scholarly journals Mystery of ice multiplication in warm-based precipitating shallow cumulus clouds

2010 ◽  
Vol 37 (10) ◽  
pp. n/a-n/a ◽  
Author(s):  
Jiming Sun ◽  
Parisa A. Ariya ◽  
Henry G. Leighton ◽  
M. K. Yau
Keyword(s):  
Cumulus Clouds ◽  
Shallow Cumulus ◽  
Ice Multiplication

scholarly journals A Cloud Microphysics Parameterization for Shallow Cumulus Clouds Based on Lagrangian Cloud Model Simulations

2018 ◽  
Vol 75 (11) ◽  
pp. 4031-4047 ◽  
Author(s):  
Yign Noh ◽  
Donggun Oh ◽  
Fabian Hoffmann ◽  
Siegfried Raasch
Keyword(s):  
Cloud Model ◽  
Cloud Microphysics ◽  
Heaviside Function ◽  
Mixing Ratio ◽  
Cumulus Clouds ◽  
Cloud Droplets ◽  
Shallow Cumulus ◽  
Initial Stage ◽  
Accretion Rates ◽  
The Moment

Abstract Cloud microphysics parameterizations for shallow cumulus clouds are analyzed based on Lagrangian cloud model (LCM) data, focusing on autoconversion and accretion. The autoconversion and accretion rates, A and C, respectively, are calculated directly by capturing the moment of the conversion of individual Lagrangian droplets from cloud droplets to raindrops, and it results in the reproduction of the formulas of A and C for the first time. Comparison with various parameterizations reveals the closest agreement with Tripoli and Cotton, such as and , where and are the mixing ratio and the number concentration of cloud droplets, is the mixing ratio of raindrops, is the threshold volume radius, and H is the Heaviside function. Furthermore, it is found that increases linearly with the dissipation rate and the standard deviation of radius and that decreases rapidly with while disappearing at > 3.5 μm. The LCM also reveals that and increase with time during the period of autoconversion, which helps to suppress the early precipitation by reducing A with smaller and larger in the initial stage. Finally, is found to be affected by the accumulated collisional growth, which determines the drop size distribution.

scholarly journals Investigating the Scale Adaptivity of a Size-Filtered Mass Flux Parameterization in the Gray Zone of Shallow Cumulus Convection

2018 ◽  
Vol 75 (4) ◽  
pp. 1195-1214 ◽  
Author(s):  
Maren Brast ◽  
Vera Schemann ◽  
Roel A. J. Neggers
Keyword(s):  
Mass Flux ◽  
Turbulent Transport ◽  
Eddy Diffusivity ◽  
Coarse Grained ◽  
Parameterization Scheme ◽  
Quasi Equilibrium ◽  
Gray Zone ◽  
Cumulus Clouds ◽  
Eddy Simulation ◽  
Shallow Cumulus

Abstract 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.

scholarly journals Automated tracking of shallow cumulus clouds in large domain, long duration Large Eddy Simulations

2013 ◽  
Vol 6 (2) ◽  
pp. 2287-2323 ◽  
Author(s):  
T. Heus ◽  
A. Seifert
Keyword(s):  
Large Data ◽  
Current Method ◽  
Large Eddy Simulations ◽  
Large Data Sets ◽  
Data Sets ◽  
Cumulus Clouds ◽  
3 Dimensional ◽  
Shallow Cumulus ◽  
Long Duration ◽  
Large Eddy

Abstract. This paper presents a method for feature tracking of fields of shallow cumulus convection in Large Eddy Simulations (LES) by connecting the projected cloud cover in space and time, and by accounting for splitting and merging of cloud objects. Existing methods tend to be either imprecise or, when using the full 3 dimensional spatial field, prohibitively expensive for large data sets. Compared to those 3-D methods, the current method reduces the memory footprint by up to a factor 100, while retaining most of the precision by correcting for splitting and merging events between different clouds. The precision of the algorithm is further enhanced by taking the vertical extent of the cloud into account. Furthermore, rain and subcloud thermals are also tracked, and links between clouds, their rain, and their subcloud thermals are made. The method compares well with results from the literature. Resolution and domain dependencies are also discussed. For the current simulations, the cloud size distribution converges for clouds larger than an effective resolution of 6Δx, and smaller than about 20% of the horizontal domains size.

scholarly journals Dynamics of Subsiding Shells in Actively Growing Clouds with Vertical Updrafts

