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How COVID-19 is impacting global weather and climate observation

Petteri Taalas, WMO secretary-general

Do you think the current – temporary – reduction of greenhouse-gas emissions and other human activities since the world went into lockdown following the COVID-19 outbreak can have a lasting impact on the environment and long-term climate trends?

There have been reported 6% reductions in carbon emissions and 40% reductions in atmospheric pollution, especially nitrous oxide emissions [over the last few months]. The pollution drop varies according to geographical location – polluted areas in China, India, Italy and France have seen short-term improvements following the drop of traffic and industrial activities. There was a phaseout of the previous continuous carbon-emission growth after the 2008 financial crisis, but thereafter the emission growth unfortunately continued. This is likely to happen once again when the COVID crisis is over, if no other efforts are made.

The COVID-19 pandemic has shown that fast and co-ordinated global action is possible in the face of emergency. What do you see as the main lessons that can be applied to tackling climate change?

As as optimist, I hope that the ability of mankind to join forces to act against a common enemy will be an asset while tackling the climate problem. One should keep in mind that both the economic and human wellbeing impacts of climate change would be an order of magnitude higher and would persist for hundreds of years, if we fail in climate mitigation.

It would be desirable to invest in climate-friendly industrial, energy and transport solutions while recovery investments are being made. In the best case this would speed up the crucially needed transition. The science community has shown – and will show – its power while tackling the COVID challenge. This may help in recovery of scientific authority after several post-truth years.

What is your key takeaway message on this 50th anniversary of Earth Day?

We are living on a unique and great planet. It is worthwhile to preserve it in good shape for the coming generations by tackling the climate change and population growth problems. Let’s make Earth great again!

Lars Peter Riishojgaard, director of the WMO’s Earth-system branch in the WMO’s infrastructure department

How does the WMO’s Global Observing System (GOS) feed into weather forecasting and climate modelling?

The observations provided by the WMO’s Global Observing System (GOS) provide the basis for any predictive modelling of weather and climate. Numerical weather prediction is what is mathematically called an initial value problem – the initial value comes from the observations, and without those no model predictions can be made. Fortunately most parts of the GOS continue to function despite the challenges of the pandemic, albeit at a reduced level for some components.

Many aspects of the GOS are automated, but what will be the major challenges if national lockdowns continue for months?

There are three major areas of impact. First, the observations provided by commercial aircraft are currently down to about 25% of normal in terms of volume. Second, we are already seeing substantial reductions in standard meteorological observations in those parts of the world where automation has not yet been widely adopted – locations in Africa, South and Central America. And third, there are challenges for the marine parts of the observing system: ships, floats, drifting and moored buoys. Most of these systems are automated, but planned repair, maintenance and resupply work is currently halted, and we are seeing a slow decline in observation numbers as a result.

Many nations in the world – particularly developing countries – were already facing challenges due to weather and climate-related hazards. In what ways does the COVID-19 pandemic exacerbate those challenges?

The impact of the COVID-19 crisis is likely to be asymmetric also in terms of its impact on weather and climate prediction. The biggest impact on the availability of observations is seen in the regions that were already the mostly poorly observed, notably Africa and the small island states everywhere on the globe. There is very little redundancy and resilience in the observing system in those areas. In terms of impact on specific weather situations, this will not be fully known until after the crisis is over and statistical studies can be done over a period of time.

With the reduction of meteorological data from commercial flights, the use of “radiosondes” has increased during the pandemic. What are these instruments and where are they being used?

Radiosondes are small instrument packages flown under balloons rising up through the atmosphere to altitudes of 20 to 30 km, transmitting measurements of wind speed, temperature and humidity back to the ground. These are flown all over the world twice per day. But over Europe, where few aircraft observations are currently available, some services have increased their radiosonde flights to four per day.

Life in a carbon-neutral world

How about space observations of Earth’s climate system – are the ground-based elements being affected?

