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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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NASA NTRS2005

MESSENGER: Exploring Mercury's Magnetosphere

The MESSENGER mission to Mercury offers our first opportunity to explore this planet s miniature magnetosphere since the brief flybys of Mariner 10. Mercury s magnetosphere is unique in many respects. The magnetosphere of Mercury is among the smallest in the solar system; its magnetic field typically stands off the solar wind only - 1000 to 2000 km above the surface. For this reason there are no closed drift paths for energetic particles and, hence, no radiation belts. The characteristic time scales for wave propagation and convective transport are short and kinetic and fluid modes may be coupled. Magnetic reconnection at the dayside magnetopause may erode the subsolar magnetosphere allowing solar wind ions to impact directly the regolith. Inductive currents in Mercury s interior may act to modify the solar wind interaction by resisting changes due to solar wind pressure variations. Indeed, observations of these induction effects may be an important source of information on the state of Mercury s interior. In addition, Mercury s magnetosphere is the only one with its defining magnetic flux tubes rooted in a planetary regolith as opposed to an atmosphere with a conductive ionospheric layer. This lack of an ionosphere is probably the underlying reason for the brevity of the very intense, but short-lived, - 1-2 min, substorm-like energetic particle events observed by Mariner 10 during its first traversal of Mercury s magnetic tail. Because of Mercury s proximity to the sun, 0.3 - 0.5 AU, this magnetosphere experiences the most extreme driving forces in the solar system. All of these factors are expected to produce complicated interactions involving the exchange and re-cycling of neutrals and ions between the solar wind, magnetosphere, and regolith. The electrodynamics of Mercury s magnetosphere are expected to be equally complex, with strong forcing by the solar wind, magnetic reconnection at the magnetopause and in the tail, and the pick-up of planetary ions all driving field-aligned electric currents. However, these field-aligned currents do not close in an ionosphere, but in some other manner. In addition to the insights- into magnetospheric physics offered by study of the solar wind - Mercury system, quantitative specification of the "external" magnetic field generated by magnetospheric currents is necessary for accurate determination of the strength and multi-polar decomposition of Mercury s intrinsic magnetic field. MESSENGER S highly capable instrumentation and broad orbital coverage will greatly advance our understanding of both the origin of Mercury s magnetic field and the acceleration of charged particles in small magnetospheres. In. this article, we review what is known about Mercury s magnetosphere and describe the MESSENGER science team s strategy for obtaining answers to the outstanding science questions surrounding the interaction of the solar wind with Mercury and its small, but dynamic, magnetosphere.

Slavin, James A.↗
NASA NTRS2008

MESSENGER: Exploring Mercury's Magnetosphere

The MESSENGER mission to Mercury offers our first opportunity to explore this planet's miniature magnetosphere since Mariner 10's brief fly-bys in 1974-5. Mercury's magnetosphere is unique in many respects. The magnetosphere of Mercury is the smallest in the solar system with its magnetic field typically standing off the solar wind only - 1000 to 2000 km above the surface. For this reason there are no closed dri-fi paths for energetic particles and, hence, no radiation belts; the characteristic time scales for wave propagation and convective transport are short possibly coupling kinetic and fluid modes; magnetic reconnection at the dayside magnetopause may erode the subsolar magnetosphere allowing solar wind ions to directly impact the dayside regolith; inductive currents in Mercury's interior should act to modify the solar In addition, Mercury's magnetosphere is the only one with its defining magnetic flux tubes rooted in a planetary regolith as opposed to an atmosphere with a conductive ionosphere. This lack of an ionosphere is thought to be the underlying reason for the brevity of the very intense, but short lived, approx. 1-2 min, substorm-like energetic particle events observed by Mariner 10 in Mercury's magnetic tail. In this seminar, we review what we think we know about Mercury's magnetosphere and describe the MESSENGER science team's strategy for obtaining answers to the outstanding science questions surrounding the interaction of the solar wind with Mercury and its small, but dynamic magnetosphere.

