scholarly journals Response of Idealized Baroclinic Wave Life Cycles to Stratospheric Flow Conditions

2009 ◽  
Vol 66 (8) ◽  
pp. 2288-2302 ◽  
Author(s):  
Torben Kunz ◽  
Klaus Fraedrich ◽  
Frank Lunkeit
Keyword(s):  
Refractive Index ◽  
Initial Conditions ◽  
Spherical Geometry ◽  
Zonal Flow ◽  
Equation Model ◽  
Life Cycles ◽  
Baroclinic Wave ◽  
Flow Conditions ◽  
Mean Flow ◽  
The North

Abstract Dynamical stratosphere–troposphere coupling through a response of baroclinic waves to lower stratospheric flow conditions is investigated from an initial value approach. A series of adiabatic and frictionless nonlinear baroclinic wave life cycles in a midlatitude tropospheric jet with different initial zonal flow conditions in the stratosphere is simulated, using a dry primitive equation model with spherical geometry. When a stratospheric jet, located at various latitudes between 35° and 70°, is removed from the initial conditions, the wavenumber-6 life cycle behavior changes from the well-known LC1 to LC2 evolution, characterized by anticyclonic and cyclonic wave breaking, respectively. Linear theory, in terms of refractive index and the structure of the corresponding fastest-growing normal mode, is found to be unable to explain this stratosphere-induced LC1 to LC2 transition. This implies that altered nonlinear wave–mean flow interactions are important. The most significant stratosphere-induced change that extends into the nonlinear baroclinic growth stage is a region of downward wave propagation in the lower stratosphere associated with positive values of the squared refractive index near 20 km. Furthermore, it is demonstrated that the difference between the response of the tropospheric circulation to LC1 and LC2 life cycles closely resembles the meridional and vertical structure of the North Atlantic Oscillation (NAO), with positive (negative) NAO-like anomalies being driven by LC1 (LC2). Thus, a weakened stratospheric jet induces the generation of negative NAO-like anomalies in the troposphere, consistent with the observed stratosphere–NAO connection.

scholarly journals Dynamics of Eddy-Driven Low-Frequency Dipole Modes. Part IV: Planetary and Synoptic Wave-Breaking Processes during the NAO Life Cycle

2008 ◽  
Vol 65 (3) ◽  
pp. 737-765 ◽  
Author(s):  
Dehai Luo ◽  
Tingting Gong ◽  
Yina Diao
Keyword(s):  
Life Cycle ◽  
Wave Breaking ◽  
Planetary Wave ◽  
Initial Conditions ◽  
Low Frequency ◽  
Phase Evolution ◽  
Life Cycles ◽  
Necessary Condition ◽  
Mean Flow ◽  
The North

Abstract Based on a highly idealized, analytical solution of the North Atlantic Oscillation (NAO) derived in Part III of this series, it is shown that wave breaking is not a necessary condition for the occurrence of NAO events. The breaking of synoptic waves can arise from the interaction between planetary and synoptic waves that gives rise to NAO events, and the type of wave breaking is dominated by the initial conditions of the two waves that determine the phase of the NAO. The planetary wave breaking (PWB) seems to be attributed to an amplification of the NAO amplitude. It is further found that both the planetary wave breaking and the cyclonic (anticyclonic) breaking of synoptic waves undergo an in-phase (out phase) evolution during the life cycles of negative (positive) phase NAO, or NAO− (NAO+), events. An interesting result found is that for NAO− (NAO+) events the breaking of synoptic waves is enhanced (weakened) during the growing phase, but is weakened (enhanced) during the decaying phase. In the absence of a topographic planetary wave (TPW), PWB occurs mainly in the midlatitude regions of the Atlantic basin for NAO− events, but is concentrated in subtropical and subpolar regions for NAO+ events. However, once the TPW is involved, the reversed planetary-scale potential vorticity (PV) gradient that characterizes the PWB exhibits a southwest–northeast (southeast–northwest) tilted tripole for NAO− (NAO+) events, in agreement with the diagnostic results presented herein. The PWB in the subtropical Atlantic is found to occur more frequently for NAO+ events than for NAO− events because the weaker subtropical mean flow is more likely to emerge during the NAO+ life cycle. In conclusion, the results of the highly idealized model used here appear to show that the PWB, synoptic wave breaking, and meridional shift of the westerly jet may be different descriptions of the NAO phenomenon.