The space-based systems are highly resilient to this particular type of crisis. Operational satellite systems, including their ground segments, are typically considered critical national assets. As such, they are planned, installed and staffed to ensure continued operation even in situations like the current one.

Computational algorithm does crystal structure prediction of magnetic materials

José Flores-Livas at Sapienza University of Rome has developed a methodology to predict the properties of magnetic systems using ab initio methods.

The research is reported in full in Journal of Physics: Condensed Matter, published by IOP Publishing – which also publishes Physics World. In this interview Flores-Livas describes that work.

What was the motivation for the research?

The motivation was to develop a computational algorithm based on structure prediction methods for a class of materials that have been poorly studied by the community due to their complexity: magnetic materials.

These are a broad set of materials characterized by the presence of an electron spin-degree of freedom. Within this general classification of magnetic materials, there are two large subdivisions: soft and hard magnetic materials. Soft magnetic materials do not stay magnetized, while hard magnetic materials remain magnetized. Hard magnets (or permanent magnets) are essential components in modern technologies, used in many electrical and electronic devices from computers, appliances to medical equipment. But they are also crucial in emerging applications, for instance; in electric vehicles and wind turbines.

The problem is that we depend primarily on three classes of permanent magnets. One of the aims of the work was to further gain insights into the delicate balance between the crystalline structure of of permanent magnets and their magnetic properties.

What did you do in the work?

Our research consisted of combining the minima hopping method (for structure prediction) with state-of-the-art first-principles magnetic calculations to scan for potentially new types of permanent magnets.

We faced many technical constraints. The size of simulation cells, convergence problems, and the complexity of the materials was always a significant restraint. This was a computational/theoretical work in which we had to make several approximations and consider simple, well-known cases, gradually working up to the most challenging magnetic materials. One innovative part of the work is how we combined two-level (spin and spin-unpolarized) calculations to overcome the demanding computational overhead. Another point that makes the work interesting for other researches is how it was automated, which provides reliable results within the same theoretical footing for a large number of magnetic systems. In this research, we investigated binary phases made of 3d-transition metals, such as FeNi, FeCo, FeMn and FeCr.

What was the most interesting and/or important finding?

One of the most striking results, apart from the developed computational machinery, was the fact that we could predict an exciting phase of FeNi. There has been much speculation about the tetrataenite phase of FeNi showing important capacities as a hard magnet. However, this phase is only found in meteorites, and experimentally it has been elusive to synthesize in laboratories.

In this work, we report a crystalline structure that has lower energy that the tetrataenite phase and has a saturation magnetization (M_s) of 1.2 M A/m and a magnetic anisotropy energy (MAE) above 1200 k J/m³. This compares with the state-of-the-art hard magnet Nd₂Fe₁₄B (M_s of 1.28 M A/m and MAE of 4900 k J/m³).

Theoretically, this system could be a good candidate for permanent magnet applications, especially considering it is free of rare-earth metals and made of abundant elements. Thus, the outcome of our research is appealing for experimental colleagues to explore further this low energy polymorph of FeNi.

Why is this research significant?

The research is significant because it shows it is possible to “access” magnetic materials from the computational point of view. There is a misconception in the community that first-principles calculations fail entirely to describe these systems. While this is well founded for a specific type of interaction (strongly correlated systems) there are other types of systems that are magnetic and can be accurately described using Kohn-Sham density functional theory.

We hope that this work will further ignite research in magnetic materials, from theory to computational developments to further experimental investigations. An essential part of this research is the transferability of the computational methodology to other types of applications. In future, we foresee the study of topological materials given rise to magnetic anisotropy energies.

What do you plan to do next?

As mentioned before, the study of topological materials and magnetism promises a vast niche for discovering exciting phenomena. However, in the short term, what we plan next is to extend our study to materials showing anti-ferromagnetism.

However, a series of developments must be conducted before reaching that stage. For instance, we need to find a way to reduce the computational overhead further and find a smart idea for initializing antiferromagnetic solutions without the use of large supercells.

