Cumulus Model Research Articles

The impact of aerosols as ice nucleating particle on microphysics and electrification in the cumulus model

Here, a heterogeneous ice nucleation parameterization associated with aerosol acting as ice nucleating particle (INP) was implanted into a two-dimensional numerical cumulus model. To explore the impact of INP on microphysical and electrical processes, a comparison was conducted with the original approach, which employs an empirical formula. Simulation results indicate that INP greatly impacted microphysical evolution in the heterogeneous ice nucleation process, reducing total liquid precipitation amounts and causing a slight precipitation delay, as well as increasing the diameter and mixing ratio of ice crystals and the expansion of the vertical distribution of ice crystals. This led to a notable change in electrification in thunderstorms. The increase of ice crystal diameter was the dominant contributor to the enhancement of electrification using the new parameterization. Additionally, unlike the structure of thunderclouds in a mature stage, which always retains a normal dipole structure adopting the empirical formula, a tripole structure developed a lower positive charge, and the polarity inversion with upper negative and lower positive charges occurred when the new parameterization was adopted. This predominately was the result of abundant ice crystals present below the reversal temperature. The electrification characteristics of thunderstorms may have a close connection with lightning activity. It has been found that charge structure changed significantly in the two cases, with the tripolar charge structure facilitating the production of inverted intra-cloud (IC) flashes and negative Cloud-to-ground (CG) flashes simulated by the new parameterization; additionally, clouds simulated using the empirical formula may be able to develop normal IC lightning and positive CG flashes. Therefore, it will be very meaningful to obtain greater insight into the characteristics of thunderstorms electrification in cumulus model with aerosols.

Heterogeneous acceleration algorithms for shallow cumulus convection scheme over GPU clusters

The physical process of atmospheric cumulus convection plays a crucial role in climate modeling, and its complex computational process severely restricts the development of high-resolution climate models. Accelerating the cumulus convective process calculation in climate models is a significant challenge. Traditional CPU-accelerated computing is increasingly unable to meet the growing demand for computing resources from high-resolution climate models. Therefore, developing an efficient cumulus convection scheme is quite valuable and necessary. In response to this demand, this paper selects the University of Washington shallow cumulus (UWshcu) model as the research object and proposes its parallel algorithms suitable for large-scale, heterogeneous, high-performance computing systems: (1) the single GPU acceleration algorithm based on CUDA C, namely GPU-UWshcu; (2) the multi-NVIDIA GPUs acceleration algorithm based on the MPI+CUDA hybrid programming model, namely CGPUs-UWshcu; (3) the multi-AMD GPUs acceleration algorithm based on MPI+HIP, namely HGPUs-UWshcu; (4) the multiple CPUs+GPUs acceleration algorithm based on MPI+OpenMP+HIP, namely MOH-UWshcu. Experimental results show that these algorithms are efficient and have good scalability. GPU-UWshcu achieves a speedup of 74.39× on a single Tesla V100 GPU compared with the serial algorithm running on an Intel Xeon E5-2680 v2 CPU core, and CGPUs-UWshcu achieves a 151.22× speedup on 16 Tesla V100 GPUs compared to a single Intel Xeon E5-2630 v4 CPU (10 cores). On the ORISE supercomputer, HGPUs-UWshcu uses 1024 AMD GPUs to achieve a 664.65× speedup compared to a single CPU (32 cores), with a parallel efficiency of 68.91% compared to using 32 GPUs. Compared to using the same number of CPU cores, MOH-UWshcu uses 8192 CPU cores+1024 GPUs to achieve a speedup of 4.98×, with 55.22 TFLOPS in double precision.

Precipitation Simulation from the Cumulus Convection Parameterization Schemes Based on the WRF Model in the Weihe River Basin, china

