Dust storms are natural phenomena that occur when strong winds lift and transport large amounts of fine particles from dry and arid regions into the atmosphere.
They can have various impacts on the environment, human health, agriculture, and transportation. But how do they affect the global climate system?
A new study by researchers from the University of Leeds and the National Center for Atmospheric Science sheds some light on this question by focusing on a high-latitude source of dust: the Copper River Valley in Alaska.
How dust storms influence cloud formation and ice nucleation
HIMANSHU SHARMA/AFP via Getty Images
One of the main ways that dust storms influence the climate is by affecting cloud formation and ice nucleation.
Clouds are composed of tiny droplets of water or ice crystals that form around particles in the air, such as dust, pollen, smoke, or pollution.
These particles are called cloud condensation nuclei (CCN) or ice nucleating particles (INP), depending on whether they promote the liquid or ice phase in clouds.
Clouds play a crucial role in regulating the Earth's energy balance, as they reflect some of the incoming solar radiation back to space (cooling effect) and trap some of the outgoing infrared radiation from the surface (warming effect).
The net effect of clouds on the climate depends on their type, location, altitude, and composition.
Dust storms can increase the number and diversity of CCN and INP in the atmosphere, which can alter the properties and behavior of clouds.
For example, dust particles can enhance the formation of ice crystals in clouds at temperatures below freezing, which can affect cloud lifetime, precipitation, and radiative forcing.
However, not all dust particles have the same ability to nucleate ice. Previous research has focused on dust from desert regions, such as the Sahara, which are located at mid to low latitudes.
The new study, published in Science Advances, examined dust from a high-latitude source: the Copper River Valley in Alaska.
How Alaskan dust differs from Saharan dust and why it matters
The Copper River Valley is a major source of glacial sediment that is transported by the river and deposited on its delta.
During periods of low water flow, such as summer and autumn, strong winds can pick up and carry large amounts of this sediment into the atmosphere.
The dust plumes can be seen from space and can travel hundreds or thousands of kilometers across North America.
The researchers collected samples of this dust using a remotely operated vehicle (ROV) operated by the Hawai'i Undersea Research Laboratory (HURL).
They analyzed the chemical and physical properties of the dust particles, as well as their ability to nucleate ice in laboratory experiments. They also used satellite data to estimate the frequency and extent of dust events in the region.
They found that Alaskan dust differs from Saharan dust in several aspects.
First, Alaskan dust contains more organic matter, such as plant debris and microorganisms, which may affect its interaction with water and ice.
Second, Alaskan dust has a higher fraction of coarse particles (>10 micrometers), which may influence its transport and deposition.
Third, Alaskan dust has a higher ice nucleation activity than Saharan dust at temperatures between -15°C and -25°C, which are relevant for mixed-phase clouds.
These differences have important implications for the climate system. The researchers estimated that Alaskan dust could contribute up to 20% of the global INP budget at these temperatures, despite accounting for only 2% of the global dust emission.
This means that Alaskan dust could have a significant impact on cloud formation and ice nucleation over large areas of North America and beyond.
The study provides new insights into how high-latitude sources of dust affect the global climate system.
It also highlights the need for more research on how other factors, such as wind patterns, precipitation regimes, and climate change, may influence dust emissions and transport from these regions.
The researchers hoped that their findings will improve our understanding and prediction of cloud processes and feedback in a changing world.
