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Hugh Morrison - One of the best experts on this subject based on the ideXlab platform.
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cloud resolving model intercomparison of an mc3e squall line case part i convective Updrafts
Journal of Geophysical Research, 2017Co-Authors: Adam Varble, Scott E. Giangrande, Hugh Morrison, Alexander Khain, Kirk North, Pavlos Kollias, Baojun Chen, Xiquan Dong, Edward R MansellAbstract:An intercomparison study of a midlatitude mesoscale squall line is performed using the Weather Research and Forecasting (WRF) model at 1 km horizontal grid spacing with eight different cloud microphysics schemes to investigate processes that contribute to the large variability in simulated cloud and precipitation properties. All simulations tend to produce a wider area of high radar reflectivity (Z_e > 45 dBZ) than observed but a much narrower stratiform area. The magnitude of the virtual potential temperature drop associated with the gust front passage is similar in simulations and observations, while the pressure rise and peak wind speed are smaller than observed, possibly suggesting that simulated cold pools are shallower than observed. Most of the microphysics schemes overestimate vertical velocity and Ze in convective Updrafts as compared with observational retrievals. Simulated precipitation rates and Updraft velocities have significant variability across the eight schemes, even in this strongly dynamically driven system. Differences in simulated Updraft velocity correlate well with differences in simulated buoyancy and low-level vertical perturbation pressure gradient, which appears related to cold pool intensity that is controlled by the evaporation rate. Simulations with stronger Updrafts have a more optimal convective state, with stronger cold pools, ambient low-level vertical wind shear, and rear-inflow jets. Updraft velocity variability between schemes is mainly controlled by differences in simulated ice-related processes, which impact the overall latent heating rate, whereas surface rainfall variability increases in no-ice simulations mainly because of scheme differences in collision-coalescence parameterizations.
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impacts of Updraft size and dimensionality on the perturbation pressure and vertical velocity in cumulus convection part ii comparison of theoretical and numerical solutions and fully dynamical simulations
Journal of the Atmospheric Sciences, 2016Co-Authors: Hugh MorrisonAbstract:AbstractThis paper compares simple theoretical expressions relating vertical velocity, perturbation pressure, Updraft size, and dimensionality for cumulus convection, derived in Part I, with numerical solutions of the anelastic buoyant perturbation pressure Poisson equation and vertical velocity w. A range of thermal buoyancy profiles representing shallow to deep moist convection are tested for both two-dimensional (2D) and three-dimensional (3D) Updrafts. The theoretical expressions give similar results for w and perturbation pressure difference from Updraft top to base Δp compared to the numerical solutions over a wide range of Updraft radius R. The theoretical expressions are also consistent with 2D and 3D fully dynamical Updraft simulations initiated by warm bubbles of varying width.Implications for nonhydrostatic modeling in the “gray zone,” with a horizontal grid spacing Δx of O(1–10) km where convection is generally underresolved, are discussed. The theoretical and numerical solutions give a scalin...
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impacts of Updraft size and dimensionality on the perturbation pressure and vertical velocity in cumulus convection part i simple generalized analytic solutions
Journal of the Atmospheric Sciences, 2016Co-Authors: Hugh MorrisonAbstract:AbstractThis study investigates relationships between vertical velocity, perturbation pressure, Updraft size, and dimensionality for cumulus convection. Generalized theoretical expressions are derived from approximate analytic solutions of the governing momentum and mass continuity equations for both two-dimensional (2D) and axisymmetric quasi-three-dimensional (3D) steady-state Updrafts. These expressions relate perturbation pressure and vertical velocity to Updraft radius R, height H, and thermal buoyancy. They suggest that the vertical velocity at the level of neutral buoyancy is reduced from perturbation pressure effects by factors of and in 2D and 3D, respectively, where is a nondimensional length, with somewhat different scalings lower in the Updraft (α is a parameter equal to the ratio of vertical velocity horizontally averaged across the Updraft to that at the Updraft center). They also indicate that Updrafts are weaker in 2D than 3D, all else being equal, with a difference of up to a factor of 2 ...
