Radiation fog properties in two consecutive events under polluted and clean conditions in the Yangtze River Delta, China: a simulation study
<p>Aerosol–cloud interaction (ACI) in fog and planetary boundary layer (PBL) conditions plays critical roles in the fog life cycle. However, it is not clear how ACI in the first fog (Fog1) affects the PBL and subsequently affects ACI in the second fog (Fog2), which is important information for...
| Main Authors: | , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2023-09-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/23/9873/2023/acp-23-9873-2023.pdf |
| Summary: | <p>Aerosol–cloud interaction (ACI) in fog and planetary boundary layer (PBL) conditions plays critical roles in the fog life cycle. However, it is not clear how ACI in the first fog (Fog1) affects the PBL and subsequently affects ACI in the second fog (Fog2), which is important information for understanding the interaction between ACI and the PBL, as well as their effects on fog properties. To fill this knowledge gap, we simulate two successive radiation fog events in the Yangtze River Delta, China, using the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem). Our simulations indicate that the PBL conditions conducive to Fog2 formation are
affected by ACI with high aerosol loading in Fog1; subsequently, the PBL
promotes ACI in Fog2, resulting in a higher liquid water content, higher
droplet number concentration, smaller droplet size, larger fog optical
depth, wider fog distribution, and longer fog lifetime in Fog2 than in Fog1.
This phenomenon is related to the following physical factors. The first
factor involves meteorological conditions conducive to Fog2 formation,
including low temperature, high humidity, and high stability. The second
factor is the feedbacks between microphysics and radiative cooling. A higher
fog droplet number concentration increases the liquid water path and fog
optical depth, thereby enhancing long-wave radiative cooling and
condensation near the fog top. The third factor is the feedbacks between
macrophysics, radiation, and turbulence. A higher fog top presents stronger
long-wave radiative cooling near the fog top than near the fog base, which
weakens temperature inversion and strengthens turbulence, ultimately
increasing the fog-top height and fog area.</p>
<p>In summary, under polluted conditions, ACI postpones the dissipation of Fog1 owing to these two feedbacks and generates PBL meteorological conditions
that are more conducive to the formation of Fog2 than those prior to Fog1.
These conditions promote the earlier formation of Fog2, further enhancing
the two feedbacks and strengthening the ACI in Fog2. Our findings are
critical for studying the interaction between aerosols, fog, and the PBL;
moreover, they shed new light on ACI.</p> |
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| ISSN: | 1680-7316 1680-7324 |