Month: May 2023

In Dust and Clouds Over Africa, Scientists Find Clues to How Hurricanes Form

By Kathryn Cawdrey, Science writer for NASA’s Earth Science News Team //OVER THE ATLANTIC OCEAN NEAR CABO VERDE//

A layer of dust, which appears brown, layered atop a cloud, as seen from the window of the DC-8 aircraft.
A layer of dust layered atop a cloud, as seen from the window of the DC-8 Airborne Laboratory. Credit: NASA/Kris Bedka

When the dust that wafts off the Sahel and Sahara regions of Africa mixes with tropical clouds, it creates what’s known as a rainy “disturbance” in the eastern Atlantic. These disturbances are hurricanes in their youngest form, and as they travel across the ocean, they can either dissipate or grow into powerful storms.

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

The CPEX-CV team operated from September 1-30, 2022. Using state-of-the-art remote-sensing lidars, radars, radiometers, and dropsondes—11-inch, lightweight tubes equipped with a parachute that is dropped from the plane to measure wind, temperature, and humidity—scientists captured and logged data for each flight. This month, the instrument teams have submitted data to their respective NASA data archive centers, the NASA Atmospheric Science Data Center and the Global Hydrometeorology Resource Center.

Satellite image of dust over the Atlantic Ocean off the northern coast of Africa. Borders are outlined in black. The dust is mostly between the mainland coast and Cabo Verde.
On September 22, 2022, the CPEX campaign encountered and measured one of the largest dust events that NASA has ever sampled. While the DC-8 Airborne Laboratory captured data with its instruments, the Visible Infrared Imaging Radiometer Suite (VIIRS) affixed to the Suomi NPP spacecraft captured the event from space as pictured above. Credit: NASA

“Combined with the global picture that satellites provide, this data offers finer details that only an airplane outfitted with instrumentation can measure,” said Will McCarty, CPEX program scientist based at NASA Headquarters in Washington, DC.

Photo taken out of a plane window. Part of the engine is seen on the right side. The sky is blue, but the lower part is clouded with puffy clouds and brown dust.
The DC-8 aircraft engines are visible through the passenger window. Each day, the team took off from Cabo Verde, an island nation in the east tropical North Atlantic Ocean, logging roughly 100 hours altogether. Credit: NASA/Amin Nehrir

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

“This can be considered discovery data,” Nehrir said. “It will inevitably help answer questions in years to come that haven’t been asked yet.”

As the plane flew, sensors on the wingtips of the aircraft measured properties of the dust and clouds. Once the plane was above the clouds, onboard remote sensing instruments captured detailed profiles of Saharan dust, wind speed and direction, temperature, moisture, and the structure of convection and rain within clouds. Together these measurements provide an overall, multidimensional view of what’s in the air over the northeast Atlantic, shedding light onto how those variables influence weather systems in their infancy stage.

Photo of NASA's DC-8 airplane flying in the sky near a puffy white cloud.
NASA’s DC-8 Airborne Laboratory—a highly modified McDonnell Douglas DC-8 jetliner—collects data for experiments in support of scientific projects serving the world’s scientific community. The CPEX team outfitted the flying lab with various remote-sensing lidars, radars, radiometers, and dropsondes to study interactions between Saharan dust and tropical clouds. Credit: NASA/Tony Landis

Multiple times in the campaign the DC-8 soared through the Intertropical Convergence Zone (ITCZ), the region where the northeast and southeast trade winds come together. The ITCZ is known by sailors as “the calms” because of its windless weather. Some of the most remote oceans of the world make up the ITCZ, Nehrir said.

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

On September 22, 2022, the CPEX campaign encountered and measured one of the largest dust events that NASA has ever sampled.

“We called it the epic dust day,” Nehrir said. “You could see the strength of these atmospheric waves that propagate off the African shore and pick up air and dust.”

These “waves” then interact with clouds and convection to influence the early stages of tropical cyclone genesis, which may or may not turn into a hurricane.

