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NASA NTRS2000

Asymptotic Solutions for Optical Properties of Large Particles with Strong Absorption

For scattering calculations involving nonspherical particles such as ice crystals, we show that the transverse wave condition is not applicable to the refracted electromagnetic wave in the context of geometric optics when absorption is involved. Either the TM wave condition (i.e., where the magnetic field of the refracted wave is transverse with respect to the wave direction) or the TE wave condition (i.e., where the electric field is transverse with respect to the propagating direction of the wave) may be assumed for the refracted wave in an absorbing medium to locally satisfy the electromagnetic boundary condition in the ray tracing calculation. The wave mode assumed for the refracted wave affects both the reflection and refraction coefficients. As a result, a nonunique solution for these coefficients is derived from the electromagnetic boundary condition. In this study we have identified the appropriate solution for the Fresnel reflection/refraction coefficients in light scattering calculation based on the ray tracing technique. We present the 3 x 2 refraction or transmission matrix that completely accounts for the inhomogeneity of the refracted wave in an absorbing medium. Using the Fresnel coefficients for an absorbing medium, we derive an asymptotic solution in an analytical format for the scattering properties of a general polyhedral particle. Numerical results are presented for hexagonal plates and columns with both preferred and random orientations. The asymptotic theory can produce reasonable accuracy in the phase function calculations in the infrared window region (wavelengths near 10 micron) if the particle size (in diameter) is on the order of 40 micron or larger. However, since strong absorption is assumed in the computation of the single-scattering albedo in the asymptotic theory, the single scattering albedo does not change with variation of the particle size. As a result, the asymptotic theory can lead to substantial errors in the computation of single-scattering albedo for small and moderate particle sizes. However, from comparison of the asymptotic results with the FDTD solution, it is expected that a convergence between the FDTD results and the asymptotic theory results can be reached when the particle size approaches 200 micron. We show that the phase function at side-scattering and backscattering angles is insensitive to particle shape if the random orientation condition is assumed. However, if preferred orientations are assumed for particles, the phase function has a strong dependence on scattering azimuthal angle. The single-scattering albedo also shows very strong dependence on the inclination angle of incident radiation with respect to the rotating axis for the preferred particle orientations.

Yang, Ping↗

NASA NTRS2002

Inclination Angles of Black Hole X-Ray Binaries Manifest Strong Gravity around Black Holes

System inclination angles have been determined for about 15 X-ray binaries, in which stellar mass black holes are considered to exist. These inclination angles range between 25 degrees and 80 degrees, but peaked between 60-70 degrees. This peak is not explained in the frame work of Newtonian gravity. However, this peak is reproduced naturally if we model the observed X-ray radiations as being produced in the accretion disks very close to the black hole horizons, where the extremely strong general and special relativistic effects, caused by the extremely strong gravity near the black hole horizons, modify the local radiation significantly as the X-rays propagate to the remote observer. Therefore the peak of the inclination angle distribution provides evidence or strong gravity around stellar mass black holes.

Zhang, S. N.↗

NASA NTRS2004

Interaction of Strong Transient Interplanetary Disturbances with the Dayside Magnetosphere

The objective of the investigation was to gain an understanding of the complex response of the magnetosphere to strong transient interplanetary disturbances. Because the project was only funded for a year, the investigation focused on only one of the three topics proposed in the original three year proposal. We investigated the response of the dayside auroral region to strong transient interplanetary disturbances. The method of the investigation was to use three-dimensional magnetohydrodynamic (MHD) simulations that employ measurements of the solar wind conditions upstream the bow shock to model actual events and then to compare the simulation results with observations from spacecraft located at downstream locations. We modeled an event that occurred on July 14,2000, for which both CLUSTER and IMAGE simultaneous observations were available. The event was marked by high solar wind dynamic pressure and a strong IMF By component. Comparisons showed a very good agreement between intensifications in the auroral emissions measured by IMAGE

Berchem, Jean↗

NASA NTRS2006

Addressing the Tension Between Strong Perimeter Control an Usability

This paper describes a strong perimeter control system for a general purpose processing system, with the perimeter control system taking significant steps to address usability issues, thus mitigating the tension between strong perimeter protection and usability. A secure front end enforces two-factor authentication for all interactive access to an enclave that contains a large supercomputer and various associated systems, with each requiring their own authentication. Usability is addressed through a design in which the user has to perform two-factor authentication at the secure front end in order to gain access to the enclave, while an agent transparently performs public key authentication as needed to authenticate to specific systems within the enclave. The paper then describes a proxy system that allows users to transfer files into the enclave under script control, when the user is not present to perform two-factor authentication. This uses a pre-authorization approach based on public key technology, which is still strongly tied to both two-factor authentication and strict control over where files can be transferred on the target system. Finally the paper describes an approach to support network applications and systems such as grids or parallel file transfer protocols that require the use of many ports through the perimeter. The paper describes a least privilege approach that dynamically opens ports on a host-specific, if-authorized, as-needed, just-in-time basis.

