A machine learning breakthrough: using satellite images to improve human lives

Berkeley-based project could support action worldwide on climate, health and poverty

UNIVERSITY OF CALIFORNIA - BERKELEY

Research News

IMAGE: DEEP STREAMS OF DATA FROM EARTH-IMAGING SATELLITES ARRIVE IN DATABASES EVERY DAY, BUT ADVANCED TECHNOLOGY AND EXPERTISE ARE REQUIRED TO ACCESS AND ANALYZE THE DATA. NOW A NEW SYSTEM, DEVELOPED... view more 

CREDIT: (PHOTO BY NASA VIA PXFUEL)

Berkeley -- More than 700 imaging satellites are orbiting the earth, and every day they beam vast oceans of information -- including data that reflects climate change, health and poverty -- to databases on the ground. There's just one problem: While the geospatial data could help researchers and policymakers address critical challenges, only those with considerable wealth and expertise can access it.

Now, a team based at the University of California, Berkeley, has devised a machine learning system to tap the problem-solving potential of satellite imaging, using low-cost, easy-to-use technology that could bring access and analytical power to researchers and governments worldwide. The study, "A generalizable and accessible approach to machine learning with global satellite imagery," was published today (Tuesday, July 20) in the journal Nature Communications.

"Satellite images contain an incredible amount of data about the world, but the trick is how to translate the data into usable insights without having a human comb through every single image," said co-author Esther Rolf, a final-year Ph.D. student in computer science. "We designed our system for accessibility, so that one person should be able to run it on a laptop, without specialized training, to address their local problems."

"We're entering a regime in which our actions are having truly global impact," said co-author Solomon Hsiang, director of the Global Policy Lab at the Goldman School of Public Policy. "Things are moving faster than they've ever moved in the past. We're changing resource allocations faster than ever. We're transforming the planet. That requires a more responsive management system that is able to see these things happen, so that we can respond in a timely, effective way."

The project was a collaboration between the Global Policy Lab, which Hsiang directs, and Benjamin Recht's research team in the department of Electrical Engineering and Computer Sciences. Other co-authors are Berkeley Ph.D. graduates Tamma Carleton, now at University of California, Santa Barbara; Jonathan Proctor, now at Harvard's Center for the Environment and Data Science Initiative; Ian Bolliger, now at the Rhodium Group; and Vaishaal Shankar, now at Amazon; and Berkeley Ph.D. student Miyabi Ishihara.

All of them were at Berkeley when the project began. Their collaboration has been remarkable for bringing together disciplines that often look at the world in different ways and speak different languages: computer science, environmental and climate science, statistics, economics and public policy.

But they have been guided by a common interest in creating an open access tool that democratizes the power of technology, making it usable even by communities and countries that lack resources and advanced technical skill. "It's like Ford's Model T, but with machine learning and satellites," Hsiang said. "It's cheap enough that everyone can now access this new technology."

--MOSAIKS: Improving lives, protecting the planet--

The system that emerged from the Berkeley-based research is called MOSAIKS, short for Multi-Task Observation using Satellite Imagery & Kitchen Sinks. It ultimately could have the power to analyze hundreds of variables drawn from satellite data -- from soil and water conditions to housing, health and poverty -- at a global scale.

The research paper details how MOSAIKS was able to replicate with reasonable accuracy reports prepared at great cost by the U.S. Census Bureau. It also has enormous potential in addressing development challenges in low-income countries and to help scientists and policymakers understand big-picture environmental change.

"Climate change is diffuse and difficult to see at any one location, but when you step back and look at the broad scale, you really see what is going on around the planet," said Hsiang, who also serves as co-director of the multi-institution Climate Impact Lab.

For example, he said, the satellite data could give researchers deep new insights into expansive rangeland areas such as the Great Plains in the U.S. and the Sahel in Africa, or into areas such as Greenland or Antarctica that may be shedding icebergs as temperatures rise.

"These areas are so large, and to have people sitting there and looking at pictures and counting icebergs is really inefficient," Hsiang explained. But with MOSAIKS, he said, "you could automate that and track whether these glaciers are actually disintegrating faster, or whether this has been happening all along."

For a government in the developing world, the technology could help guide even routine decisions, such as where to build roads.

"A government wants to build roads where the most people are and the most economic activity is," Hsiang said. "You might want to know which community is underserved, or the condition of existing infrastructure in a community. But often it's very difficult to get that information."

