5 shows overall better performances. A free simulation with the regional model Polar WRF (at a 35-km resolution) over the entire continent shows too strong and too shallow near-surface jets in katabatic regions especially in winter. This may be a consequence of an understimated coastal cold air bump and associated sea-continent pressure gradient force due to the coarse 35 km resolution of the Polar WRF simulation. Beyond documenting the vertical structure of the low troposphere over coastal East-Antarctica, this study gives insights into the reliability and accuracy of two major reanalysis products in this region on the Earth and it raises the difficulty of modeling the low-level flow over the margins of the ice sheet with a state-of-the-art climate model.

scholarly journals Zonal Momentum Balance in the Tropical Atmospheric Circulation during the Global Monsoon Mature Months

2013 ◽  
Vol 70 (2) ◽  
pp. 583-599 ◽  
Author(s):  
Wenchang Yang ◽  
Richard Seager ◽  
Mark A. Cane
Keyword(s):  
Angular Momentum ◽  
Pressure Gradient ◽  
Atmospheric Circulation ◽  
Coriolis Force ◽  
Gradient Force ◽  
Pressure Gradient Force ◽  
Global Monsoon ◽  
Upper Troposphere ◽  
Nonlinear Advection ◽  
Zonal Momentum

Abstract In this paper, zonal momentum balances of the tropical atmospheric circulation during the global monsoon mature months (January and July) are analyzed in three dimensions based on the ECMWF Interim Re-Analysis (ERA-Interim). It is found that the dominant terms in the balance of the atmospheric boundary layer (ABL) in both months are the pressure gradient force, the Coriolis force, and friction. The nonlinear advection term plays a significant role only in the Asian summer monsoon regions within the ABL. In the upper troposphere, the pressure gradient force, the Coriolis force, and the nonlinear advection are the dominant terms. The transient eddy force and the residual force (which can be explained as convective momentum transfer over open oceans) are secondary, yet cannot be neglected near the equator. Zonal-mean equatorial upper-troposphere easterlies are maintained by the absolute angular momentum advection associated with the cross-equatorial Hadley circulation. Equatorial upper-troposphere easterlies over the Asian monsoon regions are also controlled by the absolute angular momentum advection but are mainly maintained by the pressure gradient force in January. The equivalent linear Rayleigh friction, which is widely applied in simple tropical models, is calculated and the corresponding spatial distribution of the local coefficient and damping time scale are estimated from the linear regression. It is found that the linear momentum model is in general capable of crudely describing the tropical atmospheric circulation dynamics, yet the caveat should be kept in mind that the friction coefficient is not uniformly distributed and is even negative in some regions.

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