Mammatus cloud formation by settling and evaporation

Ravichandran, S.; Meiburg, Eckart; Govindarajan, Rama

doi:10.1017/jfm.2020.439

Cited by 19 publications

(28 citation statements)

References 24 publications

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“…Equations ((2.16) and (2.17)), together with (2.19), are solved using the finite volume solver Megha-5 on a uniform grid in all three space directions (Diwan et al. 2014; Prasanth 2014; Ravichandran & Wettlaufer 2020; Ravichandran, Meiburg & Govindarajan 2020). After every time step of (2.16) and (2.17), an equilibration step is implemented using (2.10) and (2.11).…”

Section: Structure Of the Problemmentioning

confidence: 99%

Melting driven by rotating Rayleigh–Bénard convection

Ravichandran

Wettlaufer

2021

J. Fluid Mech.

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Section: Structure Of the Problemmentioning

confidence: 99%

Melting driven by rotating Rayleigh–Bénard convection

Ravichandran

Wettlaufer

2021

J. Fluid Mech.

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“…Their coupling to droplet settling is a challenging topic. (iv) An extension to study the instability of the cloud bottom (e.g.mammatus cloud formation), which is a saturation interface that is susceptible to evaporative cooling and the heating of the surface-emitted longwave radiation (Garrett et al 2010;Ravichandran, Meiburg & Govindarajan 2020). The coupling of the cloud bottom to the cloud-top instability is also an important topic.…”

Section: Discussionmentioning

confidence: 99%

A linear stability analysis of two-layer moist convection with a saturation interface

2021

J. Fluid Mech.

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The linear convective instability of a mixture of dry air, water vapour and liquid water, with a stable unsaturated layer residing on an unstable saturated layer, is studied. It may serve as a prototype model for understanding the instability that causes mixing at the top of stratocumulus cloud or fog. Such a cloud-clear air interface is modelled as an infinitely thin saturation interface where radiative and evaporative cooling take place. The interface position is determined by the Clausius–Clapeyron equation, and can undulate with the evolution of moisture and temperature. In the small-amplitude regime two physical mechanisms are revealed. First, the interface undulation leads to the undulation of the cooling source, which destabilizes the system by superposing a vertical dipole heating anomaly on the convective cell. Second, the evolution of the moisture field induces non-uniform evaporation at the interface, which stabilizes the system by introducing a stronger evaporative cooling in the ascending region and vice versa in the descending region. These two mechanisms are competing, and their relative contribution to the instability is quantified by theoretically estimating their relative contribution to buoyancy flux tendency. When there is only evaporative cooling, the two mechanisms break even, and the marginal stability curve remains the same as the classic two-layer Rayleigh–Bénard convection with a fixed cooling source.

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“…This effect is quantified by the Stokes number St = τ p /τ f , which indicates how important the inertial effects are for a given droplet size. For droplets with small Stokes numbers (typically less than 50µm in diameter), it may be possible to coarse-grain them in the form of an Eulerian field for the liquid content (i.e., r l = r l (x, y, z, t)), while still retaining the inertial effects [34,35]. This, in essence, is the Eulerian approximation for liquid droplets which we use in this work.…”

Section: Eulerian Treatment Of Dropletsmentioning

confidence: 99%

“…This, in essence, is the Eulerian approximation for liquid droplets which we use in this work. Such an approximation is commonly known as the one-moment scheme in the atmospheric cloud literature (see, e.g., [34,35]). When the inertial effects are retained, the velocity field of the droplets is not divergence-free, but obeys a compressible advection equation.…”

Section: Eulerian Treatment Of Dropletsmentioning

confidence: 99%

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Direct numerical simulation of a moist cough flow using Eulerian approximation for liquid droplets

Singhal,

Ravichandran,

Diwan

2021

Preprint

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The COVID-19 pandemic has inspired several studies on the fluid dynamics of respiratory events. Here, we propose a computational approach in which respiratory droplets are coarse-grained into an Eulerian liquid field advected by the fluid streamlines. A direct numerical simulation is carried out for a moist cough using a closure model for space-time dependence of the evaporation time scale. Estimates of the Stokes number are provided, for the initial droplet size of 10µm, which are found to be << 1 thereby justifying the neglect of droplet inertia. Several of the important features of the moist-cough flow reported in the literature using Lagrangian tracking methods have been accurately captured using our scheme. Some new results are presented, including the evaporation time for a "mild" cough, a saturation-temperature diagram and a favourable correlation between the vorticity and liquid fields. The present approach is particularly useful for studying the long-range transmission of virus-laden droplets.

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Mammatus cloud formation by settling and evaporation

Abstract: Abstract

Cited by 19 publications

References 24 publications

Melting driven by rotating Rayleigh–Bénard convection

Melting driven by rotating Rayleigh–Bénard convection

A linear stability analysis of two-layer moist convection with a saturation interface

Direct numerical simulation of a moist cough flow using Eulerian approximation for liquid droplets

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