Tammy M Weckwerth - One of the best experts on this subject based on the ideXlab platform.
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thermodynamic variability within the convective boundary layer due to horizontal convective rolls
Monthly Weather Review, 1996Co-Authors: Tammy M Weckwerth, James W Wilson, Roger M WakimotoAbstract:Abstract Data from the Convection and Precipitation/Electrification (CaPE) Experiment conducted during the summer of 1991 are used to examine and quantify the horizontal variability of temperature and moisture within the convective boundary layer (CBL). Potential temperature variations were only about 0.5 K, while variations in water vapor mixing ratio values of 1.5–2.5 g kg−1 were observed throughout the CBL. Using radar, aircraft, and sounding data, it is shown that horizontal convective rolls are the likely cause of these variabilities. The enhanced moisture occurred within the roll Updraft regions, thus rolls were transporting moist air from the surface upward. The observed cloud-base heights, obtained from cloud photogrammetry, were produced from the highest moisture values within the roll Updraft regions. Since the roll ascending branches contained moisture values that were most representative of the observed cloud-base heights, it is likely that measurements from within the roll Updrafts would prov...
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observations of the sea breeze front during cape part ii dual doppler and aircraft analysis
Monthly Weather Review, 1995Co-Authors: Nolan T Atkins, Roger M Wakimoto, Tammy M WeckwerthAbstract:Abstract The three-dimensional kinematic structures of offshore and onshore flow sea-breeze fronts observed during the CaPE experiment are shown using high resolution dual-Doppler and aircraft data. The fronts interact with horizontal convective rolls (HCRs) that develop within the convective boundary layer. Nearly perpendicular intersections between the HCRs and sea-breeze front were observed during the offshore flow case. Close to the front, the HCR axes were tilted upward and lifted by the frontal Updrafts. Consequently, a deeper Updraft was created at the intersection points, providing additional impetus for cloud development. Furthermore, clouds forming at periodic intervals along the NCRs intensified as they propagated over the front. During the onshore flow case, the HCR orientation was nearly parallel to the front. Extended sections of the front “merged” with the HCRs. This process strengthened the front and is explained as the merger of like-sign vortices associated with both the front and HCRs. ...
Scott E. Giangrande - One of the best experts on this subject based on the ideXlab platform.
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cloud resolving model intercomparison of an mc3e squall line case part i convective Updrafts
Journal of Geophysical Research, 2017Co-Authors: Adam Varble, Scott E. Giangrande, Hugh Morrison, Alexander Khain, Kirk North, Pavlos Kollias, Baojun Chen, Xiquan Dong, Edward R MansellAbstract:An intercomparison study of a midlatitude mesoscale squall line is performed using the Weather Research and Forecasting (WRF) model at 1 km horizontal grid spacing with eight different cloud microphysics schemes to investigate processes that contribute to the large variability in simulated cloud and precipitation properties. All simulations tend to produce a wider area of high radar reflectivity (Z_e > 45 dBZ) than observed but a much narrower stratiform area. The magnitude of the virtual potential temperature drop associated with the gust front passage is similar in simulations and observations, while the pressure rise and peak wind speed are smaller than observed, possibly suggesting that simulated cold pools are shallower than observed. Most of the microphysics schemes overestimate vertical velocity and Ze in convective Updrafts as compared with observational retrievals. Simulated precipitation rates and Updraft velocities have significant variability across the eight schemes, even in this strongly dynamically driven system. Differences in simulated Updraft velocity correlate well with differences in simulated buoyancy and low-level vertical perturbation pressure gradient, which appears related to cold pool intensity that is controlled by the evaporation rate. Simulations with stronger Updrafts have a more optimal convective state, with stronger cold pools, ambient low-level vertical wind shear, and rear-inflow jets. Updraft velocity variability between schemes is mainly controlled by differences in simulated ice-related processes, which impact the overall latent heating rate, whereas surface rainfall variability increases in no-ice simulations mainly because of scheme differences in collision-coalescence parameterizations.