2020 ◽  
Vol 77 (4) ◽  
pp. 1353-1369 ◽  
Author(s):  
Vishnu Nair ◽  
Thijs Heus ◽  
Maarten van Reeuwijk
Keyword(s):  
Shell Thickness ◽  
Large Scale ◽  
Cloud Environment ◽  
Initial State ◽  
Cumulus Clouds ◽  
Mean Velocity ◽  
Flow Parameters ◽  
Shallow Cumulus ◽  
Order Of Magnitude ◽  
Self Similar

Abstract The dynamics of a subsiding shell at the edges of actively growing shallow cumulus clouds with updrafts is analyzed using direct numerical simulation. The actively growing clouds have a fixed in-cloud buoyancy and velocity. Turbulent mixing and evaporative cooling at the cloud edges generate a subsiding shell that grows with time. A self-similar regime is observed for first- and second-order moments when normalized with respective maximum values. Internal scales derived from integral properties of the flow problem are identified. A self-similarity analysis using these scales reveals that contrary to classical self-similar flows, the turbulent kinetic energy budget terms and velocity moments scale according to the buoyancy and not with the mean velocity. The shell thickness is observed to increase linearly with time. The buoyancy scale remains time invariant and is set by the initial cloud–environment thermodynamics. The shell accelerates ballistically with a magnitude set by the saturation value of the buoyancy of the cloud–environment mixture. In this regime, the shell is buoyancy driven and independent of the in-cloud velocity. Relations are obtained for predicting the shell thickness and minimum velocities by linking the internal scales with external flow parameters. The values thus calculated are consistent with the thickness and velocities observed in typical shallow cumulus clouds. The entrainment coefficient is a function of the initial state of the cloud and the environment, and is shown to be on the same order of magnitude as fractional entrainment rates calculated for large-scale models.

scholarly journals Precipitation susceptibility in marine stratocumulus and shallow cumulus from airborne measurements

2016 ◽  
Vol 16 (17) ◽  
pp. 11395-11413 ◽  
Author(s):  
Eunsil Jung ◽  
Bruce A. Albrecht ◽  
Armin Sorooshian ◽  
Paquita Zuidema ◽  
Haflidi H. Jonsson
Keyword(s):  
Marine Boundary Layer ◽  
Qualitative Behavior ◽  
Liquid Water Path ◽  
Cumulus Clouds ◽  
Marine Stratocumulus ◽  
Airborne Measurements ◽  
Boundary Layer Clouds ◽  
Shallow Cumulus ◽  
Stratocumulus Clouds ◽  
Field Campaigns

Abstract. Precipitation tends to decrease as aerosol concentration increases in warm marine boundary layer clouds at fixed liquid water path (LWP). The quantitative nature of this relationship is captured using the precipitation susceptibility (So) metric. Previously published works disagree on the qualitative behavior of So in marine low clouds: So decreases monotonically with increasing LWP or cloud depth (H) in stratocumulus clouds (Sc), while it increases and then decreases in shallow cumulus clouds (Cu). This study uses airborne measurements from four field campaigns on Cu and Sc with similar instrument packages and flight maneuvers to examine if and why So behavior varies as a function of cloud type. The findings show that So increases with H and then decreases in both Sc and Cu. Possible reasons for why these results differ from those in previous studies of Sc are discussed.

Parameterization of the Vertical Velocity Equation for Shallow Cumulus Clouds

2012 ◽  
Vol 140 (8) ◽  
pp. 2424-2436 ◽  
Author(s):  
Stephan R. de Roode ◽  
A. Pier Siebesma ◽  
Harm J. J. Jonker ◽  
Yoerik de Voogd
Keyword(s):  
Pressure Gradient ◽  
Vertical Velocity ◽  
Weather Prediction ◽  
Specific Humidity ◽  
Thermodynamic Quantities ◽  
Small Contribution ◽  
Cumulus Clouds ◽  
Shallow Cumulus ◽  
Sink Term ◽  
Velocity Equation