Hinke, Thomas H.↗

NASA NTRS2009

A 16-yr Comparison of Fine Particle and Aerosol Strong Acidity at the Interface Zone (1,540 m) and Within (452 m) the Planetary Boundary Layer of the Great Gulf and Presidential-Dry River Class I Wildernesses on the Presidential Range, New Hampshire

Mount Washington, NH in the White Mountain National Forest, is flanked to the north-northeast and south by two Class I Wilderness areas, the Great Gulf and Presidential Range-Dry River Wildernesses, respectively. The Clean Air Act protects Class I area natural resource values from air pollution. Aerosol sulfate, a fine particulate component that is often transported long distances, is a known contributor to visibility degradation and acidic deposition. We examined summertime fine particulate aerosol mass and sulfate, strong acidity and ammonium concentrations from 1988 to 2004 on Mount Washington at two elevations, 452 and 1,540 meters (msl). The former site is within, and the latter at the interface of, the planetary boundary layer. Comparisons of sampling interval durations (10 and 24 hours), site vs. site, and different sampling methods are made. We also examine the extent to which aerosol sulfate is neutralized. Ten hour (daytime) compared to 24 hour samples have higher mass and aerosol sulfate concentrations, however paired samples are well correlated. Fine mass concentrations compared between the 452 m and 1,540 m sites (standard temperature and pressure corrected) show a weak positive linear relationship with the later being approximately 34% lower. We attribute the lack of a strong correlation to the facts that the 1,540 m site is commonly at the interface of and even above the regional planetary boundary layer in summer and that it can intercept different air masses relative to the 452 m site. Sulfate is approximately 19% lower at the higher elevation site, but comprises a greater percentage of total fine mass; 42% compared to 35% for the high and low elevation site, respectively. Aerosol strong acidity was found to increase with increasing sulfate concentrations at both sites. At the high elevation site, elevated mass and sulfate concentrations are associated with westerly and southwesterly regional flows.

Murray, Georgia L.↗

NASA NTRS2010

Ring Current Dynamics in Moderate and Strong Storms: Comparative Analysis of TWINS and IMAGE/HENA Data with the Comprehensive Ring Current Model

We present a comparative study of ring current dynamics during strong and moderate storms. The ring current during the strong storm is studied with IMAGE/HENA data near the solar cycle maximum in 2000. The ring current during the moderate storm is studied using energetic neutral atom (ENA) data from the Two Wide-Angle Imaging Neutral- Atom Spectrometers (TWINS) mission during the solar minimum in 2008. For both storms, the local time distributions of ENA emissions show signatures of postmidnight enhancement (PME) during the main phases. To model the ring current and ENA emissions, we use the Comprehensive Ring Current Model (CRCM). CRCM results show that the main-phase ring current pressure peaks in the premidnight-dusk sector, while the most intense CRCM-simulated ENA emissions show PME signatures. We analyze two factors to explain this difference: the dependence of charge-exchange cross section on energy and pitch angle distributions of ring current. We find that the IMF By effect (twisting of the convection pattern due to By) is not needed to form the PME. Additionally, the PME is more pronounced for the strong storm, although relative shielding and hence electric field skewing is well developed for both events.

Buzulukova, N.↗

NASA NTRS2012

In Situ Detection of Strong Langmuir Turbulence Processes in Solar Type III Radio Bursts

