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NASA NTRS1978

Directional models for analysis of earth radiation budget measurements

The determination of the radiation heat flux densities at the top of the atmosphere (30 km) for spatial scales ranging from global to regional is necessary for the conversion of satellite irradiance measurements into useful earth radiation budget information. Data reduction algorithms are required which contain assumed directional characteristics of radiation emitted and scattered from the earth-atmosphere system. The directional characteristics are defined by models which express, for a given surface element at the top of the atmosphere, the exiting flux per unit solid angle for each direction out to space as a fraction of the total hemispheric flux exiting the surface element. Both longwave and shortwave directional radiation models are analyzed. It is found that the validity of the Nimbus 2-based limb darkening curves has generally been verified for the longwave data with the exception of the Antarctic snow fields where limb brightening was noticed in the earth radiation budget data.

Suttles, J. T.↗
NASA NTRS1991

Variation of superheat with subcooling in nucleate pool boiling

An analysis is presented that explains the variation of superheat with subcooling that has been observed by a number of researchers investigating nucleate boiling heat transfer at constant heat flux. It is shown that superheat initially increases with increasing subcooling near saturated conditions because of the way in which changes in active site density and average bubble frequency with increasing subcooling affect the rate of heat removal from the heater surface by enthalpy transport and microlayer evaporation. As subcooling increases further, natural convection begins to play an increasingly important role in the heat transfer process. Ultimately, natural convection is able to accommodate the entire imposed heat flux, after which superheat decreases as subcooling increases. The success of the analysis in explaining the variation of superheat with subcooling suggests that the rate of the heat removal from the heater surface is completely determined by the mechanisms of enthalpy transport, natural convection, and microlayer evaporation.

Judd, R. L.↗
NASA NTRS1992

Resonant behaviour of MHD waves on magnetic flux tubes. III - Effect of equilibrium flow

The Hollweg et al. (1990) analysis of MHD surface waves in a stationary equilibrium is extended. The conservation laws and jump conditions at Alfven and slow resonance points obtained by Sakurai et al. (1990) are generalized to include an equilibrium flow, and the assumption that the Eulerian perturbation of total pressure is constant is recovered as the special case of the conservation law for an equilibrium with straight magnetic field lines and flow along the magnetic field lines. It is shown that the conclusions formulated by Hollweg et al. are still valid for the straight cylindrical case. The effect of curvature is examined.

Goossens, Marcel↗
NASA NTRS1986

Discovery of rapid quasi-periodic oscillations in Scorpius X-1

The X-ray flux from Sco X-1 can vary quasi-periodically. Fourier analysis of 5-20 keV X-ray data taken while the source was quiescent shows a power density peak at 6 Hz, with a 2 Hz FWHM, and which corresponds to 5 percent of the flux (rms amplitude). No 6 Hz peak was observed when the source was more active, but rather a broad distribution of excess power up to 25 Hz was seen. The mode of variability switched from one to the other within 500 s, settling into the 6 Hz mode about 1 hr into quiescence. A different mode of quasi-periodic oscillation with power in a broad band between 14 and 24 Hz, corresponding to a 6 percent rms amplitude, occurred for short periods during the active phase whenever the flux reached the quiescent level.

Middleditch, J.↗
NASA NTRS1995

Magnetic flux rope versus the spheromak as models for interplanetary magnetic clouds

