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  • 1
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    Minimal Recipes for Global Cloudiness (2022)
    Details
    Publication Date: 2023-12-05
    Description: Clouds are primary modulators of Earth's energy balance. It is thus important to understand the links connecting variabilities in cloudiness to variabilities in other state variables of the climate system, and also describe how these links would change in a changing climate. A conceptual model of global cloudiness can help elucidate these points. In this work we derive simple representations of cloudiness, that can be useful in creating a theory of global cloudiness. These representations illustrate how both spatial and temporal variability of cloudiness can be expressed in terms of basic state variables. Specifically, cloud albedo is captured by a nonlinear combination of pressure velocity and a measure of the low‐level stability, and cloud longwave effect is captured by surface temperature, pressure velocity, and standard deviation of pressure velocity. We conclude with a short discussion on the usefulness of this work in the context of global warming response studies.
    Description: Plain Language Summary: Clouds are important for Earth's climate, because they affect a large portion of the planet's energy balance, and hence its mean temperature. To better understand how the interplay between cloudiness and energy balance would change in a changing climate, a better theoretical understanding of how clouds are distributed over the planet, and how this connects with the state variables of the climate system such as temperature and wind speed, is required. As theoretical understanding is currently limited, in this work we explore the possibility of very simply representing the spatiotemporal distribution of clouds over the whole planet. We believe that these simple representations advance the field in the direction of a conceptual theory of global cloudiness and its impact on the energy balance. We show that the impact of cloudiness on both solar and terrestrial radiation balance can be captured well globally with only a few predictive fields, like surface temperature or vertical wind speed, combined simply and using only three tunable parameters, and without using any supplementary information such as the particular season or location on the planet.
    Description: Key Points: Model fits are performed to the spatiotemporal observed cloudiness over all oceans, using a minimal set of predictors and parameters. Models capture global‐mean, spatial, and most of seasonal variability of cloud radiative effects. Cloud albedo and longwave effect are captured by pressure velocity and its variance, surface temperature, and lower tropospheric stability.
    Description: CONSTRAIN project EU Horizon 2020
    Keywords: ddc:551.5 ; global cloudiness ; energy balance ; cloud controlling factors
    Language: English
    Type: doc-type:article
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    CITATION GEO-LEO
  • 2
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    Tropical Continents Rainier Than Expected From Geometrical Constraints (2022)
    Details
    Publication Date: 2022-10-06
    Description: Abundant rainfall over tropical land masses sustains rich ecosystems, a crucial source of biodiversity and sink of carbon. Here, we use two characteristics of the observed tropical precipitation distribution, its distinctive zonal arrangement and its partitioning between land and ocean, to understand whether land conditions the climate to receive more than its fair share of precipitation as set by the land‐sea distribution. Our analysis demonstrates that it is not possible to explain the tropics‐wide partitioning of precipitation unless one assumes that rain is favored over land. Land receives more than its fair share of precipitation by broadening and letting the tropical rainbelts move more, effectively underpinning a negative feedback between surface water storage and precipitation. In contrast, rain is disfavored over land in climate models. Our findings suggest that the abundance of rainfall that shapes the terrestrial tropical biosphere is more robust to perturbations than models have suggested.
    Description: Plain Language Summary: Many ecosystems depend on the presence of a land surface exposed to precipitation to exist and prosper. In contrast to the marine biota, though, the terrestrial biosphere cannot directly tap into an unlimited reservoir of water molecules that can be recycled to support life. Yet, observations indicate that it rains in mean 3 mm day−1 over tropical land and 3 mm day−1 over tropical ocean, giving the surprising impression that precipitation amounts are not altered by the presence of land. Investigating the factors controlling this tropics‐wide partitioning of precipitation, we show that geometrical constraints actually would lead to a precipitation ratio of 0.86, not 1.0, if the presence of land would not matter. Comparing this theoretical value to observations, we find that the land receives more than its fair share of precipitation. This happens by broadening and letting the tropical rainbelt moves more over land. By quantifying the strength of the land control on the tropics‐wide partitioning of precipitation, we can also deduce that a negative feedback exists between evapotranspiration and precipitation. In contrast, repeating the same analysis with climate models reveals a positive feedback, questioning the ability of climate models to simulate regional tropical precipitation changes.
