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Fritts D.C.,GATS, Inc. | Wan K.,GATS, Inc. | Franke P.M.,University of Illinois at Urbana - Champaign | Lund T.,NorthWest Research Associates, Inc.
Journal of Geophysical Research: Atmospheres | Year: 2012

Previous papers by Franke et al. (2011) and Fritts et al. (2011) described the computation of radar backscatter power and vertical velocities from numerical simulations of turbulence arising due to Kelvin-Helmholtz (KH) shear instability. Comparisons of backscatter power and inferred velocities with the distributions of turbulence and the true velocities revealed biases in the identification of active or intense turbulence and in the inferred Doppler spectrum and vertical velocities throughout the flow evolution. This paper extends these analyses to off-zenith viewing angles typical of multiple-beam MF, HF, and VHF radars. These reveal similar biases in the identification of turbulence occurrence, Doppler spectra, and inferred radial velocities, with additional sensitivity to the off-zenith angle relative to the mean shear across the turbulence layer. Radial velocities are typically underestimated during turbulence generation and breakdown of the KH billows, except where turbulence refractive index gradients are strong. Doppler spectra are biased toward regions retaining strong refractive index gradients, implying strong aspect sensitivity at later stages in the evolution. Persistent tilted structures at late stages of the evolution contribute to radial velocity measurement biases that also are functions of off-zenith angle and time. © 2012. American Geophysical Union. All Rights Reserved.


Rong P.P.,Hampton University | Russell J.M.,Hampton University | Hervig M.E.,GATS, Inc. | Bailey S.M.,Virginia Polytechnic Institute and State University
Journal of Geophysical Research: Atmospheres | Year: 2012

Temperature, or alternatively, saturation vapor pressure (PSAT), dominantly controls the polar mesospheric cloud (PMC) seasonal onset and termination, characterized by a strong anticorrelated relationship between the Solar Occultation for Ice Experiment (SOFIE)-observed PMC frequency and P SAT on intraseasonal time scales. SOFIE is highly sensitive to weak clouds and can obtain a nearly full spectrum of PMCs. Both the SOFIE PMC frequency and PSAT indicate a rapid onset and termination of the season. Compared to PSAT, the water vapor partial pressure (P H2O) exhibits only a slight increase from before to after the start of the season. We are able to use the PSAT daily minimum and two averaged PH2O levels taken before and after the solstice, respectively, to estimate the start and end days of the PMC season within 1-2days uncertainty. SOFIE ice mass density and its relationship to P H2O and PSAT are examined on intraseasonal scales and for two extreme conditions, i.e., strong and weak cloud cases. In the strong cloud case, such as those bright clouds that occur during the core of the season, PH2O far exceeds PSAT and dominantly controls the ice mass density variation, while in the weak cloud case, such as those clouds that occur at the start and end of the season, PH2O and PSAT have comparable magnitudes, vary in concert, and have similar effects on the ice mass density variation. These results suggest that the long-term brightness trends reported by DeLand et al. (2007) are primarily driven by changes in water vapor (H2O), not temperature. Copyright © 2012 by the American Geophysical Union.


Massie S.T.,U.S. National Center for Atmospheric Research | Hervig M.,GATS, Inc.
Journal of Quantitative Spectroscopy and Radiative Transfer | Year: 2013

The HITRAN 2012 compilation of the real and imaginary refractive indices of the materials in aerosols and cloud particles is reviewed. Additions to HITRAN 2012 focus upon materials that are absorptive (i.e. minerals, burning vegetation, brown carbon, desert dust, and volcanic ash). The HITRAN-RI program, created to facilitate usage of the indices, is discussed. The HITRAN-RI program inter-compares the indices of different data sets and calculates optical properties (i.e. extinction, scattering, absorption, single scattering albedo, backscattering, and asymmetry parameter) for user specified size distributions and particle types. The instructional component of HITRAN-RI introduces the user to Mie calculations for spheres and coated spheres, and applies various mixing rules by which one calculates the effective indices of a multi-component particle. © 2013 Elsevier Ltd.


