Baroclinic Waves

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Chris Snyder - One of the best experts on this subject based on the ideXlab platform.

  • mesoscale energy spectra of moist Baroclinic Waves
    Journal of the Atmospheric Sciences, 2013
    Co-Authors: Michael L Waite, Chris Snyder
    Abstract:

    AbstractThe role of moist processes in the development of the mesoscale kinetic energy spectrum is investigated with numerical simulations of idealized moist Baroclinic Waves. Dry Baroclinic Waves yield upper-tropospheric kinetic energy spectra that resemble a −3 power law. Decomposition into horizontally rotational and divergent kinetic energy shows that the divergent energy has a much shallower spectrum, but its amplitude is too small to yield a characteristic kink in the total spectrum, which is dominated by the rotational part. The inclusion of moist processes energizes the mesoscale. In the upper troposphere, the effect is mainly in the divergent part of the kinetic energy; the spectral slope remains shallow (around −) as in the dry case, but the amplitude increases with increasing humidity. The divergence field in physical space is consistent with inertia–gravity Waves being generated in regions of latent heating and propagating throughout the Baroclinic wave. Buoyancy flux spectra are used to diagn...

  • mesoscale predictability of moist Baroclinic Waves convection permitting experiments and multistage error growth dynamics
    Journal of the Atmospheric Sciences, 2007
    Co-Authors: Fuqing Zhang, Chris Snyder, Richard Rotunno, Craig C Epifanio
    Abstract:

    A recent study examined the predictability of an idealized Baroclinic wave amplifying in a conditionally unstable atmosphere through numerical simulations with parameterized moist convection. It was demonstrated that with the effect of moisture included, the error starting from small random noise is characterized by upscale growth in the short-term (0–36 h) forecast of a growing synoptic-scale disturbance. The current study seeks to explore further the mesoscale error-growth dynamics in idealized moist Baroclinic Waves through convection-permitting experiments with model grid increments down to 3.3 km. These experiments suggest the following three-stage error-growth model: in the initial stage, the errors grow from small-scale convective instability and then quickly [O(1 h)] saturate at the convective scales. In the second stage, the character of the errors changes from that of convective-scale unbalanced motions to one more closely related to large-scale balanced motions. That is, some of the error from convective scales is retained in the balanced motions, while the rest is radiated away in the form of gravity Waves. In the final stage, the large-scale (balanced) components of the errors grow with the background Baroclinic instability. Through examination of the error-energy budget, it is found that buoyancy production due mostly to moist convection is comparable to shear production (nonlinear velocity advection). It is found that turning off latent heating not only dramatically decreases buoyancy production, but also reduces shear production to less than 20% of its original amplitude.

  • unstable Baroclinic Waves beyond quasigeostrophic theory
    Journal of the Atmospheric Sciences, 2000
    Co-Authors: Richard Rotunno, David J Muraki, Chris Snyder
    Abstract:

    Quasigeostrophic theory is an approximation of the primitive equations in which the dynamics of geostrophically balanced motions are described by the advection of potential vorticity. Quasigeostrophic theory also represents a leading-order theory in the sense that it is derivable from the primitive equations in the asymptotic limit of zero Rossby number. Building upon quasigeostrophic theory, and the centrality of potential vorticity, the authors have recently developed a systematic asymptotic framework from which balanced, next-order corrections in Rossby number can be obtained. The approach is illustrated here through numerical solutions pertaining to unstable Waves on Baroclinic jets. The numerical solutions using the full primitive equations compare well with numerical solutions to our equations with accuracy one order beyond quasigeostrophic theory; in particular, the inherent asymmetry between cyclones and anticyclones is captured. Explanations of the latter and the associated asymmetry of the warm and cold fronts are given using simple extensions of quasigeostrophic‐ potential-vorticity thinking to next order.