Two cumulus convection parameterization schemes, i.e., Kain-Fritsch (K-F) and Grell-3 based on the V4.1.2 Weather Research and Forecasting (WRF) model, were used to simulate the summer precipitation in the Weihe River Basin using hourly precipitation data at the resolution of 5 km and 2 km. the precipitation experiment results at different resolution were compared and analyzed. The root square error and correlation coefficient were used to verify and evaluate the simulation results. The results show that in K-F and Grell-3, the two cumulus model simulations with a resolution of 5 km can explain the spatial distribution pattern of precipitation and the diurnal variation process, and the experimental simulation results are consistent with the actual observations. The summer precipitation simulation in June, July, and August is highly sensitive to the two cumulus parameter schemes of K-F and Grell-3. The simulated precipitation value is higher than the actual value, and the root mean square errors (RMSEs) of K-F and Grell-3 schemes are 5.49-13.29 and 5.69-10.88, respectively. In terms of precipitation simulation, Grell-3 scheme is better than K-F scheme, especially in areas with heavy rainfall. When the resolution is increased to 2 km, the regions with heavy precipitation can be displayed more finely. The influence of water vapor flux and vertical velocity changes on precipitation in the Weihe River is analyzed from two aspects, i.e., water conditions and atmospheric instability. From the simulation results by the K-F scheme, the vertical velocity fluctuations are unstable and strong in the convective area, and the convective rainfall is relatively high. From the simulation results by Grell-3, the vertical velocity is large and increased rapidly, which is conducive to the generation of large-scale heavy precipitation. Both schemes are very sensitive to the simulation of water vapor transport and vertical velocity. This study provides a basis for the research on the adaptability of regional precipitation simulation.

Cumulus cloud modeling from images based on VAE-GAN

BackgroundCumulus clouds are important elements in creating virtual outdoor scenes. Modeling cumulus clouds that have a specific shape is difficult owing to the fluid nature of the cloud. Image-based modeling is an efficient method to solve this problem. Because of the complexity of cloud shapes, the task of modeling the cloud from a single image remains in the development phase. MethodsIn this study, a deep learning-based method was developed to address the problem of modeling 3D cumulus clouds from a single image. The method employs a three-dimensional autoencoder network that combines the variational autoencoder and the generative adversarial network. First, a 3D cloud shape is mapped into a unique hidden space using the proposed autoencoder. Then, the parameters of the decoder are fixed. A shape reconstruction network is proposed for use instead of the encoder part, and it is trained with rendered images. To train the presented models, we constructed a 3D cumulus dataset that included 200 3D cumulus models. These cumulus clouds were rendered under different lighting parameters. ResultsThe qualitative experiments showed that the proposed autoencoder method can learn more structural details of 3D cumulus shapes than existing approaches. Furthermore, some modeling experiments on rendering images demonstrated the effectiveness of the reconstruction model. ConclusionThe proposed autoencoder network learns the latent space of 3D cumulus cloud shapes. The presented reconstruction architecture models a cloud from a single image. Experiments demonstrated the effectiveness of the two models.

A numerical study of aerosol effects on electrification of thunderstorms

Numerical simulations are performed to investigate the effect of aerosol on microphysical and electrification in thunderstorm clouds. A two-dimensional (2-D) cumulus model with electrification scheme including non-inductive and inductive charge separation is used. The concentration of aerosol particles with distribution fitted by superimposing three log-normal distributions rises from 50 to 10,000cm−3. The results show that the response of charge separation rate to the increase of aerosol concentration is nonmonotonic. When aerosol concentration is changed from 50 to 1000cm−3, a stronger formation of cloud droplet, graupel and ice crystal results in increasing charge separation via non-inductive and inductive mechanism. However, in the range of 1000–3000cm−3, vapor competition arises in the decrease of ice crystal mixing ratio and the reduction of ice crystals size leads to a slightly decrease in non-inductive charge rate, while inductive charging rate has no significant change in magnitude. Above aerosol concentration of 3000cm−3, the magnitude of charging rate which keeps steady is insensitive to the increase in aerosol concentration. The results also suggest that non-inductive charge separation between ice crystal and graupel contributes to the main upper positive charge region and the middle negative charge region. Inductive graupel–cloud droplet charge separation, on the other hand, is found to play an important role in the development of lower charge region.

Aerosol effect on the land-ocean contrast in thunderstorm electrification and lightning frequency

Numerical simulations are carried out to investigate the effect of aerosol on microphysical, electrification and lightning frequency in thunderstorm clouds. A two-dimensional (2-D) cumulus model with electrification and lightning process is used to investigate the difference of electrification and lightning process between continental and maritime thunderclouds. The results show that in the developing stage higher concentration aerosol in continental thundercloud leads to more cloud droplets and stronger updraft in continental thundercloud than in maritime thundercloud. The continental thundercloud with more ice particles production and larger size of graupel has stronger charge separation rate than that in maritime thundercloud. However, in the dissipation stage, the enhancement of cloud water content consumption lead to a lower cloud water content in continental thundercloud, leading weaker charge separation rate than that in maritime thundercloud. In addition, ice mass flux enhancement in continental thundercloud results in stronger lightning production. The continental thundercloud produces lightning frequency 1.5 times higher than maritime thundercloud.

