Clues to Hurricane Formation Discovered by Scientists in African Dust and Clouds

When dust blowing up from the Sahel and Sahara regions of Africa mixes with tropical clouds, it creates what’s known as a rainy “turbulence” in the eastern Atlantic. These disturbances are hurricanes in their smallest form, and as they travel across the ocean, they can dissipate or turn into powerful storms.

To study these small storms, a group of NASA scientists in September 2022 spent a month flying off the northwest coast of Africa aboard NASA’s DC-8 research aircraft. Each day, the team took off from Cabo Verde, an island nation off the west coast of Africa, logging nearly 100 hours of flying time. The mission, known as the Thermal Processes Experiment – Cabo Verde (CPEX-CV), released its data publicly on April 1.

The CPEX-CV team worked from Sept. 1 to 30, 2022. Using state-of-the-art remote sensors, radars, radiometers, and projectors—lightweight 11-inch tubes fitted with a parachute dropped from the aircraft to measure wind, temperature, and humidity—scientists Record and log data for each trip. This month, instrumentation teams provided the data to NASA’s Data Archive Centers, NASA’s Atmospheric Science Data Center and the Global Hydrometeorological Resource Center.

“Combined with the global picture provided by the satellites, this data provides finer detail that only an instrument-equipped aircraft can measure,” said Will McCarty, CPEX program scientist based at NASA Headquarters in Washington, D.C.

These observations provide a window into how dust, moisture, clouds, and the ocean interact to either build up or prevent intensification of rainy disturbances that have the potential to turn into tornadoes. This data, which is open and publicly available, will benefit researchers and weather forecasters, especially those in the atmospheric science community, according to Amin Nehrir, a research scientist at NASA’s Langley Research Center in Virginia.

“This can be considered discovery data,” Nehrir said. “It will inevitably help answer questions that have yet to be asked in the years to come.”

As the plane flew, sensors on the wingtips measured the properties of dust and clouds. Once the plane was above the clouds, onboard remote sensors captured detailed desert dust profiles, wind speed and direction, temperature, humidity, convective structure and rain within the clouds. Together, these measurements provide a comprehensive, multidimensional view of what is in the air over the Northeast Atlantic, shedding light on how these variables influence childhood weather systems.

Several times in the campaign, the DC-8 flew through the Intertropical Convergence Zone (ITCZ), the area where the northeast and southeast trade winds meet together. ITCZ is known to sailors as “The Calm” due to its windless weather. Some of the world’s most remote oceans make up the international trade zone, Nahrir said.

“What amazed me most was being able to look out the window and see how the clouds changed as far as the eye could see from faint puffy clouds to dark streets to convective systems,” he said. “You can see the evolution of convective systems all in one shot.”

On September 22, 2022, the CPEX campaign and its measurement encountered one of the largest dust events NASA has ever collected.

“We called it an epic dust day,” Nahrir said. “You can see the power of these weather waves that are rippling off the African coast and picking up air and dust.”

These “waves” then interact with clouds and convection to affect the early stages of formation of tropical cyclones, which may or may not transform into a hurricane.

The 2022 CPEX-CV campaign was preceded by the CPEX campaign in 2017 and the CPEX – Aerosols & Winds campaign in 2021. Data from previous campaigns is also publicly available.

“Nine science projects and 10 instrument and support teams were funded under this campaign, so these investigators helped plan the mission, and now they’re going to bring this data back to their local institutions to see what they can do,” McCarty said. “Now it’s time for the races.”