Sloping convection in a rotating fluid

2017

Exp Fluids

unstable flows which are qualitatively similar to those previously observed in the classical thermally driven annulus. However, in contrast to the classical configuration, they typically exhibit more spatio-temporal complexity. Thus, several regimes of flow demonstrate the equilibrated coexistence of, and interaction between, free convection and baroclinic wave modes. These new features were not previously observed in the classical annulus and validate the new setup as a tool for exploring fundamental atmosphere-like dynamics in a more realistic framework. Thermal structure in the fluid is investigated and found to be qualitatively consistent with previous numerical results, with nearly isothermal conditions, respectively, above and below the heat source and sink, and stably-stratified, sloping isotherms in the near-adiabatic interior.

Section: Baroclinic Instabilitysupporting

confidence: 71%

Section: Methodsmentioning

confidence: 99%

A rotating annulus driven by localized convective forcing: a new atmosphere-like experiment

Scolan

2017

Exp Fluids

“…In common with other studies using rotating annulus experiments (e.g., see Mason, 1975 andRead et al, 2015), the parameter space is determined with reference to two principal dimensionless parameters, the thermal Rossby or Hide number defined as…”

Section: Experimental Configurationmentioning

confidence: 99%

Phase synchronization of baroclinic waves in a differentially heated rotating annulus experiment subject to periodic forcing with a variable duty cycle

Morice-Atkinson

Allen

et al. 2017

Chaos

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 timedependent 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 d 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 d was varied over the range 0:1 d 1. Reducing d 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 tongue") with respect to the detuning, although for the strongest pulse-like forcing profile some degree of synchronization was discernible even at d ¼ 0:1. Complete phase synchronization was obtained within the Arnol'd tongue itself, although the strength of the amplitude modulation of the baroclinic wave was not significantly affected. These experiments demonstrate a possible mechanism for intraseasonal and/or interannual "teleconnections" within the climate system of the Earth and other planets that does not rely on Rossby wave propagation across the planet along great circles. Synchronization is commonly discussed in the context of discrete, coupled oscillators which may be periodic or chaotic. But under some circumstances, extended nonlinear systems which are formally infinite-dimensional, such as fluid flows, may exhibit discrete oscillations and behave as if they consisted of discrete oscillating components. We study such an example in the laboratory, consisting of amplitude-modulated, azimuthally travelling baroclinic waves in a thermally driven, rotating annulus experiment. Earlier experiments showed that, under conditions in which the unperturbed travelling waves are spontaneously (either periodically or weakly chaotically) modulated in time, the amplitude modulation of the waves can be phase-locked and synchronized with periodic perturbations of the applied (axisymmetric) temperature difference between the inner and outer cylinders of the experiment. We use this potentially synchronized system to explore what happens if the periodic perturbations are applied for only a given fraction of each cycle-i.e., for a duty cycle <100%. Our systematic exploration of variations in both the duty cycle and detuning (difference in period between the natural oscillation period and that of the imposed boundary temperature variations) shows that the duty cycle acts in the same way as a variable coupling coefficient, demonstrating a narrowing of the frequency interval over which complete phase synchronization is observed as ...

“…Inspired by laboratory rotating annulus experiments [which could be viewed in some respects as an analogue of a terrestrial atmosphere, see Hide & Mason (1975)], we define two characteristic dimensionless parameters for planetary atmospheric circulations: in which R is the gas constant, Δθ h the horizontal temperature difference between the equator and the poles, Ω the planetary rotation rate, a the planetary radius, and τ f the frictional timescale within the boundary layer.…”

Section: Introductionmentioning

confidence: 99%

Diversity of Planetary Atmospheric Circulations and Climates in a Simplified General Circulation Model

Wang

2012

Proc. IAU

Abstract. The parametric dependence of terrestrial planetary atmospheric circulations and climates on characteristic parameters is studied. A simplified general circulation model-PUMA is employed to investigate the dynamic effects of planetary rotation rate and equator-to-pole temperature difference on the circulation and climate of terrestrial planetary atmospheres. Five different types of circulation regime are identified by mapping the experimental results in a 2-D parameter space defined by thermal Rossby number and frictional Taylor number. The effect of the transfer and redistribution of radiative energy is studied by building up a new two-band semi-gray radiative-convective scheme, which is capable of modelling greenhouse and anti-greenhouse effects while keeping the tunable parameters as few as possible. The results will provide insights into predicting the habitability of terrestrial exoplanets.