An evaluation of size-resolved cloud microphysics scheme numerics for use with radar observations Part II: Condensation and evaporation

2021 ◽  
Author(s):  
Hyunho Lee ◽  
Ann M. Fridlind ◽  
Andrew S. Ackerman
Keyword(s):  
Weather Forecasting ◽  
Cloud Microphysics ◽  
Model Framework ◽  
Microphysics Scheme ◽  
Climate Change Research ◽  
Numerical Diffusion ◽  
Vertical Advection ◽  
Large Eddy ◽  
Fundamental Process ◽  
Turbulence Effects

AbstractAccurate numerical modeling of clouds and precipitation is essential for weather forecasting and climate change research. While size-resolved (bin) cloud microphysics models predict particle size distributions without imposing shapes, results are subject to artificial size distribution broadening owing to numerical diffusion associated with various processes. Whereas Part 1 addressed collision-coalescence, here we investigate numerical diffusion that occurs in solving condensation and evaporation. In a parcel model framework, all of the numerical schemes examined converge to one solution of condensation and evaporation as the mass grid is refined, and the advection-based schemes are recommended over the reassigning schemes. Including Eulerian vertical advection in a column limits the convergence to some extent, but that limitation occurs at a sufficiently fine mass grid, and the number of iterations in solving vertical advection should be minimized to reduce numerical diffusion. Insubstantial numerical diffusion in solving condensation can be amplified if collision-coalescence is also active, which in turn can be substantially diminished if turbulence effects on collision are incorporated. Large-eddy simulations of a drizzling stratocumulus field reveal that changes in moments of Doppler spectra obtained using different mass grids are consistent with those obtained from the simplified framework, and that spectral moments obtained using a mass grid designed to effectively reduce numerical diffusion are generally closer to observations. Notable differences between the simulations and observations still exist, and our results suggest a need to consider whether factors other than numerical diffusion in the fundamental process schemes employed can cause such differences.

scholarly journals An Evaluation of Size-Resolved Cloud Microphysics Scheme Numerics for Use with Radar Observations. Part I: Collision–Coalescence

2019 ◽  
Vol 76 (1) ◽  
pp. 247-263 ◽  
Author(s):  
Hyunho Lee ◽  
Ann M. Fridlind ◽  
Andrew S. Ackerman
Keyword(s):  
Cloud Microphysics ◽  
Box Model ◽  
Computationally Efficient ◽  
Microphysics Scheme ◽  
Numerical Diffusion ◽  
Radar Observations ◽  
Simulation Fidelity ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Bin Microphysics

Abstract This study evaluates some available schemes designed to solve the stochastic collection equation (SCE) for collision–coalescence of hydrometeors using a size-resolved (bin) microphysics approach and documents their numerical properties within the framework of a box model. Comparing three widely used SCE schemes, we find that all converge to almost identical solutions at sufficiently fine mass grids. However, one scheme converges far slower than the other two and shows pronounced numerical diffusion at the large-drop tail of the size distribution. One of the remaining two schemes is recommended on the basis that it is well converged on a relatively coarse mass grid, stable for large time steps, strictly mass conservative, and computationally efficient. To examine the effects of SCE scheme choice on simulating clouds and precipitation, two of the three schemes are compared in large-eddy simulations of a drizzling stratocumulus field. A forward simulator that produces Doppler spectra from the large-eddy simulation results is used to compare the model output directly with radar observations. The scheme with pronounced numerical diffusion predicts excessively large mean Doppler velocities and overly broad and negatively skewed spectra compared with observations, consistent with numerical diffusion demonstrated in the box model. Statistics obtained using the recommended scheme are closer to observations, but notable differences remain, indicating that factors other than SCE scheme accuracy are limiting simulation fidelity.

scholarly journals Large-eddy simulation of radiation fog with comprehensive two-moment bulk microphysics: impact of different aerosol activation and condensation parameterizations