--The challenge: Organizing trillions of bytes of raw satellite data--

The growing fleet of imaging satellites beam data back to Earth 24/7 -- some 80 terabytes every day, according to the research, a number certain to grow in coming years.

But often, imaging satellites are built to capture information on narrow topics -- supplies of fresh water, for example, or the condition of agricultural soils. And the data doesn't arrive as neat, orderly images, like a snapshots from a photo shop. It's raw data, a mass of binary information. Researchers who access the data have to know what they're looking for.

Merely storing so many terabytes of data requires a huge investment. Distilling the layers of data embedded in the images requires additional computing power and advanced human expertise to tease out strands of information that are coherent and useful to other researchers, policymakers or funding agencies.

Inevitably, exploiting satellite images is largely limited to scholars or agencies in wealthy nations, Rolf and Hsiang said.

"If you're an elite professor, you can get someone to build your satellite for you," said Hsiang. "But there's no way that a conservation agency in Kenya is going to be able to access the technology and the experts to do this work.

"We wanted to find a way to empower them. We decided to come up with a Swiss Army Knife -- a practical tool that everyone can access."

--Like Google for satellite imagery, sort of--

Especially in low-income countries, one dimension of poverty is a poverty of data. But even communities in the U.S. and other developed countries usually don't have ready access to geospatial data in a convenient, usable format for addressing local challenges.

CAPTION

In the Indian state of Andhra Pradesh, a satellite image shows hundreds of green aquaculture ponds where local farmers grow fish and shrimp. Geospatial imaging holds enormous potential for developing nations to address challenges related to agriculture, poverty, health and human migration, scholars at UC Berkeley say. But until now, the technology and expertise needed to efficiently access and analyze satellite data usually has been limited to developed countries.

CREDIT

(NASA Earth Observatory images by Joshua Stevens, using Landsat data from the U.S. Geological Survey.)

Machine learning opens the door to solutions.

In a general sense, machine learning refers to computer systems that use algorithms and statistical modeling to learn on their own, without step-by-step human intervention. What the new research describes is a system that can assemble data delivered by many satellites and organize it in ways that are accessible and useful.

There are precedents for such systems: Google Earth Engine and Microsoft's Planetary Computer are both platforms for accessing and analyzing global geospatial data, with a focus on conservation. But, Rolf said, even with these technologies, considerable expertise is often required to convert the data into new insights.

The goal of MOSAIKS is not to develop more complex machine learning systems, Rolf said. Rather, its innovation is in making satellite data widely useable for addressing global challenges. The team did this by making the algorithms radically simpler and more efficient.

MOSAIKS starts with learning to recognize minuscule patterns in the images -- Hsiang compares it to a game of Scrabble, in which the algorithm learns to recognize each letter. In this case, however, the tiles are minuscule pieces of satellite image, 3 pixels by 3 pixels.

But MOSAIKS doesn't conclude "this is a tree" or "this is pavement." Instead, it recognizes patterns and groups them together, said Proctor. It learns to recognize similar patterns in different parts of the world.

When thousands of terabytes from hundreds of sources are analyzed and organized, researchers can choose a village or a country or a region and draw out organized data that can touch on themes as varied as soil moisture, health conditions, human migration and home values.

In a sense, Hsiang said, MOSAIKS could do for satellite databases what Google in the early days did for the Internet: map the data, make it accessible and user-friendly at low cost, and perhaps make it searchable. But Rolf, a machine learning scholar based in the Berkeley Electrical Engineering and Computer Sciences department, said the Google comparison goes only so far.

MOSAIKS "is about translating an unwieldy amount of data into usable information," she explained. "Maybe a better analogy would be that the system takes very dense information -- say, a very large article -- and produces a summary."

--Creating a living atlas of global data--

Both Hsiang and Rolf see the potential for MOSAIKS to evolve in powerful and elegant directions.

Hsiang imagines the data being collected into computer-based, continually evolving atlases. Turn to any given "page," and a user could access broad, deep data about conditions in a country or a region.

Rolf envisions a system that can take the stream of data from humanity's fleet of imaging satellites and remote sensors and transform it into a flowing, real-time portrait of Earth and its inhabitants, continually in a state of change. We could see the past and the present, and so discern emerging challenges and address them.

"We've sent so much stuff to space," Hsiang says. "It's an amazing achievement. But we can get a lot more bang for our buck for all of this data that we're already pulling down. Let's let the world use it in a useful way. Let's use it for good."