Sensitivity Studies of Convective Schemes and Model Resolutions in Simulations of Wintertime Circulation and Precipitation over the Western Himalayas

The present study examines the performance of convective parameterization schemes at two different horizontal resolutions (90 and 30 km) in simulating winter (December–February; DJF) circulation and associated precipitation over the Western Himalayas using the regional climate model RegCM4. The model integrations are carried out in a one-way nested mode for three distinct precipitation years (excess, normal and deficit) using four combinations of cumulus schemes. The National Center for Environment Prediction—Department of Energy Reanalysis-2 project utilized gridded data, observed precipitation data from the India Meteorological Department and station data from the Snow and Avalanche Study Establishment were used to evaluate model performance. The seasonal mean circulation patterns and precipitation distribution are well demonstrated by all of the cumulus convection schemes. However, model performance varies using different schemes. Statistical analysis confirms that the root mean square error is reduced by about 2–3 times and the correlation coefficient (CC) increases in the fine resolution (30 km) simulations compared to coarse resolution (90 km) simulations. A statistically significant CC (at a 10 % significance level) is found only in the fine resolution simulations. The Grell cumulus model with a Fritsch–Chappell closure (Grell-FC) is better at simulating seasonal mean patterns and inter-annual variability of two contrasting winter seasons than the other scheme combinations.

Multiscale Models for Cumulus Cloud Dynamics

AbstractCumulus clouds involve processes on a vast range of scales—including cloud droplets, turbulent mixing, and updrafts and downdrafts—and it is often difficult to determine how processes on different scales interact with each other. In this article, several multiscale asymptotic models are derived for cumulus cloud dynamics in order to (i) provide a systematic scale analysis on each scale and (ii) clarify the nature of interactions between different scales. In terms of scale analysis, it is shown that shallow cumulus updrafts can be described by balanced dynamics with a balance between source terms and ascent/descent; this is a cloud-scale version of so-called weak-temperature-gradient models. In terms of multiscale interactions, a model is derived that connects these balanced updrafts to the fluctuations within the balanced updraft envelope. These fluctuations describe parcels and updraft pulses, and this model encompasses some of the multiscale aspects of entrainment. In addition to this shallow cumulus model, to provide a broad picture of general cumulus dynamics, multiscale models are also derived for other scales; these include models for parcels and subparcel turbulent mixing and models for deep cumulus. Broadly speaking, the differences between the shallow and deep cases convey the notion that shallow cumulus dynamics are parcel dominated, whereas deep cumulus dynamics are updraft dominated; this is largely due to the difference in the apparent magnitude of the background temperature stratification. In addition to their use in guiding theory, the multiscale models also provide a framework for multiscale numerical simulations.

Can a cumulus cell complex be used to select spermatozoa for assisted reproduction?

Since the onset of intracytoplasmic sperm injection, researchers have intensified the search for the ideal spermatozoa to be used for injection. The aim of this study was to record the functional role of cumulus cell interaction with human spermatozoa as far as capacitation, acrosome reaction, morphology, zona binding and chromatin packaging quality are concerned. Using a previously described cumulus oophorus model, we recorded specific sperm functional aspects of sperm populations that transverse a cumulus cells mass. Control spermatozoa were kept under similar experimental conditions in the culture media only. Results indicated cumulus cells to be beneficial to spermatozoa as far as functional and capacitational events are concerned. The mean percentage of morphologically normal spermatozoa in the control sample was 6.9%, while the spermatozoa that traversed the cumulus oophorus (test) had a significantly higher percentage of normal forms (mean 9.5%; P < or = 0.01). We observed a decline in the percentage of CMA3-positive spermatozoa when we compared the control population (49.1%) to the test, i.e. 38.4%, (P = <0.05), thus implying that the spermatozoa with good chromatin condensation increased during cumulus penetration. Significantly more (P < or = 0.01) acrosome-reacted spermatozoa were found in the penetrated spermatozoa (mean 23%) than in the control spermatozoa (mean 11%). The test spermatozoa had a higher zona binding capacity with significantly more (P < or = 0.01) tightly bound spermatozoa on the hemizona (61 +/- 15) than the control spermatozoa (47 +/- 18). In the absence of sophisticated and expensive sperm selection products, the use of a cumulus model to select spermatozoa for intracellular sperm injection seems to be an alternative method.

