Doug Bonderud

Nov 4th 2020

Saharan Dust Doubles Down for “Godzilla” Draft Delivery


This June, European Space Agency (ESA) satellites tracked an unusual occurrence in the Saharan Air Layer (SAL): a super-dense dust storm that traveled more than 5,000 miles across the Atlantic Ocean. Nicknamed “Godzilla,” this monster meteorological movement is out of character, even for typically active Saharan dust. What prompted this massive draft delivery, and how do such mammoth manifestations impact weather worldwide?

That ol’ Dusty Trail

According to the National Oceanic and Atmospheric Administration (NOAA), “the Saharan Air Layer is a mass of very dry, dusty air that forms over the Sahara Desert during the late spring, summer, and early fall.” Typical SAL base layers start around 1 mile above the surface and take up 2 to 2.5 miles of atmosphere. Every three to five days, SAL “outbreaks” move out over the tropical North Atlantic Ocean.

While the SAL season is relatively short — NOAA notes that activity starts in mid-June, runs high until mid-August and rapidly recedes — strong winds and substantial dust volumes often push SAL outbreaks across the Atlantic to the southeastern U.S. Once there, SAL-driven dust particles and dry air can significantly inhibit the formation of specific weather events, such as cyclones and hurricanes.

The Science of SAL

There are three characteristics that set SAL events apart from other dust storms:

  • Significantly reduced moistureSaharan dust layers contain half as much moisture as the surrounding tropical atmosphere.
  • Speedy winds — Fueled by the African Easterly Jet, SAL wind speeds often clock in at 25 to 55 miles per hour, or 10 to 25 meters per second.
  • Stabilized warmth — Warm Saharan air is more buoyant than its lower, cooler counterpart, so it sits comfortably at around 1 mile off the ground. Suspended dust particles also absorb sunlight, leading to stabilized warmth as it moves west across the Atlantic.

According to Dr. Jason Dunion, a hurricane researcher from the University of Miami working with NOAA, scientists now use multiple satellites to track and study SAL events, such as NOAA-20, GOES-16 and the NOAA/NASA Suomi-NPP. As Dunion stated, “Thanks to recent advancements in satellite technology, we can better monitor and understand the SAL, from its formation over Africa to its interactions with tropical cyclones, to its impact on weather along the U.S. Gulf coast and Florida.”

Monster Mash

In June 2020, a monster SAL outbreak appeared. Tracked by the ESA’s Copernicus Sentinel-5P satellite and NASA’s Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite, this massive monster — nicknamed “Godzilla” — contained 60 percent to 70 percent more dust than a typical Saharan dust storm, making it the dustiest draft in two decades. For more than three weeks, Godzilla stomped 5,000 miles westward, finally petering out near the Caribbean and southern U.S. However, unlike its eponymous monster movies, Godzilla didn’t tear up any cities or deliver any destruction. This raises the question: If even super-SAL cells are relatively benign, why does tracking and measuring them matter?

First is the ability to predict impacts on local weather quality. As NASA notes, when Godzilla arrived in the U.S. on June 25, it spawned an air pollution event that saw local air quality indexes (AQIs) across the Florida Panhandle and up into Kansas reach “orange” levels, which indicates concentrations of dust that are unhealthy for those with breathing or lung issues.

SAL outbreaks can also impede the formation of weather events such as cyclones and hurricanes, and mitigate their impact over time. As NOAA points out, extremely dry Saharan air can weaken tropical storms by promoting downdrafts, while enhanced wind speeds can tilt cyclone vortices and weaken their internal heat engines. In addition, SAL cells can suppress local cloud and thunderstorm formation, delivering some of the hottest days of summer for southern states. Godzilla-level outbreaks increase the impact and intensity of all these outcomes, making them critical for both assessing weather patterns and tracking the path and potential of severe storms.

Wild, Wild World

While space exploration continues to capture human interest, we’ve barely scratched the scientific surface of our own wild, wild world. With shadow biospheres, SAL outbreaks and meteorites that could help us understand our place in the cosmos, Earth offers a host of opportunities to expand the sum of human knowledge.