Magnitude and timescale of liquid water path adjustments to cloud droplet number concentration perturbations for nocturnal non-precipitating marine stratocumulus
<p>Cloud liquid water path (<span class="inline-formula"><i>L</i></span>) adjusts to perturbations in cloud droplet number concentration (<span class="inline-formula"><i>N</i></span>) over time. We explore the magnitude and ti...
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| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2025-06-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/25/6141/2025/acp-25-6141-2025.pdf |
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| Summary: | <p>Cloud liquid water path (<span class="inline-formula"><i>L</i></span>) adjusts to perturbations in cloud droplet number concentration (<span class="inline-formula"><i>N</i></span>) over time. We explore the magnitude and timescale of this adjustment in nocturnal non-precipitating marine stratocumuli using large eddy simulations of baseline conditions and aerosol seeding experiments for 22 meteorological conditions. The results confirm that the <span class="inline-formula"><i>L</i></span> adjustment (<span class="inline-formula"><i>δ</i><i>L</i></span>) slope (<span class="inline-formula"><i>k</i></span>) is more negative for simulation pairs with relatively low <span class="inline-formula"><i>N</i></span> and less negative for high <span class="inline-formula"><i>N</i></span>. Overall, <span class="inline-formula"><i>k</i></span> is unlikely to be lower than <span class="inline-formula">−0.4</span> within 24 <span class="inline-formula">h</span> of seeding start, meaning the <span class="inline-formula"><i>L</i></span> adjustment is unlikely to fully offset the brightening due to the Twomey effect. After seeding, the <span class="inline-formula"><i>δ</i><i>L</i></span> becomes increasingly negative, which can be characterized by an exponential convergence. This evolution is governed by a short timescale around 5 <span class="inline-formula">h</span> and lasts for around 8–12 <span class="inline-formula">h</span>. It is driven by the feedback between entrainment, <span class="inline-formula"><i>L</i></span>, and boundary layer (BL) turbulence. Other processes, including radiation, surface fluxes, and subsidence, respond to the seeding weakly. This short timescale is insensitive to the amount of seeding, making the evolution of <span class="inline-formula"><i>δ</i><i>L</i></span> and some other deviations similar for different seeding amounts after appropriate scaling. The timescale of <span class="inline-formula"><i>k</i></span> evolution is closely related to the <span class="inline-formula"><i>δ</i><i>L</i></span> timescale and hence also short, while it could also be affected by the <span class="inline-formula"><i>δ</i><i>N</i></span> evolution. The results are most relevant to conditions where seeding is applied to a large area of marine stratocumulus in well-mixed and overcast BL where shear is not a primary source of turbulence.</p> |
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| ISSN: | 1680-7316 1680-7324 |