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Removal of barred owls slows decline of iconic spotted owls in Pacific Northwest, study finds

OREGON STATE UNIVERSITY

VIDEO: SLOW MOTION SPOTTED OWL FLIGHT. view more 

CREDIT: DAMON LESMEISTER

CORVALLIS, Ore. - A 17-year study in Oregon, Washington and California found that removal of invasive barred owls arrested the population decline of the northern spotted owl, a native species threatened by invading barred owls and the loss of old-forest habitats.

The conservation and management of northern spotted owls became one of the largest and most visible wildlife conservation issues in United States history after the U.S. Fish and Wildlife Service listed the spotted owl as threatened under the Endangered Species Act in 1990 because of rapid declines in the owl's old-forest habitats. Four years later, the Northwest Forest Plan was adopted and reduced the rate of logging of old-growth forests on federal lands.

Despite more than 30 years of protection, spotted owl populations have continued to decline, with steepest declines observed in the past 10 years. Long-term monitoring of spotted owl populations across the species' range identified rapid increases in the population of invasive barred owls as a primary reason for those declines, the researchers said.

The study published this week in PNAS by scientists at the U.S. Geological Survey, Oregon State University, and several other entities is the first to look at the wide-scale impact of barred owls on populations of spotted owls in the Pacific Northwest.

The study focused on two sites in northern California, two in Oregon and one in Washington and found that spotted owl populations stabilized in all study areas where the researchers lethally removed barred owls (0.2% decline per year on average) but continued to decline sharply in areas without removals (12.1% decline per year on average.)

CAPTION

Spotted owl

CREDIT

Chris McCafferty.

The findings in the new paper inform future management decisions about the spotted owl population.

"This study is a promising example of successful removal and suppression of an invasive and increasingly abundant competitor, with a positive demographic response from a threatened native species," said David Wiens, the lead author of the paper who is a wildlife biologist with the USGS Forest and Rangeland Ecosystem Science Center in Corvallis and a courtesy faculty member with Oregon State's Department of Fisheries, Wildlife, and Conservation Sciences.

As a species native to eastern North America, barred owls began expanding their populations westward in the early 1900s. The newly extended range now completely overlaps that of the northern spotted owl.

While barred owls look similar to spotted owls, they are larger, have a stronger ecological impact and outcompete spotted owls for habitat and food. This competition exacerbated spotted owl population declines, which were historically triggered by loss of old-forest habitat.

Mounting concerns about the threat of barred owls prompted a barred owl removal pilot project from 2009 to 2013 in California that concluded removal of barred owls, coupled with conservation of old forest, could slow or reverse population declines of spotted owls.

The research outlined in the PNAS paper expanded the pilot project to cover a much wider geographic range and a longer time period. The new research showed that barred owl removal had a strong, positive effect on survival and population trends of spotted owls that was consistent across all five study areas.

The conservation and restoration of old forests, which has been a chief focus of recovery strategies for the northern spotted owl, is a major source of controversy in the Pacific Northwest. The barred owl invasion has exacerbated this issue, placing an even higher premium on remaining old conifer forests.

"While suppression of barred owls can be difficult, costly, and ethically challenging, improvements in vital rates and population trends of spotted owls, and perhaps other threatened wildlife, can be expected when densities of barred owls are reduced from current levels," the researchers write in the paper. "Alien predators are considered to be more harmful to prey populations than native predators, and the dynamic interactions between invasive and native predators can lead to profound changes in ecosystems, often with considerable conservation and economic impacts."

Tree-ring records reveal Asian monsoon variability

CHINESE ACADEMY OF SCIENCES HEADQUARTERS

Research News

Chinese researchers along with international colleagues recently reported a 6,700-year-long, precisely dated and well-calibrated tree-ring stable isotope chronology from the Northeastern Tibetan Plateau. It reveals full-frequency precipitation variability in the Asian Summer Monsoon (ASM) from interannual to multimillennial timescales with a long-term decreasing trend and several abrupt climate change events.

The international research team comprised 20 scientists from research groups based in China, Norway, Germany, United Kingdom, USA, Sweden, Canada, and Switzerland and was jointly led by Prof. Nils Christian Stenseth from the University of Oslo and Prof. YANG Bao from the Northwest Institute of Eco-Environment and Resources of the Chinese Academy of Sciences. The team studied more than 9,500 individual oxygen isotope measurements from juniper tree rings to reconstruct ASM variability over the past 6,700 years.

