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The miracle of cloud seeding: How can small particles be used to change rainfall?
In the face of increasingly serious climate change problems, the regulation of rainfall has become increasingly important. Among them, cloud condensation nuclei (CCN), a small but important particle, is attracting the attention of the scientific community and environmental protection organizations. These tiny particles, typically just 0.2 micrometers in diameter, play a key role in weather systems and cloud formation. When water vapor condenses on the surfaces of these particles, cloud droplets are formed, a process that has profound effects on global weather patterns and climate.
Cloud condensation nuclei are a special type of aerosol. Water vapor needs to condense on a non-gaseous surface. This process affects the radiation properties of clouds and the atmosphere as a whole. In the absence of CCN, water vapor can remain supercooled at about -13 °C for hours until it spontaneously forms cloud droplets.
Characteristics and composition of CCN
The diameter of a cloud condensation nucleus is typically less than one hundredth of that of a cloud droplet. Cloud droplets are about 20 microns, while CCNs are about 0.1 microns in diameter. These particles can number between 100 and 1,000 per cubic centimeter in the air, meaning that in cities with thick smog, the amount of CCN can increase significantly. The particles come from a variety of sources, including sand, sea salt, soot and sulfates, and their water-attracting properties vary widely.
For example, sulfate and sea salt particles readily attract water, while soot and organic carbon compounds do not. This results in very different abilities of different types of particles in forming cloud droplets, and even in low-temperature areas, some particles can act as ice nuclei and promote cloud formation.
Design and Challenges of Cloud Seeding Technology
Cloud seeding is a technique that seeks to artificially promote rainfall and typically involves injecting small particles into the air to stimulate cloud formation. Whether it's through aerial salt spraying or, more innovatively, thermal lasers or drone-derived charge launches, the effectiveness of these methods remains controversial. Some studies have shown that cloud seeding can significantly change rainfall, but other studies have stressed that it has not been proven to be effective. There are also natural processes, such as particulate matter released by forest fires themselves, which can naturally become CCN.
Ocean Cloud Brightening Technology
Another concept that has generated a lot of buzz is Marine Cloud Brightening, a climate engineering technique that would like to enhance the reflectivity of clouds by injecting particles into them. Studies have shown that surface temperatures can be lowered by injecting small particles of seawater into clouds, but in this implementation, the reactive chlorine and bromine may have an adverse effect on molecular reactions in the atmosphere, thereby reducing ozone concentrations and exacerbating global warming. .
CCN and Climate Connection
Since 1987, the relationship between CCN and marine phytoplankton has sparked much discussion of climate feedbacks. Studies have shown that sulfate aerosols in the ocean mainly come from dimethyl sulfide (DMS) released by phytoplankton in seawater. Large algal blooms can freely enter the atmosphere, thereby promoting the production of CCN. This phenomenon creates a negative feedback loop that promotes cloud formation, which is in turn influenced by temperature. This process is particularly important in influencing the climate, as it could otherwise accelerate the greenhouse effect.
Impact of volcanic activityVolcanic eruptions are also a major source of CCN, releasing large amounts of particulate matter into the atmosphere, which can affect cloud structure and type. The sulfur dioxide released by the eruption is eventually converted into sulfuric acid, forming fine sulfate aerosols, which not only reflect sunlight but also cause changes in global temperatures.
As technology improves, our understanding of CCNs will improve not only climate models but also lead to more effective climate engineering techniques. Whether through cloud seeding technology or other methods, how to use these small particles to truly change rainfall remains an important topic that scientists continue to explore. When faced with the challenge of climate change, are we ready to embrace this natural change?
