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NASA NTRS2014

Dynamic Responses of the Earth's Outer Core to Assimilation of Observed Geomagnetic Secular Variation

Assimilation of surface geomagnetic observations and geodynamo models has advanced very quickly in recent years. However, compared to advanced data assimilation systems in meteorology, geomagnetic data assimilation (GDAS) is still in an early stage. Among many challenges ranging from data to models is the disparity between the short observation records and the long time scales of the core dynamics. To better utilize available observational information, we have made an effort in this study to directly assimilate the Gauss coefficients of both the core field and its secular variation (SV) obtained via global geomagnetic field modeling, aiming at understanding the dynamical responses of the core fluid to these additional observational constraints. Our studies show that the SV assimilation helps significantly to shorten the dynamo model spin-up process. The flow beneath the core-mantle boundary (CMB) responds significantly to the observed field and its SV. The strongest responses occur in the relatively small scale flow (of the degrees L is approx. 30 in spherical harmonic expansions). This part of the flow includes the axisymmetric toroidal flow (of order m = 0) and non-axisymmetric poloidal flow with m (is) greater than 5. These responses can be used to better understand the core flow and, in particular, to improve accuracies of predicting geomagnetic variability in future.

secular variation↗
NASA NTRS1995

Coronal structures deduced from photospheric magnetic field and He I lambda 10830 observations

The National Solar Observatory synoptic program provides an extensive and unique data base of high-resolution full-disk observations of the line-of-sight photospheric magnetic fields and of the He I lambda 10830 equivalent width. These data have been taken nearly daily for more than 21 years since 1974 and provide the opportunity to investigate the behavior of the magnetic fields in the photosphere and those inferred for the corona spanning on the time scales of a day to that of a solar cycle. The intensity of structures observed in He I lambda 10830 are strongly modulated by overlying coronal radiation; areas with low coronal emission are generally brighter in He I lambda 10830, while areas with high coronal emission are darker. For this reason, He I lambda 10830 was selected in the mid-1970's as way to identify and monitor coronal holes, magnetic fields with an open configuration, and the sources of high-speed solar wind streams. The He I lambda 10830 spectroheliograms also show a wide variety of other structures from small-scale, short-lived dark points (less than 30 arc-sec, hours) to the large-scale, long-lived two 'ribbon' flare events that follow the filament eruptions (1000 arc-sec, days). Such structures provide clues about the connections and changes in the large-scale coronal magnetic fields that are rooted in concentrations of magnetic network and active regions in the photosphere. In this paper, what observations of the photospheric magnetic field and He I lambda 10830 can tell us about the short- and long-term evolution of the coronal magnetic fields will be discussed, focussing on the quiet Sun and coronal holes. These data and what we infer from them will be compared with direct observations of the coronal structure from the Yohkoh Soft X-ray Telescope.

Harvey, Karen L.↗
NASA NTRS2001

A Geosynchronous Lidar System for Atmospheric Winds and Moisture Measurements

An observing system comprised of two lidars in geosychronous orbit would enable the synoptic and meso-scale measurement of atmospheric winds and moisture both of which are key first-order variables of the Earth's weather equation. Simultaneous measurement of these parameters at fast revisit rates promises large advancements in our weather prediction skills. Such capabilities would be unprecedented and a) yield greatly improved and finer resolution initial conditions for models, b) make existing costly and cumbersome measurement approaches obsolete, and c) obviate the use of numerical techniques needed to correct data obtained using present observing systems. Additionally, simultaneous synoptic wind and moisture observations would lead to improvements in model parameterizations, and in our knowledge of small-scale weather processes. Technology and science data product assessments are ongoing. Results will be presented during the conference.

Emmitt, G. D.↗
NASA NTRS1974

New space technology advances knowledge of the remote polar regions

The application of ERTS-1 imagery is rapidly increasing man's knowledge of polar regions. Products compiled from this imagery at scales of 1:250,000, 1:500,000 and 1:1,000,000 are already providing valuable information to earth scientists working in Antarctica. Significant finds detected by these bench mark products were glaciological changes, advancement in ice fronts, discovery of new geographic features, and the repositioning of nunataks, islands, and ice tongues. Tests conducted in Antarctica have proven the feasibility of tracking Navy navigation satellites to establish ground control for positioning ERTS-1 imagery in remote areas. ERTS imagery coupled with satellite geodesy shows great promise and may prove to be the most practical and cost effective way to meet the small-scale cartographic requirements of the polar science community.

