EFFECT OF SOIL MOISTURE ON SHALLOW CUMULUS CLOUD IN LARGE EDDY SIMULATION

Abstract. Large-eddy simulation (LES) models are an excellent tool to improve our understanding of aerosol–cloud interactions (ACI). We introduce a prognostic aerosol scheme with multiple aerosol species in the Dutch Atmospheric Large-Eddy Simulation model (DALES), especially focused on simulating the impact of cloud microphysical processes on the aerosol population. The numerical treatment of aerosol activation is a crucial element for simulating both cloud and aerosol characteristics. Two methods are implemented and discussed: an explicit activation scheme based on κ-Köhler theory and a more classic approach using updraught strength. Sample model simulations are based on the Rain in Shallow Cumulus over the Ocean (RICO) campaign, characterized by rapidly precipitating warm-phase shallow cumulus clouds. We find that in this pristine ocean environment virtually all aerosol mass in cloud droplets is the result of the activation process, while in-cloud scavenging is relatively inefficient. Despite the rapid formation of precipitation, most of the in-cloud aerosol mass is returned to the atmosphere by cloud evaporation. The strength of aerosol processing through subsequent cloud cycles is found to be particularly sensitive to the activation scheme and resulting cloud characteristics. However, the precipitation processes are considerably less sensitive. Scavenging by precipitation is the dominant source for in-rain aerosol mass. About half of the in-rain aerosol reaches the surface, while the rest is released by evaporation of falling precipitation. The effect of cloud microphysics on the average aerosol size depends on the balance between the evaporation of clouds and rain and ultimate removal by precipitation. Analysis of typical aerosol size associated with the different microphysical processes shows that aerosols resuspended by cloud evaporation have a radius that is only 5 % to 10 % larger than the originally activated aerosols. In contrast, aerosols released by evaporating precipitation are an order of magnitude larger.

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Large-Eddy Simulation and Parametrization of the Effects of Shear on Shallow Cumulus Convection

Boundary-Layer Meteorology ◽

10.1023/a:1001836612775 ◽

1999 ◽

Vol 91 (1) ◽

pp. 65-80 ◽

Cited By ~ 27

Author(s):

A. R. Brown

Keyword(s):

Large Eddy Simulation ◽

Cumulus Convection ◽

Eddy Simulation ◽

Shallow Cumulus ◽

Large Eddy

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LES of a Spatially Developing Atmospheric Boundary Layer: Application of a Fringe Method for the Stratocumulus to Shallow Cumulus Cloud Transition

Monthly Weather Review ◽

10.1175/mwr-d-13-00400.1 ◽

2014 ◽

Vol 142 (9) ◽

pp. 3418-3424 ◽

Cited By ~ 8

Author(s):

M. Inoue ◽

G. Matheou ◽

J. Teixeira

Keyword(s):

Boundary Layer ◽

Boundary Conditions ◽

Atmospheric Boundary Layer ◽

Cumulus Cloud ◽

Eddy Simulation ◽

Shallow Cumulus ◽

Outflow Boundary Conditions ◽

Large Eddy ◽

Inflow Condition ◽

Outflow Boundary

An arrangement of a large-eddy simulation (LES) is described that facilitates a spatially developing thermally stratified atmospheric boundary layer (ABL). When the inflow and outflow boundary conditions are specified, the LES of stably stratified ABL turns out to be challenging because spurious reflections of waves at the boundary accumulate inside the domain. To tackle this problem, a fringe method with an auxiliary LES running concurrently is applied to enforce upstream/downstream boundary conditions. An artificial forcing term is applied within a fringe region located at the beginning of the main LES domain in order to ensure statistically stationary inflow boundary conditions. The auxiliary LES, which is horizontally homogeneous in a doubly periodic domain, is used to determine the inflow condition of the main LES domain. The present scheme is used to provide an Eulerian perspective of the stratocumulus to shallow cumulus cloud (Sc–Cu) transition, one of the key cloud regimes over the subtropical ocean. In this study, the transition is triggered by increasing the sea surface temperature (SST) and the LES runs until a statistically steady evolution of the Sc–Cu transition is achieved. The flow statistics are compared with those from a recycling-type method and it is found that the fringe method is more suitable for the current applications.

