Unveiling the secrets of where the air is cleanest on the planet.

The Southern Ocean has clean air with very little aerosol – tiny particulate matter that forms naturally or is caused by human activity.

Open honeycomb clouds (circled above) and closed honeycomb clouds (circled below) in the Southern Ocean. Photo: Tahereh Alinejadtabrizi/npj Climate and Atmospheric Science — Open honeycomb clouds (circled above) and closed honeycomb clouds (circled below) in the Southern Ocean. Photo: *Tahereh Alinejadtabrizi/npj Climate and Atmospheric Science*

The Southern Ocean is far removed from major human activity, but that's not the only reason its air is among the cleanest in the world , Science Alert reported on April 14. In a new study published in the journal Nature , a team of experts from Monash University and the University of Melbourne discovered new information about cloud structure that shows how the Southern Ocean and its unique honeycomb-like clouds play a significant role in regulating the climate. They also found the crucial role of clouds and rain in cleaning the air.

These honeycomb clouds can have either a closed-cell structure—the kind of bright, white clouds that reflect sunlight back into space, cooling the Earth—or an open structure, allowing more sunlight to reach the Earth. "These complexities are a source of error in modeling Earth's climate because they aren't properly incorporated. It's crucial to strike a reasonable balance between open and closed cells, otherwise the results could be inaccurate," the research team wrote.

The team of experts believes they have found a reasonable balance and a better understanding of the role of rainfall in cleaning the air. Using satellite imagery, they compared honeycomb clouds with aerosol measurements from the Kennaook/Cape Grim observatory and rainfall from nearby gauges and found that the cleanest air samples were associated with the presence of open honeycomb clouds.

Open honeycomb clouds have a higher moisture content, about six times greater than closed, fluffy white clouds. They make the sky appear less cloudy when viewed from satellite, but in reality, they are the most effective at delivering rain showers to wash away aerosols. Closed clouds, on the other hand, appear denser but are less effective.

Open honeycomb clouds are most common in winter, resulting in the cleanest air at that time. Beyond the Southern Ocean, this cloud type also appears in the North Atlantic and North Pacific regions during winter.

Although aerosol density in the air above the Southern Ocean is influenced by many factors, rainfall plays a key role. "Precipitation is crucial, especially rain from these open, honeycomb-like clouds. Rain washes away airborne aerosol particles much like a washing machine cleans clothes," the research team wrote.

Thu Thao (According to Science Alert )

Source link