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  • American Meteorological Society  (45)
  • 1
    Online Resource
    Online Resource
    An Integrated TKE-Based Eddy Diffusivity/Mass Flux Boundary Layer Closure for the Dry Convective Boundary Layer
    American Meteorological Society ; 2011
    In:  Journal of the Atmospheric Sciences Vol. 68, No. 7 ( 2011-07-01), p. 1526-1540
    Details
    In: Journal of the Atmospheric Sciences, American Meteorological Society, Vol. 68, No. 7 ( 2011-07-01), p. 1526-1540
    Abstract: This study presents a new approach to the eddy diffusivity/mass flux (EDMF) framework for the modeling of convective boundary layers. At the root of EDMF lies a decomposition of turbulent transport mechanisms into strong ascending updrafts and smaller-scale turbulent motions. The turbulent fluxes can be therefore described using two conventional approaches: mass flux (MF) for the organized thermals and eddy diffusivity (ED) for the remaining turbulent field. Since the intensities of both MF and ED transports depend on the kinetic energy of the turbulent motions, it seems reasonable to formulate an EDMF framework based on turbulent kinetic energy (TKE). Such an approach allows for more physical and less arbitrary formulations of parameters in the model. In this study the EDMF–TKE coupling is achieved through the use of (i) a new parameterization for the lateral entrainment coefficient ɛ and (ii) the MF contribution to the buoyancy source of TKE. Some other important features of the EDMF parameterization presented here include a revised mixing length formulation and Monin–Obukhov stability scaling for the surface layer. The scheme is implemented in a one-dimensional (1D) model. Several cases of dry convective boundary layers (CBL) with different surface sensible heat fluxes in the free-convection limit are investigated. Results are compared to large-eddy simulation (LES). Good agreement between LES and the 1D model is achieved with respect to mean profiles, boundary layer evolution, and updraft characteristics. Some disagreements between the models are found to most likely relate to deficiencies in the TKE simulation in the 1D model. Comparison with other previously established ɛ parameterizations shows that the new TKE-based formulation leads to equally accurate, and in many respects better, simulation of the CBL. The encouraging results obtained with the proposed EDMF framework indicate that full integration of EDMF with higher-order closures is possible and can further improve boundary layer simulations.
    Type of Medium: Online Resource
    ISSN: 0022-4928 , 1520-0469
    URL: Article
    DOI: 10.1175/2011JAS3548.1
    RVK:
    UA 4800
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2011
    detail.hit.zdb_id: 218351-1
    detail.hit.zdb_id: 2025890-2
    SSG: 16,13
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  • 2
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    Probability Density Functions of Liquid Water Path and Total Water Content of Marine Boundary Layer Clouds: Implications for Cloud Parameterization
    American Meteorological Society ; 2012
    In:  Journal of Climate Vol. 25, No. 6 ( 2012-03-15), p. 2162-2177
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 25, No. 6 ( 2012-03-15), p. 2162-2177
    Abstract: Mathematical forms of probability density functions (PDFs) of liquid water path (LWP) and total water content for marine boundary layer clouds are investigated using the homogeneity, skewness, and kurtosis of PDFs of LWP obtained from observations described in a companion paper. First, observed LWP PDF data are divided into four categories depending on the stability between 775 and 1000 hPa in order to investigate the characteristics of the PDFs of LWP depending on stability of the atmospheric boundary layer (ABL). The relationships between cloud amount and higher moments of LWP PDFs for different ABLs show different features. When the stability becomes larger, the LWP PDFs have larger homogeneity, smaller skewness, and smaller kurtosis for similar cloud amounts. To extract useful information about the PDFs of total water content for strongly and moderately stable ABLs, the relationship between LWP PDFs and PDFs of total water content is determined by introducing a set of simple assumptions for the vertical structure of total water content in well-mixed boundary layers. By comparing the observed relationships between cloud amount and higher moments of LWP PDFs, with similar relationships deduced theoretically from various forms of PDFs of total water content, it is found that, in general, the triangular and Gaussian PDFs are a realistic approximation for PDFs of total water content in marine boundary layer clouds for strongly and moderately stable ABLs. Results concerning the correction ratio for the autoconversion rate of cloud water content to precipitation and the reduction factor for shortwave reflectance, as functions of cloud amount, are also discussed.