  • development of perturbations within growing Baroclinic Waves
    Quarterly Journal of the Royal Meteorological Society, 1998
    Co-Authors: Chris Snyder, A Joly
    Abstract:

    We explore the linear stability of a growing, three-dimensional Baroclinic wave by calculating the perturbation that grows most rapidly over various time intervals and at various stages in the development of the parent wave and its fronts. Three norms are used to measure growth: volume-integrated energy, enstrophy and stream function variance. The flow is assumed adiabatic and quasi-geostrophic for simplicity, and perturbations are required to have uniform potential vorticity. These rapidly growing perturbations can produce realistic sub-structures within the parent wave, such as upper-level vorticity maxima that propagate relative to a synoptic-scale parent wave or packets of synoptic-scale Waves within a planetary-wave basic state. For a synoptic-scale parent wave and the energy or enstrophy norms, however, the dominant characteristic of the fastest growing perturbations is that they rapidly evolve toward a final structure corresponding to a phase shift and slight change of shape of the original wave—in essence, the initial perturbation modifies the parent wave and the jet on which it propagates, which results in a modification, which grows in time, of the phase and amplitude of the parent wave. Amplifications in energy or enstrophy are also small compared to what would be estimated based on the locally large shears and Baroclinicity within the parent wave. The fronts appear to be stabilized by the combined influences of synoptic-scale horizontal deformation and the natural movement of perturbations relative to the parent wave.

  • Effects of Surface Drag on Fronts within Numerically Simulated Baroclinic Waves
    Journal of the Atmospheric Sciences, 1998
    Co-Authors: Richard Rotunno, William C. Skamarock, Chris Snyder
    Abstract:

    Abstract A comparative analysis of simulations of Baroclinic Waves with and without surface drag is presented, with particular reference to surface features. As in recent studies, the present simulations show that, compared to simulations with no drag, those with surface drag are less inclined to develop a secluded warm sector, and that drag weakens the warm front while the cold front remains strong. The authors demonstrate that analogous effects occur when Ekman pumping is used in nonlinear quasigeostrophic numerical simulations of unstable Baroclinic Waves in a channel. However, since the quasigeostrophic model produces symmetric highs and lows in the unstable Baroclinic wave, the cold and warm fronts are therefore also symmetric and hence equally affected by the Ekman pumping. The different effect that friction has on the warm front with respect to the cold front in the primitive-equation simulations is fundamentally related to the tendency for the lows to be strong and narrow and the highs weak and br...

Edmund K M Chang - One of the best experts on this subject based on the ideXlab platform.

  • the effects of variations in jet width on the growth of Baroclinic Waves implications for midwinter pacific storm track variability
    Journal of the Atmospheric Sciences, 2004
    Co-Authors: Nili Harnik, Edmund K M Chang
    Abstract:

    The effects of variations in jet width on the downstream growth of Baroclinic Waves are studied, using a simple quasigeostrophic model with a vertically varying basic state and variable channel width, as well as a simplified primitive equation model with a basic state that varies in latitude and height. This study is motivated by observations that in midwinter in the Pacific the storm track is weaker and the jet is narrower during years when the jet is strong. The linear models are able to reproduce the observed decrease of spatial growth rate with shear, if the narrowing of the jet is accounted for by assuming it decreases the meridional wavelength of the perturbations, which hampers their growth. A common suggestion has been that perturbations are weaker when the jet is strong because they move faster out of the unstable storm track region. The authors find that one needs to take into account that the jet narrows when it strengthens; otherwise, the increase of growth rate is strong enough to counteract the effect of increased advection speed. It is also found that, when the model basic state is Eady-like (small or zero meridional potential vorticity gradients in the troposphere), the short-wave cutoff for instability moves to large-scale Waves as shear is increased, due to the accompanying increase in meridional wavenumber. This results in a transition from a regime where upper-level perturbations spin up a surface circulation very rapidly, and normal-mode growth ensues, to a regime where the initial perturbations take a very long time to excite growth. Since Waves slow down when a surface perturbation develops, this can explain the observations that the storm track perturbations are more ‘‘upper level’’ during strong jet years and their group velocities increase faster than linearly with shear.

