An experimental study on the forcing of large-scale heat sources and topography on baroclinic flow

Abstract

The present work consists of two parts. In the first, an experiment is described to study the topographic forcing on the baroclinic flow. By comparison of the experiments with and without topography, the role of topography in the formation of the flow regimes is discussed. The experiments show that the travelling waves strongly vacillate with time due to the topographic forcing. Otherwise in the experiments with the same imposed external conditions but with no topography, the baroclinic waves would travel regularly with almost no vacillation. It was found that a prominent feature in the flow with topographic forcing is large-scale wave vacillation with a period of 127 annulus rotations, which is equivalent to approximately 26 days in the Earth atmosphere. The experiments show that the role of topography is to modulate the unstable baroclinic waves both in space and time. In the second part of this paper, a series of comparative experiments is introduced to study the influences of heat sources and topography on the large-scale baroclinic background flows defined as the flow patterns determined by Ω the angular velocity of the annulus rotation and ΔT, the radial temperature difference between the inner and outer walls of the annulus. The flow patterns depend on the number and disposition of the disturbance sources. As the result of nonlinear forcing of imposed heat sources the initial-axisymmetric-annular flow turns into a 4 wave flow if the number of the disturbance sources is equal to or less than two no matter which kind of disturbances, the heat source or topography, is. This means that although the mechanisms of thermo-'convective forcing of the heat sources and solid-mechanical forcing of bottom topography are essentially different, both of them can change the vorticity distribution in the flow and form new flow patterns. When the initial flow is axisymmetric-wavy owing to the forcing of heat sources, the flow becomes unstable. Either the local waves deform or vacillation occurs.