Bulletin of the American Physical Society
2005 58th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 20–22, 2005; Chicago, IL
Session BN: Atmospheric Dynamics |
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Chair: Svetlana Poroseva, Florida State University Room: Hilton Chicago PDR 1 |
Sunday, November 20, 2005 10:56AM - 11:09AM |
BN.00001: Uncertainty Quantification in Hurricane Path Forecasts using Evidence Theory Svetlana Poroseva, Julie Letschert, M. Yousuff Hussaini Results of any computations are of practical value only if information on their accuracy is also available. It is especially true of forecasting hurricane paths where accuracy is of vital importance. Most current forecasts lack such information. The present study investigates the potential of evidence theory to provide a quantitative assessment of the forecast accuracy and to develop a reliable procedure of combining different forecasts to produce the best possible prediction. Results of testing the approach in quantifying uncertainty of turbulence models encourage us to apply a similar approach to hurricane path forecasts, and it requires considerable customization to suit the hurricane forecast problem. The database for hurricanes of 1998-2001 in the Pacific Ocean is used to quantify uncertainty in forecasts produced by global models from two operational centers -- the U.S. Navy Operational Global Atmospheric Prediction System (NOGAPS) and European Centre for Medium-Range Weather Forecasts (ECMRWF). The performance of these two models is compared for each year. We also track the efficiency of annual modifications in each model. The data for hurricanes of year 2000 are used to evaluate the present approach that fuses different forecasts to improve the quality of prediction. [Preview Abstract] |
Sunday, November 20, 2005 11:09AM - 11:22AM |
BN.00002: Global Observations of the Land Breeze Stefan Llewellyn Smith, Sarah Gille, Nicholas Statom Four-times daily satellite wind observations from the QuikSCAT and ADEOS-II tandem scatterometer mission are used to study the land/sea breeze circulation. These observations provide a global view of diurnal wind variations over the ocean. Results agree with frictional linear theory: winds follow an elliptical hodograph through the course of the day, but indicate that diurnal wind variations propagate offshore progressively like nonlinear gravity waves and are detectable several hundred kilometers from the coast. [Preview Abstract] |
Sunday, November 20, 2005 11:22AM - 11:35AM |
BN.00003: Critical Averaging Time for Atmospheric Boundary Layer Fluxes H. Holmes, M. Metzger Calculation of heat and momentum fluxes in the Atmospheric Boundary Layer (ABL) requires separating the turbulent signal into mean and fluctuating components. Since the ABL is not statistically stationary, separation of these components depends on the inherent scales of motion in the flow. A new method is presented that utilizes energy spectra and cospectra analyses of raw velocity and temperature signals to select a critical averaging time, $t_c$, for calculating the unsteady mean components of those signals. The new method is applied to high quality sonic anemometry data acquired at the Surface Layer Turbulence and Environmental Science Test (SLTEST) Facility located in Utah's western desert. Results for the unstable boundary layer show a correlation between $t_c$ and the characteristic time scale based on the ratio of mixed layer depth and convective velocity. Extension of the new method toward selection of a critical averaging time appropriate for the near-neutral boundary layer will also be discussed. [Preview Abstract] |
Sunday, November 20, 2005 11:35AM - 11:48AM |
BN.00004: Large eddy simulation of ice particle growth in aircraft contrails Anup Shirgaonkar, Sanjiva Lele Dispersion of the exhaust jet of a cruising aircraft and its mixing in the vortex-wake affect the ice particle growth in contrails. A numerical study of the wake-jet system is conducted to quantify contrail growth using large eddy simulations. The ice phase is calculated using Lagrangian particle tracking. We assess the trends in ice growth with varying ambient relative humidity. Subsaturated, saturated, and highly supersaturated atmospheres are considered. Current results show that in a subsaturated atmosphere, the mean particle radius develops a distinct peak (in time) and then decays to the soot particle radius. The peak location and magnitude are dictated mainly by the atmospheric temperature. When the atmosphere is supersaturated with respect to ice, contrail growth is monotonic in the early stages. Results for ice volume density and particle size distribution will be presented. [Preview Abstract] |
Sunday, November 20, 2005 11:48AM - 12:01PM |
BN.00005: A New Hybrid Fourier Ray Method for Computing Low Froude Number Stratified Flow over Topography in the Atmosphere James Rottman, Dave Broutman A new kind of forecast model is developed for the internal wavefield generated by stratified flow over three-dimensional topography. The new model is based on high-resolution nonlinear numerical simulation of the near-field flow around the topography combined with a ray-tracing of the far-field propagation of the internal waves generated by the near-field flow. The far-field model allows for the refraction and reflection of the waves by height-dependent winds and stratification. The far-field ray-tracing code is not in the usual spatial formulation. Instead the rays are traced in a Fourier-transform domain, and the resulting ray solution is mapped into a spatial solution by inverse Fourier transform. The use of a Fourier-transform domain simplifies all aspects of the ray calculation. The initialization of the rays from the numerical model is done at very close distances to the topography, in a way that is self-consistent with ray theory assumptions. This is a direct consequence of the use of a ray formulation in the Fourier transform domain, and it means that the numerical resolution for the near-field simulation can be concentrated near the topography. An example simulation and comparison with atmospheric observations will be shown. [Preview Abstract] |
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