  • downstream development of Baroclinic Waves as inferred from regression analysis
    Journal of the Atmospheric Sciences, 1993
    Co-Authors: Edmund K M Chang
    Abstract:

    Abstract The structure and evolution of transient disturbances in the Northern Hemisphere winter season are examined using one-point regression maps and longitude-height sections derived from the European Centre for Medium-Range Weather Forecasts (ECMWF) operational analyses for seven winter seasons. With the use of unfiltered time series of normalized 300-mb meridional wind perturbations at a grid point in the Pacific storm track as the reference time series, regression statistics for perturbations in the horizontal wind, geopotential height, temperature, and vertical velocity are derived. The resulting perturbation fields exhibit characteristics of midlatitude Baroclinic Waves, such as a westward tilt with height in the velocity and height fields and eastward tilt in the temperature field, with typical wavelengths of 4000 km and periods of around 4 days. The main difference between the results of this work and previous similar analyses is in the propagation characteristics of the Baroclinic wave trains....

  • ageostrophic geopotential fluxes in downstream and upstream development of Baroclinic Waves
    Journal of the Atmospheric Sciences, 1993
    Co-Authors: Isidoro Orlanski, Edmund K M Chang
    Abstract:

    Abstract With the use of a simple primitive equation model, it is demonstrated that the convergence/divergence of ageostrophic geopotential fluxes can be a major source/sink of kinetic energy for both downstream and upstream development of Baroclinic Waves, and can play a dominant role during the early stages of wave development. It is also shown that both surface friction and β effects lead to an asymmetry in the upstream versus downstream development, with downstream development much stronger. A total group velocity is defined based on ageostrophic fluxes, and its relationship to the rate of wave packet spreading and to convective and absolute instability is discussed.

Richard Rotunno - One of the best experts on this subject based on the ideXlab platform.

  • mesoscale predictability of moist Baroclinic Waves convection permitting experiments and multistage error growth dynamics
    Journal of the Atmospheric Sciences, 2007
    Co-Authors: Fuqing Zhang, Chris Snyder, Richard Rotunno, Craig C Epifanio
    Abstract:

    A recent study examined the predictability of an idealized Baroclinic wave amplifying in a conditionally unstable atmosphere through numerical simulations with parameterized moist convection. It was demonstrated that with the effect of moisture included, the error starting from small random noise is characterized by upscale growth in the short-term (0–36 h) forecast of a growing synoptic-scale disturbance. The current study seeks to explore further the mesoscale error-growth dynamics in idealized moist Baroclinic Waves through convection-permitting experiments with model grid increments down to 3.3 km. These experiments suggest the following three-stage error-growth model: in the initial stage, the errors grow from small-scale convective instability and then quickly [O(1 h)] saturate at the convective scales. In the second stage, the character of the errors changes from that of convective-scale unbalanced motions to one more closely related to large-scale balanced motions. That is, some of the error from convective scales is retained in the balanced motions, while the rest is radiated away in the form of gravity Waves. In the final stage, the large-scale (balanced) components of the errors grow with the background Baroclinic instability. Through examination of the error-energy budget, it is found that buoyancy production due mostly to moist convection is comparable to shear production (nonlinear velocity advection). It is found that turning off latent heating not only dramatically decreases buoyancy production, but also reduces shear production to less than 20% of its original amplitude.

  • unstable Baroclinic Waves beyond quasigeostrophic theory
    Journal of the Atmospheric Sciences, 2000
    Co-Authors: Richard Rotunno, David J Muraki, Chris Snyder
    Abstract:

    Quasigeostrophic theory is an approximation of the primitive equations in which the dynamics of geostrophically balanced motions are described by the advection of potential vorticity. Quasigeostrophic theory also represents a leading-order theory in the sense that it is derivable from the primitive equations in the asymptotic limit of zero Rossby number. Building upon quasigeostrophic theory, and the centrality of potential vorticity, the authors have recently developed a systematic asymptotic framework from which balanced, next-order corrections in Rossby number can be obtained. The approach is illustrated here through numerical solutions pertaining to unstable Waves on Baroclinic jets. The numerical solutions using the full primitive equations compare well with numerical solutions to our equations with accuracy one order beyond quasigeostrophic theory; in particular, the inherent asymmetry between cyclones and anticyclones is captured. Explanations of the latter and the associated asymmetry of the warm and cold fronts are given using simple extensions of quasigeostrophic‐ potential-vorticity thinking to next order.

