Weather is a chaotic system and predicting weather conditions several weeks in advance poses considerable challenges. The accuracy of such long-range forecasts remains generally quite low. Accordingly, even moderate improvements can prove valuable for various sectors. For instance, farmers rely on these forecasts to determine optimal sowing and harvesting times, energy providers use them to anticipate fluctuations in renewable energy production, and public health officials use them to prepare for outbreaks of diseases such as malaria or dengue fever, which are correlated with specific weather conditions.

Researchers at LMU are now investigating a phenomenon that has its origin in the stratosphere, the layer of our atmosphere situated 15 to 50 kilometers above our heads. “Previous work has shown that during Northern winter the state of the circulation in the polar stratosphere may provide useful information for improved long-range forecasts, especially for weather over the North Atlantic and Eurasia,” explains Thomas Birner, Professor of Theoretical Meteorology at LMU. In particular, when the polar vortex (a band of strong eastward circumpolar flow at stratospheric levels) strongly weakens or breaks down, the North Atlantic jetstream tends to shift southward and the likelihood of cold spells over Eurasia increases. Such vortex breakdowns are relatively rare events that only happen approximately every other winter. But its time has come round again: “One such event is currently unfolding with corresponding expected impacts on Eurasian weather in the coming weeks.”

And now for the weather: cold, but less chaotic

In a study published recently in the journal Communications Earth & Environment, LMU meteorologists highlight an additional aspect of stratospheric influence on long-range weather forecasts: Weak polar vortex states, such as the one currently prevailing, are typically followed by reduced uncertainty of 3-5 week forecasts over Northern Europe. The authors found that ensembles of forecasts show a reduced range of possible weather conditions by about 25%. Such ensembles are made up of a large number of individual forecasts, which typically diverge at longer forecasting periods. After weak polar vortex events there is less spread among these forecasts over Northern Europe, making the weather more predictable.

“We attribute this reduced forecast uncertainty to the southward shift of the North Atlantic jetstream,” says Jonas Spaeth, doctoral student at LMU’s Meteorological Institute and lead author of the new study. The associated southward shift of the tracks of winter storms, which are the main source of forecast uncertainty during this season, causes less storm activity and thereby reduced forecast uncertainty over Northern Europe. Conversely, forecast uncertainty increases over Southern Europe.

“Our study sheds light on meteorological phenomena where uncertainty of weather forecasts several weeks in advance systematically reduces or increases,” says Jonas Spaeth. “Furthermore, it underscores how the practical use of long-range forecasts can benefit from a deeper understanding of the remote coupling across different atmospheric regions.”

Ultraviolet spectroscopy plays a critical role in the study of electronic transitions in atoms and rovibronic transitions in molecules. These studies are essential for tests of fundamental physics, quantum-electrodynamics theory, determination of fundamental constants, precision measurements, optical clocks, high-resolution spectroscopy in support of atmospheric chemistry and astrophysics, and strong-field physics. Scientists in the group of Nathalie Picqué at the Max-Planck Institute of Quantum Optics have now made a significant leap in the field of ultraviolet spectroscopy by successfully implementing high-resolution linear-absorption dual-comb spectroscopy in the ultraviolet spectral range. This groundbreaking achievement opens up new possibilities for performing experiments under low-light conditions, paving the way for novel applications in various scientific and technological fields.

Dual-comb spectroscopy, a powerful technique for precise spectroscopy over broad spectral bandwidths, has been mainly used for infrared linear absorption of small molecules in the gas phase. It relies on measuring the time-dependent interference between two frequency combs with slightly different repetition frequencies. A frequency comb is a spectrum of evenly spaced, phase-coherent laser lines, that acts like a ruler to measure the frequency of light with extreme precision. The dual-comb technique does not suffer from the geometric limitations associated with traditional spectrometers, and offers great potential for high precision and accuracy.

