Wave–Mean Flow Interactions in a General Circulation Model of the Troposphere and Stratosphere

1986 ◽  
Vol 43 (16) ◽  
pp. 1711-1725 ◽  
Author(s):  
Byron A. Boville
Keyword(s):  
General Circulation Model ◽  
General Circulation ◽  
Circulation Model ◽  
Mean Flow ◽  
Flow Interactions

scholarly journals Near-Surface Transport Properties and Lagrangian Statistics during Two Contrasting Years in the Adriatic Sea

2020 ◽  
Vol 8 (9) ◽  
pp. 681
Author(s):  
Saeed Hariri
Keyword(s):  
Transport Properties ◽  
General Circulation Model ◽  
General Circulation ◽  
Circulation Model ◽  
Mean Flow ◽  
Near Surface ◽  
Surface Transport ◽  
The Real ◽  
Lagrangian Statistics ◽  
The Mean

This paper describes the near-surface transport properties and Lagrangian statistics in the Adriatic semi-enclosed basin using synthetic drifters. Lagrangian transport models were used to simulate synthetic trajectories from the mean flow fields obtained by the Massachusetts Institute of Technology general circulation model (MITgcm), implemented in the Adriatic from October 2006 until December 2008. In particular, the surface circulation properties in two contrasting years (2007 had a mild winter and cold fall, while 2008 had a normal winter and hot summer) are compared here. In addition, the Lagrangian statistics for the entire Adriatic Basin after removing the Eulerian mean circulation for numerical particles were calculated. The results indicate that the numerical particles were slower in this simulation when compared with the real drifters. This is because of the reduced energetic flow field generated by the MIT general circulation model during the selected years. The numerical results showed that the balanced effects of the wind-driven recirculation in the northernmost area(which would be a sea response to the Bora wind field) and the Po River discharge cause the residence times to be similar during the two selected years (182 and 185 days in 2007 and 2008, respectively). Furthermore, the mean angular momentum, diffusivity, and Lagrangian velocity covariance values are smaller than in the real drifter observations, while the maximum Lagrangian integral time scale is the same.

scholarly journals The Impact of GCM Dynamical Cores on Idealized Sudden Stratospheric Warmings and Their QBO Interactions

2016 ◽  
Vol 73 (9) ◽  
pp. 3397-3421 ◽  
Author(s):  
Weiye Yao ◽  
Christiane Jablonowski
Keyword(s):  
General Circulation ◽  
Flow Characteristics ◽  
Circulation Model ◽  
Mean Flow ◽  
Single Vortex ◽  
Tem Analysis ◽  
Quasi Biennial Oscillation ◽  
Spectral Transform ◽  
Flow Interactions ◽  
The Impact

Abstract The paper demonstrates that sudden stratospheric warmings (SSWs) can be simulated in an ensemble of dry dynamical cores that miss the typical SSW forcing mechanisms like moist processes, land–sea contrasts, or topography. These idealized general circulation model (GCM) simulations are driven by a simple Held–Suarez–Williamson (HSW) temperature relaxation and low-level Rayleigh friction. In particular, the four dynamical cores of NCAR’s Community Atmosphere Model, version 5 (CAM5), are used, which are the semi-Lagrangian (SLD) and Eulerian (EUL) spectral-transform models and the finite-volume (FV) and the spectral element (SE) models. Three research themes are discussed. First, it is shown that SSW events in such idealized simulations have very realistic flow characteristics that are analyzed via the SLD model. A single vortex-split event is highlighted that is driven by wavenumber-1 and -2 wave–mean flow interactions. Second, the SLD simulations are compared to the EUL, FV, and SE dynamical cores, which sheds light on the impact of the numerical schemes on the circulation. Only SLD produces major SSWs, while others only exhibit minor stratospheric warmings. These differences are caused by SLD’s more vigorous wave–mean flow interactions in addition to a warm pole bias, which leads to relatively weak polar jets in SLD. Third, it is shown that tropical quasi-biennial oscillation (QBO)–like oscillations and SSWs can coexist in such idealized HSW simulations. They are present in the SLD dynamical core that is used to analyze the QBO–SSW interactions via a transformed Eulerian-mean (TEM) analysis. The TEM results provide support for the Holton–Tan effect.

scholarly journals Prognostic Residual Mean Flow in an Ocean General Circulation Model and its Relation to Prognostic Eulerian Mean Flow