Macdonald, W. R.↗
NASA NTRS1989

The formation of topological defects in phase transitions

It was argued, and fought through numerical work that the results of non-dynamical Monte Carlo computer simulations cannot be applied to describe the formation of topological defects when the correlation length at the Ginzburg temperature is significantly smaller than the horizon size. To test the current hypothesis that infinite strings at formation are essentially described by Brownian walks of size the correlation length at the Ginzburg temperature, fields at the Ginzburg temperature were equilibrated. Infinite structure do not exist in equilibrium for reasonable definitions of the Ginzburg temperature, and horizons must be included in a proper treatment. A phase transition, from small-scale to large-scale string or domain wall structure, is found to occur very close to the Ginzburg temperature, in agreement with recent work. The formation process of domain walls and global strings were investigated through the breaking of initially ordered states. To mimic conditions in the early Universe, cooling times are chosen so that horizons exist in the sample volume when topological structure formation occurs. The classical fields are evolved in real-time by the numerical solution of Langevin equations of motion on a three dimensional spatial lattice. The results indicate that it is possible for most of the string energy to be in small loops, rather than in long strings, at formation.

Hodges, Hardy M.↗
NASA NTRS1990

Results of aerodynamic testing of large-scale wing sections in a simulated natural rain environment

The NASA Langley Research Center has developed a large-scale ground testing capability for evaluating the effect of heavy rain on airfoil lift. The paper presents the results obtained at the Langley Aircraft Landing Dynamics Facility on a 10-foot cord NACA 64-210 wing section equipped with a leading-edge slat and double-slotted trailing-edge flap deflected to simulate landing conditions. Aerodynamic lift data were obtained with and without the rain simulation system turned on for an angle-of-attack range of 7.5 to 19.5 deg and for two rainfall conditions: 9 in/hr and 40 in/hr. The results are compared to and correlated with previous small-scale wind tunnel results for the same airfoil section. It appears that to first order, scale effects are not large and the wind tunnel research technique can be used to predict rain effects on airplane performance.

Bezos, Gaudy M.↗
NASA NTRS2017

NIAC Phase 1 Final Study Report on Titan Aerial Daughtercraft

Saturns giant moon Titan has become one of the most fascinating bodies in the Solar System. Even though it is a billion miles from Earth, data from the Cassini mission reveals that Titan has a very diverse, Earth-like surface, with mountains, fluvial channels, lakes, evaporite basins, plains, dunes, and seas [Lopes 2010] (Figure 1). But unlike Earth, Titans surface likely is composed of organic chemistry products derived from complex atmospheric photochemistry [Lorenz 2008]. In addition, Titan has an active meteorological system with observed storms and precipitation-induced surface darkening suggesting a hydrocarbon cycle analogous to Earths water cycle [Turtle 2011].Titan is the richest laboratory in the solar system for studying prebiotic chemistry, which makes studying its chemistry from the surface and in the atmosphere one of the most important objectives in planetary science [Decadal 2011]. The diversity of surface features on Titan related to organic solids and liquids makes long-range mobility with surface access important [Decadal 2011]. This has not been possible to date, because mission concepts have had either no mobility (landers), no surface access (balloons and airplanes), or low maturity, high risk, and/or high development costs for this environment (e,g. large, self-sufficient, long-duration helicopters). Enabling in situ mobility could revolutionize Titan exploration, similarly to the way rovers revolutionized Mars exploration. Recent progress on several fronts has suggested that small-scale rotorcraft deployed as daughtercraft from a lander or balloon mothercraft may be an effective, affordable approach to expanding Titan surface access. This includes rapid progress on autonomous navigation capabilities of such aircraft for terrestrial applications and on miniaturization, driven by the consumer mobile electronics market, of high performance of sensors, processors, and other avionics components needed for such aircraft. Chemical analysis, for example with a mass spectrometer, will be important to any Titan surface mission. Anticipating that it may be more practical to host chemical analysis instruments on a mothership than a daughtercraft, we defined system and mission concepts that deploy a small rotorcraft, termed a Titan Aerial Daughtercraft (TAD), from a lander or balloon to perform high-resolution imaging and mapping, potentially land to acquire microscopic images or other in situ measurements, and acquire samples to return to analytical instruments on the mothership. In principle, the ability to recharge batteries in TAD from a radioisotope or other long-lived power source on the mothership could enable multiple sorties. For a lander-based mission, a variety of landing sites is conceivable, including near lake margins, in dry lake beds, or in regions of plains, dunes, or putative cryovolanic or impact melt features. Such missions may require landing with greater precision than in previous missions (Huygens) and mission studies; this could also enhance the ability of TAD to reach interesting terrain from the landing site. Precision descent may also benefit balloon missions, with or without a daughtercraft, by increasing the probability that the balloon will drift over desired terrain early in its mission. Given these potential benefits, the overall concept studied here includes brief consideration of precision descent for landing or balloon deployment, followed by one or more sorties by a rotorcraft deployed from the mothership, with the ability to return to the mothership.