The high time resolution observations obtained by the WAVES experiment of the STEREO spacecraft in solar type III radio bursts show that Langmuir waves often occur as intense localized wave packets. These wave packets are characterized by short durations of only a few ms and peak intensities, which well exceed the supersonic modulational instability (MI) thresholds. These timescales and peak intensities satisfy the criterion of the solitons collapsed to spatial scales of a few hundred Debye lengths. The spectra of these wave packets consist of primary spectral peaks corresponding to beam-resonant Langmuir waves, two or more sidebands corresponding to down-shifted and up-shifted daughter Langmuir waves, and low frequency enhancements below a few hundred Hz corresponding to daughter ion sound waves. The frequencies and wave numbers of these spectral components satisfy the resonance conditions of the modulational instability (MI). Moreover, the tricoherences, computed using trispectral analysis techniques show that these spectral components are coupled to each other with a high degree of coherency as expected of the MI type of four wave interactions. The high intensities, short scale lengths, sideband spectral structures and low frequency spectral enhancements and, high levels of tricoherences amongst the spectral components of these wave packets provide unambiguous evidence for the supersonic MI and related strong turbulence processes in type III radio bursts. The implication of these observations include: (1) the MI and related strong turbulence processes often occur in type III source regions, (2) the strong turbulence processes probably play very important roles in beam stabilization as well as conversion of Langmuir waves into escaping radiation at the fundamental and second harmonic of the electron plasma frequency, fpe, and (3) the Langmuir collapse probably follows the route of MI in type III radio bursts.

Langmuir↗

NASA NTRS2016

A Strong Merger Shock in Abell 665

Deep (103 ks) Chandra observations of Abell 665 have revealed rich structures in this merging galaxy cluster, including a strong shock and two cold fronts. The newly discovered shock has a Mach number of M =3.0 +/- 0.6, propagating in front of a cold disrupted cloud. This makes Abell 665 the second cluster, after the Bullet cluster, where a strong merger shock of M is approximately 3 has been detected. The shock velocity from jump conditions is consistent with (2.7 +/- 0.7) × 10(exp 3) km s(exp −1). The new data also reveal a prominent southern cold front with potentially heated gas ahead of it. Abell 665 also hosts a giant radio halo. There is a hint of diffuse radio emission extending to the shock at the north, which needs to be examined with better radio data. This new strong shock provides a great opportunity to study the reacceleration model with the X-ray and radio data combined.

galaxies: clusters: general- galaxies: clisters; i↗

NASA NTRS2016

MAVEN Observations of Magnetic Flux Ropes with a Strong Field Amplitude in the Martian Magnetosheath During the ICME Passage on 8 March 2015

We present initial results of strong field amplitude flux ropes observed by Mars Atmosphere and Volatile EvolutioN (MAVEN) mission around Mars during the interplanetary coronal mass ejection (ICME) passage on 8 March 2015. The observed durations were shorter than 5 s and the magnetic field magnitudes peaked above 80 nT, which is a few times stronger than those usually seen in the magnetosheath barrier. These are the first unique observations that MAVEN detected such flux ropes with a strong field at high altitudes (greater than 5000 km). Across these structures, MAVEN coincidentally measured planetary heavy ions with energies higher than a few keV. The spatial properties inferred from the Grad-Shafranov equation suggest that the speed of the structure can be estimated at least an order of magnitude faster than those previously reported quiet-time counterparts. Hence, the space weather event like the ICME passage can be responsible for generating the observed strong field, fast-traveling flux ropes.

8 March 2015↗

NASA NTRS2018

Ocean Circulation Causes Strong Variability in the Mid-Atlantic Bight Nitrogen Budget

Understanding of nitrogen cycling on continental shelves, a critical component of global nutrient cycling, is hampered by limited observations compared to the strong variability on a wide range of time and space scales. Numerical models have the potential to partially alleviate this issue by filling spatio-temporal data gaps and hence resolving annual area-integrated nutrient fluxes. In this study, a three-dimensional bio geo chemical-circulation model was implemented to simulate the Mid-Atlantic Bight (MAB) nitrogen budget. Model results demonstrate that, on average, MAB net community production (NCP) was positive (plus 0.27 teragrams (Tg) Nitrogen per year), indicating net autotrophy. Inter-annual variability in NCP was strong, with annual values ranging between 0.19 and 0.41 Tg N/year. Along-shelf and across-shelf horizontal transport fluxes were the other dominant terms in the nitrogen budget and were primarily responsible for this NCP variability. The along-shelf current transported nitrogen from the north (0.65 Tg N/year) into the MAB, supplementing the nitrogen entering from terrestrial inputs (0.27 Tg N/year). However, NCP was highest in the year when total water volume transport and inorganic nitrogen input was strongest across the continental slope in the southern MAB, rather than when terrestrial inputs were greatest. Inter-annual variability of NCP appears to be linked to changes in the positions of the Gulf Stream and Slope Water Gyre. Overall, the strong spatio temporal variability of the nitrogen fluxes highlights the importance of observations throughout all seasons and multiple years in order to accurately resolve the current status and future changes of the MAB nitrogen budget.

