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  • 1
    Dissertations
    Dissertations
    Large eddy simulations of the Arctic boundary layer around the MOSAiC drift track (2023)
    Potsdam : Universität Potsdam
    Details Availability
    Call number: AWI A7-24-95703
    Description / Table of Contents: The icosahedral non-hydrostatic large eddy model (ICON-LEM) was applied around the drift track of the Multidisciplinary Observatory Study of the Arctic (MOSAiC) in 2019 and 2020. The model was set up with horizontal grid-scales between 100m and 800m on areas with radii of 17.5km and 140 km. At its lateral boundaries, the model was driven by analysis data from the German Weather Service (DWD), downscaled by ICON in limited area mode (ICON-LAM) with horizontal grid-scale of 3 km. The aim of this thesis was the investigation of the atmospheric boundary layer near the surface in the central Arctic during polar winter with a high-resolution mesoscale model. The default settings in ICON-LEM prevent the model from representing the exchange processes in the Arctic boundary layer in accordance to the MOSAiC observations. The implemented sea-ice scheme in ICON does not include a snow layer on sea-ice, which causes a too slow response of the sea-ice surface temperature to atmospheric changes. To allow the sea-ice surface to respond faster to changes in the atmosphere, the implemented sea-ice parameterization in ICON was extended with an adapted heat capacity term. The adapted sea-ice parameterization resulted in better agreement with the MOSAiC observations. However, the sea-ice surface temperature in the model is generally lower than observed due to biases in the downwelling long-wave radiation and the lack of complex surface structures, like leads. The large eddy resolving turbulence closure yielded a better representation of the lower boundary layer under strongly stable stratification than the non-eddy-resolving turbulence closure. Furthermore, the integration of leads into the sea-ice surface reduced the overestimation of the sensible heat flux for different weather conditions. The results of this work help to better understand boundary layer processes in the central Arctic during the polar night. High-resolving mesoscale simulations are able to represent temporally and spatially small interactions and help to further develop parameterizations also for the application in regional and global models.
    Type of Medium: Dissertations
    Pages: xii, 110 Seiten , Illustrationen, Diagramme
    URL: https://doi.org/10.25932/publishup-62437
    URN: urn:nbn:de:kobv:517-opus4-624374
    DOI: 10.25932/publishup-62437
    Language: English
    Note: Dissertation, Universität Potsdam, 2023 , Contents 1. Introduction 2. Boundary Layers Types of the Atmosphere 2.1. The Convective Boundary Layer (CBL) 2.2. The Neutral Boundary Layer (NBL) 2.3. The Stable Boundary Layer (SBL) 3. The Closure problem 4. Model description 4.1. Applied model versions 4.2. Governing equations 4.3. Horizontal grid 4.4. Vertical grid 4.5. Lateral boundaries 4.6. Parametrizations 4.6.1. Radiation scheme 4.6.2. Microphysics 4.6.3. Mellor-Yamada scheme 4.6.4. Smagorinsky scheme 4.6.5. Sea ice scheme 4.7. Difference to classical LES Models 5. Experimental Setup 6. MOSAiC Measurements 6.1. ARM Meteorological tower 6.2. Radiosondes 7. Model evaluation for the central Arctic 7.1. Impact of the horizontal resolution 7.1.1. Under cold, light wind conditions 7.1.2. Under stormy conditions 7.2. Impact of the sea-ice scheme 7.3. Impact of the lower boundary conditions 7.4. Impact of the parametrization schemes under cold, light wind conditions 7.4.1. Near-surface variables 7.4.2. Vertical profiles 7.4.3. Surface fluxes 7.4.4. Boundary Layer Height 7.5. Impact of the parametrization schemes under stormy conditions 7.5.1. Near-surface variables 7.5.2. Vertical profiles 7.5.3. Surface fluxes 7.5.4. Boundary Layer height 8. Discussion and Summary Acknowledgements Appendix