Saturn↗
NASA NTRS2006

The Dryline on 22 May 2002 during IHOP_2002: Convective-Scale Measurements at the Profiling Site

A detailed analysis of the structure of a double dryline observed over the Oklahoma panhandle during the first International H2O Project (IHOP_2002) convective initiation (CI) mission on 22 May 2002 is presented. A unique and unprecedented set of high temporal and spatial resolution measurements of water vapor mixing ratio, wind, and boundary layer structure parameters were acquired using the National Aeronautics and Space Administration (NASA) scanning Raman lidar (SRL), the Goddard Lidar Observatory for Winds (GLOW), and the Holographic Airborne Rotating Lidar Instrument Experiment (HARLIE), respectively. These measurements are combined with the vertical velocity measurements derived from the National Center for Atmospheric Research (NCAR) Multiple Antenna Profiler Radar (MAPR) and radar structure function from the high-resolution University of Massachusetts frequency-modulated continuous-wave (FMCW) radar to reveal the evolution and structure of the late afternoon double-dryline boundary layer. The eastern dryline advanced and then retreated over the Homestead profiling site in the Oklahoma panhandle, providing conditions ripe for a detailed observation of the small-scale variability within the boundary layer and the dryline. In situ aircraft data, dropsonde and radiosonde data, along with NCAR S-band dual-polarization Doppler radar (S-Pol) measurements, are also used to provide the larger-scale picture of the double-dryline environment. Moisture and temperature jumps of about 3 g kg(sup -1) and 1 -2 K, respectively, were observed across the eastern radar fine line (dryline), more than the moisture jumps (1-2 g kg(sup -1)) observed across the western radar fine line (secondary dryline). Most updraft plumes observed were located on the moist side of the eastern dryline with vertical velocities exceeding 3 m s(sup -1) and variable horizontal widths of 2-5 km, although some were as wide as 7-8 km. These updrafts were up to 1.5 g kg(sup -1) moister than the surrounding environment. Although models suggested deep convection over the Oklahoma panhandle and several cloud lines were observed near the dryline, the dryline itself did not initiate any storms over the intensive observation region (IOR). Possible reasons for this lack of convection are discussed. Strong capping inversion and moisture detrainment between the lifting condensation level and the level of free convection related to an overriding drier air, together with the relatively small near-surface moisture values (less than 10 g kg(sup -1)), were detrimental to CI in this case.