The researchers extracted and analyzed the oxygen isotopes from each ring in each tree independently, enabling them to build the most detailed dataset ever for the period from the mid-Holocene to the present.

These tree-ring stable isotopes offer a far more accurate archive for reconstructing full-frequency precipitation variability in North China than conventional tree-ring studies, which often fail.

By comparing this ASM precipitation reconstruction with another tree-ring oxygen record from the Animaqing Mountains, the researchers inferred that during the mid-Holocene, the ASM limit extended at least 300 km further northwest compared to its present day limit.

This allows direct comparison between the ASM's northern boundary 5,000 years ago and in the current era.

This precipitation reconstruction also provides a valuable opportunity to determine the societal and ecological responses to rapid climatic change in the past.

The reconstruction suggests that a rapid decrease in moisture availability from ~2,000-1,500 BCE caused a drought regime from ~1,675-1,185 BCE, which might have played an important role in regional forest deterioration and enhanced aeolian activity during that time.

In addition, the data also suggest that abrupt aridification starting about 2,000 BCE might have contributed to the shift of Neolithic cultures in northern China and likely triggered human migration and societal transformation during that time.

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The results were published in PNAS in an article entitled "Long-term decrease in Asian monsoon rainfall and abrupt climate change events over the past 6,700 years."

This research was financially supported by the National Natural Science Foundation of China, the Belmont Forum and the Joint Programming Initiative-Climate, Collaborative Research Action.

Farm consolidation has negative effect on wild pollinators

Traditional smallholder farming landscapes in China are being consolidated, leading to reduced wild pollinator diversity

XI'AN JIAOTONG-LIVERPOOL UNIVERSITY

Research News

 

IMAGE: TRADITIONAL SMALLHOLDER FARMS IN JIANGXI, CHINA view more 

CREDIT: DR YI ZOU

A new study by a team of researchers has found that the consolidation of traditional smallholder farms in China has a devastating effect on the biodiversity of wild pollinators in the area.

Pollinators play an essential role when it comes to supporting global food production. However, wild pollinators are on the decline for several reasons, including the loss of floral resources and nesting sites. This loss of biodiversity could have far-reaching consequences for global food production in future. "Biodiversity is essential for all life, with pollinators being one of the most important groups," says Dr Yi Zou from Xi'an Jiaotong-Liverpool University, corresponding author of the paper. "There are diverse insect pollinators in traditional smallholder agroecosystems in China supported by fine-scale field margins which contain semi-natural habitats."

Semi-natural habitats, such as forest and grassland, provide abundant resources and nesting sites and promote pollinator diversity.

However, these habitats are under threat. "China is conducting massive farmland consolidation projects, changing traditional fields to regular consolidated ones. As a result, fine-scale, semi-natural habitats are removed," says Dr Zou.

Changing traditions

Traditionally, smallholder farms in China are worked by hand and have an irregular shape informed by the landscape. There are narrow margins of semi-natural habitat between individual smallholder farms that allow farmers to move between them.

Consolidation reorganises the farmland into more uniform shapes that allow for mechanised agriculture and creates even, flat surfaces between the plots, which are sometimes paved to enable easier movement.

To assess the impact of these consolidation projects, Dr Zou and a team of researchers conducted a study in the Jiangxi province, comparing pollinator diversity of 18 rapeseed (canola) fields over two years - 2015 and 2019.

"We found that consolidated farming landscapes had about 30% lower pollinator biodiversity as opposed to traditional ones," explains Dr Zou.

"While semi-natural habitat in the areas surrounding the farmland has positive effects on both consolidated and traditional farming, it requires a great deal of land to offset the loss of margins. To compensate for the drop in diversity due to consolidation, we need an extra 55% landscape-scale semi-natural habitat, which is very difficult to achieve.

"Farmland consolidation is inevitable to improve agricultural productivity. However, the role of semi-natural habitat in supporting farmland biodiversity - and the associated beneficial services such as pollination and biological pest control - needs to be considered. For example, the establishment of fine-grained networks with flowering plant species and nesting sites may provide a feasible option to reduce negative impacts on wild pollinator diversity," concludes Dr Zou.

Methodology and findings

The researchers conducted the study in the Jiangxi Province of China in 2015 and 2019. A total of 20 study sites, with eight consolidated and 12 traditional farmlands were selected.

