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Mininni P.D.,Computational and Information Systems Laboratory | Matthaeus W.H.,University of Delaware | Pouquet A.,Computational and Information Systems Laboratory
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2011

We examine long-time properties of the ideal dynamics of three-dimensional flows, in the presence or not of an imposed solid-body rotation and with or without helicity (velocity-vorticity correlation). In all cases, the results agree with the isotropic predictions stemming from statistical mechanics. No accumulation of excitation occurs in the large scales, although, in the dissipative rotating case, anisotropy and accumulation, in the form of an inverse cascade of energy, are known to occur. We attribute this latter discrepancy to the linearity of the term responsible for the emergence of inertial waves. At intermediate times, inertial energy spectra emerge that differ somewhat from classical wave-turbulence expectations and with a trace of large-scale excitation that goes away for long times. These results are discussed in the context of partial two dimensionalization of the flow undergoing strong rotation as advocated by several authors. © 2011 American Physical Society.


News Article | January 11, 2016
Site: phys.org

The new system, named Cheyenne, will be installed this year at the NCAR-Wyoming Supercomputing Center (NWSC) and become operational at the beginning of 2017. Cheyenne will be built by Silicon Graphics International Corp. (SGI) in conjunction with centralized file system and data storage components provided by DataDirect Networks (DDN). The SGI high-performance computer will be a 5.34-petaflop system, meaning it can carry out 5.34 quadrillion calculations per second. It will be capable of more than 2.5 times the amount of scientific computing performed by Yellowstone, the current NCAR supercomputer. Funded by the National Science Foundation and the state of Wyoming through an appropriation to the University of Wyoming, Cheyenne will be a critical tool for researchers across the country studying climate change, severe weather, geomagnetic storms, seismic activity, air quality, wildfires, and other important geoscience topics. Since the supercomputing facility in Wyoming opened its doors in 2012, more than 2,200 scientists from more than 300 universities and federal labs have used its resources. "We're excited to bring more supercomputing power to the scientific community," said Anke Kamrath, director of operations and services at NCAR's Computational and Information Systems Laboratory. "Whether it's the threat of solar storms or a heightened risk in certain severe weather events, this new system will help lead to improved predictions and strengthen society's resilience to potential disasters." "Researchers at the University of Wyoming will make great use of the new system as they continue their work into better understanding such areas as the surface and subsurface flows of water and other liquids, cloud processes, and the design of wind energy plants," said William Gern, vice president of research and economic development at the University of Wyoming. "UW's relationship with NCAR through the NWSC has greatly strengthened our scientific computing and data-centric research. It's helping us introduce the next generation of scientists and engineers to these endeavors." The NWSC is located in Cheyenne, and the name of the new system was chosen to honor the support that it has received from the people of that city. It also commemorates the upcoming 150th anniversary of the city, which was founded in 1867 and named for the American Indian Cheyenne nation. The new data storage system for Cheyenne will be integrated with NCAR's existing GLADE file system. The DDN storage will provide an initial capacity of 20 petabytes, expandable to 40 petabytes with the addition of extra drives. This, combined with the current 16 petabytes of GLADE, will total 36 petabytes of high-speed storage. The new DDN system also will transfer data at the rate of 200 gigabytes per second, which is more than twice as fast as the current file system's rate of 90 gigabytes per second. The system will include powerful Intel Xeon processors, whose performance will be augmented through optimization work that has been done by NCAR and the University of Colorado Boulder. NCAR and the university performed this work through their participation in the Intel Parallel Computing Centers program. Even with its increased power, Cheyenne will be three times more energy efficient (in floating point operations per second, or flops, per watt) than Yellowstone, its predecessor, which is itself highly efficient. "The new system will have a peak computation rate of over 3 billion calculations per second for every watt of power consumed," said NCAR's Irfan Elahi, project manager of Cheyenne and section manager for high-end supercomputing services. High-performance computers such as Cheyenne allow researchers to run increasingly detailed models that simulate complex processes and how they might unfold in the future. These predictions give resource managers and policy experts valuable information for planning ahead and mitigating risk. Some of the areas in which Cheyenne is expected to accelerate research include the following: "Supercomputing is vital to NCAR's scientific research and applications, giving us a virtual laboratory in which we run experiments that would otherwise be impractical or impossible to do," said NCAR Director James Hurrell. "Cheyenne will be a key component of the research infrastructure of the United States through its provision of supercomputing specifically tailored for the atmospheric, geospace, and related sciences. The capabilities of this new system will be central to the continued improvement of our ability to understand and predict changes in weather, climate, air quality, and space weather, as well as their impacts on people, ecosystems, and society." Key features of the new Cheyenne supercomputer system: The new Cheyenne supercomputer and the existing file system are complemented by a new centralized parallel file system and data storage components. Key features of the new data storage system: The University Corporation for Atmospheric Research manages the National Center for Atmospheric Research under sponsorship by the National Science Foundation. Any opinions, findings and conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.