Kinematics of Eddy–Mean Flow Interaction in an Idealized Atmospheric Model

2013 ◽  
Vol 70 (8) ◽  
pp. 2574-2595 ◽  
Author(s):  
Sergey Kravtsov ◽  
Sergey K. Gulev
Keyword(s):  
Time Series ◽  
Storm Track ◽  
Low Frequency ◽  
Atmospheric Model ◽  
Life Cycles ◽  
Mean Flow ◽  
Atmospheric Variability ◽  
Low Frequencies ◽  
The North ◽  
Position Time Series

Abstract The authors analyze atmospheric variability simulated in a two-layer baroclinic β-channel quasigeostrophic model by combining Eulerian and feature-tracking analysis approaches. The leading mode of the model's low-frequency variability (LFV) is associated with the irregular shifts of the zonal-mean jet to the north and south of its climatological position accompanied by simultaneous intensification of the jet, while the deviations from the zonal-mean fields are dominated by propagating anomalies with wavenumbers 3–5. The model's variability is shown to stem from the life cycles of cyclones and anticyclones. In particular, synthetic streamfunction fields constructed by launching idealized composite-mean eddies along the actual full-model-simulated cyclone/anticyclone tracks reproduce nearly perfectly not only the dominant propagating waves, but also the jet-shifting LFV. The composite eddy tracks conditioned on the phase of the jet-shifting variability migrate north or south along with the zonal-mean jet. The synoptic-eddy life cycles in the states with poleward (equatorward) zonal-jet shift exhibit longer-than-climatological lifetimes; this is caused, arguably, by a barotropic feedback associated with preferred anticyclonic (cyclonic) wave breaking in these respective states. Lagged correlation and cross-spectrum analyses of zonal-mean jet position time series and the time series representing mean latitudinal location of the eddies at a given time demonstrate that jet latitude leads the storm-track latitude at low frequencies. This indicates that the LFV associated with the jet-shifting mode here is more dynamically involved than being a mere consequence of the random variations in the distribution of the synoptic systems.

The nonlinear evolution of zonally symmetric equatorial inertial instability

2003 ◽  
Vol 474 ◽  
pp. 245-273 ◽  
Author(s):  
STEPHEN D. GRIFFITHS
Keyword(s):  
Long Memory ◽  
Initial Conditions ◽  
Zonal Flow ◽  
Nonlinear Regime ◽  
Mean Flow ◽  
Coriolis Parameter ◽  
Weakly Nonlinear ◽  
Flow Change ◽  
Inertial Instability ◽  
The Mean

The inertial instability of equatorial shear flows is studied, with a view to understanding observed phenomena in the Earth's stratosphere and mesosphere. The basic state is a zonal flow of stratified fluid on an equatorial β-plane, with latitudinal shear. The simplest self-consistent model of the instability is used, so that the basic state and the disturbances are zonally symmetric, and a vertical diffusivity provides the scale selection. We study the interaction between the inertial instability, which takes the form of periodically varying disturbances in the vertical, and the mean flow, where ‘mean’ is a vertical mean.The weakly nonlinear regime is investigated analytically, for flows with an arbitrary dependence on latitude. An amplitude equation of the form dA/dt = A−k2A∫[mid ]A[mid ]2dt is derived for the disturbances, and the evolving stability properties of the mean flow are discussed. In the final steady state, the disturbances vanish, but there is a persistent mean flow change that stabilizes the flow. However, the magnitude of the mean flow change depends strongly on the initial conditions, so that the system has a long memory. The analysis is extended to include the effects of Rayleigh friction and Newtonian cooling, destroying the long-memory property.A more strongly nonlinear regime is investigated with the help of numerical simulations, extending the results up to the point where the instability leads to density contour overturning. The instability is shown to lead to a homogenization of fQ¯ around the initially unstable region, where f is the Coriolis parameter, and Q¯ is the vertical mean of the potential vorticity. As the instability evolves, the line of zero Q¯ moves polewards, rather than equatorwards as might be expected from a simple self-neutralization argument.

scholarly journals The Role of Extratropical Background Flow in Modulating the MJO Extratropical Response

2020 ◽  
Vol 33 (11) ◽  
pp. 4513-4536
Author(s):  
Cheng Zheng ◽  
Edmund Kar-Man Chang
Keyword(s):  
Rossby Waves ◽  
Intraseasonal Variability ◽  
Equation Model ◽  
Dominant Mode ◽  
Mean Flow ◽  
Background Flow ◽  
Heating Source ◽  
The North ◽  
Initial Location ◽  
Ocean Region