2015 ◽  
Vol 45 (9) ◽  
pp. 2247-2260 ◽  
Author(s):  
Juan A. Saenz ◽  
Qingshan Chen ◽  
Todd Ringler
Keyword(s):  
General Circulation Model ◽  
Ocean Circulation ◽  
General Circulation ◽  
Mesoscale Eddy ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Mean Flow ◽  
Starting Point ◽  
Horizontal Momentum ◽  
Ocean General Circulation

AbstractRecent work has shown that taking the thickness-weighted average (TWA) of the Boussinesq equations in buoyancy coordinates results in exact equations governing the prognostic residual mean flow where eddy–mean flow interactions appear in the horizontal momentum equations as the divergence of the Eliassen–Palm flux tensor (EPFT). It has been proposed that, given the mathematical tractability of the TWA equations, the physical interpretation of the EPFT, and its relation to potential vorticity fluxes, the TWA is an appropriate framework for modeling ocean circulation with parameterized eddies. The authors test the feasibility of this proposition and investigate the connections between the TWA framework and the conventional framework used in models, where Eulerian mean flow prognostic variables are solved for. Using the TWA framework as a starting point, this study explores the well-known connections between vertical transfer of horizontal momentum by eddy form drag and eddy overturning by the bolus velocity, used by Greatbatch and Lamb and Gent and McWilliams to parameterize eddies. After implementing the TWA framework in an ocean general circulation model, the analysis is verified by comparing the flows in an idealized Southern Ocean configuration simulated using the TWA and conventional frameworks with the same mesoscale eddy parameterization.

Eddy–Zonal Flow Interactions and the Persistence of the Zonal Index

2007 ◽  
Vol 64 (9) ◽  
pp. 3296-3311 ◽  
Author(s):  
Edwin P. Gerber ◽  
Geoffrey K. Vallis
Keyword(s):  
Time Scales ◽  
Time Scale ◽  
General Circulation ◽  
Large Scale ◽  
Circulation Model ◽  
Model Parameters ◽  
Mean Flow ◽  
Annular Modes ◽  
Zonal Index ◽  
Flow Interactions

Abstract An idealized atmospheric general circulation model is used to investigate the factors controlling the time scale of intraseasonal (10–100 day) variability of the extratropical atmosphere. Persistence on these time scales is found in patterns of variability that characterize meridional vacillations of the extratropical jet. Depending on the degree of asymmetry in the model forcing, patterns take on similar properties to the zonal index, annular modes, and North Atlantic Oscillation. It is found that the time scale of jet meandering is distinct from the obvious internal model time scales, suggesting that interaction between synoptic eddies and the large-scale flow establish a separate, intraseasonal time scale. A mechanism is presented by which eddy heat and momentum transport couple to retard motion of the jet, slowing its meridional variation and thereby extending the persistence of zonal index and annular mode anomalies. The feedback is strong and quite sensitive to model parameters when the model forcing is zonally uniform. However, the time scale of jet variation drops and nearly all sensitivity to parameters is lost when zonal asymmetries, in the form of topography and thermal perturbations that approximate land–sea contrast, are introduced. A diagnostic on the zonal structure of the zonal index provides intuition on the physical nature of the index and annular modes and hints at why zonal asymmetries limit the eddy–mean flow interactions.

scholarly journals Effects of the Mean Flow on Martian Transient Eddy Activity: Studies with an Idealized General Circulation Model

2019 ◽  
Vol 76 (8) ◽  
pp. 2375-2397
Author(s):  
Todd A. Mooring ◽  
Isaac M. Held ◽  
R. John Wilson
Keyword(s):  
General Circulation Model ◽  
Spatial Patterns ◽  
General Circulation ◽  
Circulation Model ◽  
Transient Eddy ◽  
Mean Flow ◽  
Eddy Activity ◽  
Idealized Model ◽  
Zonal Wavenumber ◽  
The Mean

