According to new research, giant plumes of Saharan dust, transported across the Atlantic Ocean by trade winds, can suppress hurricane formation over the ocean and affect weather in North America; but thick dust plumes can also lead to heavier rainfall from landfalling storms.
Zhu et al. uncovered a nonlinear and boomerang-shape relationship between Saharan dust and tropical cyclone rainfall. Image credit: Enrique.
“Surprisingly, the leading factor controlling hurricane precipitation is not, as traditionally thought, sea surface temperature or humidity in the atmosphere. Instead, it’s Sahara dust,” said Stanford University’s Dr. Yuan Wang.
Previous studies have found that Saharan dust transport may decline dramatically in the coming decades and hurricane rainfall will likely increase due to human-caused climate change.
However, uncertainty remains around the questions of how climate change will affect outflows of dust from the Sahara and how much more rainfall we should expect from future hurricanes.
“Hurricanes are among the most destructive weather phenomena on Earth,” Dr. Wang said.
“Even relatively weak hurricanes can produce heavy rains and flooding hundreds of miles inland.”
“For conventional weather predictions, especially hurricane predictions, I don’t think dust has received sufficient attention to this point.”
Dust can have competing effects on tropical cyclones, which are classified as hurricanes in the North Atlantic, central North Pacific, and eastern North Pacific when maximum sustained wind speeds reach 74 miles per hour or higher.
“A dust particle can make ice clouds form more efficiently in the core of the hurricane, which can produce more precipitation,” Dr. Wang said.
“Dust can also block solar radiation and cool sea surface temperatures around a storm’s core, which weakens the tropical cyclone.”
Dr. Wang and colleagues set out to first develop a machine learning model capable of predicting hurricane rainfall, and then identify the underlying mathematical and physical relationships.
They used 19 years of meteorological data and hourly satellite precipitation observations to predict rainfall from individual hurricanes.
Their results show a key predictor of rainfall is dust optical depth, a measure of how much light filters through a dusty plume.
They revealed a boomerang-shaped relationship in which rainfall increases with dust optical depths between 0.03 and 0.06, and sharply decreases thereafter.
In other words, at high concentrations, dust shifts from boosting to suppressing rainfall.
“Normally, when dust loading is low, the microphysical enhancement effect is more pronounced,” Dr. Wang said.
“If dust loading is high, it can more efficiently shield the ocean surface from sunlight, and what we call the ‘radiative suppression effect’ will be dominant.”
A paper describing the findings was published in the journal Science Advances.
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Laiyin Zhu et al. 2024. Leading role of Saharan dust on tropical cyclone rainfall in the Atlantic Basin. Science Advances 10 (30); doi: 10.1126/sciadv.adn6106
This article is a version of a press-release provided by Stanford University.