AbstractThe Madden–Julian oscillation (MJO) is the dominant mode of tropical intraseasonal variability. Many studies have found that the MJO, which acts as a tropical heating source, can excite Rossby waves that propagate into the midlatitude and modulate midlatitude circulation. The extratropical mean flow can modulate the MJO extratropical response. Rossby waves can grow or decay in different extratropical background flows, and the propagation of the Rossby waves also varies as the background flow acts as a waveguide. In this study, how extratropical mean flow modulates the MJO extratropical response is explored by using a nonlinear baroclinic primitive equation model. MJO-associated heating, as an external forcing of the model, is imposed into scenarios with different extratropical background flows. Different background flow modulates the generation and advection of the vorticity anomalies induced by the MJO, which determines the initial location and strength of the Rossby waves. The midlatitude waveguides can be different as the background flow changes. As the propagation of Rossby waves follows the waveguides, the background flow determines whether the Rossby waves are trapped in the Pacific Ocean region or can propagate to the north and to the east into North America. The experiments also show that the anomalies associated with the Rossby waves can extract energy from the midlatitude jet over the jet exit region and the southern flank of the jet. This further modulates the strength, location, and duration of the MJO extratropical response.

scholarly journals Inverse Energy Cascades in an Eddy-Induced NAO-Type Flow: Scale Interaction Mechanism

2015 ◽  
Vol 72 (9) ◽  
pp. 3417-3448 ◽  
Author(s):  
Dehai Luo ◽  
Linhao Zhong ◽  
Christian L. E. Franzke
Keyword(s):  
Large Scale ◽  
Interaction Mechanism ◽  
Zonal Flow ◽  
Scale Model ◽  
Synoptic Scale ◽  
Mean Flow ◽  
The North ◽  
Synoptic Eddies ◽  
Stretching Deformation ◽  
The North Atlantic Oscillation

Abstract In this paper, based on a new wave–eddy interaction framework, the interaction mechanism between the North Atlantic Oscillation (NAO) and synoptic-scale eddies is revealed by using the analytical solutions of a two-scale model as a description of the inverse energy cascade from nonuniform synoptic-scale eddies to the large-scale NAO flow. It is found that the spatial shape of the eddy-induced large-scale streamfunction tendency prior to the NAO onset determines the direction of eddy energy transfer, as well as the phase and growth of the NAO. However, the feedback of the intensified NAO anomaly on synoptic eddies can affect significantly the asymmetry of the NAO between negative (NAO−) and positive (NAO+) phases in amplitude and persistence through the presence or absence of the eddy straining related to cyclonic wave breaking (CWB). For the NAO+, the stretching deformation role of the NAO+ field seems dominant in the eddy variation. Because the eddy energy generation rate (EGR) weakens and tends to be negative in the downstream side of the NAO+ region, the synoptic eddies lose their energy to the NAO+-type zonal flow, thus leading to the weakening of synoptic-scale eddies. However, for the NAO−, the EGR variation shows that synoptic eddies grow over the two upstream sides of the NAO− region by extracting energy from the NAO− shearing deformation field, while losing energy to the mean flow over the upstream middle region through the stretching deformation. This process results in the eddy straining (splitting and strengthening) associated with the CWB.

scholarly journals The importance of moisture distribution for the growth and energetics of mid-latitude systems

1999 ◽  
Vol 17 (2) ◽  
pp. 242-256 ◽  
Author(s):  
V. Pavan ◽  
N. Hall ◽  
P. Valdes ◽  
M. Blackburn
Keyword(s):  
Relative Humidity ◽  
Relative Abundance ◽  
Large Scale ◽  
Initial Conditions ◽  
Equation Model ◽  
Life Cycles ◽  
Surface Fluxes ◽  
Moisture Distribution ◽  
Height Distribution ◽  
Moist Convection

