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  • richardmitnick 1:12 pm on December 20, 2019 Permalink | Reply
    Tags: "Using Satellites and Supercomputers to Track Arctic Volcanoes", , ArcticDEM project, Blue Waters supercomputer, , NASA Terra MODIS, NASA Terra satellite,   

    From Eos: “Using Satellites and Supercomputers to Track Arctic Volcanoes” 

    From AGU
    Eos news bloc

    From Eos

    New data sets from the ArcticDEM project help scientists track elevation changes from natural hazards like volcanoes and landslides before, during, and long after the events.

    1
    The 2017 Okmok eruption resulted in a new volcanic cone, as well as consistent erosion of that cone’s flanks over subsequent years. Credit: NASA image courtesy of Jeff Schmaltz, MODIS Rapid Response Team, NASA-Goddard Space Flight Center

    NASA Terra MODIS schematic


    NASA Terra satellite

    Conical clues of volcanic activity speckle the Aleutian Islands, a chain that spans the meeting place of the Pacific Ring of Fire and the edge of the Arctic. (The chain also spans the U.S. state of Alaska and the Far Eastern Federal District of Russia.) Scientists are now turning to advanced satellite imagery and supercomputing to measure the scale of natural hazards like volcanic eruptions and landslides in the Aleutians and across the Arctic surface over time.

    When Mount Okmok, Alaska, unexpectedly erupted in July 2008, satellite images informed scientists that a new, 200-meter cone had grown beneath the ashy plume. But scientists suspected that topographic changes didn’t stop with the eruption and its immediate aftermath.

    For long-term monitoring of the eruption, Chunli Dai, a geoscientist and senior research associate at The Ohio State University, accessed an extensive collection of digital elevation models (DEMs) recently released by ArcticDEM, a joint initiative of the National Geospatial-Intelligence Agency and National Science Foundation. With ArcticDEM, satellite images from multiple angles are processed by the Blue Waters petascale supercomputer to provide elevation measures, producing high-resolution models of the Arctic surface.

    NCSA U Illinois Urbana-Champaign Blue Waters Cray Linux XE/XK hybrid machine supercomputer

    3
    In this map of ArcticDEM coverage, warmer colors indicate more overlapping data sets available for time series construction, and symbols indicate different natural events such as landslides (rectangles) and volcanoes (triangles). Credit: Chunli Dai

    Dai first utilized these models to measure variations in lava thickness and estimate the volume that erupted from Tolbachik volcano in Kamchatka, Russia, in work published in Geophysical Research Letters in 2017. The success of that research guided her current applications of ArcticDEM for terrain mapping.

    Monitoring long-term changes in a volcanic landscape is important, said Dai. “Ashes easily can flow away by water and by rain and then cause dramatic changes after the eruption,” she said. “Using this data, we can even see these changes…so that’s pretty new.”

    Creating time series algorithms with the ArcticDEM data set, Dai tracks elevation changes from natural events and demonstrates their potential for monitoring the Arctic region. Her work has already shown that erosion continues years after a volcanic event, providing first-of-their-kind measurements of posteruption changes to the landscape. Dai presented this research at AGU’s Fall Meeting.

    Elevating Measurement Methods

    “This is absolutely the best resolution DEM data we have,” said Hannah Dietterich, a research geophysicist at the U.S. Geological Survey’s Alaska Volcano Observatory not involved in the study. “Certainly, for volcanoes in Alaska, we are excited about this.”

    Volcanic events have traditionally been measured by aerial surveys or drones, which are expensive and time-consuming methods for long-term study. Once a hazardous event occurs, Dietterich explained, the “before” shots in before-and-after image sets are often missing. Now, ArcticDEM measurements spanning over a decade can be utilized to better understand and monitor changes to the Arctic surface shortly following such events, as well as years later.

    For example, the volcanic eruption at Okmok resulted in a sudden 200-meter elevation gain from the new cone’s formation but also showed continuing erosion rates along the cone flanks of up to 15 meters each year.

    Landslides and Climate

    For Dai, landslides provide an even more exciting application of ArcticDEM technology. Landslides are generally unmapped, she explained, whereas “we know the locations of volcanoes, so a lot of studies have been done.”

    Mass redistribution maps for both the Karrat Fjord landslide in Greenland in 2017 and the Taan Fiord landslide in Alaska in 2015 show significant mass wasting captured by DEMs before and after the events.

    “We’re hoping that our project with this new data program [will] provide a mass wasting inventory that’s really new to the community,” said Dai, “and people can use it, especially for seeing the connection to global warming.”

    Climate change is associated with many landslides studied by Dai and her team, who focus on mass wasting caused by thawing permafrost. ArcticDEM is not currently intended for predictive modeling, but as more data are collected over time, patterns may emerge that could help inform future permafrost loss or coastal retreat in the Arctic, according to Dietterich. “It is the best available archive of data for when crises happen.”