    Type of Medium: Online Resource
    ISSN: 0894-8755 , 1520-0442
    URL: Article
    DOI: 10.1175/JCLI-D-11-00117.1
    RVK:
    UA 4548
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2012
    detail.hit.zdb_id: 246750-1
    detail.hit.zdb_id: 2021723-7
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  • 3
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    The Strong Impact of Weak Horizontal Convergence on Continental Shallow Convection
    American Meteorological Society ; 2020
    In:  Journal of the Atmospheric Sciences Vol. 77, No. 9 ( 2020-09-01), p. 3119-3137
    Details
    In: Journal of the Atmospheric Sciences, American Meteorological Society, Vol. 77, No. 9 ( 2020-09-01), p. 3119-3137
    Abstract: Idealized large-eddy simulation (LES) is a basic tool for studying three-dimensional turbulence in the planetary boundary layer. LES is capable of providing benchmark solutions for parameterization development efforts. However, real small-scale atmospheric flows develop in heterogeneous and transient environments with locally varying vertical motions inherent to open multiscale interactive dynamical systems. These variations are often too subtle to detect them by state-of-the-art remote and in situ measurements, and are typically excluded from idealized simulations. The present study addresses the impact of weak [i.e., O(10−6) s−1] short-lived low-level large-scale convergence/divergence perturbations on continental shallow convection. The results show a strong response of shallow nonprecipitating convection to the applied weak large-scale dynamical forcing. Evolutions of CAPE, mean liquid water path, and cloud-top heights are significantly affected by the imposed convergence/divergence. In contrast, evolving cloud-base properties, such as the area coverage and mass flux, are only weakly affected. To contrast those impacts with microphysical sensitivity, the baseline simulations are perturbed assuming different observationally based cloud droplet number concentrations and thus different rainfall. For the tested range of microphysical perturbations, the imposed convergence/divergence provides significantly larger impact than changes in the cloud microphysics. Simulation results presented here provide a stringent test for convection parameterizations, especially important for large-scale models progressing toward resolving some nonhydrostatic effects.
    Type of Medium: Online Resource
    ISSN: 0022-4928 , 1520-0469
    URL: Article
    DOI: 10.1175/JAS-D-19-0351.1
    RVK:
    UA 4800
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2020
    detail.hit.zdb_id: 218351-1
    detail.hit.zdb_id: 2025890-2
    SSG: 16,13
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  • 4
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    Sensitivity to Physical and Numerical Aspects of Large-Eddy Simulation of Stratocumulus
    American Meteorological Society ; 2019
    In:  Monthly Weather Review Vol. 147, No. 7 ( 2019-07-01), p. 2621-2639
    Details
    In: Monthly Weather Review, American Meteorological Society, Vol. 147, No. 7 ( 2019-07-01), p. 2621-2639
    Abstract: A series of numerical experiments where both physical and numerical model parameters are varied with respect to a reference setup is used to investigate the physics of a stratocumulus cloud and the performance of a large-eddy simulation (LES) model. The simulations show a delicate balance of physical processes with some sensitivities amplified by numerical model features. A strong feedback between cloud liquid, cloud-top radiative cooling, and turbulence leads to slow grid convergence of the turbulent fluxes. For a methodology that diagnoses cloud liquid from conserved variables, small errors in the total water amount result in large liquid water errors, which are amplified by the cloud-top radiative cooling leading to large variations of buoyancy forcing. In contrast, when the liquid–radiation–buoyancy feedback is not present in simulations without radiation, the turbulence structure of the boundary layer remains essentially identical for grid resolutions between 20 and 1.25 m. The present runs suggest that the buoyancy reversal instability significantly enhances the entrainment rate. Even though cloud-top radiative cooling is regarded as a key attribute of stratocumulus, the present simulations suggest that surface fluxes and surface shear significantly contribute to the total turbulent kinetic energy. Turbulence spectra exhibit inertial range scaling away from the confinement effects of the surface and inversion. Fine grid resolution LESs agree with observations, especially with respect to cloud liquid and vertical velocity variance, and exhibit grid convergence without any model tuning or ad hoc model choices.
