Given spume's role in mediating air‐sea exchange at the base of tropical cyclones or other storm events, the focus of studies on spray dynamics has been within the marine environment. In contrast, spume production in nonseawater bodies has been underexplored and potential differences between sea and freshwater are neglected. The laboratory remains the primary means for directly observing spray processes near the surface because of the challenges to making robust field measurements. There is no standardization on the water type used for these experiments, and the effect this has on the generation process is unknown. This adds uncertainty in our ability to make physically realistic spume generation functions that are ultimately applied to the geophysical domain. We have conducted a laboratory experiment that aims to address this simple, yet overlooked, question of whether water type impacts the spume droplet concentration entrained in the air flow above actively breaking waves. We compared directly imaged concentrations for fresh and seawater droplets produced in 10‐m equivalent winds from 36–54 m/s. Substantially higher concentrations of seawater spume were observed, as compared to freshwater across all particle sizes and wind speeds. The seawater particles' vertical distribution was concentrated near the surface, whereas the freshwater droplets were more uniformly distributed. Our statistical analysis of these findings suggests significant differences in the size‐ and height‐dependent distributions response to increased wind forcing between fresh and seawater. These unexpected findings suggest an unanticipated role of the source water physiochemical properties on the spume generation mechanism.
Natural aquatic environments such as oceans, lakes, and rivers are home to a tremendous diversity of microorganisms. Some may cross the air-water interface within droplets and become airborne, with the potential to impact the Earth’s radiation budget, precipitation processes, and spread of disease. Larger droplets are likely to return to the water or adjacent land, but smaller droplets may be suspended in the atmosphere for transport over long distances. Here, we report on a series of controlled laboratory experiments to quantify wind-driven droplet production from a freshwater source for low wind speeds. The rate of droplet production increased quadratically with wind speed above a critical value (10-m equivalent 5.7 m/s) where droplet production initiated. Droplet diameter and ejection speeds were fit by a gamma distribution. The droplet mass flux and momentum flux increased with wind speed. Two mechanisms of droplet production, bubble bursting and fragmentation, yielded different distributions for diameter, speed, and angle. At a wind speed of about 3.5 m/s, aqueous suspensions of the ice-nucleating bacterium
- NSF-PAR ID:
- 10076053
- Publisher / Repository:
- PeerJ
- Date Published:
- Journal Name:
- PeerJ
- Volume:
- 6
- ISSN:
- 2167-8359
- Page Range / eLocation ID:
- Article No. e5663
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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