Pollinator communities in focal oilseed rape fields were sampled using pan traps placed in the centre of each field.

The pan trap sampling resulted in the collection of 6,910 wild pollinators, which accounts for 85 species.

The richness of rarefied species of wild pollinators was higher in traditional sites as opposed to consolidated sites. Species richness was positively associated with the proportion of semi-natural habitat in evidence.

The study found the following conclusions:

1. Wild pollinator richness and evenness is lower in oilseed rape fields in consolidated farmland.

2. Species richness of wild pollinators is positively associated with the proportion of semi-natural habitat.

3. The loss of diversity of wild pollinators, owing to land consolidation, is substantial.

CAPTION

Consolidated smallholder farms in Jiangxi, China

CREDIT

Yi Zou

The research team consisted of: Yi Zou and Xiaoyu Shi from Xi'an Jiaotong-Liverpool University, China; Haijun Xiao and Haimin He from Jiangxi Agricultural University, China; Shudong Luo from the Ministry of Agriculture and Rural Affairs, China; Jenny A Hodgson from University of Liverpool, UK; and Felix JJA Bianchi and Wopke van der Werff from Wageningen University, The Netherlands.

Shoppers' mobility habits: retailers overestimate car use

INSTITUTE FOR ADVANCED SUSTAINABILITY STUDIES E.V. (IASS)

Research News

Retail traders often fear that reducing the amount of urban space made available for parking private vehicles would have a negative effect on their businesses. A survey conducted by researchers from the Institute for Advanced Sustainability Studies (IASS) on two shopping streets in Berlin shows that traders have a skewed perception of their customers' mobility habits. The findings of this research will facilitate better-informed decision-making around urban land-use planning.

The researchers surveyed around 2,000 customers and 145 retailers on Kottbusser Damm (Friedrichshain-Kreuzberg district) and Hermannstraße (Neukölln district). The vast majority of shoppers - 93 per cent - had not travelled to their destination by car. 91 per cent of the revenue generated by these businesses came out of the wallets of customers who walked, cycled or used public transport to reach them. Customers that drive to the shops accounted for just 9 per cent of sales.

Just 7 per cent of customers travel to businesses by car

"The results of this survey confirm the findings of studies published in 2019 on the inner cities of Offenbach, Gera, Erfurt, Weimar and Leipzig. Studies on mobility and local economic impacts conducted in other European countries, North America, and Australia paint a similar picture. The car is less relevant for local business than is often assumed in policy processes. Pedestrians, cyclists, and transit riders are the important customer groups for local business in an urban context." says IASS researcher Dirk von Schneidemesser. Retailers in the cities surveyed overestimated the share of customers who come by car - so too in Berlin, where retailers estimated that 22 per cent of their customers used this mode of transport, when in fact it was only 7 per cent.

This misperception could be due to a human tendency to assume that others behaviour in a similar manner. The survey revealed that traders who drive to their business estimated much higher customer car use (29%) than traders that use other modes of transport (between 10% and 19%). Traders were also found to overestimate the distance that customers travel to visit their businesses. In fact, over half (51%) of the shoppers surveyed lived less than 1 kilometer from the shopping street. In contrast, traders estimated that just 13% of customers live within this range.

Better infrastructure for active mobility can benefit businesses

"The findings of this survey are in line with the growing body of literature that suggests improved active travel (i.e. for pedestrians and cyclists) and transit infrastructure is likely to benefit local business", says Dirk von Schneidemesser. Business associations should consider this evidence when weighing the benefits and disadvantages of infrastructure development in order to best represent the interests of local business.

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Rapidly diversifying birds in Southeast Asia offer new insights into evolution

TRINITY COLLEGE DUBLIN

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IMAGE: A SULAWESI BABBLER FROM THE ISLAND OF WAWONI. view more 

CREDIT: ROB GRIFFIN

New findings from zoologists working with birds in Southeast Asia are shining fresh light on the connections between animal behaviour, geology, and evolution - underlining that species can diversify surprisingly quickly under certain conditions.

The zoologists, from Trinity College Dublin's School of Natural Sciences, sequenced DNA and took measurements and song recordings from Sulawesi Babblers (Pellorneum celebense), shy birds that live in the undergrowth on Indonesian islands.

Although these islands were connected by land bridges just tens of thousands of years ago, and although the babblers look so similar that they are currently all considered a single subspecies, the new study shows that their DNA, body size and song have all changed in what is a very brief period of time from an evolutionary perspective.