News Article | January 11, 2016
Site: www.scientificcomputing.com

BOULDER — The National Center for Atmospheric Research (NCAR) announced that it has selected its next supercomputer for advancing atmospheric and Earth science, following a competitive open procurement process. The new machine will help scientists lay the groundwork for improved predictions of a range of phenomena, from hour-by-hour risks associated with thunderstorm outbreaks to the timing of the 11-year solar cycle and its potential impacts on GPS and other sensitive technologies. The new system, named Cheyenne, will be installed this year at the NCAR-Wyoming Supercomputing Center (NWSC) and become operational at the beginning of 2017. Cheyenne will be built by Silicon Graphics International (SGI) in conjunction with centralized file system and data storage components provided by DataDirect Networks (DDN). The SGI high-performance computer will be a 5.34-petaflop system, meaning it can carry out 5.34 quadrillion calculations per second. It will be capable of more than 2.5 times the amount of scientific computing performed by Yellowstone, the current NCAR supercomputer. Funded by the National Science Foundation and the state of Wyoming through an appropriation to the University of Wyoming, Cheyenne will be a critical tool for researchers across the country studying climate change, severe weather, geomagnetic storms, seismic activity, air quality, wildfires and other important geoscience topics. Since the supercomputing facility in Wyoming opened its doors in 2012, more than 2,200 scientists from more than 300 universities and federal labs have used its resources. “We’re excited to bring more supercomputing power to the scientific community,” said Anke Kamrath, director of operations and services at NCAR’s Computational and Information Systems Laboratory. “Whether it’s the threat of solar storms or a heightened risk in certain severe weather events, this new system will help lead to improved predictions and strengthen society’s resilience to potential disasters.” “Researchers at the University of Wyoming will make great use of the new system as they continue their work into better understanding such areas as the surface and subsurface flows of water and other liquids, cloud processes, and the design of wind energy plants,” said William Gern, vice president of research and economic development at the University of Wyoming. “UW’s relationship with NCAR through the NWSC has greatly strengthened our scientific computing and data-centric research. It’s helping us introduce the next generation of scientists and engineers to these endeavors.” The NWSC is located in Cheyenne, and the name of the new system was chosen to honor the support that it has received from the people of that city. It also commemorates the upcoming 150th anniversary of the city, which was founded in 1867 and named for the American Indian Cheyenne nation. The new data storage system for Cheyenne will be integrated with NCAR’s existing GLADE file system. The DDN storage will provide an initial capacity of 20 petabytes, expandable to 40 petabytes with the addition of extra drives. This, combined with the current 16 petabytes of GLADE, will total 36 petabytes of high-speed storage. The new DDN system also will transfer data at the rate of 200 gigabytes per second, which is more than twice as fast as the current file system’s rate of 90 gigabytes per second. The system will include powerful Intel Xeon processors, whose performance will be augmented through optimization work that has been done by NCAR and the University of Colorado Boulder. NCAR and the university performed this work through their participation in the Intel Parallel Computing Centers program. Even with its increased power, Cheyenne will be three times more energy efficient (in floating point operations per second, or flops, per watt) than Yellowstone, its predecessor, which is itself highly efficient. “The new system will have a peak computation rate of over 3 billion calculations per second for every watt of power consumed," said NCAR’s Irfan Elahi, project manager of Cheyenne and section manager for high-end supercomputing services. High-performance computers such as Cheyenne allow researchers to run increasingly detailed models that simulate complex processes and how they might unfold in the future. These predictions give resource managers and policy experts valuable information for planning ahead and mitigating risk. Some of the areas in which Cheyenne is expected to accelerate research include the following: “Supercomputing is vital to NCAR’s scientific research and applications, giving us a virtual laboratory in which we run experiments that would otherwise be impractical or impossible to do,” said NCAR Director James Hurrell. “Cheyenne will be a key component of the research infrastructure of the United States through its provision of supercomputing specifically tailored for the atmospheric, geospace and related sciences. The capabilities of this new system will be central to the continued improvement of our ability to understand and predict changes in weather, climate, air quality and space weather, as well as their impacts on people, ecosystems and society.” Key features of the new Cheyenne supercomputer system: The new Cheyenne supercomputer and the existing file system are complemented by a new centralized parallel file system and data storage components. Key features of the new data storage system: The University Corporation for Atmospheric Research manages the National Center for Atmospheric Research under sponsorship by the National Science Foundation. Any opinions, findings and conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.


