より良いモデルの構築:過飽和度変動が雲滴濃度に影響する可能性(Building a Better Model: Supersaturation Variability May Affect Cloud Droplet Concentration)

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2024-03-27 パシフィック・ノースウェスト国立研究所(PNNL)

気候変動を予測するためには、正確なコンピュータモデリングが不可欠です。人間のエアロゾル粒子の排出は、地球のエネルギーバランスに強く影響を与える大気雲の数濃度の増加を引き起こします。大規模渦流シミュレーションと地球システムモデルは、雲に対するエアロゾルの影響を定量化するために使用されますが、これらのモデルは最小スケールの乱流を解決しません。この研究では、小規模な乱流の変動が通常の大気雲のモデルでは考えられないほどの大きな雲微粒子濃度をもたらすことを示しています。

<関連情報>

過飽和度の乱流ゆらぎによる雲凝結核活性の向上 Enhancements in Cloud Condensation Nuclei Activity From Turbulent Fluctuations in Supersaturation

Jesse C. Anderson, Payton Beeler, Mikhail Ovchinnikov, Will Cantrell, Steven Krueger, Raymond A. Shaw, Fan Yang, Laura Fierce
Geophysical Research Letters  Published: 02 September 2023
DOI:https://doi.org/10.1029/2022GL102635

Details are in the caption following the image

Abstract

The effect of aerosols on the properties of clouds is a large source of uncertainty in predictions of weather and climate. These aerosol-cloud interactions depend critically on the ability of aerosol particles to form cloud droplets. A challenge in modeling aerosol-cloud interactions is the representation of interactions between turbulence and cloud microphysics. Turbulent mixing leads to small-scale fluctuations in water vapor and temperature that are unresolved in large-scale atmospheric models. To quantify the impact of turbulent fluctuations on cloud condensation nuclei (CCN) activation, we used a high-resolution Large Eddy Simulation of a convective cloud chamber to drive particle-based cloud microphysics simulations. We show small-scale fluctuations strongly impact CCN activity. Once activated, the relatively long timescales of evaporation compared to fluctuations causes droplets to persist in subsaturated regions, which further increases droplet concentrations.

Key Points

  • Small-scale turbulence leads to variability in the supersaturation experienced by aerosol particles and cloud droplets within clouds
  • Turbulent fluctuations increase cloud droplet formation at low supersaturation levels in comparison with uniform environmental conditions
  • Atmospheric models that neglect supersaturation variability due to turbulence may underestimate the number concentration of cloud droplets

Plain Language Summary

Increases in cloud droplet number concentrations from human emissions of aerosol particles modify cloud properties, which strongly impacts Earth’s energy balance. Large Eddy Simulations and Earth System Models are used to quantify these aerosol-cloud interactions, but the spatial and temporal resolution of these models is too coarse to represent the impact of turbulence at the smallest scales. In this study, we show that small-scale turbulent fluctuations lead to cloud droplet formation even when air is, on average, subsaturated, which would be impossible in conventional models of cloud microphysics. Our findings suggest that models that neglect turbulent fluctuations in supersaturation will underestimate cloud condensation nuclei activity under specific supersaturation regimes, which will may lead to error in modeled cloud properties.

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1702地球物理及び地球化学
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