Dual-comb spectroscopy now available for low light intensities

However, dual-comb spectroscopy typically requires intense laser beams, making it less suitable for scenarios where low light levels are critical. The MPQ team have now experimentally demonstrated that dual-comb spectroscopy can be effectively employed in starved-light conditions, at power levels more than a million times weaker than those typically used. This breakthrough was achieved using two distinct experimental setups with different types of frequency-comb generators. The team developed a photon-level interferometer that accurately records the statistics of photon counting, showcasing a signal-to-noise ratio at the fundamental limit. This achievement highlights the optimal use of available light for experiments, and opens up the prospect of dual-comb spectroscopy in challenging scenarios where low light levels are essential.

The MPQ researchers addressed the challenges associated with generating ultraviolet frequency combs and building dual-comb interferometers with long coherence times, paving the way for advances in this coveted goal. They exquisitely controlled the mutual coherence of two comb lasers with one femtowatt per comb line, demonstrating an optimal build-up of the counting statistics of their interference signal over times exceeding one hour. “Our innovative approach to low-light interferometry overcomes the challenges posed by the low efficiency of nonlinear frequency conversion, and lays a solid foundation for extending dual-comb spectroscopy to even shorter wavelengths,” comments Bingxin Xu, the post-doctoral scientist who led the experiments.

Indeed, an exciting future application is the development of dual-comb spectroscopy at short wavelengths, to enable precise vacuum- and extreme-ultraviolet molecular spectroscopy over broad spectral spans. Currently, broadband extreme-UV spectroscopy is limited in resolution and accuracy, and relies on unique instrumentation at specialized facilities. “Ultraviolet dual-comb spectroscopy, while a challenging goal, has now become a realistic one as a result of our research. Importantly, our results extend the full capabilities of dual-comb spectroscopy to low-light conditions, unlocking novel applications in precision spectroscopy, biomedical sensing, and environmental atmospheric sounding,” Nathalie Picqué concludes.

A collaborative study conducted by researchers from the Arctic Research Center at Hokkaido University and the Department of Ecoscience at Aarhus University, Denmark, delves into the captivating activities of the most abundant seabird in the North Atlantic (little auk, Alle alle). The study sheds light on birds’ daily rhythmic behavior under the endless daylight of the Arctic summer. Led by Associate Professor Evgeny A. Podolskiy, Hokkaido University, the findings were published in the journal Communications Biology.

In the remote wilderness of Northwest Greenland, the research team employed passive acoustic and imaging technologies to uncover the hidden rhythms of little auk colonies. Every summer, approximately 60 million birds come to this region to breed and forage, and while their vocalization is a familiar summer soundscape for the local inhabitants, little is known to science about their daily routines and calling habits. The study revealed a “nocturnal” surge in vocalization activity, contrary to expectations of mid-latitude inhabitants familiar with a dawn chorus. Due to a lower number of birds in the afternoon, the calling and wing-flapping rates decreased. The study improves our understanding of avian behavior in continuous daylight environments.

“These findings provide a fascinating glimpse into the intricate rhythms of Arctic life, and remind us that bird counts depend on the time of day,” says Podolskiy. “Under the perpetual daylight, little auks exhibit an acoustic pattern that mirrors their behavioral cycles — such as attendance, feeding, and fledging — offering valuable insights into their ecological dynamics.”

“The little auk, also known as the dovekie, emerges as a sentinel species in monitoring Arctic environmental shifts,” says Dr. Anders Mosbech, co-author from Aarhus University. “Understanding their behavioral dynamics is paramount for effective conservation and ecosystem management in the face of rapid environmental transformations.”

“The significance of this study extends beyond mere curiosity, emphasizing the crucial role of passive acoustic monitoring in studying wildlife behavior in remote and difficult-to-access regions,” adds Podolskiy.

The study advocates for the continued use of acoustic monitoring as a non-invasive and efficient method for studying bird colonies in the Arctic. Traditional methods of field observation could be less practical due to their laborious nature and the remoteness of seabird breeding colonies. “By combining audio data with other monitoring techniques, such as time-lapse cameras or radar systems, and engaging local communities, we can enhance conservation efforts for important seabird populations while also promoting sustainability,” explains Monica Ogawa, co-author of the study and a Ph.D. candidate at the Graduate School of Environmental Science, Hokkaido University.

The research team plans to continue their investigations into the acoustic ecology of Arctic seabirds, leveraging interdisciplinary collaborations to delve deeper into the avian biology and environmental changes affecting it. Through their efforts, the researchers hope to expand our understanding of the complex web of interactions that sustain life in one of the most extreme environments on Earth.

