scholarly journals The Drag on the Barotropic Tide due to the Generation of Baroclinic Motion

2020 ◽  
Vol 50 (12) ◽  
pp. 3467-3481 ◽  
Author(s):  
Callum J. Shakespeare ◽  
Brian K. Arbic ◽  
Andrew McC. Hogg
Keyword(s):  
Wave Motion ◽  
Body Force ◽  
Wave Drag ◽  
Internal Tides ◽  
Mean Flow ◽  
Barotropic Tide ◽  
Barotropic Flow ◽  
Spring Force ◽  
Mechanical Spring ◽  
The Impact

AbstractThe interaction of a barotropic flow with topography generates baroclinic motion that exerts a stress on the barotropic flow. Here, explicit solutions are calculated for the spatial-mean flow (i.e., the barotropic tide) resulting from a spatially uniform but time-varying body force (i.e., astronomical forcing) acting over rough topography. This approach of prescribing the force contrasts with that of previous authors who have prescribed the barotropic flow. It is found that the topographic stress, and thus the impact on the spatial-mean flow, depend on the nature of the baroclinic motion that is generated. Two types of stress are identified: (i) a “wave drag” force associated with propagating wave motion, which extracts energy from the spatial-mean flow, and (ii) a topographic “spring” force associated with standing motion at the seafloor, including bottom-trapped internal tides and propagating low-mode internal tides, which significantly damps the time-mean kinetic energy of the spatial-mean flow but extracts no energy in the time-mean. The topographic spring force is shown to be analogous to the force exerted by a mechanical spring in a forced-dissipative harmonic oscillator. Expressions for the topographic stresses appropriate for implementation as baroclinic drag parameterizations in global models are presented.

scholarly journals On the Body-Force Term in Internal-Tide Generation

2007 ◽  
Vol 37 (8) ◽  
pp. 2172-2175 ◽  
Author(s):  
Chris Garrett ◽  
Theo Gerkema
Keyword(s):  
Governing Equation ◽  
Body Force ◽  
Internal Tide ◽  
The Body ◽  
Internal Tides ◽  
Force Term ◽  
Barotropic Tide ◽  
Topographic Features ◽  
Barotropic Flow ◽  
Baroclinic Tide

Abstract The generation of internal tides can be ascribed to the action of a buoyancy force caused by the flow of the barotropic tide over topographic features. It is commonly assumed that the barotropic flow can be taken as hydrostatic, but it is shown here that this leads to a linearized governing equation for the baroclinic tide that is only valid if the baroclinic tide is also hydrostatic. A governing equation for the baroclinic tide, valid for any situation, is derived here and is shown to be exactly equivalent to a simple transformation of the governing equation for the combined barotropic and baroclinic tides.

Self-Acceleration in the Parameterization of Orographic Gravity Wave Drag

2010 ◽  
Vol 67 (8) ◽  
pp. 2537-2546 ◽  
Author(s):  
John F. Scinocca ◽  
Bruce R. Sutherland
Keyword(s):  
Gravity Wave ◽  
Middle Atmosphere ◽  
Wave Train ◽  
Leading Edge ◽  
Wave Theory ◽  
Wave Drag ◽  
Tuning Parameter ◽  
Mean Flow ◽  
Propagating Waves ◽  
The Impact

Abstract A new effect related to the evaluation of momentum deposition in conventional parameterizations of orographic gravity wave drag (GWD) is considered. The effect takes the form of an adjustment to the basic-state wind about which steady-state wave solutions are constructed. The adjustment is conservative and follows from wave–mean flow theory associated with wave transience at the leading edge of the wave train, which sets up the steady solution assumed in such parameterizations. This has been referred to as “self-acceleration” and it is shown to induce a systematic lowering of the elevation of momentum deposition, which depends quadratically on the amplitude of the wave. An expression for the leading-order impact of self-acceleration is derived in terms of a reduction of the critical inverse Froude number Fc, which determines the onset of wave breaking for upwardly propagating waves in orographic GWD schemes. In such schemes Fc is a central tuning parameter and typical values are generally smaller than anticipated from conventional wave theory. Here it is suggested that self-acceleration may provide some of the explanation for why such small values of Fc are required. The impact of Fc on present-day climate is illustrated by simulations of the Canadian Middle Atmosphere Model.