Slavin, James A.↗
NASA NTRS1977

Albedo of the ocean-atmosphere system - Influence of sea foam

The influence of the ocean's optical properties and wind induced sea surface foam (white caps) on the short-wave albedo of the ocean-atmosphere system is studied by solving the radiative transfer equation using a Monte Carlo method. It is found that for a foam free ocean, the planetary albedo of a very clear ocean is at most 10 percent greater than that for a totally absorbing ocean. However, the introduction of a relatively small amount of sea foam on the surface can produce a considerable increase in the albedo, especially if the foam is highly reflecting. For example, it is shown that for foam which is totally reflecting (the foam albedo is 1), an increase in the wind speed from 6 to 14 m/sec would double the planetary albedo for small solar zenith angles.

Gordon, H. R.↗
NASA NTRS2022

Infrared Spectral Responses of the Ocean Color Instrument (OCI) Pre-assembly and Integration

The Ocean Color Instrument (OCI) to go on the Plankton, Aerosol, Cloud, ocean Ecology (PACE) Earth-observing satellite has a Short-wave infrared (SWIR) Detection Assembly (SDA). This SDA is used to measure upwelling radiation in seven discrete bands from 940 to 2260 nm. There are redundant measurements of each band for a total of 32 physical channels, which includes optical components through to detection. The relative spectral response (RSR) is measured for each channel, which is needed when accounting for the spectral distribution of sensed radiance. From the RSR, single-value performance metrics are computed including the center wavelength, the full width at half of the maximum (FWHM), and the full width at 1% of the maximum (FW1P). Besides in-band responses, the out-of-band rejection ratio (OOBRR) is also calculated for each of the channels, which is a measure of the sensitivity outside the band of interest. We find that all 32 SDA detection channels meet the spectral response requirements at the qualification temperatures at which tests were conducted.

PACE↗
NASA NTRS2022

Spectral Responses of the PACE OCI Short-Wave Infrared Detection Assembly

The Ocean Color Instrument (OCI) to go on the Plankton, Aerosol, Cloud, ocean Ecology (PACE) Earth-observing satellite has a Short-wave infrared (SWIR) Detection Assembly (SDA). This SDA is used to measure upwelling radiation in seven discrete bands from 940 to 2260 nm. There are redundant measurements of each band for a total of 32 physical channels, which includes optical components through to detection. The relative spectral response (RSR) is measured for each channel, which is needed when accounting for the spectral distribution of sensed radiance. From the RSR, single-value performance metrics are computed including the center wavelength, the full width at half of the maximum (FWHM), and the full width at 1% of the maximum (FW1P). Besides in-band responses, the out-of-band rejection ratio (OOBRR) is also calculated for each of the channels, which is a measure of the sensitivity outside the band of interest. We find that all 32 SDA detection channels meet the spectral response requirements at the qualification temperatures at which tests were conducted.

PACE↗
NASA NTRS1985

Radiation from long pulse train electron beams in space plasmas

A previous study of electromagnetic radiation from a finite train of electron pulses is extended to an infinite train of such pulses. The electrons are assumed to follow an idealized helical path through a space plasma in such a manner as to retain their respective position within the beam. This leads to radiation by coherent spontaneous emission. The waves of interest in this region are the whistler slow (compressional) and fast (torsional) Alfven waves. Although a general theory is developed, analysis is then restricted to two approximations, the short and long electron beam. Formulas for the radiation per unit solid angle from the short beam are presented as a function of both propagation and ray angles, electron beam pulse width and separation and beam current, voltage, and pitch angle. Similar formulas for the total power radiated from the long beam are derived as a function of frequency, propagation angle, and ray angle. Predictions of the power radiated are presented for representative examples as determined by the long beam theory.

