A statistical approach to the life cycle analysis of cumulus clouds selected in a virtual reality environment

Heus, Thijs; Jonker, Harm J. J.; Akker, H.E.A. van den; Griffith, Eric J.; Koutek, Michal; Post, Frits H.

doi:10.1029/2008jd010917

Cited by 60 publications

(78 citation statements)

References 56 publications

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“…3. It should be noted that the decrease in f ad is not monotonic, and shows evidence of pulsating growth as discussed in Heus et al (2009). Although the LES model output in this study is sampled only every 5 min, which is similar to the time scale of pulses, the nonmonotonic evolution of f ad is consistent with the concept that a cloud can be seen as a sequence of pulses (French et al, 1999;Heus et al, 2009).…”

Section: Difference Of R E Profiles In Growing and Decaying Cloudssupporting

confidence: 61%

Vertical profiles of droplet effective radius in shallow convective clouds

2011

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Abstract. Conventional satellite retrievals can only provide information on cloud-top droplet effective radius (r e ). Given the fact that cloud ensembles in a satellite snapshot have different cloud-top heights, Rosenfeld and Lensky (1998) used the cloud-top height and the corresponding cloud-top r e from the cloud ensembles in the snapshot to construct a profile of r e representative of that in the individual clouds. This study investigates the robustness of this approach in shallow convective clouds based on results from large-eddy simulations (LES) for clean (aerosol mixing ratio N a = 25 mg −1 ), intermediate (N a = 100 mg −1 ), and polluted (N a = 2000 mg −1 ) conditions. The cloud-top height and the cloud-top r e from the modeled cloud ensembles are used to form a constructed r e profile, which is then compared to the in-cloud r e profiles. For the polluted and intermediate cases where precipitation is negligible, the constructed r e profiles represent the in-cloud r e profiles fairly well with a low bias (about 10 %). The method used in Rosenfeld and Lensky (1998) is therefore validated for nonprecipitating shallow cumulus clouds. For the clean, drizzling case, the in-cloud r e can be very large and highly variable, and quantitative profiling based on cloudtop r e is less useful. The differences in r e profiles between clean and polluted conditions derived in this manner are however, distinct. This study also investigates the subadiabatic characteristics of the simulated cumulus clouds to reveal the effect of mixing on r e and its evolution. Results indicate that as polluted and moderately polluted clouds develop into their decaying stage, the subadiabatic fraction f ad becomes smaller, representing a higher degree of mixing, and r e becomes smaller (∼10 %) and more variable. However, for the clean case, smaller f ad corresponds to larger r e (and largerCorrespondence to: H. Xue (hxue@pku.edu.cn) r e variability), reflecting the additional influence of droplet collision-coalescence and sedimentation on r e . Finally, profiles of the vertically inhomogeneous clouds as simulated by the LES and those of the vertically homogeneous clouds are used as input to a radiative transfer model to study the effect of cloud vertical inhomogeneity on shortwave radiative forcing. For clouds that have the same liquid water path, r e of a vertically homogeneous cloud must be about 76-90 % of the cloud-top r e of the vertically inhomogeneous cloud in order for the two clouds to have the same shortwave radiative forcing.

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Section: Difference Of R E Profiles In Growing and Decaying Cloudssupporting

confidence: 61%

Vertical profiles of droplet effective radius in shallow convective clouds

2011

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“…Rather surprisingly, the total downward mass flux in the cloud shells was found to compensate virtually all the total upward mass flux of the cloud field, not so much due to the negative velocity in the shell (which is rather modest compared to the upward velocity in the cloud core), but rather due to the large area that is associated with the cloud-edge region. This view was confirmed in an observational study by Heus et al (2009a), who analysed RICO (Rain in Cumulus over the Ocean) data, adopting the strategy of conditionally averaging quantities with respect to the distance to the cloud edge.…”

Section: Relevance Of the Near Vicinity Of Cloudsmentioning

confidence: 69%

“…Observations (e.g. Ludlam and Scorer, 1953) as well as LES (Zhao and Austin, 2005a;Heus et al, 2009a) show that especially large clouds (with longer life times) are a succession of bubbles rising from roughly the same place, each penetrating further than its predecessor. This will result in an inhomogeneous interior of individual plumes.…”