Forcing of oceanic mean flows by dissipating internal tides

2012 ◽  
Vol 708 ◽  
pp. 250-278 ◽  
Author(s):  
Nicolas Grisouard ◽  
Oliver Bühler
Keyword(s):  
Numerical Study ◽  
Three Dimensional ◽  
Wave Drag ◽  
Perturbation Series ◽  
Internal Tides ◽  
Time Averaging ◽  
Mean Flow ◽  
Wave Source ◽  
Lee Waves ◽  
Lee Wave

AbstractWe present a theoretical and numerical study of the effective mean force exerted on an oceanic mean flow due to the presence of small-amplitude internal waves that are forced by the oscillatory flow of a barotropic tide over undulating topography and are also subject to dissipation. This extends the classic lee-wave drag problem of atmospheric wave–mean interaction theory to a more complicated oceanographic setting, because now the steady lee waves are replaced by oscillatory internal tides and, most importantly, because now the three-dimensional oceanic mean flow is defined by time averaging over the fast tidal cycles rather than by the zonal averaging familiar from atmospheric theory. Although the details of our computation are quite different, we recover the main action-at-a-distance result from the atmospheric setting, namely that the effective mean force that is felt by the mean flow is located in regions of wave dissipation, and not necessarily near the topographic wave source. Specifically, we derive an explicit expression for the effective mean force at leading order using a perturbation series in small wave amplitude within the framework of generalized Lagrangian-mean theory, discuss in detail the range of situations in which a strong, secularly growing mean-flow response can be expected, and then compute the effective mean force numerically in a number of idealized examples with simple topographies.

scholarly journals Impact of a simple parameterization of convective gravity-wave drag in a stratosphere-troposphere general circulation model and its sensitivity to vertical resolution

1998 ◽  
Vol 16 (2) ◽  
pp. 238-249 ◽  
Author(s):  
C. Bossuet ◽  
M. Déqué ◽  
D. Cariolle
Keyword(s):  
General Circulation ◽  
Climate Model ◽  
Positive Impact ◽  
Deep Convection ◽  
Circulation Model ◽  
Wave Drag ◽  
Horizontal Resolution ◽  
Vertical Resolution ◽  
Mean Flow ◽  
The Impact

Abstract. Systematic westerly biases in the southern hemisphere wintertime flow and easterly equatorial biases are experienced in the Météo-France climate model. These biases are found to be much reduced when a simple parameterization is introduced to take into account the vertical momentum transfer through the gravity waves excited by deep convection. These waves are quasi-stationary in the frame of reference moving with convection and they propagate vertically to higher levels in the atmosphere, where they may exert a significant deceleration of the mean flow at levels where dissipation occurs. Sixty-day experiments have been performed from a multiyear simulation with the standard 31 levels for a summer and a winter month, and with a T42 horizontal resolution. The impact of this parameterization on the integration of the model is found to be generally positive, with a significant deceleration in the westerly stratospheric jet and with a reduction of the easterly equatorial bias. The sensitivity of the Météo-France climate model to vertical resolution is also investigated by increasing the number of vertical levels, without moving the top of the model. The vertical resolution is increased up to 41 levels, using two kinds of level distribution. For the first, the increase in vertical resolution concerns especially the troposphere (with 22 levels in the troposphere), and the second treats the whole atmosphere in a homogeneous way (with 15 levels in the troposphere); the standard version of 31 levels has 10 levels in the troposphere. A comparison is made between the dynamical aspects of the simulations. The zonal wind and precipitation are presented and compared for each resolution. A positive impact is found with the finer tropospheric resolution on the precipitation in the mid-latitudes and on the westerly stratospheric jet, but the general impact on the model climate is weak, the physical parameterizations used appear to be mostly independent to the vertical resolution.Key words. Meteorology and atmospheric dynamics · Convective processes · Waves and tides

scholarly journals Effects of Remote Generation Sites on Model Estimates of M2 Internal Tides in the Philippine Sea*

2013 ◽  
Vol 43 (1) ◽  
pp. 187-204 ◽  
Author(s):  
Colette G. Kerry ◽  
Brian S. Powell ◽  
Glenn S. Carter
Keyword(s):  
Equation Model ◽  
Luzon Strait ◽  
Internal Tides ◽  
Bottom Pressure ◽  
Barotropic Tide ◽  
Philippine Sea ◽  
Baroclinic Energy Conversion ◽  
Mariana Arc ◽  
Mariana Island Arc ◽  
The Impact