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convective cloud vertical velocity and mass flux characteristics from radar wind profiler observations during goamazon2014 5
Journal of Geophysical Research, 2016Co-Authors: Scott E. Giangrande, Mary Jane Bartholomew, Alain Protat, Courtney Schumacher, Christopher R Williams, Michael Jensen, Tami Toto, Zhe Feng, Luiz A. T. MachadoAbstract:A radar wind profiler (RWP) dataset collected during the two-year DOE ARM Observations and Modeling of the Green Ocean Amazon (GoAmazon2014/5) campaign is used to estimate convective cloud vertical velocity, area fraction and mass flux profiles. Vertical velocity observations are presented using cumulative frequency histograms and weighted-mean profiles to provide insights in a manner suitable for GCM-model scale comparisons (spatial domains from 20 km to 60 km). Convective profile sensitivity to changes in environmental conditions and seasonal regime controls is also considered. Aggregate and ensemble average vertical velocity, convective area fraction and mass flux profiles, as well as magnitudes and relative profile behaviors, are found consistent with previous studies. Updrafts and downdrafts increase in magnitude with height to mid-levels (6 to 10 km), with Updraft area also increasing with height. Updraft mass flux profiles similarly increase with height, showing a peak in magnitude near 8 km. Downdrafts are observed to be most frequent below the freezing level, with downdraft area monotonically decreasing with height. Updraft and downdraft profile behaviors are further stratified according to environmental controls. These results indicate stronger vertical velocity profile behaviors under higher CAPE and lower low-level moisture conditions. Sharp contrasts in convective area fraction and mass flux profiles are most pronounced when retrievals are segregated according to Amazonian wet and dry season conditions. During this deployment, wet season regimes favored higher domain mass flux profiles, attributed to more frequent convection that offsets weaker average convective cell vertical velocities.
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a summary of convective core vertical velocity properties using arm uhf wind profilers in oklahoma
Journal of Applied Meteorology and Climatology, 2013Co-Authors: Scott E. Giangrande, Scott Collis, Jerry M Straka, Alain Protat, Christopher R Williams, Steven K KruegerAbstract:This study presents a summary of the properties of deep convective Updraft and downdraft cores over the central plains of the United States, accomplished using a novel and now-standard Atmospheric Radiation Measurement Program (ARM) scanning mode for a commercial wind-profiler system. A unique profilerbased hydrometeor fall-speed correction method modeled for the convective environment was adopted. Accuracyofthevelocity retrievalsfromthis effortis expectedtobe within2ms 21 , with minimalbiasandbase core resolution expected near 1km. Updraft cores are found to behave with height in reasonable agreement with aircraft observations of previous continental convection, including those of the Thunderstorm Project. Intense Updraft cores with magnitudes exceeding 15ms 21 are routinely observed. Downdraft cores are less frequently observed, with weaker magnitudes than Updrafts. Weak, positive correlations are found between Updraft intensity (maximum) and Updraft diameter length (coefficient r to 0.5 aloft). Negligible correlations are observed for downdraft core lengths and intensity.
Adam Varble - One of the best experts on this subject based on the ideXlab platform.
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cloud resolving model intercomparison of an mc3e squall line case part i convective Updrafts
Journal of Geophysical Research, 2017Co-Authors: Adam Varble, Scott E. Giangrande, Hugh Morrison, Alexander Khain, Kirk North, Pavlos Kollias, Baojun Chen, Xiquan Dong, Edward R MansellAbstract:An intercomparison study of a midlatitude mesoscale squall line is performed using the Weather Research and Forecasting (WRF) model at 1 km horizontal grid spacing with eight different cloud microphysics schemes to investigate processes that contribute to the large variability in simulated cloud and precipitation properties. All simulations tend to produce a wider area of high radar reflectivity (Z_e > 45 dBZ) than observed but a much narrower stratiform area. The magnitude of the virtual potential temperature drop associated with the gust front passage is similar in simulations and observations, while the pressure rise and peak wind speed are smaller than observed, possibly suggesting that simulated cold pools are shallower than observed. Most of the microphysics schemes overestimate vertical velocity and Ze in convective Updrafts as compared with observational retrievals. Simulated precipitation rates and Updraft velocities have significant variability across the eight schemes, even in this strongly dynamically driven system. Differences in simulated Updraft velocity correlate well with differences in simulated buoyancy and low-level vertical perturbation pressure gradient, which appears related to cold pool intensity that is controlled by the evaporation rate. Simulations with stronger Updrafts have a more optimal convective state, with stronger cold pools, ambient low-level vertical wind shear, and rear-inflow jets. Updraft velocity variability between schemes is mainly controlled by differences in simulated ice-related processes, which impact the overall latent heating rate, whereas surface rainfall variability increases in no-ice simulations mainly because of scheme differences in collision-coalescence parameterizations.