  • Effects of Surface Drag on Fronts within Numerically Simulated Baroclinic Waves
    Journal of the Atmospheric Sciences, 1998
    Co-Authors: Richard Rotunno, William C. Skamarock, Chris Snyder
    Abstract:

    Abstract A comparative analysis of simulations of Baroclinic Waves with and without surface drag is presented, with particular reference to surface features. As in recent studies, the present simulations show that, compared to simulations with no drag, those with surface drag are less inclined to develop a secluded warm sector, and that drag weakens the warm front while the cold front remains strong. The authors demonstrate that analogous effects occur when Ekman pumping is used in nonlinear quasigeostrophic numerical simulations of unstable Baroclinic Waves in a channel. However, since the quasigeostrophic model produces symmetric highs and lows in the unstable Baroclinic wave, the cold and warm fronts are therefore also symmetric and hence equally affected by the Ekman pumping. The different effect that friction has on the warm front with respect to the cold front in the primitive-equation simulations is fundamentally related to the tendency for the lows to be strong and narrow and the highs weak and br...

  • a comparison of primitive equation and semigeostrophic simulations of Baroclinic Waves
    Journal of the Atmospheric Sciences, 1991
    Co-Authors: Chris Snyder, William C. Skamarock, Richard Rotunno
    Abstract:

    Abstract In the course of adapting a nonhydrostatic cloud model [or primitive-equation model (PE)] for simulations of large-scale Baroclinic Waves, we have encountered systematic discrepancies between the PE solutions and those of the semigeostrophic (SG) equations. Direct comparisons using identical, uniform potential vorticity jets show that 1) the linear modes of the PE have distinctively different structure than the SG modes; 2) at finite amplitude, the PE pressure field develops lows that are deeper, and highs that are weaker, than in the SG solution; and 3) the nonlinear PE wave produces a characteristic “cyclonic wrapping” of the temperature contours on both horizontal boundaries and has an associated “bent-back” frontal structure at the surface, while in the SG solutions (for this particular basic state jet) there is an equal tendency to pull temperature contours anticyclonically around highs and cyclonically around lows. An analysis of the vorticity and potential vorticity equations for small Ros...

P L Read - One of the best experts on this subject based on the ideXlab platform.

  • phase synchronization of Baroclinic Waves in a differentially heated rotating annulus experiment subject to periodic forcing with a variable duty cycle
    Chaos, 2017
    Co-Authors: P L Read, X Moriceatkinson, E J Allen, Alfonso A Castrejonpita
    Abstract:

    A series of laboratory experiments in a thermally driven, rotating fluid annulus are presented that investigate the onset and characteristics of phase synchronization and frequency entrainment between the intrinsic, chaotic, oscillatory amplitude modulation of travelling Baroclinic Waves and a periodic modulation of the (axisymmetric) thermal boundary conditions, subject to time-dependent coupling. The time-dependence is in the form of a prescribed duty cycle in which the periodic forcing of the boundary conditions is applied for only a fraction δ of each oscillation. For the rest of the oscillation, the boundary conditions are held fixed. Two profiles of forcing were investigated that capture different parts of the sinusoidal variation and δ was varied over the range 0.1≤δ≤1. Reducing δ was found to act in a similar way to a reduction in a constant coupling coefficient in reducing the width of the interval in forcing frequency or period over which complete synchronization was observed (the “Arnol'd tongu...

  • Baroclinic Waves in an air filled thermally driven rotating annulus
    Physical Review E, 2007
    Co-Authors: Alfonso A Castrejonpita, P L Read
    Abstract:

    In this study an experimental investigation of Baroclinic Waves in air in a differentially heated rotating annulus is presented. Air has a Prandtl number of 0.707, which falls within a previously unexplored region of parameter space for Baroclinic instability. The flow regimes encountered include steady Waves, periodic amplitude vacillations, modulated amplitude vacillations, and either monochromatic or mixed wave number weak Waves, the latter being characterized by having amplitudes less than 5% of the applied temperature contrast. The distribution of these flow regimes in parameter space are presented in a regime diagram. It was found that the progression of transitions between different regimes is, as predicted by recent numerical modeling results, in the opposite sense to that usually found in experiments with high Prandtl number liquids. No hysteresis in the flow type, with respect to variations in the rotation rate, was found in this investigation.