The zoologists believe that this evolutionary divergence is likely facilitated by the babblers' understorey lifestyle, which limits the birds' movements even though they could easily fly between the islands if they chose to.

In the short time these islands have been isolated, the babbler subspecies have evolved to vary genetically from each other by as much as 1/3 as they do from more distantly related bird species that separated millions of years ago.

Fionn Ó Marcaigh, first author on the paper and a PhD Candidate in Trinity's School of Natural Sciences, said:

"Everyone has heard of Darwin's finches evolving completely different bill shapes on the Galápagos islands. The Galápagos are isolated out in the Pacific, so the birds there have had millions of years to evolve separately. But sometimes evolution can occur on much smaller scales of time and space and can be harder to detect just by looking at the animals in question.

"Unlike the Galápagos, the islands we looked at are just 20 km or less from the mainland. The more we study biodiversity, the more we realise is out there, as species and islands that have never been examined closely can turn out to be full of surprises.

"And a lot of it is under threat: in our study, the islands with the most distinct populations were those made of a particular rock type. This ultramafic rock is full of minerals like nickel, which get into the soil and change which plants can grow, to which the birds have to adapt. But that same nickel is being sought by mining companies so time is running out for the islands' biodiversity before we've even captured a full picture of it or understood how it's evolved."

CAPTION

The different subspecies of Sulawesi babblers resident on each island, They may initially look similar but DNA analyses and song recordings confirm they are rapidly diversifying.

CREDIT

Trinity College Dublin

The research, completed with the support of the Irish Research Council and collaborators in Universitas Halu Oleo, has just been published in Zoologischer Anzeiger: A Journal of Comparative Zoology.

The full paper is available Open Access from the publisher's website.

 

No excuse to continue reliance on fossil fuels, says leading nano-technologist

UNIVERSITY OF SURREY

Research News

One of the leading thinkers in nano-science has called on the energy materials community to help finally put an end to the world's reliance on fossil fuels.

In a hard-hitting editorial published by Energy and Environmental Materials, Professor Ravi Silva, Director of the Advanced Technology Institute (ATI) at the University of Surrey, argues that there are no coherent excuses left to justify the use of fossil fuels. In his paper, Professor Silva challenges the scientific community to lead the world away from a reality where fossil fuels still account for 80 per cent of the energy mix.

While the cost of clean energy generation has plummeted over recent years, Professor Silva argues that significant innovations in advanced batteries and energy storage technologies are needed to meet the International Energy Agency's goal of the planet being carbon net-zero by 2050.

For example, the transportation sector would need to see a 15-fold rise in electric vehicle sales from 10m in 2020 to 145m in 2030 - a goal entirely dependent on a leap in battery and energy storage technology, according to Professor Silva.

Professor Silva concludes that these unprecedented but much-needed goals are only possible if the scientific community usher in a new wave of energy materials that are cheap, easily deployable and have short payback times.

Professor Ravi Silva, Director of the ATI at the University of Surrey, said:

"The pandemic has been a truly horrific experience. However, one of the few positives that I can gather from the past two years is that it has allowed me to take stock and refocus on the incredible challenge of combatting climate change. It is increasingly clear that the energy materials community has a crucial role to play in weaning the world off fossil fuels.

"The cost of green energy is falling all the time - in the UK, solar and wind generation is competitive with fossil fuels. But we need to look at improvements in thin-film technologies, new polymers and other hybrid materials that can boost energy capture capabilities while reducing the cost of production if we are to have a genuine green energy revolution."

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Long-period oscillations of the Sun discovered

Ten years of data from NASA's Solar Dynamics Observatory combined with numerical models reveal the deep low musical notes of the Sun.

MAX PLANCK INSTITUTE FOR SOLAR SYSTEM RESEARCH

Research News

IMAGE: THE NORTH-SOUTH VELOCITY ASSOCIATED WITH THE RETROGRADE PROPAGATING MODE OF OSCILLATION. LEFT: OBSERVATIONS USING THE SDO/HMI INSTRUMENT. RIGHT: NUMERICAL MODEL. view more 

CREDIT: MPS/Z-C LIANG

These motions were measured by analyzing 10 years of observations from NASA's Solar Dynamics Observatory (SDO). Using computer models, the scientists have shown that the newly discovered oscillations are resonant modes and owe their existence to the Sun's differential rotation. The oscillations will help establish novel ways to probe the Sun's interior and obtain information about our star's inner structure and dynamics. The scientists describe their findings in today's issue of the journal Astronomy & Astrophysics.