Magnetic clouds form a subset of interplanetary ejecta with well-defined magnetic and thermodynamic properties. Observationally, it is well established that magnetic clouds expand as they propagate antisunward. The aim of this paper is to compare and contrast two models which have been proposed for the global magnetic field line topology of magnetic clouds: a magnetic flux tube geometry, on the one hand, and a spheromak geometry (including possible higher multiples), on the other. Traditionally, the magnetic structure of magnetic clouds has been modeled by force-free configurations. In a first step, we therefore analyze the ability of static force-free models to account for the asymmetries observed in the magnetic field profiles of magnetic clouds. For a cylindrical flux tube the magnetic field remains symmetric about closest approach to the magnetic axis on all spacecraft orbits intersecting it, whereas in a spheromak geometry one can have asymmetries in the magnetic field signatures along some spacecraft trajectories. The duration of typical magnetic cloud encounters at 1 AU (1 to 2 days) is comparable to their travel time from the Sun to 1 AU and thus magnetic clouds should be treated as strongly nonstationary objects. In a second step, therefore, we abandon the static approach and model magnetic clouds as self-similarly evolving MHD configurations. In our theory, the interaction of the expanding magnetic cloud with the ambient plasma is taken into account by a drag force proportional to the density and the velocity of expansion. Solving rigorously the full set of MHD equations, we demonstrate that the asymmetry in the magnetic signature may arise solely as a result of expansion. Using asymptotic solutions of the MHD equations, we least squares fit both theoretical models to interplanetary data. We find that while the central part of the magnetic cloud is adequately described by both models, the 'edges' of the cloud data are modeled better by the magnetic flux tube. Further comparisons of the two models necessarily involve thermodynamic properties, since real magnetic configurations are never exactly force-free and gas pressure plays an essential role. We consider a polytropic gas. Our theoretical analysis shows that the self-similar expansion of a magnetic flux tube requires the polytropic index gamma to be less than unity. For the spheromak, however, self-similar, radially expanding solutions are known only for gamma equal to 4/3. This difference, therefore, yields a good way of distinguishing between the two geometries. It has been shown recently that the polytropic relationship is applicable to magnetic clouds and that the corresponding polytropic index is approximately 0.5. This observational result is consistent with the self-similar model of the magnetic flux rope but is in conflict with the self-similar spheromak model.

Farrugia, C. J.↗
NASA NTRS2019

Annual Cycle of Planetary Boundary Layer Heights estimated from NOAA Profiler Network Data

The Planetary Boundary Layer (PBL) height over the Unites States Great and Central Plains during 1992-2012 is examined here using a combination of Wind Profiler-derived (WP) PBL height estimates and reanalysis fields from the Modern Era Retrospective Reanalysis Version 2 (MERRA-2). The combined analysis allows process study of the reasons behind the monthly mean behavior of the observed PBL heights under clear-sky conditions as well as the PBL height variability. WP PBL height monthly mean annual cycles were grouped into general categories of behavior, each analyzed using MERRA-2 fields of sensible and latent heat flux, surface temperature, net radiation and soil moisture. In the ’canonical’ category the latent heat plays little role in the determination of the monthly mean PBL height, and it follows the annual cycle of the net radiation. In the other categories, precipitation and latent heat flux had more influence in setting the annual cycle. An analysis of variance revealed that the role of latent heat in determining the PBL height variations is large (explaining up to 40% of PBL height variability) even in the ’canonical’ category for which latent heat played no role in setting the monthly mean. In other categories the latent heat explained up to 80% of the PBL height variations. The amount of that influence is shown to be related to the variability of column soil moisture.

MERRA-2↗
NASA NTRS1992

Global aspects of the Los Alamos general circulation model hydrologic cycle

The global hydrologic cycle in the Los Alamos general circulation model (GCM) is compared to available global observations. Global observations of the water vapor, water-vapor flux and water-vapor flux divergence are derived from the National Meteorological Center's final analysis for the period 1986-1989. The new precipitation data set of Legates and Willmott (1990) is used for the global precipitation observations. Global evaporation is derived as a residual of the precipitation and water-vapor flux divergence. There are a number of similarities as well as discrepancies between the GCM and observations. The large-scale nondivergent and divergent GCM circulations are remarkably similar to the observed circulations; the large-scale GCM precipitation and evaporation patterns are also qualitatively similar to observations. Discrepancies are mainly quantitative and small-scale in nature: the GCM atmosphere is relatively dry which results in a slightly greater evaporation and precipitation rate than is observed; the GCM South Pacific convergence zone is displaced too far to the northwest.

Roads, J. O.↗
NASA NTRS2010

Role of the Russell-McPherron Effect in the Acceleration of Relativistic Electrons

