Airborne study reveals surprisingly large role of desert dust in cirrus formation
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.
While scientists know that desert dust particles can sow some clouds, the extent of this relationship is a long-standing question. New research, based on the largest airborne atmospheric sampling mission ever and published in nature geosciencehighlights the role of dust in the climate system.
“Dust-initiated cirrus clouds are surprisingly abundant, accounting for 34-71% of all cirrus clouds outside the tropics,” explained lead author Karl Froyd, a CIRES scientist at NOAA’s Chemical Sciences Laboratory with the research Aerosol Properties & Processes at the time of the study. “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.”
Analysis of atmospheric measurements collected over distant oceans during NASA’s three-year Atmospheric Tomography (ATom) mission reveals that dust plays a dominant role in the formation of cirrus clouds in the northern and southern hemispheres, and that some deserts are much more efficient than others when it comes to cloud creation.
To explore the role of windblown dust in creating cirrus clouds, Froyd and his colleagues deployed a bespoke single-particle mass spectrometer, known as PALMS, on the DC-8 research aircraft. from NASA during the ATom project to measure chemical composition. of aerosol particles in the distant atmosphere. ATom flights circumnavigated the globe four times between 2016 and 2018, flying over long transects along the Pacific and Atlantic Oceans and across the Arctic and Southern Oceans.
In flight, the PALMS instrument continuously ingested atmospheric particles, one at a time, using a laser to vaporize each into their individual components before they were sent through a mass spectrometer to reveal their chemical signatures. Mineral dust is just one of many types of aerosols that this powerful instrument is able to identify.
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. Dust levels present in the upper troposphere forming cirrus clouds were quite low, well below what could be observed by satellite, but were ubiquitous. Even at low concentrations, dust played an important role in controlling cloud properties.
The extensive dust measurements collected during the ATom were incorporated into a detailed atmospheric model capable of simulating the formation of cirrus clouds to quantify the effects of dust on cirrus clouds around the world. Despite the minute amounts of dust aerosols measured in the upper troposphere, dust is still abundant enough to drive cirrus formation during all seasons in extratropical regions, including the Southern Hemisphere.
The modeling results also revealed that the downwind weather environment of the desert regions was more important for the formation of cirrus clouds 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. In contrast, dry convection and the Asian summer monsoon help remove Central Asian dust more effectively.
It is important to be able to correctly simulate the abundance of dust and the formation of cirrus clouds in the models to understand the role of cirrus clouds in the climate. Clouds strongly influence the balance of solar radiation that regulates surface temperatures, but clouds and cloud formation remain a poorly understood aspect of the climate system. Unlike the puffy white clouds we see at low altitudes that reflect sunlight, high altitude cirrus clouds have a net warming effect on our climate by trapping heat that would otherwise escape into space. The surprisingly important role of mineral dust in controlling the formation of cirrus clouds on a global scale establishes the critical role of dust in the Earth’s climate system.
“With climate change, deserts are changing around the world and dust emissions are changing with them. These new findings help focus our attention on the most important deserts in terms of cirrus formation,” Froyd added. “These results are a stark 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.”
We thought wrong about how ice forms in cirrus clouds
Karl D. Froyd et al, Dominant role of mineral dust in the formation of cirrus clouds revealed by measurements on a global scale, nature geoscience (2022). DOI: 10.1038/s41561-022-00901-w
Data from the Atmospheric Tomography Mission (ATom) are publicly available on the Oak Ridge National Laboratory Distributed Active Archive Center (ORNL DAAC).
Quote: Airborne study reveals surprisingly large role of desert dust in cirrus formation (2022, March 9) Retrieved March 10, 2022 from https://phys.org/news/2022-03-airborne-reveals-surprisingly -large-role.html
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