Abstract The application of a steady-state vertical velocity equation for parameterized moist convective updrafts in climate and weather prediction models is currently common practice. This equation usually contains an advection, a buoyancy, and a lateral entrainment term, whereas the effects of pressure gradient and subplume contributions are typically incorporated as proportionality constants a and b for the buoyancy and the entrainment terms, respectively. A summary of proposed values of these proportionality constants a and b in the literature demonstrates that there is a large uncertainty in their most appropriate values. To shed new light on this situation an analysis is presented of the full vertical budget equation for shallow cumulus clouds obtained from large eddy simulations of three different Global Energy and Water Cycle Experiment (GEWEX) Cloud System Study (GCSS) intercomparison cases. It is found that the pressure gradient term is the dominant sink term in the vertical velocity budget, whereas the entrainment term only gives a small contribution. This result is at odds with the parameterized vertical velocity equation in the literature as it employs the entrainment term as the major sink term. As a practical solution the damping effect of the pressure term may be parameterized in terms of the lateral entrainment rates as used for thermodynamic quantities like the total specific humidity. By using a least squares method, case-dependent optimal values are obtained for the proportionality constants a and b, which are linearly related with each other. This relation can be explained from a linear relationship between the lateral entrainment rate and the buoyancy.

Formulation of Autoconversion and Drop Spectra Shape in Shallow Cumulus Clouds

2020 ◽  
Vol 77 (2) ◽  
pp. 711-722
Author(s):  
Yefim Kogan ◽  
Mikhail Ovchinnikov
Keyword(s):  
Convective Cloud ◽  
Single Mode ◽  
Liquid Water Content ◽  
Cumulus Clouds ◽  
Lognormal Distributions ◽  
Precipitation Prediction ◽  
Shallow Cumulus ◽  
Drop Size Distributions ◽  
Les Model ◽  
Third Moment

Abstract Two-moment autoconversion parameterizations as compared to accretion parameterizations exhibit significant errors suggesting that additional moments are needed to increase their accuracy. We develop a three-moment autoconversion parameterization using output from an LES model with size-resolved microphysics. Adding the third moment decreases the errors of parameterization and improves precipitation prediction. However, the errors are still significantly larger than errors of accretion rate. An analysis of the cloud drop size distributions (DSDs) in the simulated tropical convective cloud system reveals that most DSDs have a significant fraction of cloud liquid water content qc in the midsize droplet range (radii from 20 to 40 μm). Our data indicate that more than 30% of DSDs have over half of qc contained in the midsize range and about 60% of spectra have, at least, one-third of qc in this range. Even when the rain/drizzle mode is small (radar reflectivity Z < −10 dBZ), there is a significant number of spectra in which fraction of qc in the midsize range is as large as 60%. These DSDs are more complex than the frequently used gamma or lognormal distributions, which exhibit a single mode and can be defined by three microphysical moments. The need to define DSDs by more than three moments explains the large errors in the three-moment autoconversion parameterization. The limitation of three-parameter gamma or lognormal distributions should be kept in mind when applying them in precipitating shallow cumulus clouds.

scholarly journals A PDF-Based Formulation of Microphysical Variability in Cumulus Congestus Clouds*

2015 ◽  
Vol 73 (1) ◽  
pp. 167-184 ◽  
Author(s):  
Yefim L. Kogan ◽  
David B. Mechem
Keyword(s):  
Mesoscale Model ◽  
Distribution Functions ◽  
Cumulus Clouds ◽  
Atmospheric Sciences ◽  
Microphysical Process ◽  
Eddy Simulation ◽  
Shallow Cumulus ◽  
Toga Coare ◽  
Accretion Rates ◽  
Cumulus Congestus

Abstract Calculating unbiased microphysical process rates over mesoscale model grid volumes necessitates knowledge of the subgrid-scale (SGS) distribution of variables, typically represented as probability distribution functions (PDFs) of the prognostic variables. In the 2014 Journal of the Atmospheric Sciences paper by Kogan and Mechem, they employed large-eddy simulation of Rain in Cumulus over the Ocean (RICO) trade cumulus to develop PDFs and joint PDFs of cloud water, rainwater, and droplet concentration. In this paper, the approach of Kogan and Mechem is extended to deeper, precipitating cumulus congestus clouds as represented by a simulation based on conditions from the TOGA COARE field campaign. The fidelity of various PDF approximations was assessed by evaluating errors in estimating autoconversion and accretion rates. The dependence of the PDF shape on grid-mean variables is much stronger in congestus clouds than in shallow cumulus. The PDFs obtained from the TOGA COARE simulations for the calculation of accretion rates may be applied to both shallow and congestus cumulus clouds. However, applying the TOGA COARE PDFs to calculate autoconversion rates introduces unacceptably large errors in shallow cumulus clouds, thus precluding the use of a “universal” PDF formulation for both cloud types.

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