2019 ◽  
Vol 19 (10) ◽  
pp. 7165-7181 ◽  
Author(s):  
Johannes Schwenkel ◽  
Björn Maronga
Keyword(s):  
Liquid Water ◽  
Liquid Water Content ◽  
Cloud Microphysics ◽  
Large Eddy Simulations ◽  
Activation Process ◽  
Radiation Fog ◽  
Microphysics Scheme ◽  
Large Eddy ◽  
Explicit Analysis ◽  
Aerosol Activation

Abstract. In this paper we study the influence of the cloud microphysical parameterization, namely the effect of different methods for calculating the supersaturation and aerosol activation, on the structure and life cycle of radiation fog in large-eddy simulations. For this purpose we investigate a well-documented deep fog case as observed at Cabauw (the Netherlands) using high-resolution large-eddy simulations with a comprehensive bulk cloud microphysics scheme. By comparing saturation adjustment with a diagnostic and a prognostic method for calculating supersaturation (while neglecting the activation process), we find that, even though assumptions for saturation adjustment are violated, the expected overestimation of the liquid water mixing ratio is negligible. By additionally considering activation, however, our results indicate that saturation adjustment, due to approximating the underlying supersaturation, leads to a higher droplet concentration and hence significantly higher liquid water content in the fog layer, while diagnostic and prognostic methods yield comparable results. Furthermore, the effect of different droplet number concentrations is investigated, induced by using different common activation schemes. We find, in line with previous studies, a positive feedback between the droplet number concentration (as a consequence of the applied activation schemes) and strength of the fog layer (defined by its vertical extent and amount of liquid water). Furthermore, we perform an explicit analysis of the budgets of condensation, evaporation, sedimentation and advection in order to assess the height-dependent contribution of the individual processes on the development phases.

Modelling study on the formation of pockets of open cells in marine stratocumulus cloud during CLARIFY

2020 ◽  
Author(s):  
Emma Simpson ◽  
Tom Choularton
Keyword(s):  
Cloud Model ◽  
Direct Interaction ◽  
Cloud Microphysics ◽  
Large Eddy Simulations ◽  
Radiation Budget ◽  
Microphysics Scheme ◽  
Marine Stratocumulus ◽  
Open Cell ◽  
The Earth ◽  
Large Eddy

<p>Due to the wide spread nature of marine stratocumulus cloud they have a significant impact on the Earth’s radiation budget. Such clouds are sensitive to the presence of aerosol, which can promote the break-up of a cloud deck into pockets of open cell convection (POC). The transition from a cloud deck to pockets of open cells changes the overall cloud albedo thus affecting the Earth’s radiation budget. The representation of stratocumulus cloud and the transition to POCs is poorly represented in current climate and weather models. This study aims to improve understanding of this process using extensive in-situ measurements made during the CLARIFY campaign of stratocumulus cloud decks, transition areas between overcast and open cell cloud structures as well as areas of POCs, to inform and compare to large-eddy simulations.</p><p>A variety of different aerosol situations occurred during CLARIFY, combinations of polluted/clean boundary layer and polluted/clean conditions above the cloud layer. Large-eddy simulations are conducted to investigate the sensitivity of clouds to changes in the observed aerosol conditions with a particular focus on whether or not the change in aerosol initiates cloud breakup.</p><p>The MetOffice NERC Cloud model (MONC) is used to preform the large-eddy simulations and employs the CASIM cloud microphysics scheme which includes activation of aerosol particles to cloud drops. Such a model set-up allows direct interaction between aerosols and clouds. Observations from CLARIFY are used to initialise and evaluate model simulations.</p>

scholarly journals An advanced scheme for wet scavenging and liquid-phase chemistry in a regional online-coupled chemistry transport model

2013 ◽  
Vol 13 (3) ◽  
pp. 1177-1192 ◽  
Author(s):  
C. Knote ◽  
D. Brunner
Keyword(s):  
Aqueous Phase ◽  
Climate Model ◽  
Transport Model ◽  
Measurement Data ◽  
Coupled System ◽  
Cloud Microphysics ◽  
Microphysics Scheme ◽  
Meteorological Model ◽  
Wet Scavenging ◽  
Phase Chemistry