Photo taken out of a plane window. Part of the engine is seen in the lower left corner. The sky is blue, but the lower part is clouded with puffy clouds and brown dust.
The CPEX-CV observations offer a window into how dust, moisture, clouds, and the ocean interact to either build or prevent intensification of the rainy disturbances that have the potential to become hurricanes. This data, which is open and available to the public, will benefit researchers and weather forecasters, especially those in the atmospheric science community. Credit: NASA/Amin Nehrir

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

“Nine science projects and 10 instrument and support teams were funded under this campaign, so those investigators helped plan the mission, and now they will take that data back to their home institutions to learn what they can,” McCarty said. “Now it’s off to the races.”

Elation Through Filtration: An Oceanographer’s Sensations at Sea

By Dante Capone, Ph.D. student at the Scripps Institution of Oceanography // ABOARD THE SALLY RIDE //

Being a biological oceanographer on a physical oceanographic voyage has highlighted a key distinction between the two disciplines.

Physical oceanographers rely on sensing – deploying instrumentation that measures properties of the water: temperature, velocity, oxygen, etc. Those data are sent back to laptops allowing for near instantaneous analysis. The day-to-day work of biological oceanography, on the other hand, may be a science best described by filtering – a task that is intertwined with most measurements in our field. We collect water and remove the particles or organisms we want to study. The finest filter might have holes that let only the tiniest particles through, while the largest filter could be something like a large net, where even fish can slip through its mesh.

On the surface, this seems to have drawbacks: the science requires elaborate (but often aesthetic) filtration racks and intensive labor both on the ship and back on shore. It may be months before samples are fully analyzed and in a nicely formatted data table on your computer. However, for me these additional steps have resulted in a greater appreciation for the science and a deeper natural intuition for the water we study.

Different interpretations of the filtration rack aboard the R/V Sally Ride
Different interpretations of the filtration rack aboard the R/V Sally Ride. Credit: Dante Capone

Filtering concentrates the colors and shapes of the particles and plankton in the water, painting them on the canvas of a small, white 25mm lens into the water below us. When passing through a phytoplankton bloom the filter may stain vibrant shades of green, yellow, or red, and with material thick enough to form plankton layer cake. Occasionally, a stray zooplankton – a jellyfish or small crustacean – may unintentionally wind up on your filter, causing the true marine biology nerds to gather around in excitement in an attempt to identify it. We note everything, pack the filters into neatly labeled vials and archive the evolution of our oceanographic journey for analysis back on land.

Tools for filtration and biological oceanographic activities.
Essential tools for filtration and biological oceanographic activities. Upper left) 200uL and 1000uL pipettes and 0.1um filter pack. Upper right) 25mm diameter Supor and glass-fiber filters. Lower left) Filter with phytoplankton and larger gelatinous salp zooplankton. Lower middle) Filters loaded onto rack. Lower right) View of filter with filter funnel from above. Credit: Dante Capone

Part of the reason I enjoy biological oceanography is the variation provided by alternating between typical work on the computer and in the lab punctuated by intense bouts of fieldwork at sea. Compared to the data analysis or paper reading we do back on land, the “sea brain” switches gears, acclimating to more hands-on work. After a handful of experiments, we’ve dialed in our tasks, placing filters, measuring and pipetting water becoming ingrained into our muscle-memory. This frees up the mind and facilitates conversations and a special kind of bonding that can only happen due to the lengthy nature of our sampling.

On the S-MODE campaign, I have been doing a lot of filtering. In my case, I’m interested in measuring grazing in the ocean. Analogous to cattle grazing grass on land, zooplankton graze phytoplankton in the ocean and convert this into energy for larger organisms, or export it to the seafloor as fecal pellets. To make my measurements, I join the party of scientists to gather around the CTD (a suite of sampling instruments) where I collect and filter water into countless labeled bottles to remove any microorganisms. Whether there are waves crashing onto the deck or sun shining on a calm sea, the excitement of science spikes our energy, allowing us to share laughter and meaningful conversation. Back in the ship’s lab we’ll carefully pour our water onto dozens of filters, often powered by lively music.

Scenes from CTD water collection party
Scenes from CTD water collection party. Courtesy of Jessica Caggiano and Jacob Wenegrat.

There may come a day soon when biological oceanography advances to the point of instantaneous measurements. Already, high-tech cameras, acoustics, optics, and even early in-situ DNA measurements pave the way to phase out filtration. However, for now we will continue to enjoy the opportunity to slow down and enjoy letting each parcel of water we collect pass through our hands.