Icy cirrus clouds born from desert dust, massive aerial survey shows
Every year, several billion metric tons of mineral dust are thrown into the atmosphere from arid regions of the world, making dust one of the most abundant types of aerosol particles in the atmosphere. Now scientists are learning that tiny bits of dust from the hottest, driest parts of Earth are a surprisingly big factor in forming the delicate, wispy ice clouds known as cirrus clouds at high altitudes. cold in the atmosphere.
Karl Froyd, a former CIRES scientist on the atmospheric tomography mission, is strapped to his workstation aboard NASA’s DC-8 during one of the flights. Measurements made by the PALMS instrument allowed the research team to document that desert dust is a major contributor to the formation of icy cirrus clouds. Credit: Dan Murphy, NOAA
While scientists know that desert dust particles cause clouds, the extent of this relationship has been a long-standing question. New research, based on the largest atmospheric sampling mission ever and published this month in nature geosciencehighlights the role of dust in the climate system.
Understanding how dust moves through the atmosphere will be important as scientists try to predict how climate change will influence weather patterns, said lead author Karl Froyd, a RAINCOATS scientist at the NOAA Chemical Sciences Laboratory at the time of the study. Cirrus clouds tend to trap heat rising from the surface that would otherwise escape into space.
“Dust-initiated cirrus clouds are surprisingly abundant, accounting for 34-71% of all cirrus clouds outside the tropics,” Froyd said. “Perhaps even more surprisingly, we found that although the Sahara Desert is by far the largest emitter of dust in the world, the deserts of Central Asia are often greater sources of cirrus formation.” Some deserts are much more efficient than others when it comes to creating clouds.
Another scientific discovery of the ATom mission
This map depicts the flight paths of NASA’s DC-8 Flight Laboratory during the Atmospheric Tomography mission from 2016 to 2018. Credit: NOAA
This information comes from analysis of data collected during the Atmospheric Tomography Project, or ATom for short, an unprecedented mission using NASA’s DC-8 research aircraft to sample all levels of the lower atmosphere above. over the world’s distant oceans, far from local sources of pollution. . The researchers encountered continental dust at almost all altitudes and latitudes sampled by the aircraft, including over the Southern Ocean, the far Pacific and Antarctica.
When connected to an atmospheric transport model, data analysis revealed that weather conditions downwind of desert regions were more important to cirrus formation than just the amount of dust emitted. The Sahara Desert, for example, accounts for 60% of global dust emissions, but only a small fraction of that dust is transported vertically into the cold temperatures of the upper troposphere where it can seed the tiny ice crystals that make up cirrus clouds. (Much of the Saharan dust is blown over the equatorial Atlantic Ocean, where it can suppress hurricane formation). In contrast, dry convection and the Asian summer monsoon help lift Central Asian dust more effectively.
“These results are a striking message to the aerosol and cloud science community, that we need to improve our treatment of dust and cloud formation in climate models to more accurately predict current and future climate,” a- he declared.
To learn more about this new research, visit the NOAA News page of the Laboratory of Chemical Sciences.
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