    Type of Medium: Online Resource
    ISSN: 0027-0644 , 1520-0493
    URL: Article
    DOI: 10.1175/MWR-D-18-0294.1
    RVK:
    RA 1000
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2019
    detail.hit.zdb_id: 2033056-X
    detail.hit.zdb_id: 202616-8
    SSG: 14
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  • 5
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    A New Methodology for Observation-Based Parameterization Development
    American Meteorological Society ; 2020
    In:  Monthly Weather Review Vol. 148, No. 10 ( 2020-10-01), p. 4159-4184
    Details
    In: Monthly Weather Review, American Meteorological Society, Vol. 148, No. 10 ( 2020-10-01), p. 4159-4184
    Abstract: We develop a methodology for identification of candidate observables that best constrain the parameterization of physical processes in numerical models. This methodology consists of three steps: (i) identifying processes that significantly impact model results, (ii) identifying observables that best constrain the influential processes, and (iii) investigating the sensitivity of the model results to the measurement error and vertical resolution of the constraining observables. This new methodology is applied to the Jet Propulsion Laboratory stochastic multiplume Eddy-Diffusivity/Mass-Flux (JPL-EDMF) model for two case studies representing nonprecipitating marine stratocumulus and marine shallow convection. The uncertainty of physical processes is characterized with uncertainty of model parameters. We find that the most uncertain processes in the JPL-EDMF model are related to the representation of lateral entrainment for convective plumes and parameterization of mixing length scale for the eddy-diffusivity part of the model. The results show a strong interaction between these uncertain processes. Measurements of the water vapor profile for shallow convection and of the cloud fraction profile for the stratocumulus case are among those measurements that best constrain the uncertain JPL-EDMF processes. The interdependence of the required vertical resolution and error characteristics of the observational system are shown. If the observations are associated with larger error, their vertical resolution has to be finer and vice versa. We suggest that the methodology and results presented here provide an objective basis for defining requirements for future observing systems such as future satellite missions to observe clouds and the planetary boundary layer.
    Type of Medium: Online Resource
    ISSN: 0027-0644 , 1520-0493
    URL: Article
    DOI: 10.1175/MWR-D-20-0114.1
    RVK:
    RA 1000
    Language: Unknown
    Publisher: American Meteorological Society
    Publication Date: 2020
    detail.hit.zdb_id: 2033056-X
    detail.hit.zdb_id: 202616-8
    SSG: 14
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  • 6
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    Challenges and Opportunities in NASA Weather Research
    American Meteorological Society ; 2016
    In:  Bulletin of the American Meteorological Society Vol. 97, No. 7 ( 2016-07-01), p. ES137-ES140
    Details
    In: Bulletin of the American Meteorological Society, American Meteorological Society, Vol. 97, No. 7 ( 2016-07-01), p. ES137-ES140
    Type of Medium: Online Resource
    ISSN: 0003-0007 , 1520-0477
    URL: Article
    DOI: 10.1175/BAMS-D-15-00195.1
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2016
    detail.hit.zdb_id: 2029396-3
    detail.hit.zdb_id: 419957-1
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  • 7
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    Observational Boundary Layer Energy and Water Budgets of the Stratocumulus-to-Cumulus Transition
    American Meteorological Society ; 2014
    In:  Journal of Climate Vol. 27, No. 24 ( 2014-12-15), p. 9155-9170
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 27, No. 24 ( 2014-12-15), p. 9155-9170