This is the next step of our research, and we hope soon to approach this challenging problem.

The full results of the study are reported in Journal of Physics: Condensed Matter.

Duck, duck, goose?

A new era in astronomy began on 14 September 2015 when the Laser Interferometer Gravitational-wave Observatory (LIGO) in the US states of Louisiana and Washington made the first direct detection of gravitational waves. These were generated some 1.3 billion years ago, when two colossal black holes collided. In the upcoming two decades or so, the European Space Agency’s Laser Interferometer Space Antenna (LISA) should be in orbit around the Sun, with three spacecraft working in perfect unison, each at a distance of 2.5 million kilometres from the other. The experiment aims to measure the background of lower-frequency primordial gravitational waves left rippling across the universe by the Big Bang. In this way, LISA is expected to open an unprecedented window for physicists to learn how our universe, as we know it, came to be.

For a book, to quote from its subtitle, “exploring the mysteries of our universe’s first seconds”, US cosmologist and particle physicist Dan Hooper’s At the Edge of Time has as much of an eye on the future of cosmology (and the potential of upcoming projects such as LISA) as it does on the most distant of pasts. As part of Princeton University Press’s “Science Essentials” series, Hooper has undertaken the daunting feat of taking what are arguably some of the most confounding topics in modern science and presenting them in a readily digestible and coherent form.

The open-ended nature of the questions raised by topics such as dark matter do not lend themselves well to the traditional narrative format

The very open-ended nature of the questions raised by topics such as dark matter, cosmic inflation and the multiverse do not lend themselves well to the traditional narrative format, as Hooper notes at the end of the first chapter, writing “If you are looking for a story with an ending that wraps up nicely, you may have chosen the wrong book.” Nevertheless, the book guides the reader through the history and many enigmas of the universe in the aftermath of the Big Bang.

Starting with the implications of Albert Einstein’s theory of relativity, Hooper touches on a multitude of cosmological concepts – including the 17 fundamental forms of energy and matter that make up the Standard Model of particle physics, and the matter–antimatter asymmetry problem – before delving into more speculative areas. These include the nature of dark matter, needed to account for the behaviour of galaxies; the possibility of multiple universes; and the existence of extra dimensions.

Hooper is a charming guide to the world of modern cosmology – one who pleasingly blasts through the tired and unhelpful stereotype of the perfectly objective scientist to paint a more relatable and human profile. “To those of us hunting dark matter, pulsars are often the bane of our efforts,” he writes, continuing with the quip that “despite all the reasons to be fascinated by these objects, there are few things in our universe that I hate more than pulsars.”

This quote crops up in what is perhaps the work’s most intriguing chapter, roughly in the middle of the book, in which Hooper discusses some of his own research, as he describes a putative signal of dark matter being annihilated, as detected in the heart of our Milky Way galaxy. Or perhaps the signal might instead be the product of unseen thousands of the aforementioned and despised pulsars. Hooper’s style here is distinct, and the chapter opening suggests it might offer a day in the life of a physicist – or, as a friend of Hooper’s is said to have put it, “So you walk into your office. You take off your coat. You get yourself a cup of coffee. How do you know what to do next?”

From a public engagement standpoint, there is merit in demystifying the daily activities of researchers for a general readership, so it feels like a missed opportunity that Hooper instead moves quickly into broader considerations, albeit in a way that still shines a light on the process of consensus-making in the production of scientific knowledge. For the cynical, however, wry amusement might be found in this chapter’s epigraph – poet James Whitcomb Riley’s aphorism about things that quack like ducks being ducks – which appears to subvert Hooper’s later caution that this is not always so when considering one’s pet interpretations.