While it is well known that high fluxes of relativistic electrons in the Earth's radiation belts are associated with high-speed solar wind and its heightened geoeffectiveness,less known is the fact that the Russell McPherron(R M) effect strongly controls whether or not a given high-speed stream is geoffective. To test whether it then follows that the R M effect also strongly controls fluxes of relativistic electrons, we perform a superposed epoch analysis across corotating interaction regions (CIR) keyed on the interfaces between slow and fast wind. A total of 394 stream interfaces were identified in the years 1994-2006. Equinoctial interfaces were separated into four classes based on the R-M effect,that is, whether the solar wind on either side of the interface was either(geo)effective (E) or ineffective (I) depending on season and the polarity of the interplanetary magnetic field (IMF). Four classes of interface identified as II, IE, EI,and EE are possible. The classes IE and EI correspond to CIRs with polarity changes indicating passage through the heliospheric current sheet. To characterize the behavior of solar wind and magnetospheric variables, we produced maps of dynamic cumulative probability distribution functions (cdfs) as a function of time over 10-day intervals centered on the interfaces. These reveal that effective high-speed streams have geomagnetic activity nearly twice as strong as ineffective streams and electron fluxes a factor of 12 higher. In addition they show that an effective low-speed stream increases the flux of relativistic electrons before the interface so that an effective to ineffective transition results in lower fluxes after the interface.We conclude that the R-M effect plays a major role in organizing and sustaining a sequence of physical processes responsible for the acceleration of relativistic electrons.

McPherron, R. L.↗
NASA NTRS1982

Energetic interplanetary nucleon flux anisotropies - The effect of earth's bow shock and magnetosheath on sunward flow

Attention is given to the combined, average effects of the bow shock and magnetosheath on the diffusive flow of interplanetary nuclei. The observations presented show that differences between 'connected' and 'unconnected' data subsets are apparent from the beginning of the analysis. Through an investigation of the mean unconnected diffusive anisotropy (those fluxes least affected by the earth's bow shock and magnetosheath) it is confirmed that the cross-field transport of MeV energy nuclei in interplanetary space is statistically significant and in the direction expected from the large-scale particle flux gradients. The direction of particle flow relative to the IMF is then used to show that nucleon flow characteristics on connected IMF differ from those on unconnected IMF. A scenario for producing this difference is then presented. It is concluded that the inclusion of the bow shock connected information biases measurements of the flux anisotropies of MeV energy H.

Christon, S. P.↗
NASA NTRS2016

Temperature-Staged Thermal Energy Storage Enabling Low Thermal Exergy Loss Reflux Boiling in Full Spectrum Solar Systems

Hybrid full spectrum solar systems (FSSS) designed to capture and convert the full solar wavelength spectrum use hybrid solar photovoltaic/thermodynamic cycles that require low thermal exergy loss systems capable of transferring high thermal energy rates and fluxes with very low temperature differentials and losses. One approach to achieving this capability are high-heat-flux reflux boiling systems that take advantage of high heat transfer boiling and condensation mechanisms. Advanced solar systems are also intermittent by their nature and their electrical generation is often out-of-phase with electric utility power demand, and their required power system cycling reduces efficiency, performance (dispatch ability), lifetime, and reliability. High temperature thermal energy storage (TES) at 300-600°C enables these reflux boiling systems to simultaneously store thermal energy internally to increase the energy dispatch ability of the associated solar system, as this can increase the power generation profile by several hours (up to 6-10 hours) per day. Many TES phase change materials (PCM’s) exist including KNO3, NaNO3, LiBr/KBr, MgCl2/NaCl/KCl, Zn/Mg, and CuCl/NaCl, which have various operating melting points and different latent heats of fusion. Common, cost effective TES PCM's are FeCl2/NaCl/KCl mixtures, whose phase change temperature can be varied and controlled by simple composition adjustments. This paper presents and discusses unique "temperature-staged" thermal energy storage configurations using these TES materials and analysis of such systems integrated into high-heat-flux reflux boiling systems. In this specific application, the TES materials are designed to operate at staged temperatures surrounding an operating design point near 350°C, while providing 18 kW of source heat transfer to operate a thermoacoustic power system during off-sun conditions (e.g., temporary cloud conditions, after sun-down). This work discusses relevant configurations, and critical thermal and entropy models of the TES configurations, which show the inherent minimization of thermal exergy during critical heat transfers within the configurations and systems envisioned.

