Stability of Finite-Amplitude Baroclinic Waves in a Two-Layer Channel Flow

The impacts of the number density of cloud condensation nuclei (CCN) and other thermodynamic quantities on moist Rayleigh convection were examined. A numerical model, consisting of a simple two-dimensional equation for Boussinesq air and a sophisticated double moment microphysics scheme, was developed. The impact of the number of CCN is most prominent in the initially formed convection, whereas the convection in the quasi-steady state does not significantly depend on the number of CCN. It is suggested that the former convection is driven by a mechanism without a background circulation, such as parcel theory. In contrast, the latter convection appears to be driven by the statically unstable background layer. Incorporating the cloud microphysics reduces the integrated kinetic energy and number of convective cell (increases the distance between the cells), with some exceptions, which are consistent with previous studies. These features are not largely sensitive to the number of CCN. It is shown in this study that the reduction in kinetic energy is mainly due to condensation (evaporation) in the upper (lower) layer, which tends to stabilize the fluid. The ensemble simulation shows that the sensitivity of the moist processes to changes the temperature at the bottom boundary, temperature lapse rate, water vapor mixing ratio, and CCN is qualitatively similar to that in the control simulation. The impact becomes strong with increasing 1 temperature lapse rate. The number of convective cell in a domain decreases with the degree of supersaturation or an increase in the domain-integrated condensate.

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Stability of Finite-Amplitude Baroclinic Waves in a Two-Layer Channel Flow

Yoshizaki

1982

Journal of the Meteorological Society of Japan

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By using a two-layer channel model, the stability and behaviours of finite-amplitude baroclinic waves are investigated in the moderately non-linear regime. Two methods which are applicable to the moderately non-linear regime are adopted. One is the method in which steady wave solutions are first obtained and then their stabilities are examined with respect to various perturbations.The other is the numerical method in which time integrations of a grid model are performed as an initial value problem. We obtain many interesting results, although we treat some cases with particular values of non-dimensional parameters except the vertical shear U. The main results are summarized as follows: (1) The stability of steady finite-amplitude baroclinic waves is determined mostly by the sideband instability. (2) The dominant wavenumber seen in a finite-amplitude state is different from that predicted by the linear theory. (3) The beta effect reduces the stable region of finite-amplitude baroclinic waves in the (*, U)-plane, where a is wavenumber.(4) The wavenumber realized in the finiteamplitude state for given values of parameters depends on the initial conditions. Such a hysteresis phenomenon in wavenumber selection is seen when the stable region contains more than two wavenumbers.(5) Both wavenumber and amplitude vacillations are simulated by numerical experiments. The sideband instability can produce such time-dependent motions. The mechanism of vacillations produced by this instability is different from those proposed by Lorenz (1963) and Pedlosky. (1976, 1977.

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Stability of Finite-Amplitude Baroclinic Waves in a Two-Layer Channel Flow

Cited by 5 publications

References 46 publications

Nonlinear Equilibration of Barotropic Waves in a Zonally Nonuniform Current

Nonlinear Equilibration of Barotropic Waves in a Zonally Nonuniform Current

Impacts of Number of Cloud Condensation Nuclei on Two-Dimensional Moist Rayleigh Convection

Stability of Finite-Amplitude Baroclinic Waves in a Two-Layer Channel Flow

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