Given the high standards of the work overall, it is a shame that At the Edge of Time’s few real flaws stem from the same elementary mistakes that so often beset popular-science texts. In parts, the book contains a lot of repetition, to the extent that I couldn’t help wondering if the material was compiled from a series of educational lectures. This issue peaks in recap summary transitions between chapters, which detract from the book’s momentum more than they add value to the material covered. Names of researchers who the average reader may not be familiar with – such as Ben Lee, Dave Schramm and Floyd Stecker – appear with such little context, their identities might as well have been forgone in favour of a crisper focus on their work. I fear I may also go to my grave deprived of an explanation of exactly what non-Gaussianities in the cosmic microwave background are – and why exactly I should care about them – after they received a largely unelaborated name-drop in one of the latter chapters.

No review of At the Edge of Time would be complete, however, without a nod to what, I confess, superficially attracted me to the book in the first instance – the psychedelic cover, illustrated by the Bali-based design duo who go by the name Sukutangan. All in all, At the Edge of Time is a delightful and compelling book – one that is ideal to introduce the general reader to modern cosmology without ducking from the field’s many unresolved facets.

2019 Princeton University Press 248pp £22hb

Hubble’s best shots: Impact of comet Shoemaker–Levy 9

It’s easy to forget that Hubble, famed as it is for images of nebulae and galaxies in deep space, is equally adept at imaging the outer planets of our solar system. This ability came into its own in the summer of 1994, when 21 fragments of the shattered comet Shoemaker–Levy 9 slammed into the giant planet Jupiter. Nobody really knew what to expect – some astronomers thought the event might be a damp squib – but over seven days in July, Jupiter was pounded, with each impact producing a huge fireball and dark bruises on Jupiter’s banded visage.

This Hubble image shows the evolution, over several days, of one of the larger impacts, referred to as site G. A daring space shuttle mission had repaired the telescope’s short-sighted optics a mere eight months earlier, and the success of the surgery quickly became clear: Hubble had a front-row seat for the impact, and produced stunning imagery that reminded us all of the power and importance of the solar system’s minor bodies.

Hubble’s best shots: The Antennae Galaxies

With so many galaxies in the universe, some of them are bound to collide. When they do, the result can be a titanic maelstrom of stars, gas and spiral arms wrapping around one another, as shown in this Hubble image of the galaxies NGC 4038 and 4039. They’re collectively known as the Antennae Galaxies, because wide-field views show huge streams of gas and stars pulled out of the galaxies by gravitational tides and stretching away like giant insect antennae. A narrower view, meanwhile, shows the two galaxies locked in an embrace with huge dark clouds of dust spilling across their distorted faces.

Few, if any, stars will collide during this merger, but the vast clouds of molecular gas within the galaxies can’t avoid one another. And so they clash, sparking intense bursts of star formation, which are visible as pink blotches of ionized hydrogen embedded in the twisted spiral arms. Eventually, the two galaxies will coalesce to form a single giant elliptical galaxy, and their supermassive black holes will find one another and merge, unleashing a burst of gravitational waves as they do so. We’ll have to wait another 400 million years for that happen, though.

Intelligent 4D CT reduces image artefacts

Comparison of spiral 4D CT and i4DCT — Comparison of routine spiral 4D CT and i4DCT imaging for regular and irregular breathing patterns. Left: normalized programmed breathing curves; green: beam-on periods; grey: beam-off periods; red: breathing pause. Right: images reconstructed at maximum inhalation; the arrow shows an artefact caused by the breathing pause. (Courtesy: *Med. Phys.* 10.1.1002/mp.14106)

Respiration-correlated CT imaging, or 4D CT, is an essential part of radiotherapy planning for thoracic and abdominal tumours. Clinical 4D CT images are often affected by artefacts, however, mainly due to irregular breathing patterns during data acquisition. A research team has now successfully validated a prototype implementation of an intelligent 4D CT (i4DCT) scanning protocol that produces fewer motion artefacts, demonstrating that breathing signal-guided 4D CT is feasible for clinical applications.

The researchers, at the University Medical Center Hamburg-Eppendorf (UKE) in Germany and Siemens Healthineers, utilized online breathing curve analysis and respiratory signal-guided 4D CT protocols to develop the i4DCT concept. In a feasibility study, they compared images of a motion phantom recorded using routine spiral 4D CT and i4DCT (Med. Phys. 10.1.1002/mp.14106).