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evaluation of cloud resolving and limited area model intercomparison simulations using twp ice observations 1 deep convective Updraft properties
Journal of Geophysical Research, 2014Co-Authors: Adam Varble, Scott Collis, Ann M Fridlind, Andrew S Ackerman, Jiwen Fan, Edward J Zipser, Ping Zhu, Jeanpierre Chaboureau, Adrian Hill, Ben ShipwayAbstract:Ten 3-D cloud-resolving model simulations and four 3-D limited area model simulations of an intense mesoscale convective system observed on 23–24 January 2006 during the Tropical Warm Pool-International Cloud Experiment (TWP-ICE) are compared with each other and with observed radar reflectivity fields and dual-Doppler retrievals of vertical wind speeds in an attempt to explain published results showing a high bias in simulated convective radar reflectivity aloft. This high-bias results from ice water content being large, which is a product of large, strong convective Updrafts, although hydrometeor size distribution assumptions modulate the size of this bias. Making snow mass more realistically proportional to D2 rather than D3 eliminates unrealistically large snow reflectivities over 40 dBZ in some simulations. Graupel, unlike snow, produces high biased reflectivity in all simulations, which is partly a result of parameterized microphysics but also partly a result of overly intense simulated Updrafts. Peak vertical velocities in deep convective Updrafts are greater than dual-Doppler-retrieved values, especially in the upper troposphere. Freezing of liquid condensate, often rain, lofted above the freezing level in simulated Updraft cores greatly contributes to these excessive upper tropospheric vertical velocities. The strongest simulated Updraft cores are nearly undiluted, with some of the strongest showing supercell characteristics during the multicellular (presquall) stage of the event. Decreasing horizontal grid spacing from 900 to 100 m slightly weakens deep Updraft vertical velocity and moderately decreases the amount of condensate aloft but not enough to match observational retrievals. Therefore, overly intense simulated Updrafts may additionally be a product of unrealistic interactions between convective dynamics, parameterized microphysics, and large-scale model forcing that promote different convective strengths than observed.
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analysis of cloud resolving simulations of a tropical mesoscale convective system observed during twp ice vertical fluxes and draft properties in convective and stratiform regions
Journal of Geophysical Research, 2012Co-Authors: Anthony D Del Genio, Agnieszka A Mrowiec, Catherine Rio, Ann M Fridlind, Andrew S Ackerman, Olivier Pauluis, Adam Varble, Jiwen FanAbstract:We analyze three cloud-resolving model simulations of a strong convective event observed during the TWP-ICE campaign, differing in dynamical core, microphysical scheme or both. Based on simulated and observed radar reflectivity, simulations roughly reproduce observed convective and stratiform precipitating areas. To identify the characteristics of convective and stratiform drafts that are difficult to observe but relevant to climate model parameterization, independent vertical wind speed thresholds are calculated to capture 90% of total convective and stratiform Updraft and downdraft mass fluxes. Convective Updrafts are fairly consistent across simulations (likely owing to fixed large-scale forcings and surface conditions), except that hydrometeor loadings differ substantially. Convective downdraft and stratiform Updraft and downdraft mass fluxes vary notably below the melting level, but share similar vertically uniform draft velocities despite differing hydrometeor loadings. All identified convective and stratiform downdrafts contain precipitation below ~10 km and nearly all Updrafts are cloudy above the melting level. Cold pool properties diverge substantially in a manner that is consistent with convective downdraft mass flux differences below the melting level. Despite differences in hydrometeor loadings and cold pool properties, convective Updraft and downdraft mass fluxes are linearly correlated with convective area, the ratio of ice in downdrafts to that inmore » Updrafts is ~0.5 independent of species, and the ratio of downdraft to Updraft mass flux is ~0.5-0.6, which may represent a minimum evaporation efficiency under moist conditions. Hydrometeor loading in stratiform regions is found to be a fraction of hydrometeor loading in convective regions that ranges from ~10% (graupel) to ~90% (cloud ice). These findings may lead to improved convection parameterizations.« less
Georgios Matheou - One of the best experts on this subject based on the ideXlab platform.