In the 1960s the Sun'ss high musical notes were discovered: The Sun rings like a bell. Millions of modes of acoustic oscillations with short periods, near 5 minutes, are excited by convective turbulence near the solar surface and are trapped in the solar interior. These 5-minute oscillations have been observed continuously by ground-based telescopes and space observatories since the mid 1990s and have been used very successfully by helioseismologists to learn about the internal structure and dynamics of our star - just like seismologists learn about the interior of the Earth by studying earthquakes. One of the triumphs of helioseismology is to have mapped the Sun's rotation as a function of depth and latitude (the solar differential rotation).

In addition to the 5-minute oscillations, much longer-period oscillations were predicted to exist in stars more than 40 years ago, but had not been identified on the Sun until now. "The long-period oscillations depend on the Sun's rotation; they are not acoustic in nature", says Laurent Gizon, lead author of the new study and director at the MPS. "Detecting the long-period oscillations of the Sun requires measurements of the horizontal motions at the Sun's surface over many years. The continuous observations from the Helioseismic and Magnetic Imager (HMI) onboard SDO are perfect for this purpose."

The team observed many tens of modes of oscillation, each with its own oscillation period and spatial dependence. Some modes of oscillation have maximum velocity at the poles, some at mid-latitudes, and some near the equator. The modes with maximum velocity near the equator are Rossby modes, which the team had already identified in 2018. "The long-period oscillations manifest themselves as very slow swirling motions at the surface of the Sun with speeds of about 5 kilometers per hour - about how fast a person walks", says Zhi-Chao Liang from MPS. Kiran Jain from NSO, together with B. Lekshmi and Bastian Proxauf from MPS, confirmed the results with data from the Global Oscillation Network Group (GONG), a network of six solar observatories in the USA, Australia, India, Spain, and Chile.

CAPTION

The east-west velocity associated with the retrograde propagating mode of oscillation. Left: observations using the SDO/HMI instrument. Right: numerical model.

CREDIT

MPS/Z-C Liang

To identify the nature of these oscillations, the team compared the observational data to computer models. "The models allow us to look inside the Sun's interior and determine the full three-dimensional structure of the oscillations", explains MPS graduate student Yuto Bekki. To obtain the model oscillations, the team began with a model of the Sun's structure and differential rotation inferred from helioseismology. In addition, the strength of the convective driving in the upper layers, and the amplitude of turbulent motions are accounted for in the model. The free oscillations of the model are found by considering small-amplitude perturbations to the solar model. The corresponding velocities at the surface are a good match to the observed oscillations and enabled the team to identify the modes.

"All of these new oscillations we observe on the Sun are strongly affected by the Sun's differential rotation", says MPS scientist Damien Fournier. The dependence of the solar rotation with latitude determines where the modes have maximum amplitudes. "The oscillations are also sensitive to properties of the Sun's interior: in particular to the strength of the turbulent motions and the related viscosity of the solar medium, as well as to the strength of the convective driving," says Robert Cameron from MPS. This sensitivity is strong at the base of the convection zone, about two hundred thousand kilometers beneath the solar surface. "Just like we are using acoustic oscillations to learn about the sound speed in the solar interior with helioseismology, we can use the long-period oscillations to learn about the turbulent processes", he adds.

"The discovery of a new type of solar oscillations is very exciting because it allows us to infer properties, such as the strength of the convective driving, which ultimately control the solar dynamo", says Laurent Gizon. The diagnostic potential of the long-period modes will be fully realized in the coming years using a new exascale computer model being developed as part of the project WHOLESUN, supported by a European Research Council 2018 Synergy Grant.

CAPTION

The east-west velocity associated with the retrograde propagating mode of oscillation. Left: observations using the SDO/HMI instrument. Right: numerical model.

CREDIT

MPS/Z-C Liang

Additional material may be downloaded from http://www2.mps.mpg.de/projects/seismo/SolarInertialModes/. The A&A Letter describing the results is available at https://www.aanda.org/10.1051/0004-6361/202141462.

