Small scale mixing processes at the top of a marine stratocumulus—a case study

Haman, Krzysztof E.; Malinowski, Szymon P.; Kurowski, Marcin J.; Gerber, H.; Brenguier, Jean‐Louis

doi:10.1002/qj.5

Cited by 72 publications

(89 citation statements)

References 35 publications

(36 reference statements)

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“…Direct mixing between air from above the inversion and the quasi-adiabatic cloud is not common and the cloud-top entrainment instability criterion should not be applied to free tropospheric air and quasi-adiabatic cloud volumes. More detailed analysis of the small-scale structure of mixing by Haman et al (2007) confirms the presence of an entrainment interfacial layer and mixing between this layer and the cloud. A survey of LES of stratocumulus by Stevens (2002) showed that entrainment rates diagnosed from LES results can vary by up to a factor of two.…”

Section: Entrainment In Stratocumulusmentioning

confidence: 74%

“…Warner, 1955, 1969a, 1969b, Blyth et al, 1988Gerber et al, 2005Gerber et al, , 2008Burnet and Brenguier, 2007;Haman et al, 2007) tend to show that stratocumulus is only slightly diluted by entrainment, whereas cumulus is much more strongly diluted. In cumulus clouds the droplet number concentration is less reduced by entrainment than the liquid water content because the majority of droplets exhibit some evaporation.…”

Section: Homogeneous and Inhomogeneous Mixingmentioning

confidence: 96%

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Droplet growth in warm turbulent clouds

Devenish

Bartello

Brenguier

et al. 2012

Quart J Royal Meteoro Soc

243

281

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In this survey we consider the impact of turbulence on cloud formation from the cloud scale to the droplet scale. We assess progress in understanding the effect of turbulence on the condensational and collisional growth of droplets and the effect of entrainment and mixing on the droplet spectrum. The increasing power of computers and better experimental and observational techniques allow for a much more detailed study of these processes than was hitherto possible. However, much of the research necessarily remains idealized and we argue that it is those studies which include such fundamental characteristics of clouds as droplet sedimentation and latent heating that are most relevant to clouds. Nevertheless, the large body of research over the last decade is beginning to allow tentative conclusions to be made. For example, it is unlikely that small-scale turbulent eddies (i.e. not the energy-containing eddies) alone are responsible for broadening the droplet size spectrum during the initial stage of droplet growth due to condensation. It is likely, though, that small-scale turbulence plays a significant role in the growth of droplets through collisions and coalescence. Moreover, it has been possible through detailed numerical simulations to assess the relative importance of different processes to the turbulent collision kernel and how this varies in the parameter space that is important to clouds. The focus of research on the role of turbulence in condensational and collisional growth has tended to ignore the effect of entrainment and mixing and it is arguable that they play at least as important a role in the evolution of the droplet spectrum. We consider the role of turbulence in the mixing of dry and cloudy air, methods of quantifying this mixing and the effect that it has on the droplet spectrum. Copyright

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Section: Entrainment In Stratocumulusmentioning

confidence: 74%

Section: Homogeneous and Inhomogeneous Mixingmentioning

confidence: 96%

Droplet growth in warm turbulent clouds

Devenish

Bartello

Brenguier

et al. 2012

Quart J Royal Meteoro Soc

243

281

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“…For example, during the DYCOMS-II experiment (e.g., Haman et al 2007) a similar approach led to the estimate of an entrainment interface layer from 0 to 70 m thick, based on high-resolution LW C and temperature measurements. It is important to recognize, however, that the ACTOS profiles should be interpreted somewhat differently because of the relative flight speeds.…”

Section: Discussionmentioning

confidence: 99%

“…Large-eddy simulation (LES) demonstrates that this conditioned layer is almost always present above stratocumulus cloud tops and that its maintenance is related to 'local' shear effects due to convective eddies (Moeng et al 2005). High spatial resolution measurements have provided further characterization of what has been termed the "entrainment interface layer," consisting of filaments of clear and cloudy air over a wide range of sizes down to the instrument resolution of 0.1 m Haman et al 2007). Based on those measurements it was suggested that after multiple mixing events the entrainment interface layer becomes conditioned to the extent that there is near buoyancy match with the air at cloud top .…”