Demoz, Belay↗
NASA NTRS2008

NaK Plugging Meter Design for the Feasibility Test Loops

The design and predicted performance of a plugging meter for use in the measurement of NaK impurity levels are presented. The plugging meter is incorporated into a Feasibility Test Loop (FTL), which is a small pumped-NaK loop designed to enable the rapid, small-scale evaluation of techniques such as in situ purification methods and to permit the measurement of bulk material transport effects (not mechanisms) under flow conditions that are representative of a fission surface power reactor. The FTL operates at temperatures similar to those found in a reactor, with a maximum hot side temperature of 900 K and a corresponding cold side temperature of 860 K. In the plugging meter a low flow rate bypass loop is cooled until various impurities (primarily oxides) precipitate out of solution. The temperatures at which these impurities precipitate are indicative of the level of impurities in the NaK. The precipitates incrementally plug a small orifice in the bypass loop, which is detected by monitoring changes in the liquid metal flow rate.

Pearson, J. Boise↗
NASA NTRS1986

Turbulence in HII regions

It has been known for many decades that the Reynolds number in HII regions must be very high and that the corresponding fine scale flow must be turbulent. Even though the theoretical relation between turbulent element separation and random velocity was derived by Kolmogoroff over forty years ago, there have been only a few attempts to test this theory and its corresponding assumptions. An attempt by Munch for M42 with marginal velocity resolution lead to ambiguous results, although more recent studies by Jean Rene Roy and his colleagues have been more credible. The internal velocities of a number of HII regions were systematically studied and the theory was tested with considerable certainty. The results should be important for the determination of the energy balance of HII regions and the relation of small scale motion to the process of star formation.

Odell, C. R.↗
NASA NTRS2011

Surface Instability of Liquid Propellant under Vertical Oscillatory Forcing

Fluid motion in a fuel tank produced during thrust oscillations can circulate sub-cooled hydrogen near the liquid-vapor interface resulting in increased condensation and ullage pressure collapse. The first objective of this study is to validate the capabilities of a Computational Fluid Dynamics (CFD) tool, CFD-ACE+, in modeling the fundamental interface transition physics occurring at the propellant surface. The second objective is to use the tool to assess the effects of thrust oscillations on surface dynamics. Our technical approach is to first verify the CFD code against known theoretical solutions, and then validate against existing experiments for small scale tanks and a range of transition regimes. A 2D axisymmetric, multi-phase model of gases, liquids, and solids is used to verify that CFD-ACE+ is capable of modeling fluid-structure interaction and system resonance in a typical thrust oscillation environment. Then, the 3D mode is studied with an assumed oscillatory body force to simulate the thrust oscillating effect. The study showed that CFD modeling can capture all of the transition physics from solid body motion to standing surface wave and to droplet ejection from liquid-gas interface. Unlike the analytical solutions established during the 1960 s, CFD modeling is not limited to the small amplitude regime. It can extend solutions to the nonlinear regime to determine the amplitude of surface waves after the onset of instability. The present simulation also demonstrated consistent trends from numerical experiments through variation of physical properties from low viscous fluid to high viscous fluids, and through variation of geometry and input forcing functions. A comparison of surface wave patterns under various forcing frequencies and amplitudes showed good agreement with experimental observations. It is concluded that thrust oscillations can cause droplet formation at the interface, which results in increased surface area and enhanced heat transfer between the liquid and gas phases as the ejected droplets travel well into the warmer gas region.

Yang, H. Q.↗
NASA NTRS1991

Jet noise generated by large-scale coherent motion

The noise generated by large scale turbulence structures and instability waves of jets is discussed. Emphasis is placed on supersonic jets with moderate to high Reynolds numbers. This is because it is in these jets that unambiguous experimental and theoretical evidence is found indicating that large turbulence structures and instability waves are directly responsible for generating the dominant part of the noise. For subsonic jets similar large turbulence structures and instability waves do play a crucial role in the dynamics, spread, and mixing of the jet fluid. However, at subsonic convection speeds, they do not appear to be efficient noise generators. Many investigators believe that the dominant noise source of subsonic jets is, in fact, the small scale turbulence. As yet, this belief has not yet received universal acceptance. The issues involved are complicated and are not easy to resolve.