Friedrichs, Marjorie A. M.↗

NASA NTRS2019

Direct Te Metallicity Calibration of R23 in Strong Line Emitters

The gas metallicity of galaxies is often estimated using strong emission lines such as the optical lines of [O iii] and [O ii]. The most common measure is "R23," defined as ([O ii]λλ3726, 3729 + [O iii]λλ4959,5007)/Hβ. Most calibrations for these strong-line metallicity indicators are for continuum selected galaxies. We report a new empirical calibration of R23 for extreme emission-line galaxies using a large sample of about 800 star-forming green pea galaxies with reliable Te -based gas-phase metallicity measurements. This sample is assembled from Sloan Digital Sky Survey (SDSS) Data Release 13 with the equivalent width of the line [O iii]λ5007 > 300 Å or the equivalent width of the line Hβ > 100 Å in the redshift range 0.011 < z < 0.411. For galaxies with strong emission lines and large ionization parameter (which manifests as log [O iii]λλ4959,5007/[O ii]λλ3726,3729 ≥0.6), R23 monotonically increases with log(O/H) and the double-value degeneracy is broken. Our calibration provides metallicity estimates that are accurate to within ~0.14 dex in this regime. Many previous R23 calibrations are found to have bias and large scatter for extreme emission-line galaxies. We give formulae and plots to directly convert R23 and [O iii]λλ4959,5007/[O ii]λλ3726,3729 to log(O/H). Since green peas are best nearby analogs of high-redshift Lyα emitting galaxies, the new calibration offers a good way to estimate the metallicities of both extreme emission-line galaxies and high-redshift Lyα emitting galaxies. We also report on 15 galaxies with metallicities less than 1/12 solar, with the lowest metallicities being 12+log(O/H) = 7.25 and 7.26.

Jiang, Tianxing↗

NASA NTRS2020

Strong Sensitivity of the Isotopic Composition of Methane to the Plausible Range of Tropospheric Chlorine

The C-13 isotopic ratio of methane, δC-13 of CH4, provides additional constraints on the CH4 budget to complement the constraints from CH4 observations. The interpretation of δC-13 observations is complicated, however, by uncertainties in the methane sink. The reaction of CH4 with Cl is highly fractionating, increasing the relative abundance of 13CH4, but there is currently no consensus on the strength of the tropospheric Cl sink. Global model simulations of halogen chemistry differ strongly from one another in terms of both the magnitude of tropospheric Cl and its geographic distribution. This study explores the impact of the inter-model diversity in Cl fields on the simulated δC-13 of CH4. We use a set of GEOS global model simulations with different predicted Cl fields to test the sensitivity of the δC-13 of CH4 to the diversity of Cl output from chemical transport models. We find that δC-13 is highly sensitive to both the amount and geographic distribution of Cl. Simulations with Cl providing 0.28% or 0.66% of the total CH4 loss bracket the δC-13 observations for a fixed set of emissions. Thus, even when Cl provides only a small fraction of the total CH4 loss and has a small impact on total CH4, it provides a strong lever on δC-13. Consequently, it is possible to achieve a good representation of total CH4 using widely different Cl concentrations, but the partitioning of CH4 loss between the OH and Cl reactions leads to strong differences in isotopic composition depending on which model’s Cl field is used. Comparing multiple simulations, we find that altering the tropospheric Cl field leads to approximately a 0.5‰ increase in δ(13)CH4for each percent increase in how much CH4 is oxidized by Cl. The geographic distribution and seasonal cycle of Cl also impacts the hemispheric gradient and seasonal cycle of δC-13. The large effect of Cl on δC-13 compared to total CH4 broadens the range of CH4 source mixtures that can be reconciled with δC-13 observations. Stronger constraints on tropospheric Cl are necessary to improve estimates of CH4 sources from δC-13 observations.