Abstract. A primitive equation model is used to study the sensitivity of baroclinic wave life cycles to the initial latitude-height distribution of humidity. Diabatic heating is parametrized only as a consequence of condensation in regions of large-scale ascent. Experiments are performed in which the initial relative humidity is a simple function of model level, and in some cases latitude bands are specified which are initially relatively dry. It is found that the presence of moisture can either increase or decrease the peak eddy kinetic energy of the developing wave, depending on the initial moisture distribution. A relative abundance of moisture at mid-latitudes tends to weaken the wave, while a relative abundance at low latitudes tends to strengthen it. This sensitivity exists because competing processes are at work. These processes are described in terms of energy box diagnostics. The most realistic case lies on the cusp of this sensitivity. Further physical parametrizations are then added, including surface fluxes and upright moist convection. These have the effect of increasing wave amplitude, but the sensitivity to initial conditions of relative humidity remains. Finally, 'control' and 'doubled CO2' life cycles are performed, with initial conditions taken from the time-mean zonal-mean output of equilibrium GCM experiments. The attenuation of the wave resulting from reduced baroclinicity is more pronounced than any effect due to changes in initial moisture.Key words. Meteorology and atmospheric dynamics (climatology; convective processes; synoptic-scale meteorology)

scholarly journals The Extratropical Transition of Tropical Cyclone Lili (1996) and Its Crucial Contribution to a Moderate Extratropical Development

2005 ◽  
Vol 133 (6) ◽  
pp. 1562-1573 ◽  
Author(s):  
Anna Agustí-Panareda ◽  
Suzanne L. Gray ◽  
George C. Craig ◽  
Chris Thorncroft
Keyword(s):  
Tropical Cyclone ◽  
Case Studies ◽  
North Atlantic ◽  
Initial Conditions ◽  
Life Cycles ◽  
Extratropical Transition ◽  
The North ◽  
Potential Vorticity Inversion ◽  
The Impact

Abstract The transition that a tropical cyclone experiences as it moves into the extratropical environment (known as extratropical transition) can result in the decay or intensification of a baroclinic cyclone. The extratropical transition (ET) of Tropical Cyclone Lili (1996) in the North Atlantic resulted in a moderate extratropical development of a baroclinic cyclone. The impact of Lili in the extratropical development that occurred during its ET is investigated. Numerical experiments are performed using potential vorticity inversion and the Met Office Unified Model to forecast the extratropical development with and without the tropical cyclone in the initial conditions. In contrast with other case studies in the literature, Lili is shown to play a crucial role during its ET in the development of a baroclinic cyclone that occurred in the same region. A hypothesis of the possible scenarios of ET is presented that links the case-to-case variability of ET case studies in the literature with a classification of the life cycles of baroclinic cyclones.

Sources of Chlorophenolic Compounds to the Fraser River Estuary

1988 ◽  
Vol 23 (1) ◽  
pp. 55-68 ◽  
Author(s):  
J. H. Carey ◽  
J. H. Hart
Keyword(s):  
River Flow ◽  
River Estuary ◽  
Low Flow ◽  
Fraser River ◽  
Pulp Mills ◽  
Flow Conditions ◽  
Downstream Site ◽  
Upstream Site ◽  
The North ◽  
Main River

Abstract The identity and concentrations of chlorophenolic compounds in the Fraser River estuary were determined under conditions of high and low river flow at three sites: a site upstream from the trifurcation and at downstream sites for each main river arm. Major chlorophenolics present under both flow regimes were 2,4,6-trichlorophenol (2,4,6-TCP), 2,3,4,6-tetrachlorophenol (2,3,4,6-TeCP), pentachlorophenol (PCP), tetrachloroguaiacol (TeCG) and a compound tentatively identified as 3,4,5-trichloroguaiacol (3,4,5-TCG). Under high flow conditions, concentrations of the guaiacols were higher than any of the Chlorophenols and concentrations of all five chlorophenolics appeared to correlate. Under low flow conditions, concentrations of chloroguaiacols were higher than Chlorophenols at the upstream site and at the downstream site on the Main Arm, whereas at the downstream site on the North Arm, concentrations of 2,3,4,6-TeCP and PCP were higher than the chloroguaiacols in some samples. Overall, the results indicate that pulp mills upstream from the estuary are important sources of chlorophenolics to the estuary under all flow conditions. Additional episodic inputs of 2,3,4,6-TeCP and PCP from lumber mills occur along the North Arm. When these inputs occur, they can cause the concentrations of Chlorophenols in the North Arm to exceed provisional objectives. If chloroguaiacols are included as part of the objective, concentrations of total chlorophenolics in water entering the estuary can approach and exceed these objectives, especially under low flow conditions.

