A recent analysis of cloud data from the California coast, along with global satellite observations, highlights the significant role of aerosol particles as small as 25–30 nanometers in cloud formation. This challenges previous assumptions and suggests that the climate impact of tiny aerosols may have been underestimated.
Clouds are complex and poorly understood components of the climate system, contributing to the greatest uncertainties in climate change predictions. Understanding clouds requires knowledge of weather patterns spanning hundreds of kilometers and the intricate microphysics occurring at the molecular level.
The study, titled “Supersaturation and Critical Size of Cloud Condensation Nuclei in Marine Stratus Clouds,” published in Geophysical Research Letters, delves into the molecular scale dynamics of cloud condensation nuclei within marine stratus clouds, which are characterized by their low-level, layered structure.
Cloud formation hinges on two fundamental factors: atmospheric supersaturation with water vapor and the presence of cloud condensation nuclei onto which water can condense and form droplets. It has long been assumed that these nuclei must exceed a critical size, typically 60 nanometers or larger.
However, research conducted by scientists from The Technical University of Denmark, the University of Copenhagen, and the Hebrew University of Jerusalem suggests otherwise. They found that proto seeds as small as 25–30 nanometers may suffice to develop into cloud condensation nuclei, challenging previous notions.
Henrik Svensmark, the lead author, emphasizes the significance of this finding, highlighting how smaller aerosols could have a more pronounced impact on cloud formation, especially in regions dominated by marine stratus clouds.
The study unveils the mechanism behind smaller aerosols becoming cloud condensation nuclei. Higher levels of water vapor supersaturation within clouds facilitate the activation of these smaller aerosols into cloud droplets, reducing the required size of the nuclei.
This revelation stems from measurements of marine stratus clouds conducted in 2014, revealing a correlation between cloud droplet abundance and atmospheric water vapor supersaturation. Combining these measurements with global satellite data allowed researchers to map global supersaturation levels.
Contrary to previous assumptions, the study finds that supersaturation levels are generally higher than previously thought. Consequently, even minuscule aerosols can function as cloud condensation nuclei, altering our understanding of cloud formation dynamics.
The implications are significant, as they challenge existing models that underestimate the impact of small aerosols on cloud formation. By demonstrating that aerosols need to grow less to become nuclei, the study highlights the importance of revising models for more accurate cloud and climate predictions.
https://phys.org/news/2024-05-climate-cloud-easier-affect-previously.html#google_vignette