Harker, K. J.↗
NASA NTRS1979

Gravity wave propagation in a diffusively separated atmosphere with height-dependent collision frequencies

Numerical calculations of gravity wave propagation through a two-component thermosphere with vertically-varying inter-species collision frequencies are performed using a direct integration method. Reflection of upgoing gravity wave energy into downgoing gravity waves appears to be small though nonnegligible at typical thermospheric periods and wavelengths. Coupling into diffusion waves is completely insignificant in most cases and may be determined in part by the relative abundance of the minor species. Temperature perturbation differences between species can be greater than 10% above 300 km altitude even though coupling into diffusion waves is small. Diffusive dissipation of gravity wave energy can be significant in the lower thermosphere and may be comparable to dissipation by viscosity and heat conduction below about 225 km altitude. Heating by diffusive dissipation may also be comparable to direct heating by solar radiation in the lower thermosphere. As a result of dissipative filtering of long-period and short-wavelength waves and the sensitivity of He-N2 density perturbation phase differences to diffusion, the AE-C satellite wave observations can only be fit by internal gravity waves with periods no greater than about 25 min and horizontal wavelengths no less than about 200 km.

Del Genio, A. D.↗
NASA NTRS1972

An economical net solar flux radiometer.

The theory and design of an economical solar flux radiometer readily adaptable to the conventional radiosonde system are presented in response to the need cited by the Atmospheric Radiation Working Group (1971) for the development of an inexpensive light-weight short-wave radiometer sonde. Prototype instrument tests and current modifications are discussed. It is shown that the basic instrument can be easily modified to measure separately the upward and downward directed flux components, in addition to the net flux.

Darkow, G. L.↗
NASA NTRS1990

Radiative transfer model validations during the First ISLSCP Field Experiment

Two simple radiative transfer models, the 5S model based on Tanre et al. (1985, 1986) and the wide-band model of Morcrette (1984) are validated by comparing their outputs with results obtained during the First ISLSCP Field Experiment on concomitant radiosonde, aerosol turbidity, and radiation measurements and sky photographs. Results showed that the 5S model overestimates the short-wave irradiance by 13.2 W/sq m, whereas the Morcrette model underestimated the long-wave irradiance by 7.4 W/sq m.

Frouin, Robert↗
NASA NTRS1995

Nonlinear Waves in Magnetized Accretion Disks

Time-dependent accretion for a magnetized disk can exhibit short timescale outbursts of high-power jets associated with bursts of disk radiation. The burst of energy in jets can produce outward propagating disturbances in preexisting (+/- z) jet flows. the disturbances are strong and can be expected to steepen and form strong shock waves. The strong linear polarization (up to approximately 30%) and large polarization position angle changes (90 deg and more) seen in the optical outbursts of some quasars clearly indicate synchrotron radiation, and this component of the radiation is probably associated with the burst in jet energy in the present model.

Lovelace, R. V. E.↗
NASA NTRS1974

Solution of the radiative transfer theory problems by the Monte Carlo method

The Monte Carlo method is used for two types of problems. First, there are interpretation problems of optical observations from meteorological satellites in the short wave part of the spectrum. The sphericity of the atmosphere, the propagation function, and light polarization are considered. Second, problems dealt with the theory of spreading narrow light beams. Direct simulation of light scattering and the mathematical form of medium radiation model representation are discussed, and general integral transfer equations are calculated. The dependent tests method, derivative estimates, and solution to the inverse problem are also considered.

Marchuk, G. I.↗
NASA NTRS1990

Instabilities in line-driven stellar winds. IV - Linear perturbations in three dimensions

Nonradial wave propagation in line-driven stellar winds is analyzed including both finite disk effects and the line-drag effect of scattered line radiation. Within the local (WKB) analysis the results apply to wavelengths both longer and shorter than the Sobolev length. The finite disk causes short-wavelength waves with lateral velocity polarization to be unstable in the idealized case of pure absorption; however, the growth rates are smaller than for radially polarized waves, and the instability is damped by a relatively small amount of scattering. Hence, in realistic stellar winds, where the driving is primarily by scattering lines, perturbations with an arbitrary mixture of lateral and radial polarizations at the wind base should quickly become nearly radially polarized farther out in the wind. The implications of these results are discussed, both for interpretation of observational signatures of wind structure and for theoretical calculations aimed at modeling the nonlinear evolution of wind instabilities.