Boundary Layer Dynamics in a Simple Model for Convectively Coupled Gravity Waves

Abstract A simplified model of intermediate complexity for convectively coupled gravity waves that incorporates the bulk dynamics of the atmospheric boundary layer is developed and analyzed. The model comprises equations for velocity, potential temperature, and moist entropy in the boundary layer as well as equations for the free tropospheric barotropic (vertically uniform) velocity and first two baroclinic modes of vertical structure. It is based on the multicloud model of Khouider and Majda coupled to the bulk boundary layer–shallow cumulus model of Stevens. The original multicloud model has a purely thermodynamic boundary layer and no barotropic velocity mode. Here, boundary layer horizontal velocity divergence is matched with barotropic convergence in the free troposphere and yields environmental downdrafts. Both environmental and convective downdrafts act to transport dry midtropospheric air into the boundary layer. Basic states in radiative–convective equilibrium are found and are shown to be consistent with observations of boundary layer and free troposphere climatology. The linear stability of these basic states, in the case without rotation, is then analyzed for a variety of tropospheric regimes. The inclusion of boundary layer dynamics—specifically, environmental downdrafts and entrainment of free tropospheric air—enhances the instability of both the synoptic-scale moist gravity waves and nonpropagating congestus modes in the multicloud model. The congestus mode has a preferred synoptic-scale wavelength, which is absent when a purely thermodynamic boundary layer is employed. The weak destabilization of a fast mesoscale wave, with a phase speed of 26 m s−1 and coupling to deep convection, is also discussed.

Testing a cumulus parametrization with a cumulus ensemble model in weak‐temperature‐gradient mode

AbstractThis paper prototypes a method for calibrating a cumulus parametrization against a cumulus ensemble model. The key to this technique is to run the cumulus model and the parametrization in identical ‘test cells’ that provide forcing typical of that seen over tropical oceans. In particular, the mean temperature profile is relaxed to a reference profile that is assumed to be characteristic of the environment of the convection. This is done by calculating the mean vertical velocity needed to balance heating due to convection, latent‐heat release, and radiation with adiabatic cooling. This ‘weak‐temperature‐gradient’ vertical‐velocity profile is then used to advect moisture vertically and, via mass continuity, through the sides of the test cell, entraining reference‐profile air as needed.As an example, a toy cumulus parametrization used previously is altered to reproduce the dependence of rainfall rate on surface wind speed shown by the cumulus ensemble model. This alteration greatly changes the behaviour of simulated large‐scale disturbances in an aquaplanet equatorial beta‐plane model. In particular, increasing the slope of the curve of rainfall rate against wind speed results in the development of much greater synoptic‐scale variance. Copyright © 2007 Royal Meteorological Society

A Parameterization for Land–Atmosphere-Cloud Exchange (PLACE): Documentation and Testing of a Detailed Process Model of the Partly Cloudy Boundary Layer over Heterogeneous Land

This paper presents a general description of, and demonstrates the capabilities of, the Parameterization for Land–Atmosphere–Cloud Exchange (PLACE). The PLACE model is a detailed process model of the partly cloudy atmospheric boundary layer and underlying heterogeneous land surfaces. In its development, particular attention has been given to three of the model's subprocesses: the prediction of boundary layer cloud amount, the treatment of surface and soil subgrid heterogeneity, and the liquid water budget. The model includes a three-parameter nonprecipitating cumulus model that feeds back to the surface and boundary layer through radiative effects. Surface heterogeneity in the PLACE model is treated both statistically and by resolving explicit subgrid patches. The model maintains a vertical column of liquid water that is divided into seven reservoirs, from the surface interception store down to bedrock. Five single-day demonstration cases are presented, in which the PLACE model was initialized, run, and compared to field observations from four diverse sites. The model is shown to predict cloud amount well in these while predicting the surface fluxes with similar accuracy. A slight tendency to underpredict boundary layer depth is noted in all cases. Sensitivity tests were also run using anemometer-level forcing provided by the Project for Inter-comparison of Land-surface Parameterization Schemes (PILPS). The purpose is to demonstrate the relative impact of heterogeneity of surface parameters on the predicted annual mean surface fluxes. Significant sensitivity to subgrid variability of certain parameters is demonstrated, particularly to parameters related to soil moisture. A major result is that the PLACE-computed impact of total (homogeneous) deforestation of a rain forest is comparable in magnitude to the effect of imposing heterogeneity of certain surface variables, and is similarly comparable to the overall variance among the other PILPS participant models. Were this result to be bourne out by further analysis, it would suggest that today's average land surface parameterization has little credibility when applied to discriminating the local impacts of any plausible future climate change.