Global model simulations of halogen chemistry↗

NASA NTRS2022

Strong Gravity Waves Associated With Tonga Volcano Eruption Revealed by Saber Observations

Using the SABER temperature profiles from January 6 to 21 2022, we studied the mesospheric gravity waves (GWs) associated with the Tonga volcano eruption on January 15. We observed that the eruption induced strong GWs in the mesosphere. Detailed analysis shows that there were strong GWs with amplitudes greater than 30 K (twice the usual GWs) on January 15. These GWs have dominant vertical wavelengths of 13.9–25.5 km and horizontal speeds of 44–81 ms(exp −1), and they have intrinsic periods (momentum flux per unit mass) of ∼2–5 hr (4–320 m(exp 2)s(exp −2)). The strong but slow GWs observed here are opposite to the fast GWs observed at different atmospheric layers after the Tonga volcano eruption, and are stronger than the GWs associated with other volcanic eruption and extreme weather events. Such that one can get a more comprehensive picture on GWs excited by a powerful source.

Mesospheric temperature↗

NASA NTRS1971

Wave growth in a strongly turbulent plasma

An equation is derived for the average nonlinear growth (damping) rate of an electrostatic mode with wave vector k for an ensemble of electrostatically turbulent, unmagnetized plasmas. Strong turbulence alters particle orbits during the course of wave growth and hence brings particles in and out of resonance with the wave. The wave growth rate in a strongly turbulent plasma therefore depends on the initial velocity distribution of particles not only at the wave speed, but in the vicinity of this speed as well. Two orbital effects are considered: turbulence modification of ensemble average orbits and turbulence-produced orbital dispersion about the average orbits. Both contribute to a resonance broadening.

Birmingham, T. J.↗

NASA NTRS1971

Resonant diffusion in the presence of strong plasma turbulence

The diffusion equation which describes the evolution of the average one particle distribution function for an ensemble of strongly turbulent plasmas is derived. The diffusion tensor is a time integral of the autocorrelation tensor of the fluctuations as observed by particles moving along statistically distributed orbits. These orbits contain the effects of fluctuations and thus differ from those encountered in weak turbulence theory. The plasma trajectory equations are used to relate each to the diffusion tensor itself when the turbulence is electrostatic. The diffusion tensor is explicity evaluated for a strongly turbulent unmagnetized plasma.

Birmingham, T. J.↗

NASA NTRS1972

The turbulent boundary layer on a porous plate - Experimental heat transfer with uniform blowing and suction, with moderately strong acceleration.

Experimental data are presented for heat transfer to the turbulent boundary layer subjected to transpiration and acceleration at constant values of the acceleration parameter K of approximately .00000145. This is a moderately strong acceleration, but not so strong as to result in laminarization of the boundary layer. The results for transpiration fractions F of -0.002, 0.0, and +0.0058 are presented in detail in tabular form, and in graphs of Stanton number versus enthalpy thickness Reynolds number. In addition, temperature profiles at several stations are presented. Stanton number results for F = -0.004, +0.002, and +0.004 are also presented, but in graphical form only. The data were obtained using air as both the free-stream and the transpired fluid, at relatively low velocities, and with temperature differences sufficiently low so that the influence of temperature-dependent fluid properties is minimal. All data were obtained with the surface maintained at a temperature invariant in the direction of flow.

Thielbahr, W. H.↗

NASA NTRS1972

Strongly coupled stress waves in heterogeneous plates.

Consideration of coupled stress waves generated by an impulsive load applied at one end of a semiinfinite plate. For the field equations governing the one-dimensional coupled waves a hyperbolic system of equations is obtained in which a strong coupling in the second derivatives exists. The method of characteristics described by Chou and Mortimer (1967) is extended to cover the case of strong coupling, and a study is made of the transient stress waves in a semiinfinite plate subjected to an initial step input. Coupled discontinuity fronts are found to propagate at different velocities. The normal plate stress and the bending moment at different time regimes are illustrated by graphs.

Wang, A. S. D.↗

NASA NTRS1972

Resonant diffusion in the presence of strong plasma turbulence.

The diffusion equation which describes the evolution of the average one-particle distribution function for an ensemble of strongly turbulent plasmas is derived. The diffusion tensor is a time integral of the autocorrelation tensor of the fluctuations as observed by particles moving along statistically distributed orbits. These orbits contain the effects of fluctuations and thus differ from those encountered in weak turbulence theory. Two statistical orbit effects quadratic in the strength of the fluctuations affect the magnitude of the diffusion: (a) modification of the ensemble average orbits by the fluctuations, and (b) statistical dispersion in particle orbits about the average. The plasma trajectory equations are used to relate each to the diffusion tensor itself when the turbulence is electrostatic. The diffusion tensor is explicitly evaluated for a strongly turbulent unmagnetized plasma.

Birmingham, T. J.↗