Abstract This study investigates the impact of remotely generated internal tides on model estimates of barotropic to baroclinic tidal conversion for two generation sites bounding the Philippine Sea: the Luzon Strait and the Mariana Island Arc. A primitive equation model is used to characterize the internal tides generated by the principal semidiurnal tide (M2) over a domain encompassing the two generation sites. Energetic internal tides are generated at the Luzon Strait where nearly 17 GW of barotropic tide energy is converted to baroclinic energy, of which 44% (4.78 GW) is radiated eastward into the Philippine Sea. From the Mariana Arc, baroclinic energy propagates westward into the Philippine Sea as a result of 3.82 GW of barotropic to baroclinic energy conversion. Simulations that focus on each generation site without influence of the other are performed, and comparisons show that remotely generated internal tides have a significant effect on local conversion at the two sites. Total conversion is greater in the absence of remotely generated internal tides at both sites: 11% greater at the Luzon Strait and 65% greater at the Mariana Arc. The first three modes of the remotely generated internal tides traverse the basin and alter the amplitude and phase of bottom pressure. The arrival of the remote internal tides varies significantly with changing stratification and mesoscale circulation. The results suggest that an important source of variability in local conversion around the globe is due to remotely generated internal tides.

Adaptive Predictive Based on Equal-Dimension and New Information for the Hydraulic Mechanism of Wave Motion Compensating Platform

2010 ◽  
Vol 20-23 ◽  
pp. 236-242 ◽  
Author(s):  
Zhi Gang Zeng ◽  
Guo Hua Chen
Keyword(s):  
Predictive Control ◽  
Wave Motion ◽  
Control Policy ◽  
Least Square ◽  
Problem Solution ◽  
New Information ◽  
Hydraulic Mechanism ◽  
Heave Motion ◽  
Adaptive Predictive Control ◽  
The Impact

A wave motion compensating platform has the function of compensating the ship’s generalized heave motion (a coupling result of roll, pitch and heave). It can decrease the impact of ship motion on some sea works and equipments. The hydraulic mechanism of platform system has the characteristics of nonlinear and big inertia. In order to compensate generalized heave motion effectively, an adaptive predictive control policy is used for controlling the hydraulic mechanism. Based on equal-dimension and new information, an automation regressive model can get adaptive multi-step prediction. The model parameter estimation based on the least square algorithm is easy to blow up and be unstable when the system has random noise. To improve the problem solution, a damped recursive least square algorithm is proposed to estimate the parameters on line. For the short regulation time, strong anti-disturbance ability and great robustness, a nonlinear PID controller whose gain parameters vary with errors is suitable for controlling the hydraulic mechanism. Using the collected experimental data, the simulations suggest that adopting the above adaptive predictive control policy to control hydraulic mechanism is able to decrease the generalized heave amplitude of wave motion compensating platform.

scholarly journals Impact of SLA assimilation in the Sicily Channel Regional Model: model skills and mesoscale features

Ocean Science ◽  
2012 ◽  
Vol 8 (4) ◽  
pp. 485-496 ◽  
Author(s):  
A. Olita ◽  
S. Dobricic ◽  
A. Ribotti ◽  
L. Fazioli ◽  
A. Cucco ◽  
...  
Keyword(s):  
Sea Level ◽  
Qualitative Evaluation ◽  
Regional Model ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
Qualitative Comparison ◽  
Mesoscale Structures ◽  
Sicily Channel ◽  
Along Track ◽  
The Impact

