Scientists have long debated whether minute aerosol particles can enhance tropical convective clouds through a mechanism known as condensational aerosol convective invigoration. This process relies on clouds developing extremely high water vapor supersaturation levels, which would allow additional aerosol particles to form new droplets, increase condensation, release latent heat, and potentially strengthen cloud updrafts.
Previous aircraft studies have generally failed to detect the necessary supersaturation levels, leading some researchers to question whether the mechanism actually occurs in nature. However, scientists contend that earlier measurements may have been conducted in environments where such extreme conditions were unlikely to develop, including relatively polluted clouds, shallow warm clouds, and regions below deeper convective zones. At higher altitudes, droplet collisions, precipitation formation, and faster-moving updrafts can reduce the total surface area of droplets, allowing water vapor supersaturation to accumulate.
A new study examining aircraft data from NASA’s Cloud, Aerosol and Monsoon Processes Philippines Experiment, conducted in 2019, found that tropical convective clouds can achieve significantly higher supersaturation levels than previously recorded. Researchers estimated these conditions using measurements of updraft speeds and cloud droplet distributions. Results showed supersaturation reaching approximately 10 percent at around negative five degrees Celsius, with levels continuing to increase at colder temperatures. A complementary investigation using data from the ESCAPE campaign over coastal Texas and Louisiana independently documented extreme supersaturation of about 11 percent in deep convective updrafts.
The strongest supersaturation levels occurred in powerful updraft regions containing relatively few droplets. When clouds held higher concentrations of droplets, their combined surface area caused more water vapor to condense onto those particles, reducing measurable supersaturation. The research demonstrates that atmospheric conditions necessary for the proposed invigoration mechanism can develop within actual tropical convective clouds, though scientists emphasize that the observations do not conclusively prove aerosols strengthen these clouds.
Researchers plan to conduct additional aircraft campaigns to test the mechanism more directly, comparing clean and polluted tropical convective clouds while focusing on powerful updraft regions. Future work will also improve methods for distinguishing between liquid and ice phases within clouds, with the ultimate goal of better understanding and predicting aerosol effects on deep convection, rainfall, lightning, and climate.
Article Attribution | Read More at Article Source
Article summary produced by Claude AI