Subsiding Shells around Shallow Cumulus Clouds

Heus, Thijs; Jonker, Harm J. J.

doi:10.1175/2007jas2322.1

Cited by 185 publications

(194 citation statements)

References 32 publications

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“…This can be interpreted either as indicative of strongly inhomogeneous mixing or homogeneous mixing with "environmental" air that is very similar in its thermodynamic properties to the cloud. The latter could be due to, for example, mixing with humid air in subsiding shells (e.g., Heus and Jonker, 2008).…”

Section: Effects Of Differences In Cloud Microphysics On Turbulent MImentioning

confidence: 99%

The fine-scale structure of the trade wind cumuli over Barbados – an introduction to the CARRIBA project

et al. 2013

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Abstract. The CARRIBA (Cloud, Aerosol, Radiation and tuRbulence in the trade wInd regime over BArbados) project, focused on high resolution and collocated measurements of thermodynamic, turbulent, microphysical, and radiative properties of trade wind cumuli over Barbados, is introduced. The project is based on two one-month field campaigns in November 2010 (climatic wet season) and April 2011 (climatic dry season). Observations are based on helicopterborne and ground-based measurements in an area of 100 km 2 off the coast of Barbados. CARRIBA is accompanied by long-term observations at the Barbados Cloud Observatory located at the East coast of Barbados since early in 2010 and which provides a longer-term context for the CARRIBA measurements. The deployed instrumentation and sampling strategy are presented together with a classification of the meteorological conditions. The two campaigns were influenced by different air masses advected from the Caribbean area, the Atlantic Ocean, and the African continent which led to distinct aerosol conditions. Pristine conditions with low aerosol particle number concentrations of ∼100 cm 3 were alternating with periods influenced by Saharan dust or aerosol from biomass burning resulting in comparably high number concentrations of ∼ 500 cm 3 . The biomass burning aerosol was originating from both the Caribbean area and Africa. The shallow cumulus clouds responded to the different aerosol conditions with a wide range of mean droplet sizes and number concentrations. Two days with different aerosol and cloud microphysical properties but almost identical meteorological conditions have been analyzed in detail. The differences in the droplet number concentration and droplet sizes appear not to show any significant change for turbulent cloud mixing, but the relative roles of droplet inertia and sedimentation in initiating coalescence, as well as the cloud reflectivity, do change substantially.

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Section: Effects Of Differences In Cloud Microphysics On Turbulent MImentioning

confidence: 99%

The fine-scale structure of the trade wind cumuli over Barbados – an introduction to the CARRIBA project

et al. 2013

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“…Some previous studies have demonstrated clouds' alteration of their environment (Zhao and Austin, 2005;Heus and Jonker, 2008;Malkus, 1954;Lee et al, 2014;Zuidema et al, 2012;Roesner et al, 1990). One example of such an effect is the "preconditioning" or "cloud-deepening" effect (Nitta and Esbensen, 1974;Roesner et al, 1990;Stevens, 2007;Stevens and Seifert, 2008), where clouds cool and moisten the upper cloudy and inversion layers and in this way encourage the development of the next generation of clouds that encounter improved environmental conditions.…”

Section: Introductionmentioning

confidence: 99%

Time-dependent, non-monotonic response of warm convective cloud fields to changes in aerosol loading

et al. 2017

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Abstract. Large eddy simulations (LESs) with bin microphysics are used here to study cloud fields' sensitivity to changes in aerosol loading and the time evolution of this response. Similarly to the known response of a single cloud, we show that the mean field properties change in a nonmonotonic trend, with an optimum aerosol concentration for which the field reaches its maximal water mass or rain yield. This trend is a result of competition between processes that encourage cloud development versus those that suppress it. However, another layer of complexity is added when considering clouds' impact on the field's thermodynamic properties and how this is dependent on aerosol loading. Under polluted conditions, rain is suppressed and the non-precipitating clouds act to increase atmospheric instability. This results in warming of the lower part of the cloudy layer (in which there is net condensation) and cooling of the upper part (net evaporation). Evaporation at the upper part of the cloudy layer in the polluted simulations raises humidity at these levels and thus amplifies the development of the next generation of clouds (preconditioning effect). On the other hand, under clean conditions, the precipitating clouds drive net warming of the cloudy layer and net cooling of the sub-cloud layer due to rain evaporation. These two effects act to stabilize the atmospheric boundary layer with time (consumption of the instability). The evolution of the field's thermodynamic properties affects the cloud properties in return, as shown by the migration of the optimal aerosol concentration toward higher values.

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“…(Stevens 2005). A significant portion of cloud research that has occurred has focused on understanding and parameterizing the transport and mixing associated with shallow cumulus and their roots within the subcloud layer (e.g., LeMone and Pennell 1976;Nicholls and LeMone 1980;Nicholls et al 1982;Tiedtke et al 1988;Siebesma 1998;Brown et al 2002;Soares et al 2004;Bellon and Stevens 2005;Zhao and Austin 2005a,b;Stevens 2007;Bretherton and Park 2008;Heus and Jonker 2008;Stechmann and Stevens 2010). However, even though the impact of cumulus convection on surface fluxes has been shown to significantly affect larger-scale circulations (Betts and Ridgway 1988) and the skill of medium-range weather forecasts (Tiedtke 1989), the coupling between shallow cumulus and the land surface deserves further analysis.…”

Section: Introductionmentioning

confidence: 99%

Surface Energy Balance and Buoyancy Response to Shallow Cumulus Shading

Lohou

Patton

2014

Journal of the Atmospheric Sciences

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The interactions surrounding the coupling between surface energy balance and a boundary layer with shallow cumuli are investigated using the National Center for Atmospheric Research's large-eddy simulation code coupled to the Noah land surface model. The simulated cloudy boundary layer is based on the already well-documented and previously simulated 21 June 1997 case at the Atmospheric Radiation Measurement Southern Great Plains central facility. The surface energy balance response to cloud shading is highly nonlinear, leading to different partitioning between sensible and latent heat flux compared to the surface not impacted by cloud. The evaporative fraction increases by about 2%-3% in the presence of shallow cumuli at the regional scale but can increase by up to 30% at any individual location. As expected, the cloud's reduction of solar irradiance largely controls the surface's response. However, the turbulence and secondary circulations associated with the cloud dynamics increases the surface flux variability. Even though they are less than 1 km in horizontal scale, the cloud-induced surface heterogeneities impact the vertical flux of heat and moisture up to approximately 20% of the height of the subcloud layer z sl , higher than the surface layer's typical extent. Above 0.2z sl , the cloud root tends to amplify the drying and the cooling of the subcloud layer. Near the entrainment zone, the cloud-induced latent heat flux increase and sensible heat flux decrease compensate each other with respect to total buoyancy and therefore do not significantly modify the subcloudlayer entrainment rate over large time scales.

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Subsiding Shells around Shallow Cumulus Clouds

Cited by 185 publications

References 32 publications

The fine-scale structure of the trade wind cumuli over Barbados – an introduction to the CARRIBA project

The fine-scale structure of the trade wind cumuli over Barbados – an introduction to the CARRIBA project

Time-dependent, non-monotonic response of warm convective cloud fields to changes in aerosol loading

Surface Energy Balance and Buoyancy Response to Shallow Cumulus Shading

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