    Abstract: The authors estimate summer mean boundary layer water and energy budgets along a northeast Pacific transect from 35° to 15°N, which includes the transition from marine stratocumulus to trade cumulus clouds. Observational data is used from three A-Train satellites, Aqua, CloudSat, and the Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO); data derived from GPS signals intercepted by microsatellites of the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC); and the container-ship-based Marine Atmospheric Radiation Measurement Program (ARM) Global Energy and Water Cycle Experiment Cloud System Study/Working Group on Numerical Experimentation (GCSS/WGNE) Pacific Cross-Section Intercomparison (GPCI) Investigation of Clouds (MAGIC) campaign. These are unique satellite and shipborne observations providing the first global-scale observations of light precipitation, new vertically resolved radiation budget products derived from the active sensors, and well-sampled radiosonde data near the transect. In addition to the observations, the European Centre for Medium-Range Weather Forecasts (ECMWF) Interim Re-Analysis (ERA-Interim) fields are utilized to estimate the budgets. Both budgets approach within 3 W m−2 averaged along the transect, although uncertainty estimates from the study are much larger than this residual. A mean entrainment rate along the transect of mm s−1 is also estimated. A gradual transition is observed in the climatological mean from the stratocumulus regime to the cumulus regime characterized by an increase in boundary layer height, latent heat flux, rain, and the horizontal advection of dry air and a decrease in entrainment of warm dry air.
    Type of Medium: Online Resource
    ISSN: 0894-8755 , 1520-0442
    URL: Article
    DOI: 10.1175/JCLI-D-14-00242.1
    RVK:
    UA 4548
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2014
    detail.hit.zdb_id: 246750-1
    detail.hit.zdb_id: 2021723-7
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  • 8
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    Extreme Convection and Tropical Climate Variability: Scaling of Cold Brightness Temperatures to Sea Surface Temperature
    American Meteorological Society ; 2016
    In:  Journal of Climate Vol. 29, No. 10 ( 2016-05-15), p. 3893-3905
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 29, No. 10 ( 2016-05-15), p. 3893-3905
    Abstract: Changes in tropical convective events provide a test bed for understanding changes of extreme convection in a warming climate. Because convective cloud top in deep convection is associated with cold brightness temperatures (BTs) in infrared window channels, variability in global convective events can be studied by spaceborne measurements of BTs. The sensitivity of BTs, directly measured by an Atmospheric Infrared Sounder (AIRS) window channel, to natural changes (the seasonal cycle and El Niño–Southern Oscillation) in tropical sea surface temperature (SST) is examined. It is found that tropical average BTs (over the ocean) at the low percentiles of their probability distributions scale with tropical average SSTs (higher SST leading to colder BTs), with the lower percentiles being significantly more sensitive to changes in SST. The sensitivity is reduced for high percentiles of BT and is insignificant for the median BT, and has similar magnitudes for the two natural changes used in the study. The regions where the lower-percentile BTs are most sensitive to SST are near the edges of the convection active areas (intertropical convergence zone and South Pacific convergence zone), including areas with active tropical cyclone activity. Since cold BTs of lower percentiles represent stronger convective events, this study provides, for the first time, global observational evidence of higher sensitivity of changes in stronger convective activity to a changing SST. This result has important potential implications in answering the key climate question of how severe tropical convection will change in a warming world.
