Environmental effects on aerosol–cloud interaction in non-precipitating marine boundary layer (MBL) clouds over the eastern North Atlantic
<p>Over the eastern North Atlantic (ENA) ocean, a total of 20 non-precipitating single-layer marine boundary layer (MBL) stratus and stratocumulus cloud cases are selected to investigate the impacts of the environmental variables on the aerosol–cloud interaction (<span class="inline-fo...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2022-01-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/22/335/2022/acp-22-335-2022.pdf |
| Summary: | <p>Over the eastern North Atlantic (ENA) ocean, a total of 20 non-precipitating single-layer marine boundary layer (MBL) stratus and stratocumulus
cloud cases are selected to investigate the impacts of the environmental variables on the aerosol–cloud interaction (<span class="inline-formula">ACI<sub>r</sub></span>) using the
ground-based measurements from the Department of Energy Atmospheric Radiation Measurement (ARM) facility at the ENA site during 2016–2018. The
<span class="inline-formula">ACI<sub>r</sub></span> represents the relative change in cloud droplet effective radius <span class="inline-formula"><i>r</i><sub>e</sub></span> with respect to the relative change in cloud
condensation nuclei (CCN) number concentration at 0.2 % supersaturation (<span class="inline-formula"><i>N</i><sub>CCN,0.2 %</sub></span>) in the stratified water vapor
environment. The <span class="inline-formula">ACI<sub>r</sub></span> values vary from <span class="inline-formula">−</span>0.01 to 0.22 with increasing sub-cloud boundary layer precipitable water vapor (<span class="inline-formula">PWV<sub>BL</sub></span>)
conditions, indicating that <span class="inline-formula"><i>r</i><sub>e</sub></span> is more sensitive to the CCN loading under sufficient water vapor supply, owing to the combined effect
of enhanced condensational growth and coalescence processes associated with higher <span class="inline-formula"><i>N</i><sub>c</sub></span> and <span class="inline-formula">PWV<sub>BL</sub></span>. The principal component
analysis shows that the most pronounced pattern during the selected cases is the co-variations in the MBL conditions characterized by the vertical
component of turbulence kinetic energy (<span class="inline-formula">TKE<sub>w</sub></span>), the decoupling index (<span class="inline-formula"><i>D</i><sub><i>i</i></sub></span>), and <span class="inline-formula">PWV<sub>BL</sub></span>. The environmental effects on
<span class="inline-formula">ACI<sub>r</sub></span> emerge after the data are stratified into different <span class="inline-formula">TKE<sub>w</sub></span> regimes. The <span class="inline-formula">ACI<sub>r</sub></span> values, under both lower
and higher <span class="inline-formula">PWV<sub>BL</sub></span> conditions, more than double from the low-<span class="inline-formula">TKE<sub>w</sub></span> to high-<span class="inline-formula">TKE<sub>w</sub></span> regime. This can be explained by
the fact that stronger boundary layer turbulence maintains a well-mixed MBL, strengthening the connection between cloud microphysical properties and
the below-cloud CCN and moisture sources. With sufficient water vapor and low CCN loading, the active coalescence process broadens the cloud droplet
size spectra and consequently results in an enlargement of <span class="inline-formula"><i>r</i><sub>e</sub></span>. The enhanced activation of CCN and the cloud droplet condensational
growth induced by the higher below-cloud CCN loading can effectively decrease <span class="inline-formula"><i>r</i><sub>e</sub></span>, which jointly presents as the increased
<span class="inline-formula">ACI<sub>r</sub></span>. This study examines the importance of environmental effects on the <span class="inline-formula">ACI<sub>r</sub></span> assessments and provides observational constraints
to future model evaluations of aerosol–cloud interactions.</p> |
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| ISSN: | 1680-7316 1680-7324 |