“The prevailing wisdom on the relationship between soil moisture and rainfall is that if you have wetter soil in the morning, you’ll have a greater occurrence of rainfall in afternoon, but it’s more complicated than that,” said lead author Josh Welty, a UArizona doctoral student in the Department of Hydrology and Atmospheric Sciences. “On a global scale, we see evidence that you can have greater chances of afternoon rainfall over both wet and dry soil conditions, depending on atmospheric moisture.”

The team, which also included researchers from the Desert Research Institute in Nevada and NASA’s Goddard Space Flight Center, used satellite-based observations of soil moisture and afternoon rainfall in the northern hemisphere from the last five years. The work was supported by NASA and is based on NASA satellite data from the Global Precipitation Measurement mission and the Soil Moisture Active Passive satellite, as well as atmospheric moisture and movement data from the Modern-Era Retrospective analysis for Research and Applications Version 2, or MERRA-2, model, which incorporates satellite observations.

The researchers found that on days when wind blows in little atmospheric moisture, afternoon rainfall is more likely to occur over wetter soils or higher relative humidity. On days when wind introduces lots of atmospheric moisture, afternoon rainfall is more likely over drier soils or lower relative humidity. The team also found that for both conditions, afternoon rainfall occurrence is more likely with warmer morning soil or air temperature.

The researchers focused on days in which afternoon rainfall occurred and noted the difference between the number of rainfall days that occurred over wetter-than-average soil and the number of rainfall days that occurred over drier-than-average soil. They then grouped their results into three categories: high, mid and low atmospheric moisture transport by wind.

This research builds on a 2018 study that identified soil moisture’s role in afternoon rainfall amount in the Southern Great Plains of Oklahoma. The new findings show that the relationship between soil moisture, afternoon rainfall and atmospheric moisture in Oklahoma doesn’t apply across the entire northern hemisphere.

“Over the Southern Great Plains, we found that when the wind brings less moisture, dry soils are associated with increases in rainfall amount; and when the wind brings greater moisture, wet soils are associated with increases in rainfall amount. In the current study, we find that, actually, in many regions, the opposite is true for the likelihood of afternoon rainfall,” Welty said.

Understanding the role of water vapor in weather is important because its effects are felt everywhere, according to Welty’s thesis adviser and paper co-author Xubin Zeng, Agnese N. Haury Endowed Chair in Environment and director of the Climate Dynamics and Hydrometeorology Center and Land-Atmosphere-Ocean Interaction Group.

“For example, for the Southern Great Plains there are many tornado activities because there is water vapor moving in from the Gulf of Mexico. Also, on the California coast you talk about severe flooding from atmospheric rivers,” which are corridors of concentrated water vapor that can quickly precipitate once hitting a mountain range, causing mass flooding,” Zeng said.

“Water vapor brought in by the winds is an important source to understand. In the past, people didn’t pay enough attention to it in studying how land conditions affect rainfall, potentially making their results misleading. Once we consider the wind’s movement of water vapor, the results become more robust,” Zeng said.

Understanding this relationship is even more important as global warming changes patterns of atmospheric moisture, soil moisture and more. Such changes will not only have effects on weather and natural disasters, but also on agriculture, Zeng said.

“The results really show the complexity of the land’s influence on weather and climate,” said physical scientist and paper co-author Joe Santanello from NASA’s Goddard Space Flight Center, who chairs the NASA-supported Local Land-Atmosphere Coupling working group to improve weather and climate models. “When you add in the human factor of irrigation or land use that changes the dryness or wetness of the soils, which we currently don’t represent well in the models, we potentially have additional downstream effects on weather and climate that we haven’t foreseen.”

The next step is to assess how these relationships play out in global climate and weather forecasting models.

“Our findings are observational, but now, we want to use computer modeling to help us understand why drier or wetter soil could enhance rainfall likelihood,” Zeng said. “We know it’s true, but we don’t quantitatively know why.”

In a new paper in Nature Structural and Molecular Biology by Tricia Serio, dean of the College of Natural Sciences and professor of biochemistry and molecular biology at UMass Amherst, and others, report an unanticipated role for prion nucleation seeds that enhances their ability to appear and resist curing. Nucleation seeds are molecule clusters that form when prions attach to one another and change shape. “Once that change occurs, it creates a very stable aggregate known as amyloid that was thought to be impossible to inactivate by normal means,” Serio notes.

The infectious prion is an unusual pathogen, a protein without nucleic acid, she explains. Prion diseases were first described in the 1800s, and include scrapie in sheep and other neurodegenerative diseases such as mad cow disease and in humans, Creutzfeldt-Jakob disease, fatal familial insomnia and kuru from ritual cannibalism in Papua, New Guinea.

Serio says, “These diseases are always fatal,” but she and colleagues including first author Janice Villali work with natural yeast prions that can’t be transmitted to humans or cause disease. “It’s a good model system that is not infectious, and it grows really fast.”

It has been known for decades that prion protein (PrP) misfolding is a key part of the disease process, she adds. In these diseases, proteins fold into 3D shapes that cause disease. In mammals, the protein quality control system responds to folding mistakes with “chaperone” molecules that seek out misfolds and try to refold and correct mistakes.