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Surface Solar Irradiance in Continental Shallow Cumulus Fields: Observations and Large-Eddy Simulation

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-19-0261.1 ◽

2019 ◽

Vol 77 (3) ◽

pp. 1065-1080 ◽

Cited By ~ 4

Author(s):

Jake J. Gristey ◽

Graham Feingold ◽

Ian B. Glenn ◽

K. Sebastian Schmidt ◽

Hong Chen

Keyword(s):

Radiative Transfer ◽

Large Eddy Simulation ◽

Great Plains ◽

Solar Irradiance ◽

Climate Models ◽

Valuable Insight ◽

Energy Potential ◽

Eddy Simulation ◽

Shallow Cumulus ◽

Large Eddy

Abstract This study examines shallow cumulus cloud fields and their surface shortwave radiative effects using large-eddy simulation (LES) along with observations across multiple days at the Atmospheric Radiation Measurement Southern Great Plains atmospheric observatory. Pronounced differences are found between probability density functions (PDFs) of downwelling surface solar irradiance derived from observations and LES one-dimensional (1D) online radiation calculations. The shape of the observed PDF is bimodal, which is only reproduced by offline three-dimensional (3D) radiative transfer calculations, demonstrating PDF bimodality as a 3D radiative signature of continental shallow cumuli. Local differences between 3D and 1D radiative transfer calculations of downwelling surface solar irradiance are, on average, larger than 150 W m−2 on one afternoon. The differences are substantially reduced when spatially averaged over the LES domain and temporally averaged over the diurnal cycle, but systematic 3D biases ranging from 2 to 8 W m−2 persist across different days. Covariations between the domain-averaged surface irradiance, framed as a surface cloud radiative effect, and the simulated cloud fraction are found to follow a consistent diurnal relationship, often exhibiting hysteresis. In contrast, observations show highly variable behavior. By subsampling the LES domain, it is shown that this is due to the limited sampling density of inherently 3D observations. These findings help to define observational requirements for detecting such relationships, provide valuable insight for evaluating weather and climate models against surface observations as they push to ever higher resolutions, and have important implications for future assessments of solar renewable energy potential.

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Explicit aerosol-cloud interaction in the Dutch Atmospheric Large-Eddy Simulation model DALES4.1-M7

10.5194/gmd-2019-147 ◽

2019 ◽

Author(s):

Marco de Bruine ◽

Maarten Krol ◽

Jordi Vilà-Guerau de Arellano ◽

Thomas Röckmann

Keyword(s):

Large Eddy Simulation ◽

Simulation Model ◽

Large Eddy Simulation Model ◽

Aerosol Cloud ◽

Eddy Simulation ◽

Aerosol Mass ◽

Shallow Cumulus ◽

Cloud Characteristics ◽

Large Eddy ◽

Order Of Magnitude

Abstract. Large-Eddy Simulations (LES) are an excellent tool to improve our understanding of the aerosol-cloud interaction (ACI). These models combine a spatial resolution high enough to resolve cloud structures with domain sizes large enough to simulate macroscale dynamics and feedback between clouds. However, most research on ACI using LES simulations is focused on changes in cloud characteristics. The feedback of ACI on the aerosol population remains relatively understudied. We introduce a prognostic aerosol scheme with multiple aerosol species in the Dutch Atmospheric Large-Eddy Simulation model (DALES), especially focused on simulating the feedback of ACI on the aerosol population. The numerical treatment of aerosol activation is a crucial element in the simulation of ACI. Two methods are implemented and discussed: an explicit activation scheme based on κ-Köhler theory and a more classic approach using updraft strength. Model simulations are validated against observations using the Rain in Shallow Cumulus over the Ocean (RICO) campaign, characterised by rapidly precipitating, warm-phase shallow cumulus clouds. We find that in this pristine ocean environment virtually all aerosols enter the cloud phase through activation while in-cloud scavenging is relatively inefficient. Despite the rapid formation of precipitation, most of the in-cloud aerosol mass is returned to the atmosphere by cloud evaporation. The strength of aerosol processing through subsequent cloud cycles is found to be particularly sensitive to the activation scheme and resulting cloud characteristics. However, the precipitation processes are considerably less sensitive. Scavenging by precipitation is the dominant source for in-rain aerosol mass. About half of the in-rain aerosol reaches the surface, while the rest is released by evaporation of falling precipitation. Whether ACI increases or decreases the average aerosol size depends on the balance between the evaporation of clouds and rain, and ultimate removal by precipitation. Analysis of typical aerosol size associated with the different microphysical processes shows that aerosols resuspended by cloud evaporation are only 5 to 10 % larger than the originally activated aerosols. In contrast, aerosols released by evaporating precipitation are an order of magnitude larger.

Download Full-text