Based on available evidence, the researchers posit in a new study published in Aquatic Mammals that the 49 orcas could belong to a subpopulation of transient killer whales or a unique oceanic population found in waters off the coast of California and Oregon.

“The open ocean is the largest habitat on our planet and observations of killer whales in the high seas are rare,” said first author Josh McInnes, a masters student in the UBC Institute for the Oceans and Fisheries (IOF).”In this case, we’re beginning to get a sense of killer whale movements in the open ocean and how their ecology and behaviour differs from populations inhabiting coastal areas.”

Three ecotypes of killer whale live along the coasts of California and Oregon: ‘residents’, ‘transients’, and ‘offshores’.

The unknown orcas have been spotted before but the new paper contains a weight of evidence gathered from nine encounters with 49 animals from 1997 to 2021, enough to form a solid hypothesis, the researchers said.

“It’s pretty unique to find a new population. It takes a long time to gather photos and observations to recognize that there’s something different about these killer whales,” said co-author Dr. Andrew Trites, IOF professor.

The 49 killer whales could not be matched with any known animals through photos or descriptions. “In one of the first encounters researchers had with a pod of these oceanic killer whales, they were observed taking on a herd of nine adult female sperm whales, eventually making off with one. It is the first time killer whales have been reported to attack sperm whales on the west coast,” said McInnes. “Other encounters include an attack on a pygmy sperm whale, predation on a northern elephant seal and Risso’s dolphin, and what appeared to be a post-meal lull after scavenging a leatherback turtle.”

Shark scars provide vital clue

A key clue to the new population’s presumed habitat range lies in cookiecutter shark bite scars observed on almost all of the orcas. This parasitic shark lives in the open ocean, meaning the new population primarily inhabit deep waters far from land.

The orcas also feature physical differences from the three main ecotypes, including in their dorsal fins and saddle patches — the grey or white patches by the fin. “While the sizes and shapes of the dorsal fins and saddle patches are similar to transient and offshore ecotypes, the shape of their fins varied, from pointed like transients to rounded like offshore killer whales,” said McInnes. “Their saddle patch patterns also differed, with some having large uniformly gray saddle patches and others having smooth narrow saddle patches similar to those seen in killer whales in tropical regions.”

Along with marine mammal stock assessment surveys, fishermen and passengers on an open-ocean birding expedition and whale-watching tour also provided observations of the unidentified killer whales, said Dr. Trites. Spotting the new population has become something of a hobby among fishermen, some of whom have bought cameras for their trips specifically to snap an encounter, the researchers said.

The researchers hope to document more sightings and gather more information, including acoustic data about the orcas’ calls and genetic information from DNA samples to further investigate how these killer whales may differ, or not, from already documented populations.

In a highly novel study published in Current Biology, researchers at the University of Alabama at Birmingham and the National Institute of Mental Health, or NIMH, describe how two major neuronal subpopulations in a part of the brain’s thalamus called the paraventricular nucleus participate in the dynamic regulation of goal pursuits. This research provides insight into the mechanisms by which the brain tracks motivational states to shape instrumental actions.

For the study, mice first had to be trained in a foraging-like behavior, using a long, hallway-like enclosure that had a trigger zone at one end and a reward zone at the other end, more than 4 feet distant.

Mice learned to wait in a trigger zone for two seconds, until a beep triggered initiation of their foraging-like behavioral task. A mouse could then move forward at its own pace to the reward zone to receive a small gulp of strawberry-flavored Ensure. To terminate the trial, the mice needed to leave the reward zone and return to the trigger area, to wait for another beep. Mice learned quickly and were highly engaged, as shown by completing a large volume of trials during training.

The researchers then used optical photometry and the calcium sensor GCaMP to continuously monitor activity of two major neuronal subpopulations of the paraventricular nucleus, or PVT, during the reward approach from the trigger zone to the reward zone, and during the trial termination from the reward zone back to the trigger zone after a taste of strawberry-flavored food. The experiments involve inserting an optical fiber into the brain just about the PVT to measure calcium release, a signal of neural activity.

