Giant dust storms in the Gulf of Alaska can last for many days and release large amounts of fine sediment or silt into the atmosphere. These storms are so extensive that they can be seen from satellites orbiting the Earth. Although it is not yet clear how the Alaskan dust may affect the global climate system, new research from the University of Leeds and the National Centre for Atmospheric Science suggests that the effect is greater than previously believed.
Research has focused on Saharan dust
Previous research has mainly focused on dust particles created by storms in the Sahara and across Africa and Asia. These storms typically occur in mid to low latitudes and involve dust generated from desert environments. In contrast, researchers at Leeds University analyzed dust from the Copper River Valley, located on the south coast of Alaska. This valley stretches for over 275 miles, and the river within it is estimated to transport 70 million tons of glacial sediment annually.
During low-water periods in the summer and autumn, winds pick up the silt and carry it across hundreds of miles of North America. The dust reaches high altitudes where it can cause ice formation in clouds. The biological material in dust particles from the Copper River Valley is greater than that in dust from the Sahara. This is because the valley is home to rich vegetation and wildlife.
How ice forms in clouds
At low temperatures, silt – tiny fragments of rock, minerals, and vegetation – act as ice nucleating particles, which promote the formation of ice crystals in clouds. The effect of ice formation in clouds on global warming or cooling depends on the amount of ice present, the number and nature of ice nucleating particles, and their interaction.
Ice formation in clouds
Dust particles in the atmosphere play a crucial role in ice formation. Without dust, water in clouds can remain liquid even if temperatures are below freezing. The study, supervised by Professor Benjamin Murray, an Atmospheric Scientist in the School of Earth and Environment at Leeds, revealed that only a small fraction of dust particles in the atmosphere can nucleate ice, and more research is needed to understand their sources and global distribution.
“Whether a cloud becomes more or less reflective of sunlight depends on how much ice is in them, so we need to be able to understand and quantify the various sources of ice-nucleating particles around the globe.
“At present, climate models tend not to represent these high-latitude dust sources, but our work indicates that we need to.”
Sarah Barr and Bethany Wyld, who are doctoral researchers at the School of Earth and Environment in Leeds, collected samples during dust storms for their investigation. Later on, the material was analyzed in the laboratory and compared to the types of dust particles that come from desert environments.
Their analysis revealed that particles from Alaska were more effective in forming ice than dust from the Sahara. This was due to the presence of microscopic fragments of biogenic substances, which are particles produced by living organisms.
On the other hand, dust from the Sahara and locations in mid to low-level latitudes are believed to have particles of a mineral called potassium feldspar as the main ice nucleating agent.
Ms. Barr, the lead author of the paper, said: “We knew that deserts like the Sahara are very important at supplying ice-nucleating particles to the atmosphere, but this paper shows that river deltas like the Copper River Valley are also very important.
“Huge quantities of dust are emitted from places like the Copper River, and we need to understand these emissions to improve our climate models.”
Image Credits
In-Article Image Credits
Massive dust storm cloud (haboob) is close to enveloping a military camp as it rolls over Al Asad, Iraq via United States Marine Corps with usage type - Public Domain. April 27, 2005Global movement of dust from an Asian dust storm animation via Wikimedia Commons by NASA with usage type - Public Domain. June 26, 2001
Featured Image Credit
Massive dust storm cloud (haboob) is close to enveloping a military camp as it rolls over Al Asad, Iraq via United States Marine Corps with usage type - Public Domain. April 27, 2005