Low frequency oscillations in turbulent Rayleigh-Benard convection

Krishnamurti, Ruby

doi:10.1007/bf02744583

Cited by 2 publications

(1 citation statement)

References 6 publications

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“…These configurations are typical for the KB and subcritical regimes. A large-scale organization into traveling clusters of tilted thermal plumes has been observed in experiments of single-phase turbulent convection in water at Pr ¼ 7 (20,21). In the present system, the moist plumes do not move around significantly.…”

Section: Self-aggregation Of Cloudssupporting

confidence: 67%

Self-aggregation of clouds in conditionally unstable moist convection

Pauluis

Schumacher

2011

Proc. Natl. Acad. Sci. U.S.A.

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The behavior of moist Rayleigh-Bénard convection is investigated using a Boussinesq model with a simplified thermodynamics for phase transitions. This idealized configuration makes the problem accessible to high-resolution three-dimensional direct numerical simulations without small-scale parameterizations of the turbulence for extended layers with aspect ratios up to 64. Our study is focused on the frequently observed conditionally unstable environment that is stably stratified for unsaturated air, but is unstable for cloudy air. We find that no sharp threshold for the transition to convective turbulence exists, a situation similar to wall-bounded shear flows. Rather, the transition depends on the amplitude of the initial perturbation of the quiescent equilibrium and on the aspect ratio of the convective domain. In contrast to the classical dry Rayleigh-Bénard case, convection is highly asymmetric with respect to the vertical direction. Moist upwelling air inside turbulent cloud aggregates is surrounded by ambient regions of slowly descending unsaturated air. It is also found that conditionally unstable moist convection is inefficient at transporting energy. Our study suggests that there is an upper bound on the Nusselt number in moist convection that is lower than that of the classical dry case.C onvective processes in the Earth's atmosphere are often associated with condensation of water vapor and the formation of clouds. These involve spatial scales as small as a micron for the activation of cloud water droplets and as large as a few kilometers for a whole cloud, with time scales ranging from milliseconds to hours (1, 2). Convective systems are often themselves embedded within larger structures, such as mesoscale cloud clusters or midlatitude baroclinic eddies. Because of their complex multiscale physics, clouds remain one of the main sources of uncertainty in predictions of future climate change (3, 4). This holds particularly true for low clouds over subtropical and tropical oceans (5), where small changes in cloud behavior can dramatically alter the amount of solar energy absorbed or reflected. Even with stateof-the-art large eddy simulations that can describe the dynamics on mesoscales in atmospheric layers with a side length of up to approximately 10 2 km and grid resolutions of 100 m or less, many of the dynamically relevant scales still remain unresolved and have to be parameterized (6). Our understanding of the formation of clouds, their life cycles, and the resulting turbulent transport is still incomplete. Further progress can be gained by increasing the resolution of the numerical model (7,8) and a refinement of the subgrid scale parameterizations to obtain the most realistic simulations of convection. Equally important for our understanding is the need to disentangle the various phenomena and to identify the most important physical processes that determine the dynamics of clouds in the atmosphere. This is the approach followed in this paper in which we analyze the behavior of convection in an ide...

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Section: Self-aggregation Of Cloudssupporting

confidence: 67%

Self-aggregation of clouds in conditionally unstable moist convection

Pauluis

Schumacher

2011

Proc. Natl. Acad. Sci. U.S.A.

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Measured oscillations of the velocity and temperature fields in turbulent Rayleigh-Bénard convection in a rectangular cell

2007

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Temperature and velocity oscillations have been found in a rectangular Rayleigh-Bénard convection cell, in which one large-scale convection roll exists. At Rayleigh number Ra=8.9x10(11) and Prandtl number Pr=4, temperature oscillations can be observed in most parts of the system and the oscillation period remains almost constant, tT=74+/-2 s. Velocity oscillation can only be found in its horizontal component vy (perpendicular to the large-scale circulation plane) near the cell sidewall, its oscillation period is also constant, tv=65+/-2 s, at these positions. Temperature and velocity oscillations have different Ra dependences, which are, respectively, indicated by the Péclect number PeT=0.55Ra0.47 and Pev=0.28Ra0.50. In comparison to the case of a cylindrical cell, we find that velocity oscillations are affected by the system geometry.

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Low frequency oscillations in turbulent Rayleigh-Benard convection

Cited by 2 publications

References 6 publications

Self-aggregation of clouds in conditionally unstable moist convection

Self-aggregation of clouds in conditionally unstable moist convection

Measured oscillations of the velocity and temperature fields in turbulent Rayleigh-Bénard convection in a rectangular cell

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