(ORDO NEWS) — Clouds in the Southern Hemisphere are more reflective than clouds in the Northern Hemisphere. This is a fact that scientists are well aware of, but so far have not been able to fully explain.
Now a new study is shedding more light on why clouds function differently in the two hemispheres. In particular, scientists have found out what role in this process is played by updrafts – the movement of warm air, which leads to condensation and the formation of clouds.
The study used data from 2018-2021 collected by the DACAPO-PESO (Aerosol, Cloud and Precipitation Observation Dynamics in the Wild Environment of the Southern Ocean) project. Observations in the cities of Leipzig in Germany, Limassol in Cyprus and Punta Arenas in Chile were taken as a basis.
Most of the Southern Hemisphere is ocean-based, not land-based, so the air is generally cleaner, with fewer aerosol particles around which water droplets and crystals can form to form brighter clouds.
“Ice crystallization is much less in mid-latitude Southern Hemisphere clouds, and such clouds contain more liquid water at the same temperatures. This means that they affect the reflection of light, as well as the thermal radiation emitted from the Earth‘s surface, in a different way than in the north. Leibniz (TROPOS).
The study found that the differences were most pronounced in the free troposphere, where air masses are at higher altitudes and where they are less affected by local pollution. Between -24°C and -8°C, clouds over Punta Arenas formed ice on average 10 to 40 percent less frequently than clouds over Leipzig.
The scientists also found that the updrafts created when westerly winds from the Pacific Ocean collide with the Andes are an important factor in this process, as is atmospheric pollution, especially when the air is even colder. In their study, the scientists call these rises of air gravitational waves.
“By measuring updrafts and downdrafts in clouds, we were able to detect the clouds affected by these waves and filter them out of the overall statistics. This allowed us to show that it is these gravity waves, and not the absence of ice, that are mainly responsible for the excess of droplets in clouds at temperatures below -25 °C,” Martin Radenz, meteorologist at TROPOS.
The next question is whether this is unique to the landscape of Chile or whether gravitational waves also affect the open ocean. Further measurements will be needed to determine how much of the excess liquid water in clouds is updrafts and how much is ice crystals, the researchers wrote.
The researchers report part of the discovery was accidental: due to travel restrictions imposed by the global pandemic, they left their monitoring systems in place for another two years, allowing them to account for additional factors such as drifting wildfire smoke from Australia in 2019. /2020
Contact us: [email protected]