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Springfield, VA, United States

Eckermann S.D.,U.S. Navy | Ma J.,Computational Physics, Inc. | Zhu X.,Johns Hopkins University
Icarus | Year: 2011

Using a Curtis-matrix model of 15μm CO 2 radiative cooling rates for the martian atmosphere, we have computed vertical scale-dependent IR radiative damping rates from 0 to 200km altitude over a broad band of vertical wavenumbers {divides}m{divides}=2π(1-500km) -1 for representative meteorological conditions at 40°N and average levels of solar activity and dust loading. In the middle atmosphere, infrared (IR) radiative damping rates increase with decreasing vertical scale and peak in excess of 30days -1 at ∼50-80km altitude, before gradually transitioning to scale-independent rates above ∼100km due to breakdown of local thermodynamic equilibrium. We incorporate these computed IR radiative damping rates into a linear anelastic gravity-wave model to assess the impact of IR radiative damping, relative to wave breaking and molecular viscosity, in the dissipation of gravity-wave momentum flux. The model results indicate that IR radiative damping is the dominant process in dissipating gravity-wave momentum fluxes at ∼0-50km altitude, and is the dominant process at all altitudes for gravity waves with vertical wavelengths ≲10-15km. Wave breaking becomes dominant at higher altitudes only for " fast" waves of short horizontal and long vertical wavelengths. Molecular viscosity plays a negligible role in overall momentum flux deposition. Our results provide compelling evidence that IR radiative damping is a major, and often dominant physical process controlling the dissipation of gravity-wave momentum fluxes on Mars, and therefore should be incorporated into future parameterizations of gravity-wave drag within Mars GCMs. Lookup tables for doing so, based on the current computations, are provided. © 2010. Source

Sassi F.,U.S. Navy | Liu H.-L.,High Altitude Observatory | Ma J.,Computational Physics, Inc. | Garcia R.R.,U.S. National Center for Atmospheric Research
Journal of Geophysical Research: Atmospheres | Year: 2013

We present numerical simulations using the Whole Atmosphere Community Climate Model, extended version, constrained below 90 km by a combination of NASA's Modern Era Retrospective Analysis for Research and Applications and the U.S. Navy's Operational Global Atmospheric Prediction System - Advanced Level Physics High Altitude assimilation products. The period examined is January and February 2009, when a large stratospheric warming occurred on 24 January 2009, with anomalous circulation persisting for several weeks after the event. In this study, we focus on the dynamical response of the lower thermosphere up to 200 km. We find evidence of migrating and nonmigrating tides, Rossby and Rossby-gravity modes, and Kelvin waves, whose amplitudes appear to be modulated at the times leading and following the stratospheric warming. While the Rossby, Rossby-gravity, and Kelvin modes are rapidly dissipated in the lower thermosphere (above 110 km), the tides maintain substantial amplitude throughout the thermosphere, but their vertical structure becomes external above about 120-150 km. Most waves identified in the simulations decrease in amplitude in the thermosphere, indicating remote forcing from below and strong dissipation by molecular diffusion at high altitudes; however, the amplitude of the migrating DW1 tide increases in the thermosphere suggesting in situ forcing. We show that the amplitude of the tides (such as the DW1) changes as the background wind alters the vorticity in the tropics, which broadens or narrows the tropical waveguide. Our results also suggest that fast Rossby normal modes (periods ≤ 10 days) are excited by instability of the zonal-mean wind distribution following the stratospheric warming. © 2013. Her Majesty the Queen in Right of Canada. American Geophysical Union. Source

Wang Y.,Computational Physics, Inc. | Ainsworth T.L.,U.S. Navy | Lee J.-S.,U.S. Navy
IEEE Transactions on Geoscience and Remote Sensing | Year: 2011

The quality of polarimetric synthetic aperture radar (PolSAR) imagery and its polarimetric decompositions depends on the accuracy of polarimetric observations of the SAR system and its calibration. Polarization distortions on the polarimetric measurement can be incurred due to nonideal system polarization quality and propagation factors, such as channel imbalance, crosstalk, and Faraday rotation at lower frequencies. All these distortions have varying impacts on different target types as well as different decomposition methods. In this paper, we assess the polarization quality of the PolSAR system in the context of polarimetric imagery analysis and quantify the various effects of polarization distortions on polarization target decompositions. A generic metric is defined to measure the polarization purity of the system. Considering the fact that target decomposition plays an important role in imagery analysis, we apply several widely used decomposition methods to showcase the polarimetric system requirement based on the defined metric. We demonstrate that this metric can be used for radar system design and polarimetric data calibration. © 2006 IEEE. Source

Agency: NSF | Branch: Continuing grant | Program: | Phase: AERONOMY | Award Amount: 230.92K | Year: 2011

This project will investigate sources of short-period gravity waves at high polar latitudes as well as the atmospheric conditions which influence their propagation. This investigation will utilize measurements of gravity waves and mesospheric wind speeds acquired by an all-sky imager and meteor radar co-located at Rothera on the Antarctic Peninsula. The observed wave data will be analyzed in conjunction with the Navy Operational Global Atmospheric Prediction System Advanced High Altitude (NOGAPS-ALPHA) forecasting and data assimilative model of the upper atmosphere, along with a Fourier ray tracing model for localization of wave source regions. This analysis will result in an identification of dominant wave sources at high latitudes, including an assessment of the importance of orographic waves, as well as a characterization of atmospheric conditions which affect wave ducting and propagation.

Agency: Department of Defense | Branch: Missile Defense Agency | Program: SBIR | Phase: Phase II | Award Amount: 1.00M | Year: 2011

Next generation ballistic missile warning, defense and surveillance systems need to anticipate, through modeling and simulation, the background radiation of the battlespace environment, including geometries that intercept the ocean background. This objective requires prior knowledge of the environmental radiance conditions for development of optimal sensors and detection approaches. Much work has been done to create ocean background models, but what is needed is an innovative architecture that efficiently and seamlessly unifies existing, improved, and/or new computer code, along with access to satellite measurements of ocean parameters, in a consistent and fully integrated computer environment that can be utilized in a plug-and-play fashion by state-of-the-art background radiation codes, such as SAMM, FLITES, the Synthetic Scene Generation Model (SSGM), and the Objective Simulation Framework (OSF) to meet missile warning and defense surveillance needs. This proposed effort will result in an innovative software product called the OCEANUS (Ocean Universal Scene) Model. OCEANUS will provide MDA with an innovative ocean scene model that incorporates ocean composition, ocean dynamics, the marine boundary layer, the land-sea interface, and the ocean observables in the ultraviolet, visible, and infrared portions of the spectrum.

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