A survey published this Friday (8) in the magazine Nature Geoscience unveils an important piece of the puzzle that seeks to explain the rain formation in the Amazon one of the most influential regions on global climate.
According to the study, the forest is capable of producing aerosols on its own that, induced by the rain itself, trigger a process of new cloud formation and precipitation thus influencing the water cycle, climate and Earth’s energy balance.
The work shows that, with rain, there is an increase in the concentration of ozone that oxidizes molecules naturally released by gases exhaled by the forest, the so-called volatile organic compounds, especially terpenes.
Oxidation produces new very small particles just above the tops of the trees, in a kind of nanoparticle explosion (smaller than 40 nanometers).
These particles, in turn, give rise to condensation nuclei that again lead to the formation of clouds even in clean air conditions during the rainy season.
The discovery opens new perspectives on the complex chemical-atmospheric, meteorological interactions and feedback cycles that scientists call the “green ocean”, that is, the Amazon’s ability to generate its own cycle of clouds and rain in a similar way to the ocean.
Until then, it was believed that the forest was unable to produce these aerosols, and the hypothesis was that they came from higher altitudes.
For there to be rain, in addition to water vapor, atmospheric particles are needed that act as condensation nuclei, that is, surfaces where the vapor can transform into droplets.
However, the origin of this process in the Amazon was still poorly understood, especially during the rainy season.
Now, an international team, with researchers from Brazil, Germany and Sweden, has analyzed an extensive set of various types of data from the Torre Alta da Amazônia Observatory, ATTO, to show this process.
Meteorological and gas information, among others, is included.
“It’s a symbiosis that occurs throughout the process. Rain on the one hand cleans the atmosphere, reducing the number of particles. However, at the same time, a process of formation of new particles begins that will grow and serve as a condensation nucleus for the next rain”, explains professor Luiz Augusto Toledo Machado, corresponding author of the article, researcher at the Institute of Physics of University of São Paulo (IF-USP) and collaborator in the Chemistry Department of the Max Planck Institute, in Germany.
Fapesp supports the work through two Thematic Projects linked to the Research Program on Global Climate Change (PFPMCG) – one of them led by Machado and the other by professor Paulo Artaxo, also from the USP Physics Institute and co-author of the article.
In the study, researchers found that, after rain, particle concentrations are highest near the top of trees (canopy), indicating that they are formed within the forest.
This process persists in the rainy season, which normally occurs from December to May, indicating continuous formation of particles within the canopy and a new population of particles.
“Our findings mark a paradigm shift in understanding the interactions between aerosol particles, clouds and precipitation in the Amazon.
These interactions are critical for understanding changes in Earth’s radiative budget, especially as climate change influences atmospheric circulation, such as El Niño and La Niña events,” says Ulrich Pöschl, director of the Department of Chemistry at the Max Planck Institute, also co-author of the work, in a statement from the institution.
According to scientists, these results are essential to understand how changes in Amazonian climate patterns can affect not only the global climate, but ecological stability.
Current framework
Brazil is experiencing one of the worst droughts in history this year, affecting several states. In the Legal Amazon, around 69% of municipalities were affected to some degree in the first six months, surpassing the same period in 2023.
There were 531 cities out of the 772 in the region, according to a survey by InfoAmazônia based on the Integrated Drought Index, from the National Center for Natural Disaster Monitoring and Alerts (Cemaden).
Driven by El Niño, the climate crisis has also affected Amazon rivers, which have been recording their lowest levels, leaving riverside populations isolated and affecting supply and transport.
According to the Brazilian Geological Service (SGB), the drought could worsen this situation until December – Hydrological Alert Bulletin of the Amazon Basin points out that the tendency is for the Negro River to “repiquet” until the last month and rise again only in January.
The Acre River, for example, had a historic low of 1.23 meters in Rio Branco at the end of September.
On the other hand, although deforestation in the Amazon fell by around 30.6% between August 2023 and July this year compared to August 2022 and July 2023 (it stood at 6,288 km² compared to 9,064 km²), according to data from the National Institute of Space Research (Inpe), forest degradation, mainly due to fires, increased.
According to Machado, deforestation and degradation have important impacts on the rain cycle in the Amazon.
“To have the gases that form the particles, you need to have a forest. With no trees and no vapor in the atmosphere, there are no particles, further reducing rainfall.”
Based on Atto data, the group was able to show how precipitation can trigger the formation of new particles in the forest canopy. Located in the middle of the Amazon, in the Uatumã Biological Reserve, around 150 km north of Manaus, Atto is jointly managed by scientists from Brazil and Germany.
It has a tower 325 meters high and two others 80 meters high.
Construction of science
In 2016, the group had already found the formation of new particles at the top of the troposphere around 14 km high, although they still did not understand the formation process and its role in climate.
To describe how these particles were produced, the scientists carried out a field experiment, which they called CAFE-Brazil, an acronym in English for Chemistry of the Atmosphere: Field Experiment in Brazil.
“In 2023, we carried out these large quantities of measurements and came to describe the entire process of how particles are formed up there”, adds Machado.
For future research, they point out the need for experiments in chambers at tree canopy level to control ozone concentration and better understand its influence on the formation of particles involved in rain.
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This content was originally published in Particles on top of Amazon trees contribute to rain formation on the CNN Brasil website.
Source: CNN Brasil
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