Rybicki, G. B.↗
NASA NTRS1993

The cone structure and focusing of the electric field of VLF and LF waves at high altitudes of the ionosphere

This paper presents a short review of the frequency and angle dependencies of the electric field radiated by an electric dipole E = E(sub 0)cos(omega)t in a magnetoplasma and detailed results of numerical calculations of (E) in the VLF and LF frequency bands 0.02f(sub b) is less than or equal to F is less than or equal to 0.5f(sub b) in the ionosphere and magnetosphere in the altitude region Z = (800 - 6000) km (F is approximately (4 - 500) kHz and f(sub b) is approximately equal to (1.1 to 0.2) MHz is the electron gyro-frequency). The amplitudes of the electric field have large maxima in four regions: close to the direction of the Earth magnetic field line B(sub 0) (it is the so called Axis field E(sub 0); in the Storey E(sub St); Reversed Storey E(sub RevSt); and Resonance E(sub Res) Cones. The maximal values of E(sub 0), E(sub Res), and E(sub Rev ST) are the most pronounced close to the low hybrid frequency, F is approximately F(sub L). The flux of the electric field is concentrated in very narrow regions, with the apexes angles of the cones delta(beta) is approximately (0.1 - 1) degree. The enhancement and focusing of the electric field increases with altitude starting at Z is greater than 800 km. At Z is greater than or equal to 1000 up to 6000 km, the relative value of E, in comparison with its value at Z equals 800 km is about (10(exp 2) to 10(exp 10)) times larger. Thus, the flux of VLF and LF electromagnetic waves in the Earth magnetoplasma produces and is guided by very narrow pencil beams, similar, let us say, to laser beams.

Alpert, Y. L.↗
NASA NTRS1994

Arctic ocean radiative fluxes and cloud forcing estimated from the ISCCP C2 cloud dataset, 1983-1990

Radiative fluxes and cloud forcings for the ocean areas of the Arctic are computed from the monthly cloud product of the International Satellite Cloud Climatology Project (ISCCP) for 1983-90. Spatially averaged short-wave fluxes are compared well with climatological values, while downwelling longwave fluxes are significantly lower. This is probably due to the fact that the ISCCP cloud amounts are underestimates. Top-of-the-atmosphere radiative fluxes are in excellent agreement with measurements from the Earth Radiation Budget Experiment (ERBE). Computed cloud forcings indicate that clouds have a warming effect at the surface and at the top of the atmosphere during winter and a cooling effect during summer. The net radiative effect of clouds is larger at the surface during winter but greater at the top of the atmosphere during summer. Overall the net radiative effect of clouds at the top of the atmosphere is one of cooling. This is in contrast to a previous result from ERBE data showing arctic cloud forcings have a net warming effect. Sensitivities to errors in input parameters are generally greater during winter with cloud amount being the most important paarameter. During summer the surface radiation balance is most sensitive to errors in the measurements of surface reflectance. The results are encouraging, but the estimated error of 20 W/sq m in surface net radiative fluxes is too large, given that estimates of the net radiative warming effect due to a doubling of CO2 are on the order of 4 W/sq m. Because it is difficult to determine the accuracy of results with existing in situ observations, it is recommended that the development of improved algorithms for the retrieval of surface radiative properties be accompanied by the simultaneous assembly of validation datasets.

Schweiger, Axel J.↗
NASA NTRS2024

Evolution of the Climate Forcing During the Two Years after the Hunga Tonga-Hunga Ha’apai Eruption

We calculate the climate forcing for the 2 ys after the 15 January 2022, Hunga Tonga-Hunga Ha'apai (Hunga) eruption. We use satellite observations of stratospheric aerosols, trace gases and temperatures to compute the tropopause radiative flux changes relative to climatology. Overall, the net downward radiative flux decreased compared to climatology. The Hunga stratospheric water vapor anomaly initially increases the downward infrared radiative flux, but this forcing diminishes as the anomaly disperses. The Hunga aerosols cause a solar flux reduction that dominates the net flux change over most of the 2 yrs period. Hunga induced temperature changes produce a decrease in downward long-wave flux. Hunga induced ozone reduction increases the short-wave downward flux creating small sub-tropical increase in total flux from mid-2022 to 2023. By the end of 2023, most of the Hunga induced radiative forcing changes have disappeared. There is some disagreement in the satellite measured stratospheric aerosol optical depth (SAOD) observations which we view as a measure of the uncertainty; however, the SAOD uncertainty does not alter our conclusion that, overall, aerosols dominate the radiative flux changes.