Abstract. Clouds are reaction chambers for atmospheric trace gases and aerosols, and the associated precipitation is a major sink for atmospheric constituents. The regional chemistry-climate model COSMO-ART has been lacking a description of wet scavenging of gases and aqueous-phase chemistry. In this work we present a coupling of COSMO-ART with a wet scavenging and aqueous-phase chemistry scheme. The coupling is made consistent with the cloud microphysics scheme of the underlying meteorological model COSMO. While the choice of the aqueous-chemistry mechanism is flexible, the effects of a simple sulfur oxidation scheme are shown in the application of the coupled system in this work. We give details explaining the coupling and extensions made, then present results from idealized flow-over-hill experiments in a 2-D model setup and finally results from a full 3-D simulation. Comparison against measurement data shows that the scheme efficiently reduces SO2 trace gas concentrations by 0.3 ppbv (−30%) on average, while leaving O3 and NOx unchanged. PM10 aerosol mass was increased by 10% on average. While total PM2.5 changes only little, chemical composition is improved notably. Overestimations of nitrate aerosols are reduced by typically 0.5–1 μg m−3 (up to −2 μg m−3 in the Po Valley) while sulfate mass is increased by 1–1.5 μg m−3 on average (up to 2.5 μg m−3 in Eastern Europe). The effect of cloud processing of aerosols on its size distribution, i.e. a shift towards larger diameters, is observed. Compared against wet deposition measurements the system tends to underestimate the total wet deposited mass for the simulated case study.

scholarly journals Development of two-moment cloud microphysics for liquid and ice within the NASA Goddard Earth Observing System Model (GEOS-5)

2014 ◽  
Vol 7 (4) ◽  
pp. 1733-1766 ◽  
Author(s):  
D. Barahona ◽  
A. Molod ◽  
J. Bacmeister ◽  
A. Nenes ◽  
A. Gettelman ◽  
...  
Keyword(s):  
Liquid Droplet ◽  
Cloud Microphysics ◽  
Linear Increase ◽  
Moist Convection ◽  
Ice Crystal ◽  
Microphysics Scheme ◽  
Earth Observing System ◽  
Cloud Properties ◽  
Satellite Retrievals ◽  
Ice Crystal Size

Abstract. This work presents the development of a two-moment cloud microphysics scheme within version 5 of the NASA Goddard Earth Observing System (GEOS-5). The scheme includes the implementation of a comprehensive stratiform microphysics module, a new cloud coverage scheme that allows ice supersaturation, and a new microphysics module embedded within the moist convection parameterization of GEOS-5. Comprehensive physically based descriptions of ice nucleation, including homogeneous and heterogeneous freezing, and liquid droplet activation are implemented to describe the formation of cloud particles in stratiform clouds and convective cumulus. The effect of preexisting ice crystals on the formation of cirrus clouds is also accounted for. A new parameterization of the subgrid-scale vertical velocity distribution accounting for turbulence and gravity wave motion is also implemented. The new microphysics significantly improves the representation of liquid water and ice in GEOS-5. Evaluation of the model against satellite retrievals and in situ observations shows agreement of the simulated droplet and ice crystal effective radius, the ice mass mixing ratio and number concentration, and the relative humidity with respect to ice. When using the new microphysics, the fraction of condensate that remains as liquid follows a sigmoidal dependency with temperature, which is in agreement with observations and which fundamentally differs from the linear increase assumed in most models. The performance of the new microphysics in reproducing the observed total cloud fraction, longwave and shortwave cloud forcing, and total precipitation is similar to the operational version of GEOS-5 and in agreement with satellite retrievals. The new microphysics tends to underestimate the coverage of persistent low-level stratocumulus. Sensitivity studies showed that the simulated cloud properties are robust to moderate variation in cloud microphysical parameters. Significant sensitivity remains to variation in the dispersion of the ice crystal size distribution and the critical size for ice autoconversion. Despite these issues, the implementation of the new microphysics leads to a considerably improved and more realistic representation of cloud processes in GEOS-5, and allows the linkage of cloud properties to aerosol emissions.