4D CT images are used for dose calculation and optimization, to define motion-adapted safety margins, and to perform 4D dose reconstruction and quality assurance after radiation treatment. When images are degraded by artefacts, it may be necessary for a patient to have an additional CT scan, exposing them to a second high radiation dose and potentially delaying their radiotherapy.

The i4DCT concept enables automated selection of CT beam-on/beam-off periods, by adapting data acquisition to a patient’s individual breathing pattern, instead of the patient having to adapt to the scanner. The i4DCT workflow consists of an initial learning period to establish a reference patient-specific breathing cycle representation, followed by online breathing signal-guided sequence mode scanning.

The process involves switching on the CT beam at a breathing state just before the patient’s typical end-inspiration state, continuously acquiring breathing signal and projection data, simultaneously analysing the breathing signal in terms of projection data coverage, and switching off the beam if predefined coverage conditions are fulfilled. The i4DCT monitors the patient’s breathing in real time, starting and stopping the sequence scanning based on online analysis of the acquired breathing curve information.

After a beam-off event, which corresponds to a breathing state close to, but after, end-inspiration, the scanner couch is moved to the next position and the process repeated until the desired scanning range is covered. The projection data are then used for retrospective image reconstruction.

Protocol validation

For the study, the researchers implemented the i4DCT core workflow on a Siemens SOMATOM go platform, and imaged a motion phantom containing a customized wooden insert with oblique aluminium plates. They examined four programmed motion curves: regular breathing; breathing pause/irregular breathing frequency; irregular breathing amplitude; and a mixture of breathing pause, and frequency and amplitude irregularity.

Principal investigators René Werner and Christian Hofmann reported that in a regular breathing scenario, both routine spiral 4D CT and i4DCT generated similar images. Spiral 4D CT images acquired during the breathing pause/irregular breathing frequency scenario contained interpolation artefacts that distorted the appearance of the central aluminium plate. However, the i4DCT acquired data did not have these artefacts. For the other two motion scenarios, i4DCT-acquired data also outperformed spiral 4D CT data, producing images of better quality with fewer artefacts.

The researchers point out that i4DCT will not generate artefact-free images for every patient and every breathing pattern. Because it relies on external breathing signals, a robust correlation of internal and external motion data is needed to produce artefact-free images.

The i4DCT scanning time was also longer: by 38%, 72%, 82% and 100%, respectively, for the four motion scenarios compared with conventional 4D CT. With the exception of the regular breathing scenario, beam-on time also was longer, but only by 13%, 20% and 25% compared with conventional 4D CT.

“The measurement results and acquired images support the conclusions of the [previously published] in silico studies and illustrate the considerable reduction in 4D CT image artefacts by real-world application of i4DCT and comparison to routine spiral 4D CT,” the authors write.

“In line with this statement, the i4DCT functionality has been integrated into Siemens go.Open Pro scanners and is called Direct i4D technology,” Werner tells Physics World. “Currently, the collaboration partners are working on a comprehensive phantom-based study to double check the Direct i4D performance for patient breathing patterns under real-world conditions. Moreover, together with other radiotherapy affiliations, the first 4D CT images of lung and liver patients have been measured and are under evaluation.”

Physics in the pandemic: ‘In military terms, the logistical supply line is interrupted’

Steven Savage sitting on the branch of a tree bent over a lake — Relaxed approach: Steven Savage on the shore of Lake Mälaren, north of Stockholm (Courtesy: Steven Savage)

I have spent my entire career researching materials technology, usually in an environment where national security is the raison d’être. I am now semi-retired, and in recent years I have become interested in the ethical impacts of new technology on society. I have lived and worked in the UK, the US and now Sweden, and my family and friends live in the UK and Belgium. I currently interact with colleagues in the US, Europe, Asia and Australia.

