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Wind Tunnel Experiments to Study Chaparral Crown Fires
Published on: November 14, 2017
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Disentangling the Microphysical Effects of Fire Particles on Convective Clouds Through A Case Study
Azusa Takeishi1,2, Trude Storelvmo3, Laura Fierce4
1Department of Geology and Geophysics Yale University New Haven CT USA.
Journal of Geophysical Research. Atmospheres : JGR
|July 28, 2020
Summary
Forest fire aerosols significantly impact cloud formation. The hygroscopicity effect of fire particles can offset their number effect, reducing cloud droplet concentrations and influencing cloud optical thickness.
Area of Science:
- Atmospheric Science
- Cloud Physics
- Aerosol Science
Background:
- Forest fire emissions introduce aerosols that alter atmospheric properties.
- Aerosol particles influence cloud droplet activation and cloud properties.
- Two key effects are the particle number concentration (number effect) and particle hygroscopicity (hygroscopicity effect).
Purpose of the Study:
- To investigate the impact of forest fire aerosols on deep convective clouds (DCCs).
- To quantify the distinct influences of the number effect and hygroscopicity effect on cloud properties.
- To assess the role of aerosol mixing state in aerosol-cloud interactions.
Main Methods:
- Utilized cloud-resolving simulations with the Weather Research and Forecasting (WRF) model coupled with Chemistry.
- Conducted a case study in a partly idealized setting.
- Analyzed the effects of varying aerosol properties and mixing states on simulated DCCs.
Main Results:
- The hygroscopicity effect was found to significantly reduce modeled droplet number concentrations, sometimes offsetting the number/size effect.
- In the studied case, droplet number concentration decreased by approximately 37% due to the hygroscopicity effect alone.
- Differences in activated droplets affected cloud optical thickness during the initial development stage of DCCs.
Conclusions:
- Accurate representation of aerosol mixing and hygroscopicity (κ) is crucial for simulating aerosol-cloud interactions, especially under fire influence.
- The impact of fire aerosols on background aerosol hygroscopicity is likely weaker in the real atmosphere than in models assuming immediate, uniform mixing.
- Understanding these complex interactions is vital for climate modeling and predicting weather patterns affected by biomass burning.
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