Regardless of their source, small solid particles or liquid droplets suspended in the air are called “aerosols”. Scientists consider clean air with low aerosol content, without distinguishing between natural and industrial sources. Recent research has revealed that clouds and rain play a crucial role in clearing the atmosphere.

Details of the study

A number of factors influence the aerosol level over the Southern Ocean. These include seasonal fluctuations in the amount of salt spray and the growth of tiny plant-like organisms called phytoplankton, which are the source of sulfate particles in the air. Less sulfate is formed during the winter months, when the air over the Southern Ocean is cleanest.

But that’s not the whole story. The Southern Ocean is also the cloudiest place on Earth. Here, like nowhere else on the planet, there are short-term, unexpected downpours. Scientists wanted to understand the role of clouds and rain in cleaning the air. The biggest obstacle to understanding these processes has been the lack of high-quality observations of clouds, precipitation and aerosols in this little-explored region of the world.

Fortunately, new generation satellites make it possible to examine cloud images in unprecedented detail. Researchers have developed a computer program to recognize different cloud models On the vast territory of the Southern Ocean. They specifically looked for the characteristic honeycomb-like clouds that play an important role in regulating the climate. Since their diameter is approximately 40-60 kilometers, they can be seen from space. Therefore, we can examine them with the help of satellite images.

When a honeycomb cell becomes cloud-filled or “closed”, it becomes whiter and brighter and reflects more sunlight into space. Thus, these clouds help keep the Earth cool. Empty or “open” honeycomb cells allow more sunlight to enter. These subtleties remain a source of error in Earth climate modeling because they are not properly accounted for. It is important to calculate the balance of open and closed cells correctly, otherwise the results may be erroneous.

What clears aerosols from the atmosphere?

So the scientists compared the honeycomb clouds with aerosol measurement data from the Kennaukee/Map Grim Observatory, as well as observations of rainfall from a nearby Bureau of Meteorology rain gauge.

The results showed that the days with the cleanest air were associated with the presence of open-cell clouds. The authors of the work believe that this is due to: these clouds appear to “break down” aerosol particles in the air, producing occasional heavy showers.

It defies all logic, but it turns out that open cells retain more moisture and produce more rain than closed cells filled with fluffy white, clouds. Open honeycomb clouds produce six times more rain than closed ones.

So the weather that appears to be less cloudy when viewed from satellite actually produces the most effective showers for clearing aerosols. Filled or closed cells that appear cloudier are less efficient.

This was one of the most surprising aspects of our findings. We found that empty radiators are much more common in the winter months when the air is the cleanest. We also wanted to know what makes cloud fields appear this way. Our analysis shows that large-scale weather systems control the structure of the cloud field. When uncontrolled storms wreak havoc on the Southern Ocean, they form these open and closed cells.
– scientists write in their work.

Clean air and better climate patterns

The study adds a new piece to the puzzle of why the Southern Ocean has the cleanest air on Earth. The key factor seems to be rain, especially rain from clear, clear, honeycomb clouds.

In winter, these cirrus clouds are found in both the North Atlantic and the North Pacific. Therefore, the study will also help explain how these clouds clear aerosols, including dust and pollution, from these regions.

The findings will help improve climate models, enabling more accurate predictions.