    Global climate trends indicate that Arctic environments will continue to change in the coming years. “If we can measure that, then we can get the linkage between global warming and its impact on the Arctic land,” said Dai.

    See the full article here.

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    Please help promote STEM in your local schools.

    Stem Education Coalition

    Eos is the leading source for trustworthy news and perspectives about the Earth and space sciences and their impact. Its namesake is Eos, the Greek goddess of the dawn, who represents the light shed on understanding our planet and its environment in space by the Earth and space sciences.

     
  • richardmitnick 4:04 pm on June 7, 2019 Permalink | Reply
    Tags: , , , Black hole accretion disks, Blue Waters supercomputer, , ,   

    From Northwestern University: “Most-detailed-ever simulations of black hole solve longstanding mystery” 

    Northwestern U bloc
    From Northwestern University

    June 06, 2019
    Amanda Morris

    An international team has constructed the most detailed, highest resolution simulation of a black hole to date. The simulation proves theoretical predictions about the nature of accretion disks — the matter that orbits and eventually falls into a black hole — that have never before been seen.

    The research published on June 5 in the MNRAS.

    Among the findings, the team of computational astrophysicists from Northwestern University, the University of Amsterdam and the University of Oxford found that the inner-most region of an accretion disk aligns with its black hole’s equator.

    This discovery solves a longstanding mystery, originally presented by physicists Jim Bardeen and Jacobus Petterson in 1975. At the time, Bardeen and Petterson argued that a spinning black hole would cause the inner region of a tilted accretion disk to align with its black hole’s equatorial plane.

    After a decades-long, global race to find the so-called Bardeen-Petterson effect, the team’s simulation found that, whereas the outer region of an accretion disk remains tilted, the disk’s inner region aligns with the black hole. A smooth warp connects the inner and outer regions. The team solved the mystery by thinning the accretion disk to an unprecedented degree and including the magnetized turbulence that causes the disk to accrete. Previous simulations made a substantial simplification by merely approximating the effects of the turbulence.

    “This groundbreaking discovery of Bardeen-Petterson alignment brings closure to a problem that has haunted the astrophysics community for more than four decades,” said Northwestern’s Alexander Tchekhovskoy, who co-led the research. “These details around the black hole may seem small, but they enormously impact what happens in the galaxy as a whole. They control how fast the black holes spin and, as a result, what effect black holes have on their entire galaxies.”

    Tchekhovskoy is an assistant professor of physics and astronomy in Northwestern’s Weinberg College of Arts and Sciences and a member of CIERA (Center for Interdisciplinary Exploration and Research in Astrophysics), an endowed research center at Northwestern focused on advancing astrophysics studies with an emphasis on interdisciplinary connections. Matthew Liska, a researcher at the University of Amsterdam’s Anton Pannenkoek Institute for Astronomy, is the paper’s first author.

    “These simulations not only solve a 40-year-old problem, but they have demonstrated that, contrary to typical thinking, it is possible to simulate the most luminous accretion disks in full general relativity,” Liska said. “This paves the way for a next generation of simulations, which I hope will solve even more important problems surrounding luminous accretion disks.”

    Elusive alignment

    Nearly everything researchers know about black holes has been learned by studying accretion disks. Without the intensely bright ring of gas, dust and other stellar debris that swirls around black holes, astronomers would not be able to spot a black hole in order to study it. Accretion disks also control a black hole’s growth and rotation speed, so understanding the nature of accretion disks is key to understanding how black holes evolve and function.

    “Alignment affects how accretion disks torque their black holes,” Tchekhovskoy said. “So it affects how a black hole’s spin evolves over time and launches outflows that impact the evolution of their host galaxies.”

    From Bardeen and Petterson until present day, simulations have been too simplified to find the storied alignment. Two main issues have acted as a barrier for computational astrophysicists. For one, accretion disks come so close to the black hole that they move through warped space-time, which rushes into the black hole at immense speed. Complicating matters further, the black hole’s rotation forces space-time to spin around it. Properly accounting for both of these crucial effects requires general relativity, Albert Einstein’s theory that predicts how objects affect the geometry of space-time around them.

    Second, astrophysicists have not had computing power to account for magnetic turbulence, or the stirring inside of the accretion disk. This stirring is what causes the disk’s particles to hold together in a circular shape and what causes gas eventually to fall into the black hole.

    “Imagine you have this thin disk. Then, on top of that, you have to resolve the turbulent motions inside the disk,” Tchekhovskoy said. “It becomes a really difficult problem.”

    Without being able to resolve these features, computational scientists were unable to simulate realistic black holes.