scholarly journals Broadening of Modeled Cloud Droplet Spectra Using Bin Microphysics in an Eulerian Spatial Domain

2018 ◽  
Vol 75 (11) ◽  
pp. 4005-4030 ◽  
Author(s):  
Hugh Morrison ◽  
Mikael Witte ◽  
George H. Bryan ◽  
Jerry Y. Harrington ◽  
Zachary J. Lebo
Keyword(s):  
Cloud Condensation Nuclei ◽  
Cloud Droplet ◽  
Droplet Size Distribution ◽  
Dynamical Models ◽  
Mixing Processes ◽  
Numerical Diffusion ◽  
Vertical Advection ◽  
1D Model ◽  
Bin Microphysics ◽  
Condensational Growth

Abstract This study investigates droplet size distribution (DSD) characteristics from condensational growth and transport in Eulerian dynamical models with bin microphysics. A hierarchy of modeling frameworks is utilized, including parcel, one-dimensional (1D), and three-dimensional large-eddy simulation (LES). The bin DSDs from the 1D model, which includes only vertical advection and condensational growth, are nearly as broad as those from the LES and in line with observed DSD widths for stratocumulus clouds. These DSDs are much broader than those from Lagrangian microphysical calculations within a parcel framework that serve as a numerical benchmark for the 1D tests. In contrast, the bin-modeled DSDs are similar to the Lagrangian microphysical benchmark for a rising parcel in which Eulerian transport is not considered. These results indicate that numerical diffusion associated with vertical advection is a key contributor to broadening DSDs in the 1D model and LES. This DSD broadening from vertical numerical diffusion is unphysical, in contrast to the physical mixing processes that previous studies have indicated broaden DSDs in real clouds. It is proposed that artificial DSD broadening from vertical numerical diffusion compensates for underrepresented horizontal variability and mixing of different droplet populations in typical LES configurations with bin microphysics, or the neglect of other mechanisms that broaden DSDs such as growth of giant cloud condensation nuclei. These results call into question the ability of Eulerian dynamical models with bin microphysics to investigate the physical mechanisms for DSD broadening, even though they may reasonably simulate overall DSD characteristics.

scholarly journals Numerical framework and performance of the new multiple-phase cloud microphysics scheme in RegCM4.5: precipitation, cloud microphysics, and cloud radiative effects

2016 ◽  
Vol 9 (7) ◽  
pp. 2533-2547 ◽  
Author(s):  
Rita Nogherotto ◽  
Adrian Mark Tompkins ◽  
Graziano Giuliani ◽  
Erika Coppola ◽  
Filippo Giorgi
Keyword(s):  
Radiative Forcing ◽  
Climate Model ◽  
Regional Climate ◽  
Cloud Microphysics ◽  
Microphysics Scheme ◽  
Additional Information ◽  
Mixing Ratios ◽  
Multiple Phase ◽  
Realistic Representation ◽  
And Performance

Abstract. We implement and evaluate a new parameterization scheme for stratiform cloud microphysics and precipitation within regional climate model RegCM4. This new parameterization is based on a multiple-phase one-moment cloud microphysics scheme built upon the implicit numerical framework recently developed and implemented in the ECMWF operational forecasting model. The parameterization solves five prognostic equations for water vapour, cloud liquid water, rain, cloud ice, and snow mixing ratios. Compared to the pre-existing scheme, it allows a proper treatment of mixed-phase clouds and a more physically realistic representation of cloud microphysics and precipitation. Various fields from a 10-year long integration of RegCM4 run in tropical band mode with the new scheme are compared with their counterparts using the previous cloud scheme and are evaluated against satellite observations. In addition, an assessment using the Cloud Feedback Model Intercomparison Project (CFMIP) Observational Simulator Package (COSP) for a 1-year sub-period provides additional information for evaluating the cloud optical properties against satellite data. The new microphysics parameterization yields an improved simulation of cloud fields, and in particular it removes the overestimation of upper level cloud characteristics of the previous scheme, increasing the agreement with observations and leading to an amelioration of a long-standing problem in the RegCM system. The vertical cloud profile produced by the new scheme leads to a considerably improvement of the representation of the longwave and shortwave components of the cloud radiative forcing.