Mininni P.D.,University of Buenos Aires | Mininni P.D.,Computational and Information Systems Laboratory | Pouquet A.,Computational and Information Systems Laboratory | Pouquet A.,Earth and Sun Systems Laboratory
Physics of Fluids | Year: 2010

We study the intermittency properties of the energy and helicity cascades in two 15363 direct numerical simulations of helical rotating turbulence. Symmetric and antisymmetric velocity increments are examinedas well as probability density functions of the velocity field and of the helicity density. It is found that the direct cascade of energy to small scales is scale invariant and nonintermittentwhereas the direct cascade of helicity is highly intermittent. Furthermorethe study of structure functions of different orders allows us to identify a recovery of isotropy of strong events at very small scales in the flow. Finallywe observe the juxtaposition in space of strong laminar and persistent helical columns next to time-varying vortex tanglesthe former being associated with the self-similarity of energy and the latter with the intermittency of helicity. © 2010 American Institute of Physics.


Mininni P.D.,University of Buenos Aires | Mininni P.D.,Computational and Information Systems Laboratory | Pouquet A.,Computational and Information Systems Laboratory | Pouquet A.,Earth and Sun Systems Laboratory
Physics of Fluids | Year: 2010

We present results from two 15363 direct numerical simulations of rotating turbulence where both energy and helicity are injected into the flow by an external forcing. The dual cascade of energy and helicity toward smaller scales observed in isotropic and homogeneous turbulence is broken in the presence of rotation, with the development of an inverse cascade of energy now coexisting with direct cascades of energy and helicity. In the direct cascade range, the flux of helicity dominates over that of energy at low Rossby number. These cascades have several consequences for the statistics of the flow. The evolution of global quantities and of the energy and helicity spectra is studied, and comparisons with simulations at different Reynolds and Rossby numbers at lower resolution are done to identify scaling laws. © 2010 American Institute of Physics.