    Location: AWI Reading room
    Branch Library: AWI Library
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  • 2
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    LES results to accompany measurements at the POLARSTERN Research Vessel during the PASCAL field campaign on 7 June 2017 (2023)
    PANGAEA
    Details
    Publication Date: 2023-11-09
    Description: This archive contains Large Eddy Simulation (LES) results to accompany measurements made at the Polarstern Research Vessel during the PASCAL field campaign on 7 June 2017, when the Polarstern was located in the sea ice north of Svalbard. The Dutch Atmospheric Large-Eddy Simulation model (DALES) was applied, adopting a Lagrangian framework that follows domains as embedded in relatively warm air masses as they moved towards the Polarstern. The simulated doubly periodic domain has a size of 2.56x2.56x1.28 km, discretized at a resolution of 20x20x10 m. The domain arrives at the Polarstern at 10:48 UTC on 7 June 2017 coinciding with a radiosonde release. The Polarstern was located at 10.93 E, 81.18 N.The large-scale forcings are derived from ECMWF analysis and forecast data. Adjustments were made in the initial profiles to correct for biases in the analysis state concerning inversion height, mixed layer temperature and the presence of Specific Humidity Inversions (SHI). This adjustment technique is described in detail by Neggers et al. (2019, doi:10.1029/2019MS001671). Two experiments are included in this archive: a control experiment including an SHI, and an additional experiment with the SHI removed. The configuration of the experiments is fully described by Egerer et al. (2020, doi:10.5194/acp-2020-584).
    Keywords: AC3; Arctic Amplification; Arctic mixed layer; ARK-XXXI/1.1,PASCAL; DALES; File format; File name; File size; LES; mixed-phase clouds; Model; PASCAL; Polarstern; PS106_LES2; PS106/1; Uniform resource locator/link to file
    Type: Dataset
    Format: text/tab-separated-values, 8 data points
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  • 3
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    LES results to accompany measurements at the POLARSTERN Research Vessel during the PASCAL field campaign on 6 June 2017 (2023)
    PANGAEA
    Details
    Publication Date: 2023-11-09
    Description: This archive contains Large Eddy Simulation (LES) results to accompany measurements made at the Polarstern Research Vessel during the PASCAL field campaign on 6 June 2017, when the Polarstern was located in the sea ice north of Svalbard. The Dutch Atmospheric Large-Eddy Simulation model (DALES) was applied, adopting a Lagrangian framework that follows domains as embedded in relatively warm air masses as they moved towards the Polarstern. The simulated doubly periodic domain has a size of 2.56x2.56x1.28 km, discretized at a resolution of 20x20x10 m. The domain arrives at the Polarstern at 10:52 UTC on 6 June 2017 coinciding with a radiosonde release. The Polarstern was located at 10.84 E, 81.95 N.The large-scale forcings are derived from ECMWF analysis and forecast data. Adjustments were made in the initial profiles to correct for biases in the analysis state concerning inversion height, mixed layer temperature and the presence of Specific Humidity Inversions (SHI). This adjustment technique is described in detail by Neggers et al. (2019, doi:10.1029/2019MS001671). Two experiments are included in this archive: a control experiment including an SHI, and an additional experiment with the SHI removed. The configuration of the experiments is fully described by Egerer et al. (2020, doi:10.5194/acp-2020-584).