    Cracking the code

    To develop a code capable of carrying out simulations of titled accretion disks around black holes, Liska and Tchekhovskoy used graphical processing units (GPUs) instead of central processing units (CPUs). Extremely efficient at manipulating computer graphics and image processing, GPUs accelerate the creation of images on a display. They are much more efficient than CPUs for computing algorithms that process large swaths of data.

    Tchekhovskoy likens GPUs to 1,000 horses and CPUs to a 1,000-horsepower Ferrari.

    “Let’s say you need to move into a new apartment,” he explained. “You will have to make a lot of trips with this powerful Ferrari because it won’t fit many boxes. But if you could put one box on each horse, you could move everything in one go. That’s the GPU. It has a lot of elements, each of which is slower than those in the CPU, but there are so many of them.”

    Liska also added a method called adaptive mesh refinement, which uses a dynamic mesh, or grid, that changes and adapts to the flow of movement throughout the simulation. It saves energy and computer power by focusing only on specific blocks in the grid where movement occurs.

    The GPUs substantially accelerated the simulation, and the adaptive mesh increased resolution. These improvements allowed the team to simulate the thinnest accretion disk to date, with a height-to-radius ratio of 0.03. When the disk was simulated this thin, the researchers could see alignment occur right next to the black hole.

    “The thinnest disks simulated before had a height-to-radius ratio of 0.05, and it turns out that all of the interesting things happen at 0.03,” Tchekhovskoy said.

    In a surprise finding, even with these incredibly thin accretion disks, the black hole still emitted powerful jets of particles and radiation.

    “Nobody expected jets to be produced by these disks at such slight thicknesses,” Tchekhovskoy said. “People expected that the magnetic fields that produce these jets would just rip through these really thin disks. But there they are. And that actually helps us resolve observational mysteries.”

    The study, “Bardeen-Petterson alignment, jets and magnetic truncation in GRMHD simulations of tilted thin accretion discs,” was supported by the National Science Foundation (award numbers 1615281, OAC-1811605 and PHY-1125915), the Netherlands Organisation for Scientific Research, The Royal Society and NASA.

    The simulation used in the work was performed on the Blue Waters supercomputers at the National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign.

    NCSA U Illinois Urbana-Champaign Blue Waters Cray Linux XE/XK hybrid machine supercomputer

    See the full article here .

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    Please help promote STEM in your local schools.

    Stem Education Coalition

    Northwestern South Campus
    South Campus

    On May 31, 1850, nine men gathered to begin planning a university that would serve the Northwest Territory.

    Given that they had little money, no land and limited higher education experience, their vision was ambitious. But through a combination of creative financing, shrewd politicking, religious inspiration and an abundance of hard work, the founders of Northwestern University were able to make that dream a reality.

    In 1853, the founders purchased a 379-acre tract of land on the shore of Lake Michigan 12 miles north of Chicago. They established a campus and developed the land near it, naming the surrounding town Evanston in honor of one of the University’s founders, John Evans. After completing its first building in 1855, Northwestern began classes that fall with two faculty members and 10 students.
    Twenty-one presidents have presided over Northwestern in the years since. The University has grown to include 12 schools and colleges, with additional campuses in Chicago and Doha, Qatar.

    Northwestern is recognized nationally and internationally for its educational programs.

     
  • richardmitnick 10:32 am on January 10, 2018 Permalink | Reply
    Tags: , Blue Waters supercomputer, , Relativistic jets’ behavior   

    From Northwestern University: “Black hole breakthrough: new insight into mysterious jets” 

    Northwestern U bloc
    Northwestern University

    January 09, 2018
    Kayla Stoner

    Supercomputer power enables advanced simulations of relativistic jets’ behavior.

    Through first-of-their-kind supercomputer simulations, researchers, including a Northwestern University professor, have gained new insight into one of the most mysterious phenomena in modern astronomy: the behavior of relativistic jets that shoot from black holes, extending outward across millions of light years.

    Advanced simulations created with one of the world’s most powerful supercomputers show the jets’ streams gradually change direction in the sky, or precess, as a result of space-time being dragged into the rotation of the black hole. This behavior aligns with Albert Einstein’s predictions about extreme gravity near rotating black holes, published in his famous theory of general relativity.


    This simulation produced using the Blue Waters supercomputer is the first simulation ever to demonstrate that relativistic jets follow along with the precession of the tilted accretion disk around the black hole. At close to a billion computational cells, it is the highest resolution simulation of an accreting black hole ever achieved.

    “Understanding how rotating black holes drag the space-time around them and how this process affects what we see through the telescopes remains a crucial, difficult-to-crack puzzle,” said Alexander Tchekhovskoy, assistant professor of physics and astronomy at Northwestern’s Weinberg College of Arts and Sciences. “Fortunately, the breakthroughs in code development and leaps in supercomputer architecture are bringing us ever closer to finding the answers.”

