An observational study of the structure of stratiform cloud sheets: Part II. Entrainment

Nicholls, S.; Turton, Jon

doi:10.1002/qj.49711247210

Cited by 144 publications

(88 citation statements)

References 33 publications

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“…A lower subsidence velocity would therefore lead to a more rapid deepening of the boundary layer if the entrainment velocity would remain unaffected. This deepening would increase decoupling of the boundary layer (Park et al, 2004;Wood and Bretherton, 2004) and therefore it was hypothesized that weaker subsidence would increase the pace of stratocumulus transitions (e.g. Wyant et al, 1997;Bretherton et al, 1999).…”

Section: Introductionmentioning

confidence: 99%

How large-scale subsidence affects stratocumulus transitions

2016

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Abstract. Some climate modeling results suggest that the Hadley circulation might weaken in a future climate, causing a subsequent reduction in the large-scale subsidence velocity in the subtropics. In this study we analyze the cloud liquid water path (LWP) budget from large-eddy simulation (LES) results of three idealized stratocumulus transition cases, each with a different subsidence rate. As shown in previous studies a reduced subsidence is found to lead to a deeper stratocumulus-topped boundary layer, an enhanced cloud-top entrainment rate and a delay in the transition of stratocumulus clouds into shallow cumulus clouds during its equatorwards advection by the prevailing trade winds. The effect of a reduction of the subsidence rate can be summarized as follows. The initial deepening of the stratocumulus layer is partly counteracted by an enhanced absorption of solar radiation. After some hours the deepening of the boundary layer is accelerated by an enhancement of the entrainment rate. Because this is accompanied by a change in the cloudbase turbulent fluxes of moisture and heat, the net change in the LWP due to changes in the turbulent flux profiles is negligibly small.

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Section: Introductionmentioning

confidence: 99%

How large-scale subsidence affects stratocumulus transitions

2016

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“…The key to the problem is in understanding mixing across the entrainment interface layer (EIL) located between the FT and the STBL (e.g., Caughey et al, 1982;Nicholls and Turton, 1986;Lenschow et al, 2000;Gerber et al, 2005). 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.…”

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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“…Turbulence plays a central role in the life cycle of clouds by influencing their formation, maintenance, and dissipation processes (Nicholls and Turton, 1986;Bretherton et al, 2004). Mixing associated with turbulent motions is responsible for entrainment (Nicholls and Turton, 1986;Stevens, 2002), which has direct bearing on the aerosols and moisture available to a cloud layer and thereby the cloud microphysical composition.…”

Section: Introductionmentioning

confidence: 99%

“…Mixing associated with turbulent motions is responsible for entrainment (Nicholls and Turton, 1986;Stevens, 2002), which has direct bearing on the aerosols and moisture available to a cloud layer and thereby the cloud microphysical composition. Vertical mixing also shapes the atmospheric thermodynamic structure within which a cloud exists.…”

Section: Introductionmentioning

confidence: 99%

Evaluation of turbulent dissipation rate retrievals from Doppler Cloud Radar

2012

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Abstract. Turbulent dissipation rate retrievals from cloud radar Doppler velocity measurements are evaluated using independent, in situ observations in Arctic stratocumulus clouds. In situ validation data sets of dissipation rate are derived using sonic anemometer measurements from a tethered balloon and high frequency pressure variation observations from a research aircraft, both flown in proximity to stationary, ground-based radars. Modest biases are found among the data sets in particularly low-or high-turbulence regimes, but in general the radar-retrieved values correspond well with the in situ measurements. Root mean square differences are typically a factor of 4-6 relative to any given magnitude of dissipation rate. These differences are no larger than those found when comparing dissipation rates computed from tetheredballoon and meteorological tower-mounted sonic anemometer measurements made at spatial distances of a few hundred meters. Temporal lag analyses suggest that approximately half of the observed differences are due to spatial sampling considerations, such that the anticipated radar-based retrieval uncertainty is on the order of a factor of 2-3. Moreover, radar retrievals are clearly able to capture the vertical dissipation rate structure observed by the in situ sensors, while offering substantially more information on the time variability of turbulence profiles. Together these evaluations indicate that radar-based retrievals can, at a minimum, be used to determine the vertical structure of turbulence in Arctic stratocumulus clouds.

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An observational study of the structure of stratiform cloud sheets: Part II. Entrainment

Cited by 144 publications

References 33 publications

How large-scale subsidence affects stratocumulus transitions

How large-scale subsidence affects stratocumulus transitions

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

Evaluation of turbulent dissipation rate retrievals from Doppler Cloud Radar

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