  • wave interactions and the transition to chaos of Baroclinic Waves in a thermally driven rotating annulus
    Philosophical Transactions of the Royal Society A, 1997
    Co-Authors: Wolfgerrit Fruh, P L Read
    Abstract:

    A series of laboratory experiments is presented investigating regular and chaotic Baroclinic Waves in a high–Prandtl number fluid contained in a rotating vessel and subjected to a horizontal temperature gradient. The study focuses on nonlinear aspects of mixed–mode states at moderate values of the forcing parameters within the regular wave regime. Frequency entrainment and phase locking of resonant triads and sidebands were found to be widespread. Cases were analysed in phase space reconstructions through a singular value decomposition of multi–variate time series. Four forms of mixed–mode states were found, each in well–defined regions of parameter space: (1) a nonlinear interference vacillation associated with strong phase locking through higher harmonics; (2) a modulated amplitude vacillation showing strong phase coherence in triads involving the long wave; (3) an intermittent bursting of secondary modes; (4) an attractor switching flow, where the dominant wave number switched at irregular intervals between two possible wave numbers. Many of the mixed–mode states are suggested to arise from homoclinic bifurcations, whereas no secondary Hopf bifurcations were found. One of the postulated homoclinic bifurcations was consistent with a bifurcation through intermittency. The bifurcation sequences, however, were strongly affected by phase locking between different wave number components and frequency locking between drift and modulation frequencies. When all free frequencies were locked, the flow reduced to a limit cycle which subsequently became unstable through an incomplete period–doubling cascade. The only observed case of torus–doubling was also associated with strong phase locking. Most of the observed regimes were consistent with low–dimensional dynamics involving a limited number of domain–filling modes, which can be represented in phase space reconstructions and characterized by invariants such as attractor dimensions and the Lyapunov exponents. Some flows associated with a weak structural vacillation, however, were not consistent with low–dimensional dynamics. It appeared rather that they were the result of spatially localized instabilities consistent with high–dimensional dynamics, which can be parametrized as stochastic dynamics.

  • Rotating Annulus Flows and Baroclinic Waves
    Rotating Fluids in Geophysical and Industrial Applications, 1992
    Co-Authors: P L Read
    Abstract:

    Many aspects of the thermally-driven circulation in the atmosphere or oceans can be studied on the laboratory scale via the cylindrical rotating annulus. In this paper, we review the basic geophysical motivation for such experiments, and discuss all the principal flow regimes so far studied. Particular emphasis is placed (a) on the underlying dynamics of the steady axisymmetric flow, (b) the structure and stability of the Baroclinic wave regime, and (c) the possible transition scenarios to chaotic and/or irregular flow studied to date.

Luis Gimeno - One of the best experts on this subject based on the ideXlab platform.

  • Baroclinic Waves phase-lockings by double tropopause events
    2020
    Co-Authors: J M Castanheira, Luis Gimeno
    Abstract:

    Double tropopause events in Global Positioning radio occultation CHAMP and COSMIC data are analyzed. High frequency (> 60%) of double tropopause events is found in the subtropical regions. In accordance with other studies, the statistics of tropopause heights suggest that the dominant process for double tropopause events is associated with an overlapping of the tropical tropopause on the extratropical one. Here we show that the overlapping variability is associated with Baroclinic wave patterns in the subtropical and middle latitudes. The wave signature in the data can be uncovered due to wave phase-lockings by single and double tropopause events.

  • association of double tropopause events with Baroclinic Waves
    Journal of Geophysical Research, 2011
    Co-Authors: J M Castanheira, Luis Gimeno
    Abstract:

    [1] We herein propose a method for identifying breaks in the subtropical tropopause as found in the ERA Interim reanalysis data. The method uses the identification of double tropopauses and allows the quantification of the extension of the overlap between the tropical and extratropical tropopauses. The correlations between the meridional extension of the superposition of tropopauses and the fields of geopotential, potential vorticity, or potential temperature, reveal Baroclinic wave patterns. Similar wave patterns were also identified in the potential temperature fields derived from GPS radio occultation COSMIC data. The zonal propagation velocity of the anomalies in the meridional extension of the overlap was estimated using Hovmoller diagrams. The estimated zonal velocities suggest that the variability in the superposition of the tropopauses is associated with Baroclinic Rossby wave patterns in the subtropical upper troposphere and lower stratosphere.