Tam, Christopher K. W.↗
NASA NTRS1993

New perspectives for high accuracy SLR with second generation geodesic satellites

This paper reports on the accuracy limitations imposed by geodesic satellite signatures, and on the potential for achieving millimetric performances by means of alternative satellite concepts and an optimized 2-color system tradeoff. Long distance laser ranging, when performed between a ground (emitter/receiver) station and a distant geodesic satellite, is now reputed to enable short arc trajectory determinations to be achieved with an accuracy of 1 to 2 centimeters. This state-of-the-art accuracy is limited principally by the uncertainties inherent to single-color atmospheric path length correction. Motivated by the study of phenomena such as postglacial rebound, and the detailed analysis of small-scale volcanic and strain deformations, the drive towards millimetric accuracies will inevitably be felt. With the advent of short pulse (less than 50 ps) dual wavelength ranging, combined with adequate detection equipment (such as a fast-scanning streak camera or ultra-fast solid-state detectors) the atmospheric uncertainty could potentially be reduced to the level of a few millimeters, thus, exposing other less significant error contributions, of which by far the most significant will then be the morphology of the retroreflector satellites themselves. Existing geodesic satellites are simply dense spheres, several 10's of cm in diameter, encrusted with a large number (426 in the case of LAGEOS) of small cube-corner reflectors. A single incident pulse, thus, results in a significant number of randomly phased, quasi-simultaneous return pulses. These combine coherently at the receiver to produce a convolved interference waveform which cannot, on a shot to shot basis, be accurately and unambiguously correlated to the satellite center of mass. This paper proposes alternative geodesic satellite concepts, based on the use of a very small number of cube-corner retroreflectors, in which the above difficulties are eliminated while ensuring, for a given emitted pulse, the return of a single clean pulse with an adequate cross-section.

Lund, Glenn↗
NASA NTRS1994

Toward Real Time Neural Net Flight Controllers

NASA Ames Research Center has an ongoing program in neural network control technology targeted toward real time flight demonstrations using a modified F-15 which permits direct inner loop control of actuators, rapid switching between alternative control designs, and substitutable processors. An important part of this program is the ACTIVE flight project which is examining the feasibility of using neural networks in the design, control, and system identification of new aircraft prototypes. This paper discusses two research applications initiated with this objective in mind: utilization of neural networks for wind tunnel aircraft model identification and rapid learning algorithms for on line reconfiguration and control. The first application involves the identification of aerodynamic flight characteristics from analysis of wind tunnel test data. This identification is important in the early stages of aircraft design because complete specification of control architecture's may not be possible even though concept models at varying scales are available for aerodynamic wind tunnel testing. Testing of this type is often a long and expensive process involving measurement of aircraft lift, drag, and moment of inertia at varying angles of attack and control surface configurations. This information in turn can be used in the design of the flight control systems by applying the derived lookup tables to generate piece wise linearized controllers. Thus, reduced costs in tunnel test times and the rapid transfer of wind tunnel insights into prototype controllers becomes an important factor in more efficient generation and testing of new flight systems. NASA Ames Research Center is successfully applying modular neural networks as one way of anticipating small scale aircraft model performances prior to testing, thus reducing the number of in tunnel test hours and potentially, the number of intermediate scaled models required for estimation of surface flow effects.

Jorgensen, C. C.↗
NASA NTRS2003

Evidence for Filamentary Jet Structure: The Light Curve of GRB 011211

We report on the discovery of the optical afterglow of the X-ray rich, long-duration gamma-ray burst GRB 011211, and the oscillatory behavior present in its optical and X-ray afterglow light curve. The time scale of the fluctuations, -1 hour, is much smaller than the time of the observations, -12 hours from the onset of the gamma-ray burst. The character and strength of the fluctuations visible in the optical data are unprecedented, and are inconsistent with causally connected variations in the emission of a symmetric, relativistic blast wave. Moreover, the differential time lag between the short-term variations in X-ray and optical energies suggests they do not arise from the same emitting region. Such variability may imply that local spherical symmetry is broken because the energy content across the jet-emitting surface is not uniform, indicating the detection of a small scale substructure within the jet itself.