    Description: Key Points: A conceptual model of tropical precipitation is derived to understand the tropics‐wide partitioning of precipitation between land and ocean. The size and location of continent constrain the tropical land‐to‐ocean precipitation ratio to lie between 0.74 and 0.95 with a mean of 0.86. Observed ratios from six data sets are larger than these values, indicating that land receives more than its fair share of precipitation.
    Description: http://hdl.handle.net/21.11116/0000-000A-1DEC-D
    Keywords: ddc:551.6
    Language: English
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  • 3
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    Upper Bounds of Maximum Land Surface Temperatures in a Warming Climate and Limits to Plant Growth (2023)
    Details
    Publication Date: 2024-02-28
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Extremely high land surface temperatures affect soil ecological processes, alter land‐atmosphere interactions, and may limit some forms of life. Extreme surface temperature hotspots are presently identified using satellite observations or deduced from complex Earth system models. We introduce a simple, yet physically based analytical approach that incorporates salient land characteristics and atmospheric conditions to globally identify locations of extreme surface temperatures and their upper bounds. We then provide a predictive tool for delineating the spatial extent of land hotspots at the limits to biological adaptability. The model is in good agreement with satellite observations showing that temperature hotspots are associated with high radiation and low wind speed and occur primarily in Middle East and North Africa, with maximum temperatures exceeding 85°C during the study period from 2005 to 2020. We observed an increasing trend in maximum surface temperatures at a rate of 0.17°C/decade. The model allows quantifying how upper bounds of extreme temperatures can increase in a warming climate in the future for which we do not have satellite observations and offers new insights on potential impacts of future warming on limits to plant growth and biological adaptability.〈/p〉
    Description: Plain Language Summary: While satellite imagery can identify extreme land surface temperatures, land and atmospheric conditions for the onset of maximum land surface temperature (LST) have not yet been globally explored. We developed a physically based analytical model for quantifying the value and spatial extent of maximum LST and provide insights into combinations of land and atmospheric conditions for the onset of such temperature extremes. Results show that extreme LST hotspots occur primarily in the Middle East and North Africa with highest values near 85°C. Importantly, persistence of surface temperatures exceeding 75°C limits vegetation growth and disrupts primary productivity such as in Lut desert in Iran. The study shows that with global warming, regions with prohibitive land surface temperatures will expand.〈/p〉
    Description: Key Points: 〈list list-type="bullet"〉 〈list-item〉 〈p xml:lang="en"〉Hotspots for high land surface temperatures (LSTs) were globally identified using a physically based analytical approach incorporating land and atmospheric conditions〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉High LSTs primarily occur in Middle East and North Africa with values exceeding 85°C〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Maximum LSTs rising at a rate of 0.17°C/decade may limit plant growth and biological adaptability in a warming world〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: Hamburg University of Technology
    Description: European Union's Horizon Europe Research and Innovation Programme
    Description: https://disc.gsfc.nasa.gov/datasets/M2I1NXLFO_5.12.4/summary
    Description: https://disc.gsfc.nasa.gov/datasets/M2T1NXRAD_5.12.4/summary
    Description: https://doi.org/10.5067/MODIS/MCD12C1.006
    Description: https://doi.org/10.3133/ofr20111073
    Description: https://www.nccs.nasa.gov/services/data-collections/land-based-products/nex-gddp-cmip6
    Description: https://doi.org/10.3334/ORNLDAAC/1247
    Keywords: ddc:551.5 ; maximum land surface temperature (LST) ; land conditions ; atmospheric conditions ; LST hotspots
    Language: English
    Type: doc-type:article
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  • 4
    Electronic Resource
    Electronic Resource
    ATMOSPHERIC MOIST CONVECTION (2005)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Earth and Planetary Sciences 33 (2005), S. 605-643 
    Details
    ISSN: 0084-6597
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Geosciences , Physics