M R Schoeberl↗
NASA NTRS2014

Temperature and Humidity Profiles in the TqJoint Data Group of AIRS Version 6 Product for the Climate Model Evaluation

The Atmospheric Infrared Sounder (AIRS) mission is entering its 13th year of global observations of the atmospheric state, including temperature and humidity profiles, outgoing long-wave radiation, cloud properties, and trace gases. Thus AIRS data have been widely used, among other things, for short-term climate research and observational component for model evaluation. One instance is the fifth phase of the Coupled Model Intercomparison Project (CMIP5) which uses AIRS version 5 data in the climate model evaluation. The NASA Goddard Earth Sciences Data and Information Services Center (GES DISC) is the home of processing, archiving, and distribution services for data from the AIRS mission. The GES DISC, in collaboration with the AIRS Project, released data from the version 6 algorithm in early 2013. The new algorithm represents a significant improvement over previous versions in terms of greater stability, yield, and quality of products. The ongoing Earth System Grid for next generation climate model research project, a collaborative effort of GES DISC and NASA JPL, will bring temperature and humidity profiles from AIRS version 6. The AIRS version 6 product adds a new "TqJoint" data group, which contains data for a common set of observations across water vapor and temperature at all atmospheric levels and is suitable for climate process studies. How different may the monthly temperature and humidity profiles in "TqJoint" group be from the "Standard" group where temperature and water vapor are not always valid at the same time? This study aims to answer the question by comprehensively comparing the temperature and humidity profiles from the "TqJoint" group and the "Standard" group. The comparison includes mean differences at different levels globally and over land and ocean. We are also working on examining the sampling differences between the "TqJoint" and "Standard" group using MERRA data.

climate model evaluation↗
NASA NTRS1994

Participation in the scientific activities of the Waves in Space Plasma (WISP) project

This is the Final Report for Contract NAG5-1925, that consisted of experiment design, for possible use by the space science mission called WISP (Waves in Space Plasma). This mission is under study by the Canadian Space Agency and by NASA. Two WISP configurations are contemplated, under the name of BICEPS: one is called BOLAS, and the other WISPRS. Both these configurations are meant to perform bistatic sounding of the ionosphere, at a height close to F(sub 2) H(sub max) (about 350 Km), with a pair of satellites, either tethered or in free flight. Investigation A (with Y.L. Alpert as P.I.) addresses the subject of parametric decay effects, expected to arise in a magnetoplasma under the influence of high-intensity HF fields. Criteria were formulated that could be used in searching for parametric instabilities and of electric fields in the ionosphere and magnetosphere, by in-situ satellites, such as the BICEPS Pair. Investigation B (with M.D.Grossi as P.I.) addressed the bistatic measurement, by the BICEPS pair,of ionospheric features, such as large-scale and small-scale disturbances, travelling ionospheric disturbances, electron density irregularities, spread-F phenomena, etc. These measurements by BICEPS could be correlated with the waveform distortion and degradation experienced by microwave links from geosynchronous height to ground, such as the ACTS satellite, expected to radiate pulses as short as 1 nanosecond in the band 20 to 30 GHz. These links are transionospheric and propagate e.m. waves in the volume of the ionosphere where BICEPS operates. It will be possible, therefore, to correlate the two classes of measurements, and learn the causative mechanisms that are responsible for the time-spread and frequency-spread nature of communications waveforms at microwave, in geosynchronous height to ground paths.

Alpert, Yakov L.↗