Fritts D.C.,GATS, Inc. | Wang L.,GATS, Inc.
Journal of the Atmospheric Sciences | Year: 2013

Part I of this paper employs four direct numerical simulations (DNSs) to examine the dynamics and energetics of idealized gravity wave-fine structure (GW-FS) interactions. That study and this companion paper were motivated by the ubiquity of multiscale GW-FS superpositions throughout the atmosphere. These DNSs exhibit combinations of wave-wave interactions and local instabilities that depart significantly from those accompanying idealized GWs or mean flows alone, surprising dependence of the flow evolution on the details of the FS, and an interesting additional pathway to instability and turbulence due to GW-FS superpositions. This paper examines the mechanical and thermal energy dissipation rates occurring in two of these DNSs. Findings include 1) dissipation that tends to be much more localized and variable than that due toGW instability in the absence of FS, 2) dissipation statistics indicative of multiple turbulence sources, 3) strong influences of FS shears on instability occurrence and turbulence intensities and statistics, and 4) significant differences between mechanical and thermal dissipation rate fields having potentially important implications for measurements of these flows. © 2013 American Meteorological Society.


Hervig M.E.,GATS, Inc. | Gordley L.L.,GATS, Inc.
Journal of Geophysical Research: Atmospheres | Year: 2010

The temperature and shape of ice particles in polar mesospheric clouds (PMCs) were determined using observations near 3 m wavelength from the Solar Occultation for Ice Experiment (SOFIE). The resulting ice temperatures are 5-20 K colder than the current SOFIE temperatures retrieved from CO2 transmission measurements. Particle shape is described using oblate spheroids, and the axial ratios determined in this study are slightly more spherical than previous results obtained using SOFIE observations assuming constant temperature (1.9 at the altitude of peak mass density compared to 2.3 previously). Using ice temperatures in an equilibrium PMC model results in ice mass densities that are much higher than observed. SOFIE observations indicate that the amount of H2O that can enter the ice phase is related to ice concentration, suggesting that ice nucleation plays an important role in determining PMC formation and variability. This result may also imply that the neglect of transient phenomena in the equilibrium PMC model may be a large source of error. SOFIE observations do not support the existence of amorphous ice particles near the summer mesopause but rather indicate that cubic ice is ubiquitous. Copyright 2010 by the American Geophysical Union.


Siskind D.E.,U.S. Navy | Stevens M.H.,U.S. Navy | Hervig M.E.,GATS, Inc. | Randall C.E.,University of Colorado at Boulder
Geophysical Research Letters | Year: 2013

Observations of polar mesospheric clouds by the Aeronomy of Ice in the Mesosphere Explorer show that for the Northern summers of 2007-2010, the cloud ice water content (IWC) and occurrence frequency varied with the meteorological forcing from the Southern winter stratosphere. With the increase in solar flux in the last two years, expectations were that the clouds would decrease due to reduced water vapor (H2O) and/or higher temperatures. Surprisingly, we observe more clouds in 2011 and 40% greater IWC in 2011 and 2012. The increase is particularly pronounced in the clouds with highest IWC. These high IWC clouds are associated with significant enhancements in total H2O (vapor and ice). We suggest this implies an additional source of H2O and that this is provided by space traffic exhaust. A preliminary estimate of the H2O released from summertime space traffic over the last six years is qualitatively consistent with this suggestion. © 2013 American Geophysical Union. All Rights Reserved.


Krall J.,U.S. Navy | Huba J.D.,U.S. Navy | Fritts D.C.,GATS, Inc.
Geophysical Research Letters | Year: 2013

The Naval Research Laboratory three-dimensional simulation code SAMI3/ESF is used to study the response of the postsunset ionosphere to plane gravity waves. The effect of the vertical wind component of the wave is included as well as the effect of the background vertical wind, which can suppress equatorial spread F (ESF). It is shown that the strength of the coupling of the gravity wave to ESF increases with the vertical wavelength of the gravity wave. Long vertical wavelength modes (λ > 100 km) are more effective for seeding ESF. Key Points GW/ESF coupling increases with the vertical wavelength of the gravity wave The results are only partially consistent with the hypothesis of Tsunoda [2010] We demonstrate that an upward vertical background wind can suppress ESF ©2013. American Geophysical Union. All Rights Reserved.


