A University of Miami scientist is mining a rich dataset from her smoke-clouds field campaign in the southeast Atlantic Ocean
Paquita Zuidema is a research scientist at the University of Miami’s Rosenstiel of School of Marine, Atmospheric, and Earth Science. Outside her office window on the school’s campus bordering Biscayne Bay, the ocean glitters on most days and marine clouds pile up in the distance.
To Zuidema, those clouds (and others) are like books on a shelf―pages to be read in a quest to understand how these dramatic, fleeting, complex outward signs of Earth’s water cycle help drive weather and climate.
A self-described “cloud whisperer,” she has been in the business for nearly two decades.
Plainly, clouds are not all business to Zuidema, a hiker and a trail runner whose hobby as a nature photographer keeps her looking up.
“I love looking at clouds,” she said in a career profile a few years ago. “I do like thinking about why they are there. But I also think they are beautiful.”
On the business side, Zuidema has most recently focused on marine clouds over the southeast Atlantic Ocean. Her interest was piqued years ago by the remoteness of this ocean region and its data sparsity.
Intriguingly, these low clouds, gathered in vast decks, are seasonally influenced by smoke from biomass-burning fires more than 1,800 miles away, in Africa.
In what Zuidema calls “a region of superlatives,” such smoke is the source of a third of atmospheric carbon from wildfires and controlled burns―far more than the well-publicized fires in boreal regions of North America.
After her PhD, support for her work often came from the Atmospheric System Research (ASR) program at the U.S. Department of Energy (DOE).
LASIC and Lasting Data
In part, Zuidema’s success at getting ASR funding relates to her ability to leverage the measurement assets of an ASR sister operation, DOE’s Atmospheric Radiation Measurement (ARM) user facility. In 30-plus years, ARM atmospheric observatories and mobile facilities across the world have swept in a trove of continuous, long-term data―4 petabytes worth as of February 2023.
Her funding success also relates to her reputation for good fieldwork.
In 2016 and 2017, Zuidema led an ambitious 17-month ARM field campaign called Layered Atlantic Smoke Interactions with Clouds (LASIC). The mission was to learn more about aerosols from African seasonal biomass burning that reach far out at sea, the influence of such seasonal burning on the radiative properties of clouds, and how much short-wave absorbing aerosol is present in vertical columns of the atmosphere.
“LASIC is dominated by biomass burning aerosol about half of the year,” she says of her campaign’s main science target. “That’s very unique. It’s interesting you can be so far away from land and yet have an aerosol environment that is so dominated by smoke.”
From there, Zuidema led a 2017―2020 ASR project that allowed her to dig through LASIC’s voluminous data. She and co-investigator Pablo Saide at the University of California, Los Angeles, set out to study the characteristics of aerosols that absorb shortwave radiation. Across the world, most of these shortwave-absorbing aerosols above low clouds occur in the southeast Atlantic.
“People tend to think that aerosols cool the climate,” she says. “But in fact, aerosol can also warm the climate if the aerosol is capable of absorbing sunlight and overlies a bright reflective surface such as the southeast Atlantic stratocumulus deck. The smoke that comes off the African fires is very highly absorbing of sunlight―more than the wildfire smoke in the United States, for example.”
Related climate warming will impact precipitation patterns, adds Zuidema, since such warming “reduces the amount of heat release needed from rain to balance the earth’s energy budget. It also changes and when rain occurs.”
Effects on rainfall matter greatly in Africa, she says, where some places are starved for precipitation.
Absorbing aerosols can also impact how many low clouds there are and how bright or dim they get. (Brighter clouds reflect more sunlight and have a net cooling effect.)
In the 2017―2020 ASR project, Zuidema and Saide also used LASIC data to study how quickly clouds adjust to the presence of such aerosols.
More recently, armed with ASR funding for a 2020―2023 project, Zuidema is leading efforts to build on the earlier examinations of shortwave-absorbing aerosols.
“With this one,” she says of the second LASIC-related ASR project, “we’re doing continuing analysis.”
Studies based on LASIC observations in this project resulted in at least six papers in 2022 alone.
One example, from August 2022, was led by Michael Diamond of the Cooperative Institute for Research in Environmental Sciences in Colorado. It examines how large-scale cloud-smoke interactions affect the stratocumulus-to-cumulus cloud transition in the southeastern Atlantic. (Both Zuidema and Saide were coauthors.)
This consequential transition between two cloud regimes, from a net ocean-cooling one to an ocean-warming one, needs to be better represented in climate models.
