A Numerical Study of Tilted-Trough Vacillation Observed in a Differentially Heated Rotating Fluid Annulus

[摘要] A tilted-trough vacillation observed in a laboratory experiment is simulated by the use of a nonuniform global grid numerical model. The main results are as follows.(1) A stable tilted-trough vacillation with a definite period has been simulated under steady external conditions. The flow fields are highly rotationally symmetric over the whole duration of the tilted- trough vacillation; the amplitudes of the sidebands are of the order of one thousandth of those of the adjacent dominant mode and harmonics. The amplitudes of harmonics and sidebands decrease exponentially with the increase of their wavenumbers.(2) There is a time variation of the inclination of the deviatoric pressure field from the vertical direction in the cylindrical surface as well as the time variation of its tilt from the radial direction in the horizontal plane. Rates of radial transport of heat and angular momentum vary periodically according to these variations of inclination and tilt, respectively.(3) Dynamical energies and their conversion rates also show distinct time variations. The conversion rate from the zonal mean to the deviatoric kinetic energy CKZKE is positive during the vacillation cycle, although it is one order of magnitude smaller than the conversion rate from the potential to the deviatoric kinetic energy; the rate CKZKE for steady baroclinic waves developing for considerably lower rotation speeds is negative. Therefore, the tilted-trough vacillation is interpreted as the behavior of baroclinic waves affected by weak barotropic instability.

[学科分类] 大气科学