Section: Steady-plume Assumptionmentioning

confidence: 99%

“…Observational studies by, for example, Jonas (1990), Rodts et al (2003) and more recently by Wang et al (2009) and Heus et al (2009a), reveal how the (thermo)dynamic and microphysical properties of the near-cloud environment differ significantly from the environmental properties further away from the cloud. Studying individual cloud transects, Jonas (1990) noted the presence of a thin shell of subsiding air surrounding clouds and pointed out the importance of it for understanding the droplet spectrum in clouds, taking into account that the shell in principle could contain air with cloud-top properties.…”

Section: Relevance Of the Near Vicinity Of Cloudsmentioning

confidence: 99%

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Entrainment and detrainment in cumulus convection: an overview

Rooy

Bechtold

Fröhlich

et al. 2012

Quart J Royal Meteoro Soc

294

256

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Entrainment and detrainment processes have been recognised for a long time as key processes for cumulus convection and have recently witnessed a regrowth of interest mainly due to the capability of large-eddy simulations (LES) to diagnose these processes in more detail. This article has a twofold purpose. Firstly, it provides a historical overview of the past research on these mixing processes, and secondly, it highlights more recent important developments. These include both fundamental process studies using LES aiming to improve our understanding of the mixing process, but also more practical studies targeted toward an improved parametrised representation of entrainment and detrainment in large-scale models. A highlight of the fundamental studies resolves a long-lasting controversy by showing that lateral entrainment is the dominant mixing mechanism in comparison with the cloud-top entrainment in shallow cumulus convection. The more practical studies provide a wide variety of new parametrisations with sometimes conflicting approaches to the way in which the effect of the free tropospheric humidity on the lateral mixing is taken into account. An important new insight that will be highlighted is that, despite the focus in the literature on entrainment, it appears that it is rather the detrainment process that determines the vertical structure of the convection in general and the mass flux especially. Finally, in order to speed up progress and stimulate convergence in future parametrisations, stronger and more systematic use of LES is advocated.

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“…Even this measure, though, is not perfect. Cloud life phases do not take equal amounts of non-dimensional time -the dissipation phase can happen gradually or catastrophically; rejuvenating pulses of buoyant air can occur in existing clouds, essentially reverting lucky clouds to the youthful growth phase (Heus et al, 2009).…”

Section: Introductionmentioning

confidence: 99%

On clocks and clouds

2014

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Abstract. Cumulus clouds exhibit a life cycle that consists of (a) the growth phase (increasing size, most notably in the vertical direction); (b) the mature phase (growth ceases; any precipitation that develops is strongest during this period); and (c) the dissipation phase (cloud dissipates because of precipitation and/or entrainment; no more dynamical support). Although radar can track clouds over time and give some sense of the age of a cloud, most aircraft in situ measurements lack temporal context. We use large eddy simulations of trade wind cumulus cloud fields from cases during the Barbados Oceanographic and Meteorological Experiment (BOMEX) and Rain In Cumulus over the Ocean (RICO) campaigns to demonstrate a potential cumulus cloud "clock." We find that the volume-averaged total water mixing ratio r t is a useful cloud clock for the 12 clouds studied. A cloud's initial r t is set by the subcloud mixed-layer mean r t and decreases monotonically from the initial value due primarily to entrainment. The clock is insensitive to aerosol loading, environmental sounding and extrinsic cloud properties such as lifetime and volume. In some cases (more commonly for larger clouds), multiple pulses of buoyancy occur, which complicate the cumulus clock by replenishing r t . The clock is most effectively used to classify clouds by life phase.

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A statistical approach to the life cycle analysis of cumulus clouds selected in a virtual reality environment

Cited by 60 publications

References 56 publications

Vertical profiles of droplet effective radius in shallow convective clouds

Vertical profiles of droplet effective radius in shallow convective clouds

Entrainment and detrainment in cumulus convection: an overview

On clocks and clouds

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