The behavior of trade‐wind cloudiness in observations and models: The major cloud components and their variability

Nuijens, Louise; Medeiros, Brian; Sandu, Irina; Ahlgrimm, Maike

doi:10.1002/2014ms000390

Cited by 66 publications

(85 citation statements)

References 35 publications

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“…The AMIP framework provides a test of the atmospheric component of climate models given a realistic SST distribution. Monthly average output is used during the interval 1979-2005; using monthly mean output limits some interpretation of relationships between clouds and their environment because much of the variance is associated with faster timescales (12,24).…”

Section: Climate Modelsmentioning

confidence: 99%

“…3 are the profiles of CF in the Barbados region during the summer and winter months, and, as seen above, the profiles show the clouds differ with season in the Barbados region as the regional circulation changes. In both seasons, there are frequent low-level clouds with maxima near the lifted condensation level (LCL) and higher up near the trade inversion (6,24). The dotted lines in Fig.…”

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confidence: 91%

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Clouds at Barbados are representative of clouds across the trade wind regions in observations and climate models

Medeiros

Nuijens

2016

Proc. Natl. Acad. Sci. U.S.A.

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Trade wind regions cover most of the tropical oceans, and the prevailing cloud type is shallow cumulus. These small clouds are parameterized by climate models, and changes in their radiative effects strongly and directly contribute to the spread in estimates of climate sensitivity. This study investigates the structure and variability of these clouds in observations and climate models. The study builds upon recent detailed model evaluations using observations from the island of Barbados. Using a dynamical regimes framework, satellite and reanalysis products are used to compare the Barbados region and the broader tropics. It is shown that clouds in the Barbados region are similar to those across the trade wind regions, implying that observational findings from the Barbados Cloud Observatory are relevant to clouds across the tropics. The same methods are applied to climate models to evaluate the simulated clouds. The models generally capture the cloud radiative effect, but underestimate cloud cover and show an array of cloud vertical structures. Some models show strong biases in the environment of the Barbados region in summer, weakening the connection between the regional biases and those across the tropics. Even bearing that limitation in mind, it is shown that covariations of cloud and environmental properties in the models are inconsistent with observations. The models tend to misrepresent sensitivity to moisture variations and inversion characteristics. These model errors are likely connected to cloud feedback in climate projections, and highlight the importance of the representation of shallow cumulus convection.trade wind clouds | climate models | shallow cumulus | Barbados I s the cloud structure and variability observed at a single location over a long time representative of more general regimes of clouds? This is the conceit of long-term observational "super sites" but has rarely been evaluated (1, 2). This work focuses on clouds found in trade wind regions, which are mostly shallow cumulus, and asks whether findings from the Barbados Cloud Observatory (BCO) are generalizable to the broader tropics in observations and climate models. We will evaluate cloud properties and the environment in which the clouds form across 12 climate models within these regions. This emphasis on the trades is motivated by several factors: (i) Previous studies suggest these are the regions that lead to much of the spread in estimates of climate sensitivity (3, 4), (ii) there is a dearth of evaluation of shallow cumulus in climate models (5), and (iii) space-based and ground-based observations of the trades have recently become available (6-8). This focus on trade wind regions is unique but builds upon previous, broader model evaluations that have, among other things, shown improvements in near-global cloud properties in the latest generation of climate models (9) and provided an overview of the vertical structure of cloud fraction (CF) and cloud water content over tropical oceans (10). Ref. 11 explores low-level, tropical clou...

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Section: Climate Modelsmentioning

confidence: 99%

mentioning

confidence: 91%

Clouds at Barbados are representative of clouds across the trade wind regions in observations and climate models

Medeiros

Nuijens

2016

Proc. Natl. Acad. Sci. U.S.A.

