Time filter

Source Type

Bellevue, WA, United States

Robins R.E.,North West Research Associates Inc. | Jost G.,University of Texas at Austin
Proceedings - 2010 DoD High Performance Computing Modernization Program Users Group Conference, HPCMP UGC 2010

In this paper, we describe the development of a parallel version of the IR3D (Incompressible Realistic 3-D) code, which simulates the environmental effects on the evolution of vortices trailing behind control surfaces of underwater vehicles. The objective of the project was to parallelize and optimize the existing implementation for clusters of multi-core nodes. The primary motivation was to reduce turnaround time and add the capability to handle large problem sizes. Furthermore we were aiming for portability and scalability. The code solves the 3D Boussinesq equations for incompressible fluids. Fast-Fourier transforms (FFTs) are used for the calculation of horizontal derivatives and a higher-order compact finite difference scheme is used for vertical derivatives. To ensure incompressibility, the code employs a projection method for which we developed a new Poisson Solver. This solver works by computing 2D FFTs in horizontal-planes, numerically solving the resulting ordinary differential equations (ODEs) for Fourier coefficients, and then doing Fourier inversion. Parallelization is based on the Message Passing Interface (MPI) programming paradigm. We present performance and scalability results of PIR3D (Parallel IR3D) on a variety of hardware platforms and discuss methods for further optimization by exploiting additional by exploiting additional levels of parallelism. © 2011 IEEE. Source

Twohy C.H.,Oregon State University | Twohy C.H.,North West Research Associates Inc.
Journal of the Atmospheric Sciences

Mineral dust particles have been shown to act as cloud condensation nuclei, and they are known to interact with developing tropical storms over the Atlantic downwind of the Sahara. Once present within liquid droplets, they have the potential to act as freezing ice nuclei and further affect the microphysics, dynamics, and evolution of tropical storms. However, few measurements of mineral dust particles in tropical convective clouds exist. This study indicates that about one-third of droplets sampled in small convective clouds in the tropical eastern Atlantic contained dust particles, and dust was the dominant residual particle type sampled in ice crystals from anvil outflow. However, estimated number and mass concentrations of dust in anvil ice were small compared to the amount of dust available within the Saharan air layer itself. © 2015 American Meteorological Society. Source

McLinden C.A.,Environment Canada | McLinden C.A.,University of Saskatchewan | Bourassa A.E.,University of Saskatchewan | Brohede S.,Chalmers University of Technology | And 22 more authors.
Bulletin of the American Meteorological Society

Into year 11 of a 2-yr mission, OSIRIS is redefining how limb-scattered sunlight can be used to probe the atmosphere, even into the upper troposphere. © 2012 American Meteorological Society. Source

Yamazaki Y.,High Altitude Observatory | Yamazaki Y.,Lancaster University | Richmond A.D.,High Altitude Observatory | Maute A.,High Altitude Observatory | And 7 more authors.
Journal of Geophysical Research: Space Physics

Quiet time daily variations of the geomagnetic field near the magnetic equator due to the equatorial electrojet are simulated using the National Center for Atmospheric Research Thermosphere-Ionosphere Electrodynamics General Circulation Model (TIE-GCM) and compared to those observed by ground-based magnetometers. Simulations are run both with and without tidal forcing at the height of the model lower boundary (∼97km). When the lower boundary forcing is off, the wind that generates an electromotive force in the model is primarily the vertically nonpropagating diurnal tide, which is excited in the thermosphere due to daytime solar ultraviolet heating. The lower boundary tidal forcing adds the effect of upward propagating tides, which are excited in the lower atmosphere and propagate vertically to the thermosphere. The main objective of this study is to evaluate the relative importance of these thermospherically generated tides and upward propagating tides in the generation of the equatorial electrojet. Fairly good agreement is obtained between model and observations when the model is forced by realistic lower boundary tides based on temperature and wind measurements from the Thermosphere-Ionosphere- Mesosphere Energetics and Dynamics (TIMED) satellite, as determined by Wu et al. (2012). The simulation results show that the effect of upward propagating tides increases the range of the geomagnetic daily variation in the magnetic-northward component at the magnetic equator approximately by 100%. It is also shown that the well-known semiannual change in the daily variation is mostly due to upward propagating tides, especially the migrating semidiurnal tide. These results indicate that upward propagating tides play a substantial role in producing the equatorial electrojet and its seasonal variability. Key Points The ground magnetic effect of the equatorial electrojet is simulated Upward propagating tides explain about 50% the magnetic effect The semiannual variation is mainly due to upward propagating tides ©2014. American Geophysical Union. All Rights Reserved. Source

Grachev A.A.,University of Colorado at Boulder | Andreas E.L.,North West Research Associates Inc. | Fairall C.W.,National Oceanic and Atmospheric Administration | Guest P.S.,Naval Postgraduate School, Monterey | Persson P.O.G.,University of Colorado at Boulder
Boundary-Layer Meteorology

Measurements of atmospheric turbulence made over the Arctic pack ice during the Surface Heat Budget of the Arctic Ocean experiment (SHEBA) are used to determine the limits of applicability of Monin-Obukhov similarity theory (in the local scaling formulation) in the stable atmospheric boundary layer. Based on the spectral analysis of wind velocity and air temperature fluctuations, it is shown that, when both the gradient Richardson number, Ri, and the flux Richardson number, Rf, exceed a 'critical value' of about 0. 20-0. 25, the inertial subrange associated with the Richardson-Kolmogorov cascade dies out and vertical turbulent fluxes become small. Some small-scale turbulence survives even in this supercritical regime, but this is non-Kolmogorov turbulence, and it decays rapidly with further increasing stability. Similarity theory is based on the turbulent fluxes in the high-frequency part of the spectra that are associated with energy-containing/flux-carrying eddies. Spectral densities in this high-frequency band diminish as the Richardson-Kolmogorov energy cascade weakens; therefore, the applicability of local Monin-Obukhov similarity theory in stable conditions is limited by the inequalities Ri < Ricr and Rf < Rfcr. However, it is found that Rfcr = 0. 20-0. 25 is a primary threshold for applicability. Applying this prerequisite shows that the data follow classical Monin-Obukhov local z-less predictions after the irrelevant cases (turbulence without the Richardson-Kolmogorov cascade) have been filtered out. © 2012 Springer Science+Business Media B.V. Source

Discover hidden collaborations