Abstract. The impact of the assimilation of MyOcean sea level anomalies along-track data on the analyses of the Sicily Channel Regional Model was studied. The numerical model has a resolution of 1/32° degrees and is capable to reproduce mesoscale and sub-mesoscale features. The impact of the SLA assimilation is studied by comparing a simulation (SIM, which does not assimilate data) with an analysis (AN) assimilating SLA along-track multi-mission data produced in the framework of MyOcean project. The quality of the analysis was evaluated by computing RMSE of the misfits between analysis background and observations (sea level) before assimilation. A qualitative evaluation of the ability of the analyses to reproduce mesoscale structures is accomplished by comparing model results with ocean colour and SST satellite data, able to detect such features on the ocean surface. CTD profiles allowed to evaluate the impact of the SLA assimilation along the water column. We found a significant improvement for AN solution in terms of SLA RMSE with respect to SIM (the averaged RMSE of AN SLA misfits over 2 years is about 0.5 cm smaller than SIM). Comparison with CTD data shows a questionable improvement produced by the assimilation process in terms of vertical features: AN is better in temperature while for salinity it gets worse than SIM at the surface. This suggests that a better a-priori description of the vertical error covariances would be desirable. The qualitative comparison of simulation and analyses with synoptic satellite independent data proves that SLA assimilation allows to correctly reproduce some dynamical features (above all the circulation in the Ionian portion of the domain) and mesoscale structures otherwise misplaced or neglected by SIM. Such mesoscale changes also infer that the eddy momentum fluxes (i.e. Reynolds stresses) show major changes in the Ionian area. Changes in Reynolds stresses reflect a different pumping of eastward momentum from the eddy to the mean flow, in turn influencing transports through the channel.

scholarly journals Compensation between Resolved Wave Driving and Parameterized Orographic Gravity Wave Driving of the Brewer–Dobson Circulation and Its Response to Climate Change

2014 ◽  
Vol 27 (14) ◽  
pp. 5601-5610 ◽  
Author(s):  
Michael Sigmond ◽  
Theodore G. Shepherd
Keyword(s):  
Climate Change ◽  
Gravity Wave ◽  
Northern Hemisphere ◽  
Rossby Wave ◽  
Climate Model ◽  
Wave Drag ◽  
High Latitudes ◽  
Remarkable Degree ◽  
The Impact

Abstract Following recent findings, the interaction between resolved (Rossby) wave drag and parameterized orographic gravity wave drag (OGWD) is investigated, in terms of their driving of the Brewer–Dobson circulation (BDC), in a comprehensive climate model. To this end, the parameter that effectively determines the strength of OGWD in present-day and doubled CO2 simulations is varied. The authors focus on the Northern Hemisphere during winter when the largest response of the BDC to climate change is predicted to occur. It is found that increases in OGWD are to a remarkable degree compensated by a reduction in midlatitude resolved wave drag, thereby reducing the impact of changes in OGWD on the BDC. This compensation is also found for the response to climate change: changes in the OGWD contribution to the BDC response to climate change are compensated by opposite changes in the resolved wave drag contribution to the BDC response to climate change, thereby reducing the impact of changes in OGWD on the BDC response to climate change. By contrast, compensation does not occur at northern high latitudes, where resolved wave driving and the associated downwelling increase with increasing OGWD, both for the present-day climate and the response to climate change. These findings raise confidence in the credibility of climate model projections of the strengthened BDC.

scholarly journals Markovian inhomogeneous closures for Rossby waves and turbulence over topography

2018 ◽  
Vol 858 ◽  
pp. 45-70
Author(s):  
Jorgen S. Frederiksen ◽  
Terence J. O’Kane
Keyword(s):  
Turbulent Flows ◽  
Rossby Waves ◽  
Time History ◽  
Direct Interaction ◽  
Mean Flow ◽  
Current Time ◽  
Fluctuation Dissipation ◽  
Large Ensembles ◽  
Direct Interaction Approximation ◽  
The Impact

Manifestly Markovian closures for the interaction of two-dimensional inhomogeneous turbulent flows with Rossby waves and topography are formulated and compared with large ensembles of direct numerical simulations (DNS) on a generalized $\unicode[STIX]{x1D6FD}$-plane. Three versions of the Markovian inhomogeneous closure (MIC) are established from the quasi-diagonal direct interaction approximation (QDIA) theory by modifying the response function to a Markovian form and employing respectively the current-time (quasi-stationary) fluctuation dissipation theorem (FDT), the prior-time (non-stationary) FDT and the correlation FDT. Markov equations for the triad relaxation functions are derived that carry similar information to the time-history integrals of the non-Markovian QDIA closure but become relatively more efficient for long integrations. Far from equilibrium processes are studied, where the impact of a westerly mean flow on a conical mountain generates large-amplitude Rossby waves in a turbulent environment, over a period of 10 days. Excellent agreement between the evolved mean streamfunction and mean and transient kinetic energy spectra are found for the three versions of the MIC and two variants of the non-Markovian QDIA compared with an ensemble of 1800 DNS. In all cases mean Rossby wavetrain pattern correlations between the closures and the DNS ensemble are greater than 0.9998.

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