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“…On the contrary, in large-eddy simulations (LES) and in observations the cloud-base fraction of trade-wind cumuli appears to be much more resilient to changes in environmental conditions than in climate models, both in the current (Nuijens et al 2014(Nuijens et al , 2015a and projected warmer climate (Rieck et al 2012;Bretherton 2015). Interpreting these results remains difficult.…”

Section: Introductionmentioning

confidence: 99%

“…The cloud amount predicted by LES, though often resilient to changes in thermodynamic conditions, is known to be sensitive to various aspects of the simulation such as resolution, microphysics, numerics or domain size (Vial et al 2017, and references therein). Theoretically, the apparent resilience of cloud-base cloud fraction has been interpreted as the consequence of a ''cumulus-valve mechanism'' whereby clouds act as a valve which helps maintain the top of the subcloud layer close to the lifting condensation level and thus regulate the area covered by cumulus updrafts at cloud base (Albrecht et al 1979;Neggers et al 2006;Stevens 2006;Nuijens et al 2015a). However, this idea has not been tested observationally.…”

Section: Introductionmentioning

confidence: 99%

EUREC4A: A Field Campaign to Elucidate the Couplings Between Clouds, Convection and Circulation

et al. 2017

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Trade-wind cumuli constitute the cloud type with the highest frequency of occurrence on Earth, and it has been shown that their sensitivity to changing environmental conditions will critically influence the magnitude and pace of future global warming. Research over the last decade has pointed out the importance of the interplay between clouds, convection and circulation in controling this sensitivity. 123Surv Geophys (2017) 38:1529-1568 https://doi.org/10.1007/s10712-017-9428-0 cumuli at cloud base is very sensitive to changes in environmental conditions, while process models suggest the opposite. To understand and resolve this contradiction, we propose to organize a field campaign aimed at quantifying the physical properties of tradecumuli (e.g., cloud fraction and water content) as a function of the large-scale environment. Beyond a better understanding of clouds-circulation coupling processes, the campaign will provide a reference data set that may be used as a benchmark for advancing the modelling and the satellite remote sensing of clouds and circulation. It will also be an opportunity for complementary investigations such as evaluating model convective parameterizations or studying the role of ocean mesoscale eddies in air-sea interactions and convective organization.

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“…Specific limitations of modeled clouds include both features which differ from what one observes (e.g., ''too few, too bright,'' [Webb et al, 2001;Nam et al, 2012]) as well as features which are inadequately understood (e.g., controls on cloud vertical structure [Nuijens et al, 2015], and organization [Bretherton et al, 2005;Muller and Held, 2012;Wing and Emanuel, 2014]). An important component of these limitations is the delicacy of the interactions between clouds and circulations Sherwood et al, 2014].…”

Section: Introductionmentioning

confidence: 99%

Radiative convective equilibrium as a framework for studying the interaction between convection and its large‐scale environment

Silvers

Stevens

Mauritsen

et al. 2016

J Adv Model Earth Syst

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An uncertain representation of convective clouds has emerged as one of the key barriers to our understanding of climate sensitivity. The large gap in resolved spatial scales between General Circulation Models (GCMs) and high resolution models has made a systematic study of convective clouds across model configurations difficult. It is shown here that the simulated atmosphere of a GCM in Radiative Convective Equilibrium (RCE) is sufficiently similar across a range of domain sizes to justify the use of RCE to study both a GCM and a high resolution model on the same domain with the goal of improved constraints on the parameterized clouds. Simulations of RCE with parameterized convection have been analyzed on domains with areas spanning more than two orders of magnitude ( ), all having the same grid spacing of . The simulated climates on different domains are qualitatively similar in their degree of convective organization, the precipitation rates, and the vertical structure of the clouds and water vapor, with the similarity increasing as the domain size increases. Sea surface temperature perturbation experiments are used to estimate the climate feedback parameter for the differently configured experiments, and the cloud radiative effect is computed to examine the role which clouds play in the response. Despite the similar climate states between the domains the feedback parameter varies by more than a factor of two; the hydrological sensitivity parameter is better behaved, varying by a factor of 1.4. The sensitivity of the climate feedback parameter to domain size is related foremost to a nonsystematic response of low‐level clouds as well as an increasingly negative longwave feedback on larger domains.

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The behavior of trade‐wind cloudiness in observations and models: The major cloud components and their variability

Cited by 66 publications

References 35 publications

Clouds at Barbados are representative of clouds across the trade wind regions in observations and climate models

Clouds at Barbados are representative of clouds across the trade wind regions in observations and climate models

EUREC4A: A Field Campaign to Elucidate the Couplings Between Clouds, Convection and Circulation

Radiative convective equilibrium as a framework for studying the interaction between convection and its large‐scale environment

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