Modeling of Stratocumulus Cloud Layers in a Large Eddy Simulation Model with Explicit Microphysics

Kogan, Yefim L.; Khairoutdinov, M. P.; Lilly, Douglas K.; Kogan, Z. N.; Liu, Qingfu

doi:10.1175/1520-0469(1995)052<2923:moscli>2.0.co;2

Cited by 104 publications

(39 citation statements)

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“…If the supersaturation in strong updrafts above cloud base is approximately steady state, then the left hand side of equation (1) is zero, and the supersaturation production (first right-hand-side term) is balanced by the superstation depletion from condensation (second right-hand-side term). Further, expressing the condensation rate as the growth of all drops and neglecting additional size dependencies in the grow rate factor (G) yields the equation below [Ghan et al, 2011;Kogan et al, 1995;Squires, 1952],…”

Section: 1002/2015jd023647mentioning

confidence: 99%

Aerosol transport and wet scavenging in deep convective clouds: A case study and model evaluation using a multiple passive tracer analysis approach

et al. 2015

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Wet scavenging of aerosols by continental deep convective clouds is studied for a supercell storm complex observed over Oklahoma during the Deep Convective Clouds and Chemistry campaign. A new passive-tracer-based transport analysis framework is developed to characterize convective transport using vertical profiles of several passive trace gases. For this case, the analysis estimates that observed passive gas mixing ratios in the upper troposphere convective outflow consist of 47% low level (<3 km) inflow air, 32% entrained midtroposphere air, and 21% upper troposphere air. The new analysis framework is used to estimate aerosol wet scavenging efficiencies. Observations yield high overall scavenging efficiencies of 81% for submicron aerosol mass. Organic, sulfate, and ammonium aerosols have similar wet scavenging efficiencies (80%-84%). The apparent scavenging efficiency for nitrate aerosol is much lower (57%), but the scavenging efficiency for nitrate aerosol plus nitric acid combined (84%) is close to the other species. Scavenging efficiencies for aerosol number are high for larger particles (84% for 0.15-2.5 μm diameter) but are lower for smaller particles (64% for 0.03-0.15 μm). The storm is simulated using the chemistry version of the Weather Research and Forecasting model. Compared to the observation-based analysis, the standard model strongly underestimates aerosol scavenging efficiencies by 32% and 41% in absolute differences for submicron mass and number. Adding a new treatment of secondary activation significantly improves simulated aerosol scavenging, producing wet scavenging efficiencies that are only 7% and 8% lower than observed efficiencies. This finding emphasizes the importance of secondary activation for aerosol wet removal in deep convective storms.

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Section: 1002/2015jd023647mentioning

confidence: 99%

Aerosol transport and wet scavenging in deep convective clouds: A case study and model evaluation using a multiple passive tracer analysis approach

et al. 2015

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“…However, a numerical artefact currently happens at the interface between a cloud and its environment, when cloudy air is progressively advected in a clear grid box (Clark, 1973;Klaassen and Clark, 1985;Grabowski, 1989;Grabowski and Smolarkiewicz, 1990;Kogan et al, 1995;Stevens et al, 1996a;Grabowski and Morrison, 2008), for instance at the top of a stratoculumus layer. Indeed, explicit calculation of supersaturation is problematic, because it is a second order variable compared to the model prognostic variables T and r t .…”

Section: O Thouron Et Al: Supersaturation Calculation In Large Eddymentioning

confidence: 99%

Supersaturation calculation in large eddy simulation models for prediction of the droplet number concentration

2012

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Abstract.A new parameterization scheme is described for calculation of supersaturation in LES models that specifically aims at the simulation of cloud condensation nuclei (CCN) activation and prediction of the droplet number concentration. The scheme is tested against current parameterizations in the framework of the Meso-NH LES model. It is shown that the saturation adjustment scheme, based on parameterizations of CCN activation in a convective updraft, overestimates the droplet concentration in the cloud core, while it cannot simulate cloud top supersaturation production due to mixing between cloudy and clear air. A supersaturation diagnostic scheme mitigates these artefacts by accounting for the presence of already condensed water in the cloud core, but it is too sensitive to supersaturation fluctuations at cloud top and produces spurious CCN activation during cloud top mixing. The proposed pseudo-prognostic scheme shows performance similar to the diagnostic one in the cloud core but significantly mitigates CCN activation at cloud top.

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“…An approach to reproducing or recycling aerosol particles was presented by Kogan et al (1995) to attempt to account for the fact that smaller droplets (likely formed from smaller aerosol particles) will evaporate first and more readily. Here, the regenerated aerosols are assumed to go to the smallest size bin in the aerosol distribution until it attains its preactivated value (i.e., the number concentration that was set during the model initialization), then the second smallest bin is filled, and so on.…”

Section: Continuous Solute Spectrummentioning

confidence: 99%

A continuous spectral aerosol-droplet microphysics model

Lebo

Seinfeld

2011

Atmos. Chem. Phys.

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Abstract.A two-dimensional (2-D) continuous spectral aerosol-droplet microphysics model is presented and implemented into the Weather Research and Forecasting (WRF) model for large-eddy simulations (LES) of warm clouds. Activation and regeneration of aerosols are treated explicitly in the calculation of condensation/evaporation. The model includes a 2-D spectrum that encompasses wet aerosol particles (i.e., haze droplets), cloud droplets, and drizzle droplets in a continuous and consistent manner and allows for the explicit tracking of aerosol size within cloud droplets due to collision-coalescence. The system of differential equations describing condensation/evaporation (i.e., mass conservation and energy conservation) is solved simultaneously within each grid cell. The model is demonstrated by simulating a marine stratocumulus deck for two different aerosol loadings (100 and 500 cm −3 ), and comparison with the more traditional microphysics modeling approaches (both 1-D bin and bulk schemes) is evaluated. The simulations suggest that in a 1-D bin microphysics scheme, without regeneration, too few particles are produced and hence the mode of the droplet size spectrum occurs at a larger size relative to the 2-D bin model results. Moreover, with regeneration, the 1-D scheme produces too many small droplets and thus shifts the mode toward smaller sizes. These large shifts in the droplet size distribution can potentially have significant effects on the efficiency of the collision-coalescence process, fall speeds, and ultimately precipitation.

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Modeling of Stratocumulus Cloud Layers in a Large Eddy Simulation Model with Explicit Microphysics

Cited by 104 publications

References 0 publications

Aerosol transport and wet scavenging in deep convective clouds: A case study and model evaluation using a multiple passive tracer analysis approach

Aerosol transport and wet scavenging in deep convective clouds: A case study and model evaluation using a multiple passive tracer analysis approach

Supersaturation calculation in large eddy simulation models for prediction of the droplet number concentration

A continuous spectral aerosol-droplet microphysics model

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