News Article | February 15, 2017
Site: www.scientificcomputing.com

The National Center for Atmospheric Research (NCAR) is launching operations this month of one of the world's most powerful and energy-efficient supercomputers, providing the nation with a major new tool to advance understanding of the atmospheric and related Earth system sciences. Named "Cheyenne," the 5.34-petaflop system is capable of more than triple the amount of scientific computing performed by the previous NCAR supercomputer, Yellowstone. It also is three times more energy efficient. Scientists across the country will use Cheyenne to study phenomena ranging from wildfires and seismic activity to gusts that generate power at wind farms. Their findings will lay the groundwork for better protecting society from natural disasters, lead to more detailed projections of seasonal and longer-term weather and climate variability and change, and improve weather and water forecasts that are needed by economic sectors from agriculture and energy to transportation and tourism. "Cheyenne will help us advance the knowledge needed for saving lives, protecting property, and enabling U.S. businesses to better compete in the global marketplace," said Antonio J. Busalacchi, president of the University Corporation for Atmospheric Research. "This system is turbocharging our science." UCAR manages NCAR on behalf of the National Science Foundation (NSF). Cheyenne currently ranks as the 20th fastest supercomputer in the world and the fastest in the Mountain West, although such rankings change as new and more powerful machines begin operations. It is funded by NSF as well as by the state of Wyoming through an appropriation to the University of Wyoming. Cheyenne is housed in the NCAR-Wyoming Supercomputing Center (NWSC), one of the nation's premier supercomputing facilities for research. Since the NWSC opened in 2012, more than 2,200 scientists from more than 300 universities and federal labs have used its resources. "Through our work at the NWSC, we have a better understanding of such important processes as surface and subsurface hydrology, physics of flow in reservoir rock, and weather modification and precipitation stimulation," said William Gern, vice president of research and economic development at the University of Wyoming. "Importantly, we are also introducing Wyoming’s school-age students to the significance and power of computing." The NWSC is located in Cheyenne, and the name of the new system was chosen to honor the support the center has received from the people of that city. The name also commemorates the upcoming 150th anniversary of the city, which was founded in 1867 and named for the American Indian Cheyenne Nation. Cheyenne was built by Silicon Graphics International, or SGI (now part of Hewlett Packard Enterprise Co.), with DataDirect Networks (DDN) providing centralized file system and data storage components. Cheyenne is capable of 5.34 quadrillion calculations per second (5.34 petaflops, or floating point operations per second). The new system has a peak computation rate of more than 3 billion calculations per second for every watt of energy consumed. That is three times more energy efficient than the Yellowstone supercomputer, which is also highly efficient. The data storage system for Cheyenne provides an initial capacity of 20 petabytes, expandable to 40 petabytes with the addition of extra drives.  The new DDN system also transfers data at the rate of 220 gigabytes per second, which is more than twice as fast as the previous file system’s rate of 90 gigabytes per second. Cheyenne is the latest in a long and successful history of supercomputers supported by the NSF and NCAR to advance the atmospheric and related sciences. “We’re excited to provide the research community with more supercomputing power,” said Anke Kamrath, interim director of NCAR’s Computational and Information Systems Laboratory, which oversees operations at the NWSC. “Scientists have access to increasingly large amounts of data about our planet. The enhanced capabilities of the NWSC will enable them to tackle problems that used to be out of reach and obtain results at far greater speeds than ever.” High-performance computers such as Cheyenne allow researchers to run increasingly detailed models that simulate complex events and predict how they might unfold in the future. With more supercomputing power, scientists can capture additional processes, run their models at a higher resolution, and conduct an ensemble of modeling runs that provide a fuller picture of the same time period. "Providing next-generation supercomputing is vital to better understanding the Earth system that affects us all, " said NCAR Director James W. Hurrell. "We're delighted that this powerful resource is now available to the nation's scientists, and we're looking forward to new discoveries in climate, weather, space weather, renewable energy, and other critical areas of research." Some of the initial projects on Cheyenne include: Long-range, seasonal to decadal forecasting: Several studies led by George Mason University, the University of Miami, and NCAR aim to improve prediction of weather patterns months to years in advance. Researchers will use Cheyenne's capabilities to generate more comprehensive simulations of finer-scale processes in the ocean, atmosphere, and sea ice. This research will help scientists refine computer models for improved long-term predictions, including how year-to-year changes in Arctic sea ice extent may affect the likelihood of extreme weather events thousands of miles away. Wind energy: Projecting electricity output at a wind farm is extraordinarily challenging as it involves predicting variable gusts and complex wind eddies at the height of turbines, which are hundreds of feet above the sensors used for weather forecasting. University of Wyoming researchers will use Cheyenne to simulate wind conditions on different scales, from across the continent down to the tiny space near a wind turbine blade, as well as the vibrations within an individual turbine itself. In addition, an NCAR-led project will create high-resolution, 3-D simulations of vertical and horizontal drafts to provide more information about winds over complex terrain. This type of research is critical as utilities seek to make wind farms as efficient as possible. Space weather: Scientists are working to better understand solar disturbances that buffet Earth's atmosphere and threaten the operation of satellites, communications, and power grids. New projects led by the University of Delaware and NCAR are using Cheyenne to gain more insight into how solar activity leads to damaging geomagnetic storms. The scientists plan to develop detailed simulations of the emergence of the magnetic field from the subsurface of the Sun into its atmosphere, as well as gain a three-dimensional view of plasma turbulence and magnetic reconnection in space that lead to plasma heating. Extreme weather: One of the leading questions about climate change is how it could affect the frequency and severity of major storms and other types of severe weather. An NCAR-led project will explore how climate interacts with the land surface and hydrology over the United States, and how extreme weather events can be expected to change in the future. It will use advanced modeling approaches at high resolution (down to just a few miles) in ways that can help scientists configure future climate models to better simulate extreme events. Climate engineering: To counter the effects of heat-trapping greenhouse gases, some experts have proposed artificially cooling the planet by injecting sulfates into the stratosphere, which would mimic the effects of a major volcanic eruption. But if society ever tried to engage in such climate engineering, or geoengineering, the results could alter the world's climate in unintended ways. An NCAR-led project is using Cheyenne's computing power to run an ensemble of climate engineering simulations to show how hypothetical sulfate injections could affect regional temperatures and precipitation. Smoke and global climate: A study led by the University of Wyoming will look into emissions from wildfires and how they affect stratocumulus clouds over the southeastern Atlantic Ocean. This research is needed for a better understanding of the global climate system, as stratocumulus clouds, which cover 23 percent of Earth's surface, play a key role in reflecting sunlight back into space. The work will help reveal the extent to which particles emitted during biomass burning influence cloud processes in ways that affect global temperatures.