Jakobsson, P.↗
NASA NTRS1997

Candle Flames in Microgravity

This work is a study of a candle flame in a microgravity environment. The purpose of the work is to determine if a steady (or quasi-steady) flame can exist in a microgravity environment, study the characteristics of the steady flame, investigate the pre-extinction flame oscillations observed in a previous experiment in more detail, and finally, determine the nature of the interactions between two closely spaced candle flames. The candle flame is used as a model combustion system, in that in microgravity it is one of the only examples of a non-propagating, steady-state, pure diffusion flame. Others have used the candle to study a number of combustion phenomena including flame flicker, flame oscillations, electric field effects and enhanced and reduced gravitational effects in flames. The present work is a continuation of a small-scale Shuttle experiment on candle flames. That study showed that the candle flame lifetimes were on the order of 40 seconds, the flames were dim blue after a transient ignition period, and that just prior to extinction the flames oscillated spontaneously for about five seconds at a frequency of 1 Hz. The authors postulated that the gas phase in the immediate vicinity of the flame was quasi-steady. Further away from the flame, however, the assertion of a quasi-steady flame was less certain, thus the authors did not prove that a steady flame could exist. They also speculated that the short lifetime of the candle flame was due to the presence of the small, weakly perforated box that surrounded the candle. The Candle Flames in Microgravity (CFM) experiment, with revised hardware, was recently flown aboard the Mir orbiting station, and conducted inside the glovebox facility by Dr. Shannon Lucid. In addition to the purposes described above, the experiments were NASA's first ability to ascertain the merits of the Mir environment for combustion science studies. In this article, we present the results of that experiment. We are also in the process of developing a numerical model of the microgravity candle flame. The status and results of the modeling efforts to date are also presented.

Dietrich, Daniel L.↗
NASA NTRS1990

Mesoscale variability of free tropospheric humidity near San Nicolas Island during FIRE

Humidity variability at the top of the marine boundary layer (MBL) and in the free troposphere was examined using a variety of measurements taken on and around San Nicolas Island (SNI) during the FIRE IFO in July, 1987. Doppler wind profiler reflectivity recorded at two minute time resolution has provided the most continuous record and detail of small scale humidity fluctuations. Rawinsonde data were available from both an island site and the research vessel Point Sur. The information extractable from these sources is somewhat limited due to the frequency of launches (3 to 4/day at SNI and 6/day on the Point Sur). Some additional data were available from instrumented aircraft although scheduling flights in the neighborhood of the island was difficult due to restrictions on the air space. Other relevant data were collected at SNI near the radar and rawinsonde launch sites. A continuous record of cloud base altitude was logged by a ceilometer. Doppler acoustic sounder (sodar) reflectivity data provided a good record of inversion height. The sodar also monitored turbulent temperature fluctuations in the MBL. A small ground station recorded hourly averages of solar irradiance and downward longwave irradiance. The analysis in progress of the various data sets for two adjacent two day periods from 11 July to 14 July is described. The earlier period was chosen because the marine inversion was unusually high and there was increased frequency of rawinsonde launches at SNI. The later period was chosen because of the significant descent with time of an elevated inversion indicated by the radar data. Throughout the four day period, but especially in the first half, the turbulent humidity structure calculated from Doppler radar reflectivity shows excellent agreement with humidity profiles evaluated from rawinsonde data.

White, A. B.↗
NASA NTRS1992

The gravitational wave contribution to cosmic microwave background anisotropies and the amplitude of mass fluctuations from COBE results

A stochastic background of primordial gravitational waves may substantially contribute, via the Sachs-Wolfe effect, to the large-scale cosmic microwave background (CMB) anisotropies recently detected by COBE. This implies a bias in any resulting determination of the primordial amplitude of density fluctuations. We consider the constraints imposed on n is less than 1 ('tilted') power-law fluctuation spectra, taking into account the contribution from both scalar and tensor waves, as predicted by power-law inflation. The gravitational wave contribution to CMB anisotropies generally reduces the required rms level of mass fluctuation, thereby increasing the linear bias parameter, even in models where the spectral index is close to the Harrison-Zel'dovich value n = 1. This 'gravitational wave bias' helps to reconcile the predictions of CDM models with observations on pairwise galaxy velocity dispersion on small scales.

Lucchin, Francesco↗