    Keywords: AC3; Arctic Amplification; Arctic mixed layer; ARK-XXXI/1.1,PASCAL; DALES; File format; File name; File size; LES; mixed-phase clouds; Model; PASCAL; Polarstern; PS106_LES1; PS106/1; Uniform resource locator/link to file
    Type: Dataset
    Format: text/tab-separated-values, 8 data points
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  • 4
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    ARM’s Impact on Numerical Weather Prediction at ECMWF (2016)
    American Meteorological Society
    Details
    Publication Date: 2016-04-01
    Print ISSN: 0065-9401
    Electronic ISSN: 1943-3646
    Topics: Geography , Geosciences , Physics
    Published by American Meteorological Society
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  • 5
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    Investigating the Scale Adaptivity of a Size-Filtered Mass Flux Parameterization in the Gray Zone of Shallow Cumulus Convection (2018)
    American Meteorological Society
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    Publication Date: 2018-04-01
    Description: In this study, the scale adaptivity of a new parameterization scheme for shallow cumulus clouds in the gray zone is investigated. The eddy diffusivity/multiple mass flux [ED(MF)n] scheme is a bin-macrophysics scheme in which subgrid transport is formulated in terms of discretized size densities. While scale adaptivity in the ED component is achieved using a pragmatic blending approach, the MF component is filtered such that only the transport by plumes smaller than the grid size is maintained. For testing, ED(MF)n is implemented into a large-eddy simulation (LES) model, replacing the original subgrid scheme for turbulent transport. LES thus plays the role of a nonhydrostatic testing ground, which can be run at different resolutions to study the behavior of the parameterization scheme in the boundary layer gray zone. In this range, convective cumulus clouds are partially resolved. The authors find that for quasi-equilibrium marine subtropical conditions at high resolutions, the clouds and the turbulent transport are predominantly resolved by the LES. This partitioning changes toward coarser resolutions, with the representation of shallow cumulus clouds gradually becoming completely carried by the ED(MF)n. The way the partitioning changes with grid spacing matches the behavior diagnosed in coarse-grained LES fields, suggesting that some scale adaptivity is captured. Sensitivity studies show that the scale adaptivity of the ED closure is important and that the location of the gray zone is found to be moderately sensitive to some model constants.
    Print ISSN: 0022-4928
    Electronic ISSN: 1520-0469
    Topics: Geography , Geosciences , Physics
    Published by American Meteorological Society
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  • 6
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    The Atmospheric Boundary Layer and the “Gray Zone” of Turbulence: A Critical Review (2020)
    American Geophysical Union
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    Publication Date: 2020-06-29
    Print ISSN: 2169-897X
    Electronic ISSN: 2169-8996
    Topics: Geosciences , Physics
    Published by American Geophysical Union
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  • 7
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    A simple equilibrium model for shallow-cumulus-topped mixed layers (2006)
    Springer
    Details
    Publication Date: 2006-10-06
    Print ISSN: 0935-4964
    Electronic ISSN: 1432-2250
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Published by Springer
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  • 8
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    Size dependence in chord characteristics from simulated and observed continental shallow cumulus (2020)
    Copernicus
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    Publication Date: 2020-09-03
    Description: In this study we compare long-term Doppler and Raman lidar observations against a full month of large eddy simulations of continental shallow cumulus clouds. The goal is to evaluate if the simulations can reproduce the mean observed vertical velocity and moisture structure of cumulus clouds and their associated subcloud circulations, as well as to establish if these properties depend on the size of the cloud. We propose methods to compare continuous chords of cloud detected from Doppler and Raman lidars with equivalent chords derived from 1D and 3D model output. While the individual chords are highly variable, composites of thousands of observed and millions of simulated chords contain a clear signal. We find that the simulations underestimate cloud size and fraction but successfully reproduce the observed structure of vertical velocity and moisture perturbations. There is a clear scaling of vertical velocity and moisture anomalies below the chords with chord size, but the moisture anomalies are only 1 %–2 % higher than the horizontal mean values. The differences between the observations and simulations are smaller than the difference in sampling the modeled chords in time or space. The shape of the vertical velocity and moisture anomalies from cloud chords sampled spatially from 3D model snapshots is almost perfectly symmetric. In contrast, the chords sampled temporally from the lidar observations and 1D model output have a marked asymmetry, with stronger updrafts and higher moisture anomalies occurring earlier on.