Hendricks, Terry J.↗
NASA NTRS1979

Observations of the diffuse interstellar EUV radiation field

Results are reported for observations and a preliminary theoretical analysis of the diffuse interstellar EUV radiation field exhibiting positive measurable fluxes in the wavelength range from 912 to 1150 A. The observations were made with the UV spectrometers on the two Voyager spacecraft, and a spectral half-width of 30 A was obtained. The procedures used in the analysis are described in detail, particularly those relating to the elimination of thermal and cosmic-ray noise, internal instrumental scattering from bright lines, and possible contributions from direct starlight. Measurements in several directions reveal diffuse intensities at 975 A ranging from a maximum of about 10 to the -7th erg/sq cm per (sec sr A) near the galactic plane to an upper limit of 10 to the -8th erg/sq cm per (sec sr A). A comparison of the present measurements with various theoretical predictions and previous measurements indicates reasonable agreement with some theoretical predictions of the interstellar EUV intensity.

Sandel, B. R.↗
NASA NTRS1973

An estimate of particle flux from Pioneer 8 and 9 part 2

Five years of particle impact data obtained from Pioneer 8 and 9 have established reliable frequency levels for the near ecliptic region covered. This analysis is concerned with obtaining a multiplier which permits an estimate of the particle flux through a 1-A.U. sphere centered at the sun.

Wolf, H.↗
NASA NTRS1991

Analysis of radiative and phase-change phenomena with application to space-based thermal energy storage

The simplified geometry for the analysis is an infinite, axis symmetric annulus with a specified solar flux at the outer radius. The inner radius is either adiabatic (modeling Flight Experiment conditions), or convective (modeling Solar Dynamic conditions). Liquid LiF either contacts the outer wall (modeling ground based testing), or faces a void gap at the outer wall (modeling possible space based conditions). The analysis is presented in three parts: Part 3 considers and adiabatic inner wall and linearized radiation equations; part 2 adds effects of convection at the inner wall; and part 1 includes the effect of the void gap, as well as previous effects, and develops the radiation model further. The main results are the differences in melting behavior which can occur between ground based 1 g experiments and the microgravity flight experiments. Under 1 gravity, melted PCM will always contact the outer wall having the heat flux source, thus providing conductance from this source to the phase change front. In space based tests where a void gap may likely form during solidification, the situation is reversed; radiation is now the only mode of heat transfer and the majority of melting takes place from the inner wall.

Lund, Kurt O.↗
NASA NTRS2023

Using Orbiting Carbon Observatory-2 (OCO-2) column CO2 retrievals to rapidly detect and estimate biospheric surface carbon flux anomalies

The global carbon cycle is experiencing continued perturbations via increases in atmospheric carbon concentrations, which are partly reduced by terrestrial biosphere and ocean carbon uptake. Greenhouse gas satellites have been shown to be useful in retrieving atmospheric carbon concentrations and observing surface and atmospheric CO2 seasonal-to-interannual variations. However, limited attention has been placed on using satellite column CO2 retrievals to evaluate surface CO2 fluxes from the terrestrial biosphere without advanced inversion models at low latency. Such applications could be useful to monitor, in near real time, biosphere carbon fluxes during climatic anomalies like drought, heatwaves, and floods, before more complex terrestrial biosphere model outputs and/or advanced inversion modelling estimates become available. Here, we explore the ability of Orbiting Carbon Observatory-2 (OCO-2) column-averaged dry air CO2 (XCO2) retrievals to directly detect and estimate terrestrial biosphere CO2 flux anomalies using a simple mass-balance approach. An initial global analysis of surface–atmospheric CO2 coupling and transport conditions reveals that the western US, among a handful of other regions, is a feasible candidate for using XCO2 for detecting terrestrial biosphere CO2 flux anomalies. Using the CarbonTracker model reanalysis as a test bed, we first demonstrate that a well-established mass-balance approach can estimate monthly surface CO2 flux anomalies from XCO2 enhancements in the western United States. The method is optimal when the study domain is spatially extensive enough to account for atmospheric mixing and has favorable advection conditions with contributions primarily from one background region. We find that errors in individual soundings reduce the ability of OCO-2 XCO2 to estimate more frequent, smaller surface CO2 flux anomalies. However, we find that OCO-2 XCO2 can often detect and estimate large surface flux anomalies that leave an imprint on the atmospheric CO2 concentration anomalies beyond the retrieval error/uncertainty associated with the observations. OCO-2 can thus be useful for low-latency monitoring of the monthly timing and magnitude of extreme regional terrestrial biosphere carbon anomalies.

