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Baroclinic Waves

The Experts below are selected from a list of 243 Experts worldwide ranked by ideXlab platform

Chris Snyder – 1st expert 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.

Edmund K M Chang – 2nd expert 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 – 3rd expert 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…