Airborne Dust Causes Ripple Effect on Climate Far Away
When a small pebble drops into a serene pool of water, it causes a ripple in the water in every direction, even disturbing distant still waters. NASA researchers have found a similar process at work in the atmosphere: tiny particles in the air called aerosols can cause a rippling effect on the climate thousands of miles away from their source region.
Image right: Dust from Africa's Saharan Desert lingers in high altitudes as it crosses the Atlantic Ocean. This picture was taken from an aircraft northeast of Barbados in 2006. Cumulus clouds can be seen poking through the tops of the dust layer, which is seen as a milky white haze. Click image to enlarge. Credit: NOAA
The researchers found that dust particles from the desert regions in northern Africa can produce climate changes as far away as the northern Pacific Ocean. Large quantities of dust from North Africa are injected into the atmosphere by dust storms and rising air. Airborne dust absorbs sunlight and heats the atmosphere. The heating effect ripples through the atmosphere, affecting surface and air temperatures as the dust travels.
"These highs and lows in air temperatures caused by radiation-absorbing aerosols can lead to 'teleconnection’, which refers to changes in weather and climate in one place caused by events happening far away, often more than half way around the globe," said William Lau, Chief of the Laboratory for Atmospheres at NASA's Goddard Space Flight Center, Greenbelt, Md., and author of a study published last fall in the Journal of Climate. "North African dust can be lifted high into the atmosphere by storms and then transported across the Atlantic and Caribbean, where its effect can be far-reaching."
Image left: A massive sandstorm blowing off the northwest African desert blanketed hundreds of thousands of square miles of the eastern Atlantic Ocean with Saharan Sand. It was seen from the SeaWiFS satellite on Feb. 26, 2000, as it reached 1,000 miles into the Atlantic Ocean. Click image to enlarge. Credit: NASA GSFC and ORBIMAGE
From a climate point of view, aerosols can block solar radiation (incoming heat and light from the sun) from hitting the Earth's land surface. When sunlight is blocked, it can cause the Earth's surface to cool, and/or the aerosols can absorb solar radiation and cause the atmosphere in the vicinity of the airborne dust to get warmer.
According to Lau, researchers thought for years that heat changes in the atmosphere from aerosols only caused local changes in temperatures. However, "we now know they may cause more than local changes to climate," he said. Lau's computer model indicates that the heat changes caused by aerosols affect the heat balance in the air over North Africa. That change in heat creates large waves in the atmosphere that ripple as far away as Eurasia and the North Pacific.
"Elevated aerosols in large quantities such as dust from North Africa, or biomass burning may have global impacts," said Lau. "We expect to observe more and more real-world examples of this teleconnection phenomenon with the high volume of aerosols generated by nature and human activities around the world."
+ Teleconnections information
Goddard Space Flight Center