Abstract The extent to which the eddy statistics of the Martian atmosphere can be inferred from the mean state and highly simplified assumptions about diabatic and frictional processes is investigated using an idealized general circulation model (GCM) with Newtonian relaxation thermal forcing. An iterative technique, adapted from previous terrestrial studies, is used to generate radiative equilibrium temperatures such that the three-dimensional time-mean temperature fields of the idealized model match means computed from the Mars Analysis Correction Data Assimilation (MACDA). Focusing on a period of strong Northern Hemisphere eddy activity prior to winter solstice, it is found that the idealized model reproduces some key features of the spatial patterns of the MACDA eddy temperature variance and kinetic energy fields. The idealized model can also simulate aspects of MACDA’s seasonal cycle of spatial patterns of low-level eddy meridional wind and temperature variances. The most notable weakness of the model is its eddy amplitudes—both their absolute values and seasonal variations are quite unrealistic, for reasons unclear. The idealized model was also run with a mean flow based on output from the Geophysical Fluid Dynamics Laboratory (GFDL) full-physics Mars GCM. The idealized model captures the difference in mean flows between MACDA and the GFDL Mars GCM and reproduces a bias in the more complex model’s eddy zonal wavenumber distribution. This implies that the mean flow is an important influence on transient eddy wavenumbers and that improving the GFDL Mars GCM’s mean flow would make its eddy scales more realistic.

Low-Frequency Variability in a Turbulent Baroclinic Jet: Eddy–Mean Flow Interactions in a Two-Level Model

2010 ◽  
Vol 67 (2) ◽  
pp. 452-467 ◽  
Author(s):  
Joseph Bernstein ◽  
Brian Farrell
Keyword(s):  
Time Scale ◽  
General Circulation ◽  
Channel Model ◽  
Low Frequency ◽  
Circulation Model ◽  
Coupled System ◽  
Mean Flow ◽  
Low Frequency Variability ◽  
Flow Interactions ◽  
The Waves

Abstract The origin of low-frequency variability in the midlatitude jet is investigated using a two-level baroclinic channel model. The model state fields are separated into slow and fast components using intermediate time- scale averaging. In the equation for the fast variables the nonlinear wave–wave interactions are parameterized as a stochastic excitation. The slowly varying ensemble mean eddy fluxes obtained from the resulting stochastic turbulence model are coupled with the slowly varying mean flow dynamics. This forms a coupled set of deterministic equations on the slow time scale that governs the dynamics of the eddy–mean flow interaction. The equilibria of this coupled system are found as a function of the excitation strength, which controls the level of turbulence. At low levels of turbulence the equilibrated flow with zonally symmetric mean forcing remains zonally symmetric, but as excitation increases it undergoes zonal symmetry-breaking bifurcations. Time-dependent flows arising from these bifurcations take the form of westward-propagating wavelike structures resembling blocking patterns. Features of these waves are characteristic of blocking in both observations and atmospheric general circulation model simulations including retrogression, eddy variance concentrated upstream of the waves, and eddy momentum flux forcing the waves.

scholarly journals Wave–Mean-Flow Interactions in Moist Baroclinic Life Cycles

2017 ◽  
Vol 74 (7) ◽  
pp. 2143-2162 ◽  
Author(s):  
Ray Yamada ◽  
Olivier Pauluis
Keyword(s):  
General Circulation ◽  
Large Scale ◽  
Circulation Model ◽  
Moisture Flux ◽  
Life Cycles ◽  
Heat Fluxes ◽  
Latent Heating ◽  
Mean Flow ◽  
Momentum Exchange ◽  
Flow Interactions

Abstract Previous studies show that the moist Eliassen–Palm (EP) flux captures a greater eddy momentum exchange through form drag than the dry EP flux in the midlatitude climate. This suggests that the eddy moisture flux acts to decrease the baroclinicity of the zonal jet. This study investigates such a mechanism in moist baroclinic life cycles, which are simulated in an idealized general circulation model with large-scale condensation as the only moist process. The runs are analyzed using a linear diagnostic based on the Kuo–Eliassen equation to decompose the jet change into parts driven by individual forcing terms. It is shown that the wave-induced latent heating drives an indirect Eulerian-mean cell on the equatorward flank of the jet, which acts to reduce the baroclinicity in that region. The eddy sensible heat fluxes act to reduce the baroclinicity near the center of the jet. The moist baroclinic forcing strengthens as the amount of initially available moisture increases. The effect of the eddy moisture flux on the transformed Eulerian-mean (TEM) and isentropic dynamics is also considered. It is shown that the circulation and EP flux on moist isentropes is around 4 times as strong and extends farther equatorward than on dry isentropes. The equatorward extension of the moist EP flux coincides with the region where the baroclinic forcing is driven by latent heating. The moist EP flux successfully captures the moisture-driven component of the baroclinic forcing that is not seen in the dry EP flux.

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