Section: Introductionmentioning

confidence: 99%

Observation of a Self-Limiting, Shear-Induced Turbulent Inversion Layer Above Marine Stratocumulus

Katzwinkel

Siebert

Shaw

2011

Boundary-Layer Meteorol

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High-resolution measurements of thermodynamic, microphysical, and turbulence properties inside a turbulent inversion layer above a marine stratocumulus cloud layer are presented. The measurements are performed with the helicopter-towed measurement payload Airborne Cloud Turbulence Observation System (ACTOS), which allows for sampling with low true air speeds and steep profiles through cloud top. Vertical profiles show that the turbulent inversion layer consists of clear air above the cloud top, with nearly linear profiles of potential temperature, horizontal wind speed, absolute humidity, and concentration of interstitial aerosol. The layer is turbulent, with an energy dissipation rate nearly the same as that in the lower cloud, suggesting that the two are actively coupled, but with significant anisotropic turbulence at the large scales within the turbulent inversion layer. The turbulent inversion layer is traversed six times and the layer thickness is observed to vary between 37 and 85 m, whereas the potential temperature and horizontal wind speed differences at the top and bottom of the layer remain essentially constant. The Richardson number therefore increases with increasing layer thickness, from approximately 0.2 to 0.7, suggesting that the layer develops to the point where shear production of turbulence is sufficiently weak to be balanced by buoyancy suppression. This picture is consistent with prior numerical simulations of the evolution of turbulence in localized stratified shear layers. It is observed that the large eddy scale is suppressed by buoyancy and is on the order of the Ozmidov scale, much less than the thickness of the turbulent inversion layer, such that direct mixing between the cloud top and the free troposphere is inhibited, and the entrainment velocity tends to decrease with increasing turbulent inversion-layer thickness. Qualitatively, the turbulent inversion layer likely grows through nibbling rather than engulfment.

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“…Data from in situ measurements (e.g., Caughey et al, 1982;Nicholls, 1989;Lenschow et al, 2000;De Roode and Wang, 2007) and the results of numerical simulations (e.g., Moeng et al, 2005;Yamaguchi and Randall, 2008) clearly indicate that the top of Sc is located below the capping inversion and does not directly interact with the FT above. The thickness of the EIL, related to the distance between the cloud top and inversion, varies from a few meters to a few tens of meters (e.g., Haman et al, 2007;Kurowski et al, 2009;Katzwinkel et al, 2012), and differs for different Sc cases (Carman et al, 2012).…”

Section: Introductionmentioning

confidence: 99%

Physics of Stratocumulus Top (POST): turbulent mixing across capping inversion

et al. 2013

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Abstract. High spatial resolution measurements of temperature and liquid water content, accompanied by moderateresolution measurements of humidity and turbulence, collected during the Physics of Stratocumulus Top experiment are analyzed. Two thermodynamically, meteorologically and even optically different cases are investigated. An algorithmic division of the cloud-top region into layers is proposed. Analysis of dynamic stability across these layers leads to the conclusion that the inversion capping the cloud and the cloud-top region is turbulent due to the wind shear, which is strong enough to overcome the high static stability of the inversion. The thickness of this mixing layer adapts to wind and temperature jumps such that the gradient Richardson number stays close to its critical value. Turbulent mixing governs transport across the inversion, but the consequences of this mixing depend on the thermodynamic properties of cloud top and free troposphere. The effects of buoyancy sorting of the mixed parcels in the cloud-top region are different in conditions that permit or prevent cloud-top entrainment instability. Removal of negatively buoyant air from the cloud top is observed in the first case, while buildup of the diluted cloud-top layer is observed in the second one.

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Small scale mixing processes at the top of a marine stratocumulus—a case study

Cited by 72 publications

References 35 publications

Droplet growth in warm turbulent clouds

Droplet growth in warm turbulent clouds

Observation of a Self-Limiting, Shear-Induced Turbulent Inversion Layer Above Marine Stratocumulus

Physics of Stratocumulus Top (POST): turbulent mixing across capping inversion

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