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a joint probability density based decomposition of turbulence in the atmospheric boundary layer
Monthly Weather Review, 2017Co-Authors: Maria J Chinita, Georgios Matheou, Joao Paulo TeixeiraAbstract:AbstractIn convective flows, vertical turbulent fluxes, covariances between vertical velocity and scalar thermodynamic variables, include contributions from local mixing and large-scale coherent motions, such as Updrafts and downdrafts. The relative contribution of these motions to the covariance is important in turbulence parameterizations. However, the flux partition is challenging, especially in regions without convective cloud. A method to decompose the vertical flux based on the corresponding joint probability density function (JPD) is introduced. The JPD-based method partitions the full JPD into a joint Gaussian part and the complement, which represent the local mixing and the large-scale coherent motions, respectively. The coherent part can be further divided into Updraft and downdraft parts based on the sign of vertical velocity. The flow decomposition is independent of water condensate (cloud) and can be applied in cloud-free convection, the subcloud layer, and stratiform cloud regions. The metho...
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eddy diffusivity mass flux and shallow cumulus boundary layer an Updraft pdf multiple mass flux scheme
Journal of the Atmospheric Sciences, 2012Co-Authors: Kay Suselj, Joao Paulo Teixeira, Georgios MatheouAbstract:AbstractIn this study, the eddy diffusivity/mass flux (EDMF) approach is used to combine parameterizations of nonprecipitating moist convection and boundary layer turbulence. The novel aspect of this EDMF version is the use of a probability density function (PDF) to describe the moist Updraft characteristics. A single bulk dry Updraft is initialized at the surface and integrated vertically. At each model level, the possibility of condensation within the Updraft is considered based on the PDF of Updraft moist conserved variables. If the Updraft partially condenses, it is split into moist and dry Updrafts, which are henceforth integrated separately. The procedure is repeated at each of the model levels above. The single bulk Updraft ends up branching into numerous moist and dry Updrafts. With this new approach, the need to define a cloud-base closure is circumvented. This new version of EDMF is implemented in a single-column model (SCM) and evaluated using large-eddy simulation (LES) results for the Barbado...
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an eddy diffusivity mass flux approach to the vertical transport of turbulent kinetic energy in convective boundary layers
Journal of the Atmospheric Sciences, 2011Co-Authors: Marcin L Witek, Joao Paulo Teixeira, Georgios MatheouAbstract:AbstractIn this study a new approach to the vertical transport of the turbulent kinetic energy (TKE) is proposed. The principal idea behind the new parameterization is that organized Updrafts or convective plumes play an important role in transferring TKE vertically within convectively driven boundary layers. The parameterization is derived by applying an Updraft environment decomposition to the vertical velocity triple correlation term in the TKE prognostic equation. The additional mass flux (MF) term that results from this decomposition closely resembles the features of the TKE transport diagnosed from the large-eddy simulation (LES) and accounts for 97% of the LES-diagnosed transport when the Updraft fraction is set to 0.13. Another advantage of the MF term is that it is a function of the Updraft vertical velocity and can be readily calculated using already existing parameterization. The new MF approach, combined with several eddy diffusivity (ED) formulations, is implemented into a simplified 1D TKE p...
