New study maps out Earth's global atmospheric rivers
Scientists have mapped wind "rivers" in Earth’s atmosphere that are responsible for transporting huge quantities of potentially dangerous aerosols around the planet. Particles that travel through these atmospheric rivers eventually descend to cause havoc by lowering air quality and reducing visibility for days on end.
Every year massive amounts of airborne particles known as aerosols are transported around the globe by high speed jets of wind, in what are known as "atmospheric rivers." These aerosols range from pollutants from the burning of fossil fuels and volcanic ash, to carbon molecules released in raging forest fires, and even particles of dust and sand swept up from the vast Sahara Desert.
The transportation of aerosols through the atmosphere can occasionally be a force for good, such as when the airborne material falls back to the surface and enriches the soil – a process that helps to keep rain forests healthy. In human population centers, however, concentrations of aerosols can lower visibility, and more importantly be seriously detrimental to respiratory health.
Just last year an enormous plume of dust originating from the Sahara Desert was lofted high into the atmosphere, and transported across the North Atlantic Ocean. Two days after leaving the west coast of Africa, aerosols from the event – which was nicknamed "Godzilla" due to its size – were recorded lowering the air quality in the Caribbean. A few days later it had reached the southeastern United States, where it triggered an air pollution event that persisted for several days, stretching from Kansas to southern Florida.
In recent decades, scientists have been attempting to shine a light on how aerosols are moved through the atmosphere. Whilst numerous studies on atmospheric rivers have been published in the past, they generally dealt with specific events and locations.
A new NASA-led study has taken a global approach to mapping the nature of atmospheric rivers, by combining a repurposed aerosol-tracking algorithm with an advanced computer model of Earth’s climate.
The algorithm used by the team had first been designed to track water vapor passing through atmospheric rivers. However, the researchers were able to modify it to track a number of aerosols including sulfate emitted during volcanic eruptions, along with sea salt, dust and carbon particles.
This algorithm was then fed into a cutting-edge digital model of our planet, that creates a representation of Earth’s atmosphere once every six hours based on a vast array of satellite and ground-based data sources.
The team members used the model to track the position and frequency of atmospheric rivers between 1997 and 2014. They discovered that the atmospheric rivers did not transport a steady stream of material all year round. Instead, it was found that between 40 and 100 percent of the aerosols moved through the rivers were transported in a limited number of Godzilla-like extreme events.
Furthermore, the type of aerosol transported varied from location to location. It was found that certain regions in Asia, the Sahara and Nambia were predominantly sources of dusty aerosols. Meanwhile the Eastern US, northern India and Africa tended to be the source of soot from wildfires and carbon created from the burning of fossil fuels.
This new approach to analyzing atmospheric rivers on a global scale will allow researchers to begin to probe the numerous characteristics of the phenomenon, such as how they interact with storms and trap heat. It will also help expand the scientific community’s understanding of how they affect air quality on a large scale, and also how the atmospheric rivers transport plant pathogens across long distances to the detriment of farmers and food production.
A paper on the research has been published in the journal Geophysical Research Letters.