LES Analysis of Turbulence Effects on Unsteady Flows Past a Circular Cylinder

2003 ◽  
Author(s):  
Tetsuro Tamura ◽  
Yoshiyuki Ono ◽  
Kohji Hashida
Keyword(s):  
Circular Cylinder ◽  
Shear Layer ◽  
Bluff Body ◽  
Unsteady Flows ◽  
Aerodynamic Characteristics ◽  
Cylinder Wake ◽  
Eddy Simulation ◽  
Inflow Boundary Condition ◽  
Large Eddy ◽  
Turbulence Effects

Recent advancement of LES (Large Eddy Simulation) technique for turbulent wake has made it possible to numerically investigate the turbulence effects on aerodynamic characteristics of a bluff body. Here we carry out LES of wake flows past a circular cylinder in the subcritical Reynolds number regime. For inflow boundary condition, homogeneous turbulence generated statistically is given time-sequentially. We bring into focus the interaction between the oncoming turbulence and the shear layer separated from a circular cylinder. Shear layer instability easily occurs under such a stimulation and details of its behavior are visualized. Turbulence effects on unsteady flows in the cylinder wake are discussed. The resulting aerodynamic characteristics and their physical mechanism are clarified.

scholarly journals Forward Semi-Lagrangian Advection with Mass Conservation and Positive Definiteness for Falling Hydrometeors

2010 ◽  
Vol 138 (5) ◽  
pp. 1778-1791 ◽  
Author(s):  
Hann-Ming Henry Juang ◽  
Song-You Hong
Keyword(s):  
Linear Method ◽  
Mass Conservation ◽  
Terminal Velocity ◽  
Cloud Microphysics ◽  
Squall Line ◽  
Test Bed ◽  
Time Step ◽  
Microphysics Scheme ◽  
Advection Scheme ◽  
Lagrangian Advection

Abstract A semi-Lagrangian advection scheme is developed for falling hydrometeors in hopes of replacing the conventional Eulerian scheme that has been widely used in the cloud microphysics scheme of numerical atmospheric models. This semi-Lagrangian scheme uses a forward advection method to determine the advection path with or without iteration, and advected mass in a two-time-level algorithm with mass conservation. Monotonicity is considered in mass-conserving interpolation between Lagrangian grids and model Eulerian grids, thus making it a positive definite advection scheme. For mass-conserving interpolation between the two grid systems, the piecewise constant method (PCM), piecewise linear method (PLM), and piecewise parabolic method (PPM) are proposed. The falling velocity at the bottom cell edge is modified to avoid unphysical deformation by scanning from the top layer to the bottom of the model, which enables the use of a large time step with reasonable accuracy. The scheme is implemented and tested in the Weather Research and Forecasting (WRF) Single-Moment 3-Class Microphysics Scheme (WSM3). In a theoretical test bed with constant terminal velocity, the proposed semi-Lagrangian algorithm shows that the higher-order interpolation scheme produces less diffusive features at maximal precipitation. Results from another idealized test bed with mass-weighted terminal velocity demonstrate that the accuracy of the proposed scheme is still satisfactory even with a time step of 120 s when the mean terminal velocity averaged at the departure and arrival points is employed. A two-dimensional (2D) squall-line test using the WSM3 scheme shows that the control run with the Eulerian advection scheme and the semi-Lagrangian run with the PCM method reveal similar results, whereas behaviors using the PLM and PPM are similar with higher-resolution features, such as mammatus-like clouds.

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