Contrasting Responses of Idealised and Realistic Simulations of Shallow Cumuli to Aerosol Perturbations

Spill, George; Stier, Philip; Field, Paul R.; Dagan, Guy

doi:10.1029/2021gl094137

Cited by 3 publications

(1 citation statement)

References 39 publications

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“…However, traditionally, these tools are unable to directly account for changes in the dynamics and thermodynamics of the large‐scale climate system, and hence lack an important component of clouds' response (Abbott & Cronin, 2021; Anber et al., 2019). For example, it was recently shown that the representation of large‐scale effects on the CRM domain, that is, the lateral boundary conditions or “large‐scale forcing” (LSF), could artificially determine clouds' response to aerosol perturbation (Dagan, Stier, Spill, et al., 2022; Spill et al., 2021). Specifically, it was shown that the recent efforts to couple local cloud response with changes in the large‐scale vertical velocity (Abbott & Cronin, 2021) could result in an unrealistic increase in the environmental humidity and thus overestimate clouds' sensitivity to aerosols (Dagan, Stier, Spill, et al., 2022).…”

Section: Introductionmentioning

confidence: 99%

Sub‐Tropical Aerosols Enhance Tropical Cloudiness—A Remote Aerosol‐Cloud Lifetime Effect

Dagan

2022

J Adv Model Earth Syst

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Earth's climate is changing (Masson-Delmotte et al., 2021). Reliable climate predictions are essential for developing climate change mitigation and adaptation strategies. However, climate predictions are still highly uncertain due largely to our limited understanding of the role of clouds in climate change. A major source of uncertainty is related to the cloud response to anthropogenic aerosols (Bellouin et al., 2019). It has been shown that aerosol-cloud-interaction (ACI) mechanisms are cloud-regime-dependent (Altaratz et al., 2014;Christensen et al., 2016;Dagan & Stier, 2020b;Gryspeerdt & Stier, 2012), and most previous studies have evaluated them on a per-regime basis. However, since the different cloud regimes in the atmosphere are connected by the global circulation, aerosol effects on one regime may also affect the properties of different regimes, as well as the transition between the different regimes (Christensen et al., 2020;Dagan & Chemke, 2016;Goren et al., 2019). These inter-cloud regime connections are under-explored and not fully understood.High-resolution, limited-area, cloud-resolving model (CRM) simulations and large-eddy simulations (LES) are the main tools to explore ACI mechanisms. However, traditionally, these tools are unable to directly account for changes in the dynamics and thermodynamics of the large-scale climate system, and hence lack an important component of clouds' response (Abbott & Cronin, 2021;Anber et al., 2019). For example, it was recently shown that the representation of large-scale effects on the CRM domain, that is, the lateral boundary conditions or "large-scale forcing" (LSF), could artificially determine clouds' response to aerosol perturbation (Dagan, Stier, Spill, et al., 2022;Spill et al., 2021). Specifically, it was shown that the recent efforts to couple local cloud response with changes in the large-scale vertical velocity (Abbott & Cronin, 2021) could result in an unrealistic Abstract Clouds' susceptibility to aerosols is considered to be a leading source of uncertainty in climate research. An inability to account simultaneously for the large range of scales involved in cloud-aerosol-climate interactions has hindered the progress of research. In this study, using a novel system of idealized large-eddysimulations that explicitly resolves clouds but also accounts, in an idealized manner, for large-scale changes in the thermodynamic and dynamic conditions and for inter-cloud regime coupling, it is shown that aerosol perturbation in the sub-tropics increases cloudiness in the tropics. Specifically, aerosol-driven sub-tropical rain suppression leads to increased advection of cold and moist air from the sub-tropics to the tropics, thus enhancing tropical cloudiness. The increased tropical cloudiness has a strong cooling effect by reflecting more of the incoming solar radiation. The classical "aerosol-cloud lifetime effect" is shown here to have a small local effect (in the sub-tropics) but a strong remote effect (sub-tropical aerosols increase cloudiness in the tropics)...

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Section: Introductionmentioning

confidence: 99%

Sub‐Tropical Aerosols Enhance Tropical Cloudiness—A Remote Aerosol‐Cloud Lifetime Effect

Dagan

2022

J Adv Model Earth Syst

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Boundary conditions representation can determine simulated aerosol effects on convective cloud fields

Dagan

Stier

Spill

et al. 2022

Commun Earth Environ

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Anthropogenic aerosols effect on clouds remains a persistent source of uncertainty in future climate predictions. The evolution of the environmental conditions controlling cloud properties is affected by the clouds themselves. Hence, aerosol-driven modifications of cloud properties can affect the evolution of the environmental thermodynamic conditions, which in turn could feed back to the cloud development. Here, by comparing many different cloud resolving simulations conducted with different models and under different environmental condition, we show that this feedback loop is strongly affected by the representation of the boundary conditions in the model. Specifically, we show that the representation of boundary conditions strongly impacts the magnitude of the simulated response of the environment to aerosol perturbations, both in shallow and deep convective clouds. Our results raise doubts about the significance of previous conclusions of aerosol-cloud feedbacks made based on simulations with idealised boundary conditions.

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Interactions between trade wind clouds and local forcings over the Great Barrier Reef: a case study using convection-permitting simulations

Zhao,

Huang,

Siems

et al. 2024

Atmos. Chem. Phys.

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Abstract. Trade wind clouds are ubiquitous across the subtropical oceans, including the Great Barrier Reef (GBR), playing an important role in modulating the regional energy budget. These shallow clouds, however, are by their nature sensitive to perturbations in both their thermodynamic environment and microphysical background. In this study, we employ the Weather Research and Forecasting (WRF) model with a convection-permitting configuration at 1 km resolution to examine the sensitivity of the trade wind clouds to different local forcings over the GBR. A range of local forcings including coastal topography, sea surface temperature (SST), and local aerosol loading is examined. This study shows a strong response of cloud fraction and accumulated precipitation to orographic forcing both over the mountains and upwind over the GBR. Orographic lifting, low-level convergence, and lower troposphere stability are found to be crucial in explaining the cloud and precipitation features over the coastal mountains downwind of the GBR. However, clouds over the upwind ocean are more strongly constrained by the trade wind inversion, whose properties are, in part, regulated by the coastal topography. On the scales considered in this study, the warm-cloud fraction and the ensuant precipitation over the GBR show only a small response to the local SST forcing, with this response being tied to the surface flux and lower troposphere stability. Cloud microphysical properties, including cloud droplet number concentration, liquid water path, and precipitation, are sensitive to the changes in atmospheric aerosol population over the GBR. While cloud fraction shows little responses, a slight deepening of the simulated clouds is evident over the upwind region in correspondence to the increased aerosol number concentration. A downwind effect of aerosol loading on simulated cloud and precipitation properties is further noted.

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Contrasting Responses of Idealised and Realistic Simulations of Shallow Cumuli to Aerosol Perturbations

Cited by 3 publications

References 39 publications

Sub‐Tropical Aerosols Enhance Tropical Cloudiness—A Remote Aerosol‐Cloud Lifetime Effect

Sub‐Tropical Aerosols Enhance Tropical Cloudiness—A Remote Aerosol‐Cloud Lifetime Effect

Boundary conditions representation can determine simulated aerosol effects on convective cloud fields

Interactions between trade wind clouds and local forcings over the Great Barrier Reef: a case study using convection-permitting simulations

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