Study on the Effect of Updraft to Precipitation Processees using Two-Dimensional Cumulus Model

The effect of updraft to precipitation processes is investigated numerically. We use the numerical simulation model which has detailed cloud microphysics and represents cold rain processes. We recognize that the relationship between updraft and rainfall amount is not monotonous. This relationship is explained by referring the results of simulation that the hail occasion is important for heavy rainfall. We supporse that there is suitable updraft strength to cause heavy rainfall and that heavier updraft does not cause heavier rainfall. This supposiotion is qualitatively confirmed through comparison with rain gage data at Gozaisho-yama, Shiga Prefecture.

Simple Cumulus Models in One-Dimensional Radiative Convective Equilibrium Problems

The cumulus model presented by Lindzen et al. for calculating one-dimensional radiative convective equilibria is examined. When only the balance of moist static energy is considered, the value of the convective mass flux Mc is required to be externally specified. Dependency of equilibrium solutions on Mc shows that an upper limit of the value of Mc exists above which the temperature in the region of upward motion is lower than that in the region of downward motion; that is, the buoyancy is negative. Lindzen et al. tried to specify the value of Mc by introducing the surface heat fluxes. However, it is found that the buoyancy of their solution is negative. In order to obtain an appropriate equilibrium solution where the buoyancy is positive, the balance of kinetic energy, especially the dissipative process, should be considered. It is found that the value of Mc, which gives a realistic value of the dissipation rate, is close to the upper limit. In order to have a solution with a more realistic temperature profile, the model assumption that Mc is independent of time and height should be released. Calculations on the greenhouse effect show that dependency of Mc on the total optical thickness changes sign within the range of the observed dissipation rate. The water vapor content at the tropopause becomes larger as the total optical thickness increases.

A model of the effect of cumulus clouds on the redistribution and transformation of pollutants

A one‐dimensional time‐dependent cumulus model was developed to study the effects of convective clouds on air pollutants. The model contains two drafts, core and periphery, surrounded by a stagnant environment. There are exchanges between the two drafts and between cloud and environment, both by dynamic entrainment/detrainment and by turbulence. Application to a “base case” with given initial conditions and producing a cloud 7 km thick is analyzed. Microphysical exchanges involved mainly cloud water, rain, and graupel. The warm rain mechanism seems to dominate, including a frozen drop stage. At lower temperatures the ice mechanism is also effective. Only a minor fraction of the SO2 entering the cloud becomes oxidized and is partly rained out to the ground as sulfate. Although H2O2 is the main and faster oxidant, O3 also contributes in a rather large proportion. Oxidation of NOx with subsequent dissolution of the acids is negligible, unless the OH radical concentration in the air is very high. Production and deposition of acidity depends on SO2 concentration in a very nonlinear way, but approximately linearly on H2O2 concentration. The acidity concentration of precipitation varies substantially under different regions of the cloud. Consideration of solutes in solid phase is shown to appreciably influence the results. The model was also applied to small, 2‐km‐thick cumuli, and the results compared with those of a three‐dimensional model and with observations, with reasonable agreement.

Viewing zenith angle dependence of cloudiness determined from coincident GOES East and GOES West data