The pandemic has had relatively little impact on my life as a scientist. In this, I consider myself fortunate. I write technical reports, grant proposals and journal papers, and I participate in telephone and video meetings from my home office in much the same way as before. I go to my place of work when needed, which of late is less frequently since more of my colleagues are now also working from home. Virtual coffee breaks are a poor substitute for the real thing (and the keyboard gets sticky), but they are better than nothing.

A different path

Sweden has taken a much more relaxed approach to the challenges posed by COVID-19 than most other nations. While other states rapidly imposed mandatory countrywide quarantines and restrictions on non-essential travel, Sweden continues to follow a “softly, softly” policy – one that was even described (recently, in a quality daily newspaper) as a laissez-faire attitude. However, that is the policy of the government, which in my view (perhaps I am being unjust) seems to be a hive of (in)activity. In recent years this has become the status quo, so perhaps this is an example of normal attitudes being applied in abnormal times. In contrast, many employers were quick to allow staff to work from home even if they were healthy, and everyone was required to stay away if they showed any symptoms. Sweden is already highly “digitized” so perhaps this was easier for us than for other countries.

There are restrictions on gatherings of more than 50 people, and restaurants may only offer table service – no buffets or eating at the bar. There is a voluntary code of social distancing, which in the main does seem to be observed, although an increasing number of complaints are being made related to city-centre bars and restaurants, and a form of policing is now being implemented. Public transport continues to operate, and Stockholm, like other major cities, has experienced crowded buses and trains due to absences of drivers and other staff. Most domestic air travel has ceased, simply because there are no passengers. Shops remain open, albeit with fewer customers than usual. However, the hardware stores seem to be benefitting as citizens take on home improvement projects. Swedes are keen do-it-yourself enthusiasts! There has been little evidence of hoarding, and shelves in food stores remain well-stocked.

Worrying signs

The health service seems to be coping, although it seems that all efforts are devoted to treating COVID-19 patients, with all other activities on hold. This is clearly worrying, especially for patients needing immediate treatment. Early fears that the hospitals, intensive care units and ventilator capacity would be overwhelmed seem to be unfounded, but having said that, and despite optimistic comments from some, there is little to suggest that the infection rate is dropping. It doesn’t help that testing is still relatively infrequent, although recently a few hundred random tests were performed to estimate the level of infection in the Stockholm population. Another worrying sign is that many care homes for the elderly have cases of coronavirus. The mortality in Sweden is significantly higher, by perhaps an order of magnitude, than our neighbours Norway and Finland, both of which were quick to impose strict quarantine measures.

Because of these facts, there is increasing criticism, supported by national and international experts, of the Swedish strategy. Most worrying for me personally is the lack of transparency shown by Swedish authorities, primarily the Public Health Agency, which is releasing very little information other than correct but unhelpful statements like “very little is known for certain” and “numbers are unreliable because they may relate to different measurement methods”. I am worried, not so much for my own safety but for those more vulnerable.

Searching questions

There is a downside and an upside to any event, and the COVID-19 outbreak is no exception, as it presents an opportunity that even the maddest of mad scientists would not consider presenting for ethical review as an experiment. While we acknowledge the disastrous effects of the pandemic both on citizens and on national economies, we must also ask, what can we learn from this? Better still, what must we learn from this?

Lack of preparedness on the part of local, national and international authorities and healthcare organisations is a recurring theme, in Sweden and elsewhere (Finland, which has maintained a robust level of national preparedness, is a notable exception in our region). Shortages of simple personal protective equipment (PPE) such as masks, gloves, visors, and gowns, as well as devices such as ventilators, continue to cause concern. Sweden and much of the Western world has clearly taken the “just-in-time” economically optimized philosophy to an extreme. Emergency stocks of elementary equipment and medicine such as paracetamol and sedatives have been reduced or eliminated.