Baumgarten G.,Leibniz Institute of Atmospheric Physics | Fritts D.C.,GATS, Inc.
Journal of Geophysical Research: Atmospheres | Year: 2014

Noctilucent clouds (NLCs) have been imaged during two nights in summer 2009 from northern Germany (Kühlungsborn, 54°N) and middle Norway (Trondheim, 64°N). For the first time a horizontal resolution of 10 to 20 m at the altitude of the clouds (about 83 km) and a temporal resolution of about 1 s was achieved. Additional imaging using a coarser resolution provided monitoring of the larger-scale (∼100 km) structures observed in the clouds. Two series of NLC images are described that reveal apparent Kelvin-Helmholtz (KH) billow structures having very different morphologies and apparent transitions to turbulence and mixing. One series exhibits deep KH billows and apparent secondary instabilities in the billow exteriors having streamwise alignment (and spanwise wave number), suggesting a small initial Richardson number (Ri). A second series of images suggests a larger and less unstable Ri, a slower KH billow evolution, shallower billows, and turbulence and mixing confined to the billow cores. We suggest that systematic exploration of these dynamics employing NLC imaging may enable characterization and quantification of KH instability occurrence statistics and of their contributions to turbulence and mixing in the summer mesopause environment with unique sensitivity to their small-scale dynamics. ©2014. American Geophysical Union. All Rights Reserved.


Grant
Agency: National Aeronautics and Space Administration | Branch: | Program: SBIR | Phase: Phase I | Award Amount: 99.96K | Year: 2009

The innovation proposed here is a digital array gas radiometer (DAGR), a new design for a gas filter correlation radiometer (GFCR) to accurately measure and monitor CO2, CO, CH4, N2O and other key trace gases in the boundary layer from space, aircraft or ground-based platforms. GFCR is a well-known and proven technology for trace gas detection and monitoring. However, its effectiveness in downlooking applications has been limited, primarily because variations in surface albedo degrade the performance. Our DAGR approach builds on traditional GFCR concepts and combines several new key elements: two-dimensional detector arrays, pupil imaging (imaging the aperture), and a novel calibration approach. With these enhancements and appropriate signal processing, the DAGR design overcomes the historical limitations of GFCR in downlooking applications. In addition, this design significantly boosts the sensitivity and expands the dynamic range traditionally available to these sensors. Finally, the innovation provides a calibration technique that nearly eliminates errors due to detector drift effects. The result will be a compact, static, robust system that can accurately measure important boundary layer species from a variety of platforms.


Grant
Agency: National Aeronautics and Space Administration | Branch: | Program: SBIR | Phase: Phase II | Award Amount: 599.74K | Year: 2010

The digital array gas radiometer (DAGR) is a new sensor design for accurate measurement and monitoring of trace gases in the boundary layer from space, aircraft, or ground-based platforms using scattered sunlight. Target gases include CH4, CO, CO2, N¬2O and other species critical to climate science, environmental monitoring and commercial pollution compliance efforts. The DAGR approach builds on traditional gas-filter correlation radiometry (GFCR), a well-known and proven technology for trace gas sensing. The effectiveness of GFCR, however, has historically been limited in downlooking applications primarily because variations in surface albedo degrade its performance. In our Phase I effort, we investigated and demonstrated the ability of the DAGR design to overcome these limitations. With the successful completion of these feasibility studies, the technology has been increased to TRL-3. In the Phase II effort, we will construct and test a prototype DAGR sensor for CH4 detection and monitoring, advancing the technology to TRL-5. CH4 was chosen as our target gas to meet the pressing commercial need for an improved natural gas leak detection system. For NASA, the DAGR prototype will significantly advance the technology needed for future missions such as ASCENDS, GEOCAPE, and GACM. DAGR represents a major advance in using backscattered light for detecting concentrations of key molecular species.

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