The dependence of observed cloudiness on the satellite or viewing zenith angle (VZA) is examined, using a combination of two cloud amount data sets derived from nearly simultaneous, collocated Geostationary Operational Environmental Satellite (GOES) West and GOES East radiances over the Pacific Ocean during May 1979 and July 1983. A third data set, GOES Prime, is used to estimate the amount of cloud variation due to changes in sensor resolution with VZA. The data are analyzed for single‐layer and total cloudiness, as derived with a hybrid bispectral threshold method. The frequencies of occurrence for low, middle, and high clouds, 96%, 47%, and 28%, respectively, are typical of oceanic cloud populations. Cloud fractions increased with increasing VZA for almost all cases. Low clouds showed the greatest increases for small cloud amounts around 0.1, while the greatest increases for high clouds were found for cloud amounts around 0.5. Midlevel clouds showed only a slight dependence on VZA. Total cloudiness increased the most, reflecting its predominantly low‐cloud composition. Uncertainties in retrieved cloud fraction also increase with the VZA. Resolution changes with VZA were estimated to cause up to 28% of the increase in cloudiness for certain low‐cloud amounts. Very little of the high‐cloud increases were the result of resolution changes. Simple geometrical formulas were used to model the results. A single‐layer cumulus model was found to be the best fit to the layer cloud data. A formulation combining the single‐layer models was used to describe the variation of total cloud cover with VZA. The regression fit of these data to the multilayer model reduced the mean bias errors due to VZA effects from ≈0.058 to ≈0.004. It is concluded that the effects of the VZA should be incorporated in the construction of satellite‐derived climatologies and other Earth‐observing applications.

Radiative Transfer to Space through a Precipitating Cloud at Multiple Microwave Frequencies. Part I: Model Description

Abstract In a two-part study we investigate the impact of time-dependent cloud microphysical structure on the transfer to space of passive microwave radiation at several frequencies across the EHF and lower SHF portions of the microwave spectrum in order to explore the feasibility of using multichannel passive-microwave retrieval techniques for the estimation of precipitation from space-based platforms. A series of numerical sensitivity experiments have been conducted that were designed to quantify the impact of an evolving cumulus cloud in conjunction with a superimposed rain layer on the transfer to space of microwave radiation emitted and scattered from the cloud layers, rain layer and the underlying surface. The specification of cloud microphysics has been based on the results of a time-dependent two-dimensional numerical cumulus model developed by Hall (1980). An assortment of vertically homogeneous rain layers, described by the Marshall-Palmer rain drop distribution, has been inserted in the model a...

On the role of vertical resolution in the analysis of shallow convective fields

The present paper is an attempt to demonstrate the fact that misleading information about the thermodynamic structure of shallow cumulus fields is obtained when standard isobaric level (SIL) data input is used. The 1-D cumulus model serves as the main tool of examination and the reference input data are those of significant levels (SL) in soundings. The computed cloud tops (SIL) exceeded (SL) tops in nearly 80% of the cases and the excesses are more than 1 kilometre in 25% of the cases. Some discrepancies were also found in potential stability analysis. The local changes in equivalent potential temperature may be seriously affected and even falsified. The important role of high resolution in studies of mesoscale phenomena was again accentuated.

Mixing Mechanisms in Cumulus Congestus Clouds. Part II: Numerical Simulations

Abstract The entrainment mechanisms of deep convective clouds in South Africa are simulated by using both axially and slab-symmetric cumulus models having very high spatial and temporal resolutions. The simulated clouds on three different days show a structured organization with small-scale features such as in-cloud downdrafts. The mixing processes are examined by analyzing the time variation of dynamic and thermodynamic quantities along computed parcel trajectories. The calculations indicate that most of the entrainment occurs at the cloud top. Evaporative cooling and perturbation pressure cause downdrafts that transport highly diluted air from the cloud top down to lower levels. The penetrative downdrafts are mainly located near the edges of the cloud. In the presence of wind shear the downshear portion of the clouds becomes cooler and more diluted, and it is associated with stronger downdrafts compared to the upshear side. The asymmetric organization is attributed to turbulent exchange of horizontal mo...

A Diagnostic Modeling Study of the Stratiform Region Associated with a Tropical Squall Line

Abstract Wind and thermodynamic data analyzed in the startiform region of a tropical squall line have been combined with a kinematic, three-dimensional cloud model to study the precipitation processes in this region. The flux of condensate into the stratiform region from the convective region has been parameterized by specifying vertical profiles of cloud water, cloud ice, snow and graupel at the boundary between these two regions, through the use of a one-dimensional time-dependent cumulus model. A standard case, in which all four forms of condensate stream into the stratiform (anvil) is studied in detail. The graupel entering this region rapidly removes snow advected into the anvil from the cells as well as snow produced by the mesoscale updraft. The snow produced by the mesoscale updraft actively contributes to this precipitation by providing mass for the graupel particles to feed upon. A series of sensitivity studies are discussed which reveal two distinct regions: a precipitation region due to fallou...