The weakness of this approach is now painfully clear. In military terms, the logistical supply line is interrupted. That a very large amount of PPE originates from a single source – China – is also a weakness, open not only to accidental catastrophes such as COVID-19 but also to deliberate geopolitical manipulation. This fact has been widely recognized for at least a decade, without any significant action being taken.

Much of the Western world has clearly taken the “just-in-time” economically optimized philosophy to an extreme

Also worrying is that fact that existing crisis management plans have, in at least some cases, never been implemented. There are newspaper reports of a regional crisis management plan (which included an emergency supply of PPE) from one Swedish region dating back to 2006, but this has still not been implemented. Similar reports are emerging from the UK.

Simple numbers, complex reality

Information is important; accurate and timely information even more so. Although China recently revised its initial number of deaths upward, indicating a reason to carefully examine the data, there seem to have been relatively few deliberate attempts to spread “false news” or “alternative facts”. Nevertheless, the information available has, in my opinion, fallen short of being adequate. We have been supplied with simple numbers: of infected patients, of intensive care patients, of deaths and more recently rates of infection, and the inevitable comparisons between different nations. Sweden, having chosen to apply a policy of voluntary social distancing, is frequently used for comparison, but since the numbers are based on different parameters they are likely to be misleading. Even deaths are unlikely to be reported accurately, since the cause of death may or may not be attributed to COVID-19, and there is latency in the reporting.

What especially concerns me is the psychological impact of the pandemic. I have little evidence of any attempts in any country to address this aspect, other than occasional platitudes that boil down to “don’t panic, we have the situation under control” – platitudes that are frequently and immediately contradicted by someone on the “front line”. The people of Sweden and other nations need reliable and timely information to ally their fears; open and transparent discussion of alternatives; and explanations for the actions taken. For me, “don’t panic” sends entirely the wrong message.

In this case, time will not tell which strategy (to quarantine or not) was right or wrong. Is Sweden following a sensible policy? There seems to be mounting evidence against this, but the question is far too complex for a simple yes/no answer. Which is most important – the national economy or human life? There is no right or wrong answer, simply varying degrees of better or worse solutions. What is important is to learn from the experience. There is sound scientific evidence that the risk for pandemics is increasing (see, for example, the World Health Organization’s 2019 annual report A world at risk) but as noted, there is little point in performing a risk assessment, developing crisis management plans and then putting it all on a shelf to gather dust.

For me, “don’t panic” sends entirely the wrong message.

In the meantime, I continue to work using video conference calls, telephone and email. These are increasingly essential tools – imagine the current crisis without modern communication! A truly horrifying thought. This crisis will pass, as have previous pandemics, natural and human-made catastrophes. Let us hope we take to heart those lessons which can be learnt and take precautions against making the same mistakes again. To quote one of the world’s greatest statesmen, “Never let a good crisis go to waste.”

Tears of wine created by gravity induced shock waves

The role of gravity in producing distinctive dribbles of wine called tears has been explained by scientists in the US. Andrea Bertozzi and colleagues at the University of California, Los Angeles have shown the forces on a film of wine on the side of a glass create a “reverse undercompressive shock wave” that breaks up to form tears

Tears – sometimes called legs or fingers – are best observed in higher alcohol wines at room temperature. Using a martini glass with a fixed wall angle also helps. To create tears, begin by covering the glass and swirling the wine. Then set down the glass and remove the cover after a few seconds. You should see a circular wave sloshing around the glass that climbs up above the meniscus. As it travels, the wave creates small droplets that fall back into the glass in shape reminiscent of human tears that endure for much longer than the wave.

For more than a century, physicists have known that wine climbs the side of a glass in a process called Marangoni flow. In 1855, James Thompson (brother to Lord Kelvin) was the first to describe the effect. Ten years later the Italian physicist Carlo Marangoni wrote about the flow in a dissertation – and ultimately lent his name. Then in 1878, the American polymath Willard Gibbs published a theory describing Marangoni flow.

