A new study by an international team of scientists from Germany, Chile and Cyprus has made it possible to explain the long-observed differences in the behavior of stratus clouds in different hemispheres. It turned out that ascending currents of warm air have a decisive influence on their behavior, which actually lead to condensation and the formation of clouds. In the Southern Hemisphere, clouds are different in shape and have a significantly lower reflectivity compared to clouds in the Northern Hemisphere. An article about this was published in the journal Atmospheric Chemistry and Physics.
The study used three years of data for 2018-2021 collected under the DACAPO-PESO project. The concentration of ice crystals in the clouds was estimated using an infrared laser lidar, and the clouds were monitored by microwave radar. The resulting data covers areas around Leipzig in Germany, Limassol in Cyprus and Punta Arenas in Chile - in the latter case, it was the most extensive data set on aerosols, clouds and precipitation ever collected in this region.
Most of the Southern Hemisphere is oceanic rather than land-based, so the air is generally cleaner, with fewer aerosol particles around which cloud droplets and crystals can form to form brighter clouds. “Clouds in the mid-latitudes of the Southern Hemisphere contain much less ice crystals and more liquid water at the same temperatures,” explains one of the authors of the work, German meteorologist Patrick Seifert from the Institute for Tropospheric Research of the Leibniz Association in Leipzig. “This means that they have a different effect on the sunlight passing through them, as well as on the thermal radiation emitted from the surface of the Earth, than in the north.”
The study showed that the differences were most pronounced in the free troposphere at high altitudes, where the air layers are less affected by local pollution. At temperatures ranging from –24°C to –8°C, clouds over Punta Arenas formed ice on average 10–40% less frequently than clouds over Leipzig.
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