    Notes: Various forms of atmospheric moist convection are reviewed through a consideration of three prevalent regimes: stratocumulus; trade-wind; and deep, precipitating, maritime convection. These regimes are chosen because they are structural components of the general circulation of the atmosphere and because they highlight distinguishing features of this polymorphous phenomenon. In particular, the ways in which varied forms of moist convection communicate with remote parts of the flow through mechanisms other than the rearrangement of fluid parcels are emphasized. These include radiative, gravity wave, and/or microphysical (precipitation) processes. For each regime, basic aspects of its phenomenology are presented along with theoretical frameworks that have arisen to help rationalize the phenomenology. Recent developments suggest that the increased capacity for numerical simulation and increasingly refined remote sensing capabilities bodes well for major advances in the coming years.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.earth.33.092203.122658
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    A GCSS Boundary-Layer Cloud Model Intercomparison Study Of The First Astex Lagrangian Experiment (1999)
    Springer
    Boundary layer meteorology 93 (1999), S. 341-380 
    Details
    ISSN: 1573-1472
    Keywords: Cloud-topped boundary layers ; Stratocumulus ; Drizzle ; Cloud-radiation feedback ; Entrainment ; Large-eddy simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Three single-column models (all with an explicit liquid water budget and compara-tively high vertical resolution) and three two-dimensional eddy-resolving models (including one with bin-resolved microphysics) are compared with observations from the first ASTEX Lagrangian experiment. This intercomparison was a part of the second GCSS boundary-layer cloud modelling workshop in August 1995. In the air column tracked during the first ASTEX Lagrangian experiment, a shallow subtropical drizzling stratocumulus-capped marine boundary layer deepens after two days into a cumulus capped boundary layer with patchy stratocumulus. The models are forced with time varying boundary conditions at the sea-surface and the capping inversion to simulate the changing environment of the air column. The models all predict the observed deepening and decoupling of the boundary layer quite well, with cumulus cloud evolution and thinning of the overlying stratocumulus. Thus these models all appear capable of predicting transitions between cloud and boundary-layer types with some skill. The models also produce realistic drizzle rates, but there are substantial quantitative differences in the cloud cover and liquid water path between models. The differences between the eddy-resolving model results are nearly as large as between the single column model results. The eddy resolving models give a more detailed picture of the boundary-layer evolution than the single-column models, but are still sensitive to the choice of microphysical and radiative parameterizations, sub-grid-scale turbulence models, and probably model resolution and dimensionality. One important example of the differences seen in these parameterizations is the absorption of solar radiation in a specified cloud layer, which varied by a factor of four between the model radiation parameterizations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1002005429969
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  • 6
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    Linking Large‐Eddy Simulations to Local Cloud Observations (2021)
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    Publication Date: 2021-07-04
    Description: In order to enhance our understanding of clouds and their microphysical processes, it is crucial to exploit both observations and models. Local observations from ground‐based remote sensing sites provide detailed information on clouds, but as they are limited in dimension, there is no straightforward way to use them to guide large‐scale model development. We show that large‐eddy simulations (LES) performed on similar temporal and spatial scales as the local observations can bridge this gap. Recently, LES with realistic topography and lateral boundary conditions became feasible for domains spanning several 100 km. In this study, we show how these simulations can be linked to observations of the Jülich Observatory for Cloud Evolution (JOYCE) for a 9‐day period in spring 2013. We discuss the advantages and disadvantages of very large versus small but more constrained domains as well as the differences compared to more idealized setups. The semi‐idealized LES include time‐varying forcing but are run with homogeneous surfaces and periodic boundary conditions. These assumptions seem to be the reason why they struggle to represent the observed varying conditions. The simulations using the “realistic” setup are able to represent the general cloud structure (timing, height, phase). It seems that the smaller and more constrained domain allows for a tighter control on the synoptic situation and is the preferred choice to ensure the comparability to the local observations. These simulations together with measures as the shown Hellinger distance will allow us to gain more insights into the representativeness of column measurements in the future.