But prions misfold so quickly that chaperones can’t keep up, Serio says. “That part was known,” she adds, but scientists still could not figure out what was limiting the chaperone system, allowing prions to persist. “One key factor controlling the transition from harmless protein to invincible disease menace was so hidden and obscure that it had not been previously proposed,” she says.

Then, after a conference where she had talked intensely all day about prions, Serio had the crucial dream. “It came to me that the size of the aggregate nucleation seed mattered,” she recalls. “So we went back and designed experiments to test the minimum size idea by mathematical modeling with co-first author Jason Dark, and it worked. That led to this investigation and why we’re really excited about this paper.”

The first revelation was a surprise, Serio recalls — prion aggregates come in different sizes. “Everybody knew of the nucleation seed, but no one knew they could be different sizes for the same protein.” As prion proteins physically attach and the complex switches from one state to another, this minimum size is really important — but why?

It turns out, Serio says, that the seed complex must double in size for the disease to persist. It it starts with four molecules, it must reach eight. “This minimum size determines whether the chaperone can win. Four has to get to eight, but if you catch it early enough, if you pull out one side of the square, the amyloid structure can’t double. Chaperones prevent the disease by preventing it from doubling in that first round.”

Another discovery is that if the minimum nucleation seed starting size is 10 and it must reach 20 to create two amyloids, that complex is an easier problem for chaperones to nip, Serio points out. “In yeast, the bigger the initial seed, the more difficult it is for the disease to resist chaperones and take hold because these protein quality controls have more time to act; the smaller seed is harder to cure because it doubles more quickly.”

She adds, “We realized that if we could control this transformation, we could stop the disease from arising, but we also realized that the same barrier would control going backwards and unfolding an established amyloid. The literature says that’s a silly idea because prions survive and resist killing so well. But once we figured out this minimum size, we showed that it could also predict the frequency of prion curing under different growth conditions. Looking back, we can’t figure out how we missed it.”

Serio says she and her team now know there are at least three nucleation sizes possible, and, “I suspect that it will turn out to be an infinite number,” she adds. “In fact, we have shown that we can shift the nucleation size by changing the shape of the prion or by expressing a mutant form of the protein, opening the door to therapeutic intervention to reverse this process.”

When told maybe that’s not the best comparison, Zhang laughed and made a confession: “To be honest, I’ve never watched that movie!”

Zhang — an assistant professor of mechanical engineering at Binghamton University, State University of New York — has much more benign plans for his latest study, which will be published in the May issue of the journal Additive Manufacturing.

Working with PhD students Fanghang Deng and Quang-Kha Nguyen, Zhang developed what he calls “the first liquid metal lattice in the world,” which is made from Field’s alloy. The mix of bismuth, indium and tin — named after its inventor, Simon Quellen Field — becomes liquid at the relatively low melting point of 62°C (144°F).

Field’s alloy is currently used as a liquid-metal coolant in nuclear engineering, among other applications, but the Watson team demonstrates other potential applications. They combined the metal lattice material with a rubber shell through a hybrid manufacturing process. This novel process integrates 3D printing, vacuum casting and conformal coating (which is used on electronic circuitry to protect against moisture, dust, chemicals and temperature extremes).

“Without the shell, it won’t work, because the liquid metal will flow away,” Zhang said. “The shell skeleton controls the overall shape and integrity, so the liquid metal itself can be confined in the channels. We spent over half a year developing this manufacturing process, because this new lattice material is very hard to process. You need to find the best materials and processing parameters.”

The Watson team made a series of prototypes that regain their shapes after being heated to the melting point, including “spider web”-like mesh antennas, honeycombs and soccer balls, as well as the letters BUME (for Binghamton University mechanical engineering, of course). Perhaps the most Terminator-like one, though, is a hand that slowly opens as the metal lattice melts.

These prototypes offer remarkable visuals, but the properties behind them could inspire myriad uses. When the liquid metal is in a solid state, it is very safe and strong. It absorbs a lot of energy when crushed; then, after some heating and cooling, it returns to its original shape and can be reused.

Zhang has studied lattice materials since his PhD work at the University of Pittsburgh in 2012, and he sees in this new liquid metal research many possibilities for NASA or private space-faring companies. For instance, satellite designers could pack the “spider web” into a small package and then unfold it as an antenna when in orbit. Perhaps structures for future settlements on the moon or Mars could take up less room onboard an exploration vessel and then be expanded when astronauts reach their destination.

It might even make sense to build an interplanetary ship using a metal lattice material, he said: “A spacecraft may crash if it lands on the moon or Mars with some kind of impact. Normally, engineers use aluminum or steel to produce the cushion structures, but after you land on the moon, the metal absorbs the energy and deforms. It’s over — you can use it only once.”

“Using this Field’s alloy, you can crash into it like other metals, but then heat it up later to recover its shape. You can use it over and over again.”

The Watson team is already exploring how to build on this metal lattice research, including different structure types and improved coating materials. Zhang still has a final goal in mind: “Our dream is to build a liquid metal lattice robot, and now we have a hand, so we’re one step further.”

Just as long as it’s a friendly robot.