    Print ISSN: 1680-7316
    Electronic ISSN: 1680-7324
    Topics: Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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  • 9
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    Investigating the Diurnal Evolution of the Cloud Size Distribution of Continental Cumulus Convection Using Multiday LES (2019)
    American Meteorological Society
    Details
    Publication Date: 2019-02-20
    Description: The diurnal dependence of cumulus cloud size distributions over land is investigated by means of an ensemble of large-eddy simulations (LESs). A total of 146 days of transient continental shallow cumulus are selected and simulated, reflecting a low midday maximum of total cloud cover, weak synoptic forcing, and the absence of strong surface precipitation. The LESs are semi-idealized, forced by large-scale model output but using an interactive surface. This multitude of cases covers a large parameter space of environmental conditions, which is necessary for identifying any diurnal dependencies in cloud size distributions. A power-law exponential function is found to describe the shape of the cloud size distributions for these days well, with the exponential component capturing the departure from power-law scaling at the larger cloud sizes. To assess what controls the largest cloud size in the distribution, the correlation coefficients between the maximum cloud size and various candidate variables reflecting the boundary layer state are computed. The strongest correlation is found between total cloud cover and maximum cloud size. Studying the size density of the cloud area revealed that larger clouds contribute most to a larger total cloud cover, and not the smaller ones. Besides cloud cover, cloud-base and cloud-top height are also found to weakly correlate with the maximum cloud size, suggesting that the classic idea of deeper boundary layers accommodating larger convective thermals still holds for shallow cumulus. Sensitivity tests reveal that the results are only minimally affected by the representation of microphysics and the output resolution.
    Print ISSN: 0022-4928
    Electronic ISSN: 1520-0469
    Topics: Geography , Geosciences , Physics
    Published by American Meteorological Society
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  • 10
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    Impact Mechanisms of Shallow Cumulus Convection on Tropical Climate Dynamics* (2007)
    American Meteorological Society
    Details
    Publication Date: 2007-06-01
    Description: Subtropical shallow cumulus convection is shown to play an important role in tropical climate dynamics, in which convective mixing between the atmospheric boundary layer and the free troposphere initiates a chain of large-scale feedbacks. It is found that the presence of shallow convection in the subtropics helps set the width and intensity of oceanic ITCZs, a mechanism here termed the shallow cumulus humidity throttle because of the control exerted on the moisture supply to the deep convection zones. These conclusions are reached after investigations based on a tropical climate model of intermediate complexity, with sufficient vertical degrees of freedom to capture (i) the effects of shallow convection on the boundary layer moisture budget and (ii) the dependency of deep convection on the free-tropospheric humidity. An explicit shallow cumulus mixing time scale in this simple parameterization is varied to assess sensitivity, with moist static energy budget analysis aiding to identify how the local effect of shallow convection is balanced globally. A reduction in the mixing efficiency of shallow convection leads to a more humid atmospheric mixed layer, and less surface evaporation, with a drier free troposphere outside of the convecting zones. Advection of drier free-tropospheric air from the subtropics by transients such as dry intrusions, as well as by mean inflow, causes a substantial narrowing of the convection zones by inhibition of deep convection at their margins. In the tropical mean, the reduction of convection by this narrowing more than compensates for the reduction in surface evaporation. Balance is established via a substantial decrease in tropospheric temperatures throughout the Tropics, associated with the reduction in convective heating. The temperature response—and associated radiative contribution to the net flux into the column—have broad spatial scales, while the reduction of surface evaporation is concentrated outside of the convecting zones. This results in differential net flux across the convecting zone, in a sense that acts to destabilize those areas that do convect. This results in stronger large-scale convergence and more intense convection within a narrower area. Finally, mixed layer ocean experiments show that in a coupled ocean–atmosphere system this indirect feedback mechanism can lead to SST differences up to +2 K between cases with different shallow cumulus mixing time, tending to counteract the direct radiative impact of low subtropical clouds on SST.
    Print ISSN: 0894-8755
    Electronic ISSN: 1520-0442
    Topics: Geography , Geosciences , Physics
    Published by American Meteorological Society
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