    Description: Plain Language Summary: Clouds are still a cause for uncertainty in our understanding of climate and climate feedbacks. Due to the large range of involved scales—from small droplets up to storm systems—their representation in weather and climate models is an ongoing challenge. While new and sophisticated measurements of the atmospheric column could provide new insights into important processes, their linking to models is not trivial and is ongoing research. In this study, we are presenting and exploring different approaches to combine local observations of clouds with state‐of‐the‐art high‐resolution simulations. And we are presenting a setup, which shows a promising representation of the observed clouds and is constrained enough to be applicable for long‐term statistics—one of the key requirements for improvements and evaluation clouds in of weather and climate models.
    Description: Key Points: Large‐eddy simulations including external variability can bridge the gap between ground‐based observations of clouds and large‐scale models. For comparison with local observations, it is important to take external variability (e.g., large‐scale forcing and surface) into account. ICON‐LEM offers new possibilities to simulate small scales while considering external variability.
    Keywords: 551.5 ; clouds ; heterogeneity ; ICON‐LEM ; large‐scale forcing ; LES ; remote sensing
    Type: article
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  • 7
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    Climate and carbon cycle changes from 1850 to 2100 in MPI-ESM simulations for the Coupled Model Intercomparison Project phase 5 (2013)
    In:  EPIC3Journal of Advances in Modeling Earth Systems, 5(3), pp. 572-597, ISSN: 19422466
    Details
    Publication Date: 2016-04-12
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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    PAPER (OA)
  • 8
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    Mesoscale marine tropical precipitation varies independently from the spatial arrangement of its convective cells (2021)
    Details
    Publication Date: 2021-07-25
    Description: The relationship between mesoscale convective organization, quantified by the spatial arrangement of convection, and oceanic precipitation in the tropical belt is examined using the output of a global storm-resolving simulation. The analysis uses a 2D watershed segmentation algorithm based on local precipitation maxima to isolate individual precipitation cells and derive their properties. 10° by 10° scenes are analyzed using a phase-space representation made of the number of cells per scene and the mean area of the cells per scene to understand the controls on the spatial arrangement of convection and its precipitation. The presence of few and large cells in a scene indicates the presence of a more clustered distribution of cells, whereas many small cells in a scene tend to be randomly distributed. In general, the degree of clustering of a scene (Iorg) is positively correlated to the mean area of the cells and negatively correlated to the number of cells. Strikingly, the degree of clustering, whether the cells are randomly distributed or closely spaced, to a first order does not matter for the precipitation amounts produced. Scenes of similar precipitation amounts appear as hyperbolae in our phase-space representation, hyperbolae that follow the contours of the precipitating area fraction. Finally, including the scene-averaged water vapour path (WVP) in our phase-space analysis reveals that scenes with larger WVP contain more cells than drier scenes, whereas the mean area of the cells only weakly varies with WVP. Dry scenes can contain both small and large cells, but they can contain only few cells of each category.
    Keywords: 551.5 ; convection ; object-based approaches ; organization ; precipitation ; storm-resolving modelling
    Language: English
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  • 9
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    Changes in the Tropical Lapse Rate due to Entrainment and Their Impact on Climate Sensitivity (2021)
    Details
    Publication Date: 2022-03-31
    Description: The tropical temperature in the free troposphere deviates from a theoretical moist‐adiabat. The overall deviations are attributed to the entrainment of dry surrounding air. The deviations gradually approach zero in the upper troposphere, which we explain with a buoyancy‐sorting mechanism: the height to which individual convective parcels rise depends on parcel buoyancy, which is closely tied to the impact of entrainment during ascent. In higher altitudes, the temperature is increasingly controlled by the convective parcels that are warmer and more buoyant because of weaker entrainment effects. We represent such temperature deviations from moist‐adiabats in a clear‐sky one‐dimensional radiative‐convective equilibrium model. Compared with a moist‐adiabatic adjustment, having the entrainment‐induced temperature deviations lead to higher clear‐sky climate sensitivity. As the impact of entrainment depends on the saturation deficit, which increases with warming, our model predicts even more amplified surface warming from entrainment in a warmer climate.