scholarly journals Quantifying the Effects of Wave—Current Interactions on Tidal Energy Resource at Sites in the English Channel Using Coupled Numerical Simulations

Energies ◽  
2021 ◽  
Vol 14 (12) ◽  
pp. 3625
Author(s):  
Jon Hardwick ◽  
Ed B. L. Mackay ◽  
Ian G. C. Ashton ◽  
Helen C. M. Smith ◽  
Philipp R. Thies
Keyword(s):  
Wave Model ◽  
Tidal Energy ◽  
English Channel ◽  
Flow Conditions ◽  
Mean Flow ◽  
Radiation Stress ◽  
Large Wave ◽  
Stress Gradients ◽  
The Mean ◽  
Flow Power

Numerical modeling of currents and waves is used throughout the marine energy industry for resource assessment. This study compared the output of numerical flow simulations run both as a standalone model and as a two-way coupled wave–current simulation. A regional coupled flow-wave model was established covering the English Channel using the Delft D-Flow 2D model coupled with a SWAN spectral wave model. Outputs were analyzed at three tidal energy sites: Alderney Race, Big Roussel (Guernsey), and PTEC (Isle of Wight). The difference in the power in the tidal flow between coupled and standalone model runs was strongly correlated to the relative direction of the waves and currents. The net difference between the coupled and standalone runs was less than 2.5%. However, when wave and current directions were aligned, the mean flow power was increased by up to 7%, whereas, when the directions were opposed, the mean flow power was reduced by as much as 9.6%. The D-Flow Flexible Mesh model incorporates the effects of waves into the flow calculations in three areas: Stokes drift, forcing by radiation stress gradients, and enhancement of the bed shear stress. Each of these mechanisms is discussed. Forcing from radiation stress gradients is shown to be the dominant mechanism affecting the flow conditions at the sites considered, primarily caused by dissipation of wave energy due to white-capping. Wave action is an important consideration at tidal energy sites. Although the net impact on the flow power was found to be small for the present sites, the effect is site specific and may be significant at sites with large wave exposure or strong asymmetry in the flow conditions and should thus be considered for detailed resource and engineering assessments.

scholarly journals Spreading of warm ocean waters around Greenland as a possible cause for glacier acceleration

2012 ◽  
Vol 53 (60) ◽  
pp. 257-266 ◽  
Author(s):  
E. Rignot ◽  
I. Fenty ◽  
D. Menemenlis ◽  
Y. Xu
Keyword(s):  
Initial Conditions ◽  
Independent Study ◽  
Ocean Temperature ◽  
The North ◽  
Subsurface Ocean ◽  
Subsurface Waters ◽  
Glacier Flow ◽  
Horizontal Grid ◽  
Possible Cause

AbstractWe examine the pattern of spreading of warm subtropical-origin waters around Greenland for the years 1992–2009 using a high-resolution (4km horizontal grid) coupled ocean and sea-ice simulation. The simulation, provided by the Estimating the Circulation and Climate of the Ocean, Phase II (ECCO2) project, qualitatively reproduces the observed warming of subsurface waters in the subpolar gyre associated with changes of the North Atlantic atmospheric state that occurred in the mid-1990s. The modeled subsurface ocean temperature warmed by 1.5˚C in southeast and southwest Greenland during 1994–2005 and subsequently cooled by 0.5˚C; modeled subsurface ocean temperature increased by 2–2.5˚C in central and then northwest Greenland during 1997–2005 and stabilized thereafter, while it increased after 2005 by <0.5˚C in north Greenland. Comparisons with in situ measurements off the continental shelf in the Labrador and Irminger Seas indicate that the model initial conditions were 0.4˚C too warm in the south but the simulated warming is correctly reproduced; while measurements from eastern Baffin Bay reveal that the model initial conditions were 1.0˚C too cold in the northwest but the simulated ocean warming brought modeled temperature closer to observations, i.e. the simulated warming is 1.0˚C too large. At several key locations, the modeled oceanic changes off the shelf and below the seasonal mixed layer were rapidly transmitted to the shelf within troughs towards (model-unresolved) fjords. Unless blocked in the fjords by shallow sills, these warm subsurface waters had potential to propagate down the fjords and melt the glacier fronts. Based on model sensitivity simulations from an independent study (Xu and others, 2012), we show that the oceanic changes have very likely increased the subaqueous melt rates of the glacier fronts, and in turn impacted the rates of glacier flow.

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