    Type of Medium: Online Resource
    ISSN: 0894-8755 , 1520-0442
    URL: Article
    DOI: 10.1175/JCLI-D-15-0214.1
    RVK:
    UA 4548
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2016
    detail.hit.zdb_id: 246750-1
    detail.hit.zdb_id: 2021723-7
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  • 9
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    Sensitivities in Large-Eddy Simulations of Mixed-Phase Arctic Stratocumulus Clouds Using a Simple Microphysics Approach*
    American Meteorological Society ; 2015
    In:  Monthly Weather Review Vol. 143, No. 11 ( 2015-11-01), p. 4393-4421
    Details
    In: Monthly Weather Review, American Meteorological Society, Vol. 143, No. 11 ( 2015-11-01), p. 4393-4421
    Abstract: Arctic mixed-phase stratocumulus clouds are maintained by feedbacks between microphysical and dynamical phenomena, but the details of these interactions are incompletely understood. Although large-eddy simulations are a promising means of elucidating microphysics–turbulence relationships, the use of sophisticated microphysical schemes complicates analysis of their results. Here, the ability of a simplified one-moment scheme to capture basic features of this cloud type is investigated through simulations based on Mixed-Phase Arctic Cloud Experiment (MPACE), SHEBA/FIRE-ACE, and Indirect and Semi-Direct Aerosol Campaign (ISDAC) intercomparison studies. The results of the simple scheme show reasonable agreement with liquid and ice water path predictions reported by models using schemes of similar or greater complexity. Additional tests are performed to evaluate the sensitivity of the results to three main parameters of the scheme: the snow and ice size distribution intercept parameters and the exponent appearing in the temperature-dependent phase-partition function, which is used to diagnose cloud condensate amounts. Sensitivities of the SHEBA and ISDAC cases, both of which have low surface heat fluxes and low precipitation rates, tend to be similar, while the MPACE case, with higher surface fluxes and precipitation rates, shows somewhat different trends. Results of all three cases are found to be sensitive to the snow size distribution intercept parameter, but this quantity can be adequately estimated using a recently developed diagnostic expression based on observations of Arctic clouds.
    Type of Medium: Online Resource
    ISSN: 0027-0644 , 1520-0493
    URL: Article
    URL: Article
    DOI: 10.1175/MWR-D-14-00319.1
    DOI: 10.1175/MWR-D-14-00319.s1
    RVK:
    RA 1000
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2015
    detail.hit.zdb_id: 2033056-X
    detail.hit.zdb_id: 202616-8
    SSG: 14
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  • 10
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    A Novel Framework for Evaluating and Improving Parameterized Subtropical Marine Boundary Layer Cloudiness
    American Meteorological Society ; 2019
    In:  Monthly Weather Review Vol. 147, No. 9 ( 2019-09-01), p. 3241-3260
    Details
    In: Monthly Weather Review, American Meteorological Society, Vol. 147, No. 9 ( 2019-09-01), p. 3241-3260
    Abstract: A single-column model (SCM) is used to simulate a variety of environmental conditions between Los Angeles, California, and Hawaii in order to identify physical elements of parameterizations that are required to reproduce the observed behavior of marine boundary layer (MBL) cloudiness. The SCM is composed of the JPL eddy-diffusivity/mass-flux (EDMF) mixing formulation and the RRTMG radiation model. Model forcings are provided by the Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA2). Simulated low cloud cover (LCC), rain rate, albedo, and liquid water path are compared to collocated pixel-level observations from A-Train satellites. This framework ensures that the JPL EDMF is able to simulate a continuum of real-world conditions. First, the JPL EDMF is shown to reproduce the observed mean LCC as a function of lower-tropospheric stability. Joint probability distributions of lower-tropospheric cloud fraction, height, and lower-tropospheric stability (LTS) show that the JPL EDMF improves upon its MERRA2 input but struggles to match the frequency of observed intermediate-range LCC. We then illustrate the physical roles of plume lateral entrainment and eddy-diffusivity mixing length in producing a realistic behavior of LCC as a function of LTS. In low-LTS conditions, LCC is mostly sensitive to the ability of convection to mix moist air out of the MBL. In high-LTS conditions, LCC is also sensitive to the turbulent mixing of free-tropospheric air into the MBL. In the intermediate LTS regime typical of stratocumulus–cumulus transition there is proportional sensitivity to both mixing mechanisms, emphasizing the utility of a combined eddy-diffusivity/mass-flux approach for representing mixing processes.
    Type of Medium: Online Resource
    ISSN: 0027-0644 , 1520-0493
    URL: Article
    DOI: 10.1175/MWR-D-18-0394.1
    RVK:
    RA 1000
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2019
    detail.hit.zdb_id: 2033056-X
    detail.hit.zdb_id: 202616-8
    SSG: 14
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