    Description: Plain Language Summary: The tropical temperature structure is determined by regions with deep convection, which is believed to be moist‐adiabatic. However, both models and observations show that the temperature deviates from moist‐adiabats. This is because convective parcels often mix with dry environmental air during ascent, pushing the temperature away from the moist‐adiabatic structure. More importantly, the tropical temperature is not dominated by one or a few strongest convective plumes, but rather controlled by the combined effect of many convective plumes of different strengths and depths. Therefore, the tropical temperature structure reflects the composition of convection happening at different values of boundary‐layer energy and mixing processes of variable efficiency with the environment. Using an idealized model, we find that representing such a deviation in the temperature structure increases the surface warming, because the resulting temperature lapse rate (LR) is more similar to a constant LR, showing less temperature increases higher than a moist‐adiabatic LR. This effect is likely amplified in a warmer climate due to this mixing process becoming more efficient in pushing the temperature further away from moist‐adiabats.
    Description: Key Points: The tropical temperature profile in the free troposphere deviates from that following a moist‐adiabatic lapse rate (LR). The deviations from the moist‐adiabatic LR can be explained by entrainment with a buoyancy‐sorting mechanism. The temperature deviations from moist‐adiabats increase climate sensitivity.
    Description: https://doi.org/10.5281/zenodo.1313687
    Description: https://cds.climate.copernicus.eu/cdsapp#%21/dataset/reanalysis-era5-pressure-levels-monthly-means?tab=overview
    Description: https://esgf-data.dkrz.de/projects/cmip6-dkrz/
    Description: http://hdl.handle.net/21.11116/0000-0008-FDA6-0
    Keywords: ddc:551.5
    Language: English
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  • 10
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    Characterization and Evolution of Organized Shallow Convection in the Downstream North Atlantic Trades (2021)
    Details
    Publication Date: 2022-03-29
    Description: Four previously identified patterns of meso‐scale cloud organization in the trades — called Sugar, Gravel, Flowers, and Fish — are studied using long‐term records of ground‐based measurements, satellite observations and reanalyzes. A deep neural network trained to detect these patterns is applied to satellite imagery to identify periods during which a particular pattern is observed over the Barbados Cloud Observatory. Surface‐based remote sensing at the observatory is composited and shows that the patterns can be distinguished by differences in cloud geometry. Variations in total cloudiness among the patterns are dominated by variations in cloud‐top cloudiness. Cloud amount near cloud base varies little. Each pattern is associated with a distinct atmospheric environment whose characteristics are traced back to origins that are not solely within the trades. Sugar air‐masses are characterized by weak winds and of tropical origin. Fish are driven by convergence lines originating from synoptical disturbances. Gravel and Flowers are most native to the trades, but distinguish themselves with slightly stronger winds and stronger subsidence in the first case and greater stability in the latter. The patterns with the higher cloud amounts and more negative cloud‐radiative effects, Flowers and Fish, are selected by conditions expected to occur less frequently with greenhouse warming.
    Description: Key Points: Meso‐scale patterns of trade‐wind clouds are identified with a neural network and characterized based on observations. The four analyzed patterns distinguish themselves by stratiform cloudiness and less by cloudiness at the lifting condensation level. Two patterns are imprinted by tropical, respectively extra‐tropical intrusions.
    Description: European Union's Horizon 2020 Research and Innovation Programme
    Description: NASA
    Description: https://doi.org/10.5281/zenodo.4767674
    Keywords: ddc:551.5
    Language: English
    Type: doc-type:article
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