The two subpopulations in the paraventricular nucleus are identified by presence or absence of the dopamine D2 receptor, noted as either PVT^D2(+) or PVT^D2(-), respectively. Dopamine is a neurotransmitter that allows neurons to communicate with each other.

“We discovered that PVT^D2(+) and PVT^D2(-) neurons encode the execution and termination of goal-oriented actions, respectively,” said Sofia Beas, Ph.D., assistant professor in the UAB Department of Neurobiology and a co-corresponding author of the study. “Furthermore, activity in the PVT^D2(+) neuronal population mirrored motivation parameters such as vigor and satiety.”

Specifically, the PVT^D2(+) neurons showed increased activity during the reward approach and decreased activity during trial termination. Conversely, PVT^D2(-) neurons showed decreased activity during the reward approach and increased activity during trial termination.

“This is novel because people didn’t know there was diversity within the PVT neurons,” Beas said. “Contrary to decades of belief that the PVT is homogeneous, we found that, even though they are the same types of cells (both release the same neurotransmitter, glutamate), PVT^D2(+) and PVT^D2(-) neurons are doing very different jobs. Additionally, the findings from our study are highly significant as they help interpret contradictory and confusing findings in the literature regarding PVT’s function.”

For a long time, the thalamic areas such as the PVT had been considered just a relay station in the brain. Researchers now realize, Beas says, that the PVT instead processes information, translating hypothalamic-derived needs states into motivational signals via projections of axons — including the PVT^D2(+) and PVT^D2(-) axons — to the nucleus accumbens, or NAc. The NAc has a critical role in the learning and execution of goal-oriented behaviors. An axon is a long cable-like extension from a neuron cell body that transfers the neuron’s signal to another neuron.

Researchers showed that these changes in neuron activity at the PVT were transmitted to the NAc by measuring neural activity with an optical fiber inserted where the terminals of the PVT axons reach the NAc neurons. The activity dynamics at the PVT-NAc terminals largely mirrored the activity dynamics the researchers saw at the PVT neurons — namely increased neuron activity signal of PVT^D2(+) during reward approach and increased neuron activity of PVT^D2(-) during trial termination.

“Collectively, our findings strongly suggest that motivation-related features and the encoding of goal-oriented actions of posterior PVT^D2(+) and PVT^D2(-) neurons are being relayed to the NAc through their respective terminals,” Beas said.

During each mouse recording session, the researchers recorded eight to 10 data samples per second, resulting in a very big dataset. In addition, these types of recordings are subject to many potential confounding variables. As such, the analysis of this data was another novel aspect of this study, through use of a new and robust statistical framework based on Functional Linear Mixed Modeling that both account for the variability of the recordings and can explore the relationships between the changes of photometry signals over time and various co-variates of the reward task, such as how quickly mice performed a trial, or how the hunger levels of the animals can influence the signal.

One example of how researchers correlated motivation with task performance was separating the trial times into “fast” groups, two to three seconds to the reward zone from the trigger zone, and “slow” groups, nine to 11 seconds to the reward zone.

“Our analyses showed that reward approach was associated with higher calcium signal ramps in PVT^D2(+) neurons during fast compared to slow trials,” Beas said. “Moreover, we found a correlation between signal and both latency and velocity parameters. Importantly, no changes in posterior PVT^D2(+) neuron activity were observed when mice were not engaged in the task, as in the cases where mice were roaming around the enclosure but not actively performing trials. Altogether, our findings suggest that posterior PVT^D2(+) neuron activity increases during reward-seeking and is shaped by motivation.”

Deficits in motivation are associated with psychiatric conditions like substance abuse, binge eating and the inability to feel pleasure in depression. A deeper understanding of the neural basis of motivated behavior may reveal specific neuronal pathways involved in motivation and how they interact. This could lead to new therapeutic targets to restore healthy motivational processes in patients.

Co-authors with Beas in the study, “Dissociable encoding of motivated behavior by parallel thalamo-striatal projections,” are Isbah Khan, Claire Gao, Gabriel Loewinger, Emma Macdonald, Alison Bashford, Shakira Rodriguez-Gonzalez, Francisco Pereira and Mario Penzo, NIMH, Bethesda, Maryland. Beas was a post-doctoral fellow at the NIMH before moving to UAB last year.

