Clouds in the Northern and Southern hemispheres have some characteristics that differentiate them from each other. Scientists have known this for a long time, they just didn’t understand how this difference was produced. Now, a study led by the Leibniz Institute for Tropospheric Research (TROPOS) appears to have grasped some of this dynamic.
The researchers collected three years’ worth of atmospheric data at three specific locations on the planet. Two in the Northern Hemisphere — in Leipzig, Germany, and in Limassol, Cyprus — and one in the Southern Hemisphere — in Punta Arenas, Chile.
The objective was to understand how pollutant aerosols and water droplets in clouds behaved over each of these locations. The southern hemisphere stands out for cleaner air because it has more oceans than continents. But, in addition to having cleaner air, the Southern Hemisphere, by concentrating more water than the North, also has higher humidity.
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A result of this is the formation of whiter clouds and therefore more reflective and with a low concentration of ice crystals.
Other causes for the difference between Northern and Southern Hemisphere clouds
Still, the team looked at other causes that contribute to the formation of cleaner clouds in the southern hemisphere. Research has shown that clouds are often influenced by so-called waves of atmospheric gravity.
These waves are basically formed by the strong wind that comes from the west of the Pacific and, when colliding with the Andes, this air mass moves vertically. So, these gravity waves are created.
The waves filter the clouds, allowing the water droplets to persist even at low temperatures. “They are primarily responsible for excess cloud droplets at temperatures below -25°C,” said Martin Radenz, lead author of the study.
Now the team wants to find out if gravity waves influence cloud formation only over Chile or if the same dynamics occur in other regions of the Southern Ocean, but the recent results will already help to improve climate models.
The study was presented in the journal Atmospheric Chemistry and Physics.