Andrew F. Feldman↗
NASA NTRSDate not supplied

CERES Top-of-atmosphere and Surface fluxes in the Arctic: A comparison with ARISE and MOSAiC measurements

Uncertainty in the NASA Clouds and the Earth’s Radiant Energy System (CERES)-derived irradiances is larger over sea ice than any other surface type and comes from several sources. This presentation summarizes results from comparisons of CERES data with the year-long Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition in the central Arctic and the Arctic Radiation and Icebridge Sea ice Experiment (ARISE). The CERES Synoptic 1degree (SYN1deg) product overestimates the downwelling shortwave flux by 11.40 Wm–2 and underestimates the upwelling shortwave flux by –15.70 Wm–2 and downwelling longwave fluxes by –12.58 Wm–2 at the surface during summer. In addition, large differences are found in the upwelling longwave flux when the surface approaches the melting point (approximately 0C). The large negative bias in upwelling shortwave flux can be attributed in large part to lower surface albedo (–0.15) in satellite footprint relative to surface sensors. The CERES-MOSAiC broadband albedo differences (approximately 20 Wm–2) explain a larger portion of the upwelling shortwave flux difference than the spectral albedo shape differences (approximately 3 Wm–2). The ARISE results indicate the some of these differences in the SW are due to the scene identification and representation of anisotropy in partly cloud scenes. Switching from imager-based to passive microwave-based sea ice data in the CERES inversion process reduces the differences in the grid box average fluxes and in the sea ice partly cloudy scene anisotropy in the instantaneously-matched footprints. Our analysis indicates that calibration and sampling uncertainty limit the ability to place strong constraints (<7%) on CERES TOA fluxes with aircraft measurements. The results indicate that improvements in the surface albedo and cloud data would substantially reduce the uncertainty in the Arctic surface radiation budget derived from CERES data products.

Patrick C Taylor↗
NASA NTRS1994

A new measurement of the flux of the light cosmic-ray nuclei at high energies

A new cosmic-ray detector utilizing a ring-imaging Cerenkov counter to determine the energy of light cosmic-ray nuclei was flown on high-altitude balloon from Fort Sumner, NM, in 1991 September. We describe the design and performance of this instrument and discuss the data analysis procedures. The measurement provides a new determination of the absolute flux and differential energy spectrum of the primary cosmic-ray species helium between 40 and 320 GeV/nucleon. The experiment also yields the spectra of carbon and oxygen and some information on the intensities of the secondary nuclei Li, Be, and B. A comparison between our results and previous measurements of heavier nuclei (Z greater than or equal to 4) from HEAO 3 and Spacelab 2 indicates good consistency between these measurements. The data set is compared with the results of a leaky box propagation model. We find good agreement with this model if the abundance of helium relative to oxygen at the source is taken to be 25 +/- 6 and if the source spectrum is given by a power law in energy proportional to E(exp -2.15).

Buckley, J.↗
NASA NTRS1992

Effect of flux penetration on the load capacity of passive superconducting bearings

A dramatic improvement has been made in the load capacity of a superconductor magnet pair. The measured load capacities that stood at 0.1 psi two years back were improved now to an impressive 40 psi. This improvement is mainly due to better processing techniques developed by the superconducting material processing community. The analysis indicates that, by using these processing techniques that efficiently prevent flux penetration, high load capacities were achieved. With these developments, it is possible to insert passive bearings into actual applications within the next few years.

Rao, Dantam K.↗
NASA NTRS1986

Mesospheric ozone changes associated with 27-day solar ultraviolet flux variations

Solar ultraviolet flux changes associated with the 27-day solar rotational period cause corresponding variations in mesospheric ozone near the maximum of the 11-year sunspot cycle. This statement is based on a correlation and spectral analysis of ozone mixing ratios, deduced from Solar Mesospheric explorer satellite-based measurements of 1.27-micron O2 airglow emission and solar flux observations made from the same spacecraft in 1982. With the Lyman-alpha flux taken as an indicator of solar ultraviolet variability, spectral analysis shows a primary period of 27.1 days with a secondary period of 13.5 days. The 27.1-day period is observed in the ozone mixing ratio data together with other periods, including 13.5 days. Both a classical statistical analysis and a time series treatment show that, for 244 days, there is a correlation between ozone and solar flux near 50 km and between 65 and 70 km. Calculations predict a positive correlation over the entire mesosphere if there is no change in temperature accompanying the solar flux. Lack of correlation is temperature induced.

Aikin, A. C.↗