Support came from National Institutes of Health award K99/R00 MH126429, a NARSAD Young Investigator Award by the Brain and Behavior Research Foundation, and NIMH Intramural Research Program award 1ZIAMH002950.

The researchers looked at threatened spring-run Chinook salmon in tributaries of the Sacramento River. It found that restored sites that produce lots of fish may be especially vulnerable to changes such as drought. Such sites should be coupled with other varying sites that support the salmon population in diverse ways.

“The fish need all the different opportunities,” said Flora Cordoleani, a NOAA Fisheries and University of California Santa Cruz researcher who led the research published this week in Ecosphere. “Fish with one life history that favors certain habitat are not going to save the population in the long term. We need diverse habitats to support diverse life histories that help provide resilience.”

Life history refers to salmon traits such as their juvenile migration timing, growth rates, and food preferences. For instance, some juvenile salmon migrate to the ocean in their first year, while others may spend the year growing in freshwater first. That timing may benefit them in some years, but leave them more vulnerable in others, such as during drought.

Spring Chinook salmon were once found across the state and formed the backbone of California’s commercial salmon fishery. They are now greatly diminished and survive in only a few key watersheds with worsening trends in numbers. State and federal biologists last fall collected a few remaining spring-run Chinook salmon to begin a captive broodstock that will safeguard the genetic heritage of the species.

Habitat Mix Benefits Fish

Fish benefit most when they have access to a mosaic of interconnecting habitat from streamside vegetation to open floodplains, the research found. Young salmon may grow rapidly when wet years inundate floodplains and produce plentiful food, “but that happens pretty rarely,” Cordoleani said. “The key is for the fish to have access to all those habitats, so if something happens to one of them, the fish don’t all disappear.”

The new research goes beyond earlier studies showing that later-migrating fish had better survival rates. It shows how that played out on the landscape of three creeks that feed the Sacramento River, one of the biggest salmon-producing rivers on the West Coast.

Cordoleani and her team examined Butte Creek, the focus of extensive restoration that produced a large increase in fish numbers that had access to the floodplain. They examined salmon otoliths — small ear bones — that record clues about each fish’s life history. They found few later-migrating fish, which made the fish there more vulnerable to sharp declines during drought years that may become more common with climate change.

Two other nearby streams, Mill and Deer Creek, offered different conditions and hosted more fish that migrated later as yearlings (juveniles oversummering in freshwater). While they did not see the big increases in fish abundance that Butte Creek did, their salmon better survived droughts. Combining the three sites that complement each other increases the resilience of the Central Valley spring run stock complex — the term for all the individual populations combined.

“The sum of the parts is much greater, because they are doing different things and supporting the fish in different ways,” said Rachel Johnson, the senior author of the research and scientist at NOAA Fisheries’ Southwest Fisheries Science Center. “Some of those qualities may turn out to be more or less important as the climate changes.”

But relying on these three creeks is not enough. “Spring-run Chinook are already playing the climate stock market with only a few stocks in their portfolio,” Johnson said. They were once found in every major watershed. She said a lesson of the research is that more habitat options help fish survive a volatile climate by providing more opportunities to survive and thrive.

Providing that array of options requires restoring diverse habitat areas that complement each other at the landscape scale and returning salmon to historical habitats that had long vanished. Cordoleani and her team hope that this research encourages restoration planners to implement projects that create a mosaic of different habitats across watersheds that support diverse fish survival strategies. These actions will also balance each other to help stabilize numbers in the long term.

The study was published today in Circulation Research, an official journal of the American Heart Association.

“The impact of circadian rhythms on cardiovascular function and disease development is well established,” said the study’s lead author Tobias Eckle, MD, PhD, professor of anesthesiology at the University of Colorado School of Medicine. “However, translational preclinical studies targeting the heart’s circadian biology are just now emerging and are leading to the development of a novel field of medicine termed circadian medicine.”

The senior author is Professor Tami A. Martino, PhD, distinguished chair in molecular and cardiovascular research at the University of Guelph in Ontario, Canada.