New method predicts 'stealth' solar storms before they wreak geomagnetic havoc on Earth

For the first time, stealth coronal mass ejections can be detected before they wreak havoc on Earth without the need for dedicated spacecraft

FRONTIERS

Research News

 

IMAGE: THE NOVEL IMAGING TECHNIQUES APPLIED TO REMOTE SENSING DATA OF THE CORONAL MASS EJECTION ON 08 OCT 2016. A-D: INTENSITY OF EXTREME UV (EUV; 21.1 NM) CAPTURED BY THE ATMOSPHERIC... view more 

CREDIT: PALMERIO, NITTA, MULLIGAN ET AL.

On 23 July 2012, humanity escaped technological and economic disaster. A diffuse cloud of magnetized plasma in the shape of a slinky toy tens of thousands of kilometers across was hurled from the Sun at a speed of hundreds of kilometers per second.

This coronal mass ejection (CME) just missed the Earth because its origin on the Sun was facing away from our planet at the time. Had it hit the Earth, satellites might have been disabled, power grids around the globe knocked out, GPS systems, self-driving cars, and electronics jammed, and railway tracks and pipelines damaged. The cost of the potential damage has been estimated at between $600bn and $2.6trn in the US alone.

While CMEs as large as the 2012 event are rare, lesser ones cause damage on Earth about once every three years. CMEs need between one and a few days to reach Earth, leaving us some time to prepare for the potential geomagnetic storm. Current efforts to limit any damage include steering satellites out of harm's way or redirecting the power load of electrical grids. But many CMEs -- called 'stealth CMEs' because they don't produce any clear signs close to the Sun's surface -- aren't detected until they reach Earth.

Now, an International Space Science Institute (ISSI) team of scientists from the US, Belgium, UK, and India shows how to detect potentially damaging stealth CMEs, trace them back to their region of origin on the Sun, extrapolate their trajectory, and predict if they will hit Earth. The results were recently published in the journal Frontiers in Astronomy and Space Sciences.

Visualizing the invisible

"Stealth CMEs have always posed a problem, because they often originate at higher altitudes in the Sun's corona, in regions with weaker magnetic fields. This means that unlike normal CMEs -- which typically show up clearly on the Sun as dimmings or brightenings -- stealth CMEs are usually only visible on devices called coronagraphs designed to reveal the corona," said corresponding author Dr Erika Palmerio, a researcher at the Space Sciences Laboratory of the University of California at Berkeley.

"If you see a CME on a coronagraph, you don't know where on the Sun it came from, so you can't predict its trajectory and won't know whether it will hit Earth until too late."

Palmerio continued: "But here we show that many stealth CMEs can in fact be detected in time if current analysis methods for remote sensing are adapted. Put simply, we compared 'plain' remote sensing images of the Sun with the same image taken between eight and 12 hours earlier, to capture very slow changes in the lower corona, up to 350,000km from the Sun's surface. In many cases, these 'difference images' revealed small, previously overlooked changes in the loops of magnetic fields and plasma that are hurled from the Sun. We then zoom in on these with another set of imaging techniques to further analyze the stealth CME's approximate origin, and predict whether it is headed towards Earth."

Stealth CMEs leave overlooked signs

Palmerio and collaborators looked at four stealth CMEs that occurred between 2008 and 2016. Unusually for stealth CMEs, their origin on the Sun was approximately known only because NASA's twin STEREO spacecraft, launched in 2006, had happened to capture them 'off-limb'. This means it was viewed outside the Sun's disc from another angle than from Earth.

With the new imaging techniques, the authors revealed previously undetected, tiny dimmings and brightenings on the Sun at the region of origin of all four stealth CMEs. They conclude that the technique can be used for the early detection of risky stealth CMEs.

"This result is important because it shows us what to look for if we wish to predict the impact on Earth from solar eruptions," said Palmerio.

"Another important aspect of our study -- using geometric techniques to locate a CME's approximate source region and model its 3D structure as it expands and moves towards Earth -- can only be implemented when we have more dedicated observatories with different perspectives, like the STEREO spacecraft."

The authors predict that the new European Space Agency's Solar Orbiter, launched in February 2020, will help with this, just like similar initiatives which are currently discussed by researchers worldwide.

"Data from more observatories, analyzed with the techniques developed in our study, could also help with an even more difficult challenge: namely to detect so-called 'super stealth CMEs', which don't even show up on coronagraphs," said coauthor Dr Nariaki V Nitta, a senior researcher at Lockheed Martin Solar and Astrophysics Laboratory in Palo Alto, US.

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