The paper also points to two other campaigns in the same region that happened at the same time as LASIC and had similar science missions. One was ORACLES, the Observations of Aerosols above Clouds and their Interactions, funded by NASA. The other was the UK-sponsored CLARIFY―the CLouds and Aerosols Radiative Impacts and Forcing: Year 2017.
Like LASIC, CLARIFY deployed from Ascension but used an aircraft to sample the atmosphere above the LASIC site.
An instrument intercomparison among the three campaigns makes it possible to draw inferences about how aerosol ages as it moves away from Africa. This lifecycle evolution was examined in a 2022 paper led by Art Sedlacek at Brookhaven National Laboratory in New York.
Broadly, Zuidema and others have so far observed that early in the biomass-burning season, in June and July, the smoke penetrates the low clouds in the marine boundary layer, burning them off and reducing their number.
“But later in the season,” says Zuidema, the smoke “is more likely to be above the low clouds―and ends up strengthening the low cloud deck.”
In addition, the character of the smoke changes as it ages.
The most absorption of sunlight per particle occurs in the middle of the biomass-burning season, which may be explained, she says, “by the fuel becoming drier by then.”
These seasonal changes in the character of the transported smoke were the subject of a 2022 paper for which Zuidema is a coauthor. The work was funded through an ASR project that includes the paper’s lead author, Haochi Che, now a postdoctoral researcher at Tel Aviv University in Israel.
Before LASIC, satellite retrievals showed a greater seasonal waxing and waning of clouds than in a comparable region in the southeast Pacific.
“We didn’t have an explanation then,” says Zuidema. “Now we do.”
A Life of Languages
Zuidema grew up speaking Dutch in her native Holland. (Her father, R. Tom Zuidema, was a cultural anthropologist who studied the Incas and other Andean civilizations of South America.)
From age 4 to 7, she was immersed in Spanish when her family lived in Peru.
In Illinois, where her father next took a teaching post, Zuidema perfected her English.
“Science and math,” she says of her peripatetic childhood, “were the things that didn’t change.”
Zuidema went on to learn the language of physics at the University of Illinois at Urbana-Champaign (B.S., 1983), the language of technology and public policy at the Massachusetts Institute of Technology (M.S., civil engineering, 1987), and finally (in two stages) the language of clouds, aerosols, and precipitation.
That language training began during her study for two master’s degrees at the University of Washington (physics and atmospheric sciences, 1993). At UW, she worked with Dennis Hartmann, an expert in climate dynamics and the Earth’s energy budget.
Together, the two degrees, she says, helped her combine her interests in science and social issues. Studying the atmosphere turned out to be the right intersection of her interests.
Of course, doctoral studies completed Zuidema’s language training in atmospheric sciences.
That was at the University of Colorado, Boulder (PhD, 2004). It was a place that she and her husband, Brian Mapes, could both go. (Mapes, who researches tropical convection, had just finished his PhD at UW. Today, he and Zuidema are both at the University of Miami, where they occasionally coauthor academic papers.)
Her PhD dissertation was a study of 3-dimensional radiative transfer.
Chasing Low Clouds
And low marine clouds in the southeastern Atlantic?
Zuidema’s inspiration to look at them started on the other side of the world during a 2006 experiment in the southeastern Pacific Ocean called VOCALS: the international VAMOS Ocean-Cloud-Atmosphere-Land Study.
VOCALS took place in a region of the Pacific where one-fifth of the global fish catch originates. This same fraction of the Pacific also hosts the planet’s most extensive decks of stratocumulus clouds.
“It was a really great experiment,” says Zuidema. “We learned a lot about the southeastern Pacific low cloud deck.”
From there, she backed away and took a wider look and the Southern Hemisphere.
“The Atlantic just pops out,” says Zuidema. “Nobody had been there for a while and there hadn’t been any campaigns in the new satellite era.”
At the same time, aerosol scientists were discussing the challenges of using satellite remote sensing to infer aerosols and aerosol properties, she says. “Getting the vertical structure and absorption properties is hard to do from space.”
Taken together, too little data from an intriguing span of the ocean and problems with remote sensing there “made the southeast Atlantic seem like a perfect region to go after outstanding questions,” says Zuidema, including questions “on low clouds and aerosols and how they interact.”
LASIC eventually added a wealth of durable datasets about the atmosphere in a “data-starved” region, she says. The ASR projects that followed inspired and informed many papers and made advances in modeling possible.
“We’re making step-by-step progress,” says Zuidema. “I’ve been really lucky to have had continuity in the funding.”# # #
Author: Corydon Ireland, Science Writer, Pacific Northwest National Laboratory
This work was supported by the U.S. Department of Energy’s Office of Science, through the Biological and Environmental Research program as part of the Atmospheric System Research program.