Pouquet A.,Computational and Information Systems Laboratory | Pouquet A.,U.S. National Center for Atmospheric Research | Mininni P.D.,Computational and Information Systems Laboratory | Mininni P.D.,CONICET
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences | Year: 2010

Invariance properties of physical systems govern their behaviour: energy conservation in turbulence drives a wide distribution of energy among modes, as observed in geophysical or astrophysical flows. In ideal hydrodynamics, the role of the invariance of helicity (correlation between velocity and its curl, measuring departures from mirror symmetry) remains unclear since it does not alter the energy spectrum. However, in the presence of rotation, significant differences emerge between helical and non-helical turbulent flows. We first briefly outline some of the issues such as the partition of energy and helicity among modes. Using massive numerical simulations, we then show that smallscale structures and their intermittency properties differ according to whether helicity is present or not, in particular with respect to the emergence of Beltrami core vortices that are laminar helical vertical updraft vortices. These results point to the discovery of a small parameter besides the Rossby number, a fact that would relate the problem of rotating helical turbulence to that of critical phenomena, through the renormalization group and weak-turbulence theory. This parameter can be associated with the adimensionalized ratio of the energy to helicity flux to small scales, the three-dimensional energy cascade being weak and self-similar. copy; 2010 The Royal Society.


Marino R.,National institute for astrophysics | Marino R.,Computational and Information Systems Laboratory | Sorriso-Valvo L.,CNR Institute of Neuroscience | D'Amicis R.,National institute for astrophysics | And 4 more authors.
Astrophysical Journal | Year: 2012

The occurrence and nature of a nonlinear energy cascade within the intermediate scales of solar wind Alfvénic turbulence represents an important open issue. Using in situ measurements of fast, high latitude solar wind taken by the Ulysses spacecraft at solar minima, it is possible to show that a nonlinear energy cascade of imbalanced turbulence is only observed when the solar wind owns peculiar properties. These are the reduction of the local correlation between velocity and magnetic field (weak cross-helicity); the presence of large-scale velocity shears; and the steepening and extension down to low frequencies of the turbulent spectra. Our observations suggest the important role of both large-scale velocity and Alfvénicity of the field fluctuations for the validation of the Yaglom law in solar wind turbulence. © 2012 The American Astronomical Society. All rights reserved.


Thalabard S.,Computational and Information Systems Laboratory | Thalabard S.,CEA Saclay Nuclear Research Center | Rosenberg D.,Computational and Information Systems Laboratory | Pouquet A.,Computational and Information Systems Laboratory | Mininni P.D.,Computational and Information Systems Laboratory
Physical Review Letters | Year: 2011

We examine turbulent flows in the presence of solid-body rotation and helical forcing in the framework of stochastic Schramm-Löwner evolution (SLE) curves. The data stem from a run with 15363 grid points, with Reynolds and Rossby numbers of, respectively, 5100 and 0.06. We average the parallel component of the vorticity in the direction parallel to that of rotation and examine the resulting ωz field for scaling properties of its zero-value contours. We find for the first time for three-dimensional fluid turbulence evidence of nodal curves being conformal invariant, belonging to a SLE class with associated Brownian diffusivity κ=3.6±0.1. SLE behavior is related to the self-similarity of the direct cascade of energy to small scales and to the partial bidimensionalization of the flow because of rotation. We recover the value of κ with a heuristic argument and show that this is consistent with several nontrivial SLE predictions. © 2011 American Physical Society.


Pouquet A.,University of Colorado at Boulder | Pouquet A.,Computational and Information Systems Laboratory | Marino R.,Computational and Information Systems Laboratory
Physical Review Letters | Year: 2013

The ocean and the atmosphere, and hence the climate, are governed at large scale by interactions between pressure gradient and Coriolis and buoyancy forces. This leads to a quasigeostrophic balance in which, in a two-dimensional-like fashion, the energy injected by solar radiation, winds, or tides goes to large scales in what is known as an inverse cascade. Yet, except for Ekman friction, energy dissipation and turbulent mixing occur at a small scale implying the formation of such scales associated with breaking of geostrophic dynamics through wave-eddy interactions or frontogenesis, in opposition to the inverse cascade. Can it be both at the same time? We exemplify here this dual behavior of energy with the help of three-dimensional direct numerical simulations of rotating stratified Boussinesq turbulence. We show that efficient small-scale mixing and large-scale coherence develop simultaneously in such geophysical and astrophysical flows, both with constant flux as required by theoretical arguments, thereby clearly resolving the aforementioned contradiction. © 2013 American Physical Society.

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