The study reviews current circadian medicine research, focusing on the use of intense light therapy following surgery, utilizing light to treat cardiac injury, exploring how cardiovascular disease can differ between men and women and administering drugs at specific times of day to coincide with the body’s internal clock to speed healing.

It also urges more aggressive use of this therapy in humans, rather than relying on mostly animal models.

“There are literally millions of patients who could benefit from this,” Eckle said. “The treatments are almost all low-risk. Some involve using light boxes and others use drugs that are already on the market.”

Circadian rhythms significantly influence how the cardiovascular system operates. Timing is everything. Blood pressure and heart rates follow distinct patterns, peaking during the day and ebbing at night. When this is disrupted, it leads to worse cardiovascular disease outcomes including myocardial infarction and heart failure.

Light is critical in maintaining the proper balance and functioning of the body. Shift employees who may work night hours then day hours often have worse cardiac outcomes.

Eckle, who has studied circadian rhythm and health for years, said intense light can help heal the body after heart surgery while protecting it from injury during surgery, including reducing the chances of cardiac ischemia.

According to the researchers, when light hits the human eye it is transmitted to the suprachiasmatic nucleus, a structure in the brain’s hypothalamus that regulates most circadian rhythms in the body. Intense light stabilizes the PER2 gene and increases levels of adenosine, which blocks electrical signals in the heart that cause irregular rhythms, making it cardiac protective.

Eckle has used light therapy with patients after surgery and seen positive results including lower levels of troponin, a key protein whose elevation can signal a heart attack or stroke.

Given the mounting evidence that intense light and timed drug treatments are effective, he said, it is time to move forward with more clinical trials.

“Circadian rhythms play a crucial role in cardiovascular health, influencing the timing of onset and severity of cardiovascular events and contributing to the healing process from disease,” Eckle said. “Studies in humans are clearly required. Regarding intense light therapy, chronotherapy and restricted feeding are low-risk strategies that should be tested sooner than later.”

“Much of the physics of the known universe already have fundamental solutions or are too complex to get an exact answer,” said Willie Padilla, professor of electrical and computer engineering at Duke. “In any field, finding a truly novel, fundamental, exact result like this is rare.”

The research appeared online March 8in the journal Nanophotonics.

Whether building an antenna or developing sunscreen, there are many instances where certain types of light need to be absorbed. One trick to maximizing that amount is increasing the thickness of the material absorbing the energy.

However, the needed thickness for a transparent material to provide that absorption was unknown till now.

More than 20 years ago, Konstantin N. Rozanov of the Institute for Theoretical and Applied Electrodynamics in Moscow, Russia, figured out the most light over a range of wavelengths that a device of a certain thickness could absorb if one side was lined with metal. This scenario creates a boundary on one side where all light either reflects back or is absorbed, providing a constraint that allows a certain mathematical approach to crack the problem.

Taking away that metal edge and allowing the light to continue through, however, is a horse of an entirely different color on the electromagnetic spectrum.

“Rozanov used a clever trick where he worked in wavelength instead of frequency,” said Yang Deng, a research assistant working in Padilla’s laboratory. “But several researchers have since tried using that approach to this problem and failed.”

To come up with a new mathematical approach, Padilla and Deng collaborated with Vahid Tarokh, the Rhodes Family Professor of Electrical and Computer Engineering at Duke. Tarokh’s research spans a wide range of topics while pursuing new formulations and approaches to getting the most out of datasets.

Without getting too deep into the mathematical weeds, it can be said that Tarokh was able to figure out how to shape the problem so that it could be solved, pulling a rabbit from a mathematical hat.

“Hindsight is 20/20, but even mathematicians call these creative strategies ‘tricks,'” Padilla said.

Beyond the novelty of solving a long-sought-after problem, the researchers say their work has practical implications in several areas. Metal-backed absorbers won’t let any type of electromagnetic energy pass through. But there are certain applications where you might want to block some frequencies while letting others pass.

For example, cellular phones might want to be able to block certain types of harmful electromagnetic radiation while letting others like GPS or Bluetooth through. Knowing what the fundamental limits of this type of goal will allow engineers to know when more work optimizing their design will not be worth the effort.

This research was supported by the Department of Energy (DESC0014372).