Marangoni flow occurs at the interface of two liquids with different surface tensions. With tears, the difference is created by the rapid evaporation of alcohol from a film of wine clinging to the inner surface of the glass above the fill line. The loss of alcohol increases the surface tension of the remaining liquid in the film relative to the wine in the glass below. This pulls liquid up from the glass, which eventually falls back down in dribbles called tears, legs or fingers. What had puzzled researchers, is why the liquid forms tears, rather than flowing back down in a sheet or stream.

Upgraded class project

Although Marangoni flows have been studied for 165 years, the underlying theory was not complete. In 2019 Andrea Bertozzi was preparing a lecture on tears of wine and told Physics World: “I thought that I would do a fun lecture and I could even bring some wine to do a demonstration. As I was preparing my materials and going through the research papers in detail, I realized that there was a big gap in the literature”.

She adds, “Part of my lecture ended up being about what was missing and what we could do about it scientifically. My student Yonatan Dukler decided to make this topic his class project”. That project has now been extended and the results published in Physical Review Fluids with Dukler as the lead author and Hangjie Ji and Claudia Falcon lending a hand.

Reverse undercompressive shock

The four researchers realized that the current theory of tear formation did not do a very good job at describing the role of gravity, which pulls the liquid down the side of the glass in the form of tears. The team created a quantitative model that assumed a constant surface tension gradient up the side of the glass. They discovered that the thickness of the liquid film climbing up the glass plays a crucial role in the formation of tears.

If the liquid crept up the glass in a uniform thick film it would simple stream back down again, rather than creating tears. Instead, experiments and calculations done by Bertozzi and colleagues show that the liquid moves up in a bulge-like wave that leaves a thinner film behind it. This can be described as a “reverse undercompressive shock wave”, which is known to be unstable. This means that small inhomogeneities along the wave can cause it to break up into tears.

According to Omar Matar of Imperial College London, the research is “a significant result that illustrates the richness in physics and underlying mathematical structure of the tears of wine problem, which continues to be a source of fascination to scientists in the present day”. He adds that the work, “represents a departure point to a number of exciting future directions that allow us to explore such factors as the influence of the three-dimensional geometry of the glass, and the development of surface tension gradients up the glass, on the morphology of the tears”.

Hubble’s best shots: NGC 1866, a great ball of stars

Our universe contains two types of star clusters. Open clusters are found in the discs of galaxies, and are formed of young stars that soon drift away into the environs of the galaxies’ spiral arms. Globular clusters, on the other hand, are compact and ancient, dating back to the dawn of the age of galaxies, and are formed of hundreds of thousands of stars packed into a space no more than 100 light years across.

Globular clusters exist in the halo around a galaxy, and as you might expect with so many stars so close together, they make wonderful subjects for Hubble portraits. A good example is this image of the globular cluster NGC 1866, which lives on the outskirts of the Large Magellanic Cloud. This cluster harbours a mystery. While models of the formation of globular clusters depict all their stars being born in one huge burst, some such clusters, including NGC 1866, seem to contain several generations of stars, based on how much heavy metal the stars contain. Hubble’s detailed observations are helping to identify such clusters – an important step on the road to figuring out their history.

Hubble’s best shots: Eta Carinae

Hidden beneath the expanding lobes of gas and dust in this multi-wavelength view is one of the most massive and volatile stars in the Milky Way. Eta Carinae was just another nondescript star until 1843, when it underwent a dramatic outburst and briefly became the second-brightest star in the night sky. It’s unclear exactly what prompted this explosive episode, but we do know that Eta Carinae – actually a double star system concealed at the epicentre of the two lobes – shed an enormous amount of mass from its outer layers in the process.

Hubble’s false-colour image combines visible light observations by its Wide Field Camera 3 with ultraviolet-light data from the its Ultraviolet Imaging Spectrograph. It shows the presence of gas – magnesium in blue, and shocked nitrogen gas presented here in red – that could have been ejected by the star shortly before its outburst, and which could therefore provide clues as to what caused the tumultuous eruption.

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