    The study, published in the Monthly Notices of the Royal Astronomical Society, is a collaboration between Tchekhovskoy, Matthew Liska and Casper Hesp. Liska and Hesp are the study’s lead authors and graduate students at The University of Amsterdam, Netherlands.

    Rapidly spinning black holes not only engulf matter but also emit energy in the form of relativistic jets. Similar to how water in a bathtub forms a whirlpool as it goes down a drain, the gas and magnetic fields that feed a supermassive black hole swirl to form a rotating disk — a tangled spaghetti of magnetic field lines mixed into a broth of hot gas. As the black hole consumes this astrophysical soup, it gobbles up the broth but leaves the magnetic spaghetti dangling out of its mouth. This makes the black hole into a kind of launching pad from which energy, in the form of relativistic jets, shoots from the web of twisted magnetic spaghetti.

    The jets emitted by black holes are easier to study than the black holes themselves because the jets are so large. This study enables astronomers to understand how quickly the jet direction is changing, which reveals information about the black hole spin as well as the orientation and size of the rotating disk and other difficult-to-measure properties of black hole accretion.

    Whereas nearly all previous simulations considered aligned disks, in reality, most galaxies’ central supermassive black holes are thought to harbor tilted disks — meaning the disk rotates around a separate axis than the black hole itself. This study confirms that if tilted, disks change direction relative to the black hole, precessing around like a spinning top. For the first time, the simulations showed that such tilted disks lead to precessing jets that periodically change their direction in the sky.

    An important reason precessing jets were not discovered earlier is that 3-D simulations of the region surrounding a rapidly spinning black hole require an enormous amount of computational power. To address this issue, the researchers constructed the first black hole simulation code accelerated by graphical processing units (GPUs). A National Science Foundation grant enabled them to carry out the simulations on Blue Waters, one of the largest supercomputers in the world, located at the University of Illinois.

    U Illinois Urbana-Champaign Blue Waters Cray Linux XE/XK hybrid machine supercomputer


    Comparing a low resolution simulation (left) to the high-resolution simulation produced using Blue Waters (right) show the effect of resolution on tilted accretion models. The high resolution model shows that precession and alignment slow down as a result of disk expansion due to magnetic turbulence.

    The confluence of the fast code, which efficiently uses a cutting-edge GPU architecture, and the Blue Waters supercomputer allowed the team to carry out simulations with the highest resolution ever achieved – up to a billion computational cells.

    “The high resolution allowed us, for the first time, to ensure that small-scale turbulent disk motions are accurately captured in our models,” Tchekhovskoy said. “To our surprise, these motions turned out to be so strong that they caused the disk to fatten up and the disk precession to stop. This suggests that precession can come about in bursts.”

    Because accretion onto black holes is a highly complex system akin to a hurricane, but located so far away we cannot discern many details, simulations offer a powerful way of making sense of telescope observations and understanding the behavior of black holes.

    The simulation results are important for further studies involving rotating black holes, which are currently being conducted all over the world. Through these efforts, astronomers are attempting to understand recently discovered phenomena such as the first detections of gravitational waves from neutron star collisions and the accompanying electromagnetic fireworks as well as regular stars being engulfed by supermassive black holes.

    The calculations also are being applied to interpreting the observations of the Event Horizon Telescope (EHT), which captured the first recordings of the supermassive black hole shadow in the center of the Milky Way.

    Additionally, the jets’ precession could explain fluctuations in the intensity of light coming from around black holes, called quasi-periodic oscillations (QPOs). Such oscillations can occur similarly to the way in which the rotating beam of a lighthouse increases in intensity as it passes by an observer. QPOs were first discovered near black holes (as X-rays) in 1985 by Michiel van der Klis (University of Amsterdam), who is a co-author of the new article.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Northwestern South Campus
    South Campus

    On May 31, 1850, nine men gathered to begin planning a university that would serve the Northwest Territory.

    Given that they had little money, no land and limited higher education experience, their vision was ambitious. But through a combination of creative financing, shrewd politicking, religious inspiration and an abundance of hard work, the founders of Northwestern University were able to make that dream a reality.

    In 1853, the founders purchased a 379-acre tract of land on the shore of Lake Michigan 12 miles north of Chicago. They established a campus and developed the land near it, naming the surrounding town Evanston in honor of one of the University’s founders, John Evans. After completing its first building in 1855, Northwestern began classes that fall with two faculty members and 10 students.
    Twenty-one presidents have presided over Northwestern in the years since. The University has grown to include 12 schools and colleges, with additional campuses in Chicago and Doha, Qatar.

    Northwestern is recognized nationally and internationally for its educational programs.

     
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