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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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At least 955 records · Page 53
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Observations of ionospheric convection vortices - Signatures of momentum transfer

Several classes of traveling vortices in the dayside ionospheric flow have been detected and tracked using the Greenland magnetometer chain. One class observed during quiet times consists of a continuous series of vortices moving generally antisunward for several hours at a time. Assuming each vortex to be the convection pattern produced by a small field aligned current moving across the ionosphere, the amount of field aligned current was found by fitting a modeled ground magnetic signature to measurements from the chain of magnetometers. The calculated field aligned current is seen to be steady for each vortex and neighboring vortices have currents of opposite sign. Low altitude DMSP observations indicate the vortices are on field lines which map to the inner edge of the low latitude boundary layer. Because the vortices are conjugate to the boundary layer, repeat in a regular fashion and travel antisunward, it is argued that this class of vortices is caused by surface waves at the magnetopause. No strong correlations between field aligned current strength and solar wind density, velocity, or Bz is found.

Mchenry, M. A.↗
NASA NTRS1986

The detection of photospheric X-ray pulsations from PG 1159-035 with EXOSAT

The detection of soft X-ray pulsations from the hot, helium-rich, degenerate object, PG 1159-035 is reported. These observations, obtained with the Low Energy experiment on EXOSAT, show the presence of large-amplitude soft X-ray (44-150 A) pulsations analogous to several of the low-amplitude, nonradial, g-mode pulsations which are observed in the optical. These soft X-ray pulsations, with periods of 516 s, 524 s, and 539 s, arise from the photosphere of PG 1159-035 and constitute the first observations of stellar atmospheric pulsational phenomena in the X-ray band.

Barstow, M. A.↗
NASA NTRS1991

Mars Observer mission plan

The paper describes plans devised for operating the Mars Observer mission during its five phases of activity: the launch, the cruise, the orbit insertion, the mapping, and the Mars 1994 support. The latter phase is to provide a data relay for a Sovier mission to Mars which will be launched in 1994. These plans will be used to plan detailed sequencing strategies for the Mars Observer mission. The low-altitude orbit and a full Martian year of observations will provide, both in temporal and spatial coverage and resolution, the most comprehensive study of an extraterrestrial planet to date.

Blume, William H.↗
NASA NTRS1992

Low-redshift Lyman-alpha absorption lines and the dark matter halos of disk galaxies

Ultraviolet observations of the low-redshift quasar 3C 273 using the Hubble Space Telescope have revealed many more Lyman-alpha absorption lines than would be expected from extrapolation of the absorption systems seen toward QSOs at z about 2. It is shown here that these absorption lines can plausibly be produced by gas at large radii in the disks of spiral and irregular galaxies; the gas is confined by the dark matter halos and ionized and heated by the extragalactic radiation field. This scenario does not require the extragalactic ionizing radiation field to decline as rapidly with decreasing z as the QSO emissivity. Observations of Ly-alpha absorption through the halos of known galaxies at low redshift will constrain both the extragalactic background and the properties of galactic halos.

Maloney, Philip↗
NASA NTRS1981

Energetic particle events /greater than or equal to 30 keV/ of Jovian origin observed by Voyager 1 and 2 in interplanetary space

Detailed observations of ion events of Jovian origin as observed by the low energy charge particle (LECP) instrumentation on Voyager 1 and 2 during the inbound and outbound pass for both spacecraft are reported. The general characteristics of these events are examined, and a comparison is made with similar observations at earth. Careful attention is given to the compositional signature of the Jovian ion events. Two of the specific events discussed in detail are selected to display the range of variability and complexity of the Jovian-produced interplanetary ion events. The observations are seen as strongly implying that the Jovian magnetosphere is the source of a significant fraction of the particles.

Zwickl, R. D.↗
NASA NTRS2015

Active and Widespread Halogen Chemistry in the Tropical and Subtropical Free Troposphere

Halogens in the troposphere are increasingly recognized as playing an important role for atmospheric chemistry, and possibly climate. Bromine and iodine react catalytically to destroy ozone (O3), oxidize mercury, and modify oxidative capacity that is relevant for the lifetime of greenhouse gases. Most of the tropospheric O3 and methane (CH4) loss occurs at tropical latitudes. Here we report simultaneous measurements of vertical profiles of bromine oxide (BrO) and iodine oxide (IO) in the tropical and subtropical free troposphere (10degN to 40degS), and show that these halogens are responsible for 34% of the column-integrated loss of tropospheric O3. The observed BrO concentrations increase strongly with altitude (approx.3.4 pptv at 13.5 km), and are 2-4 times higher than predicted in the tropical free troposphere. BrO resembles model predictions more closely in stratospheric air. The largest model low bias is observed in the lower tropical transition layer (TTL) over the tropical eastern Pacific Ocean, and may reflect a missing inorganic bromine source supplying an additional 2.5-6.4 pptv total inorganic bromine (Bry), or model overestimated Bry wet scavenging. Our results highlight the importance of heterogeneous chemistry on ice clouds, and imply an additional Bry source from the debromination of sea salt residue in the lower TTL. The observed levels of bromine oxidize mercury up to 3.5 times faster than models predict, possibly increasing mercury deposition to the ocean. The halogen-catalyzed loss of tropospheric O3 needs to be considered when estimating past and future ozone radiative effects.

Wang, Siyuan↗
NASA NTRS2013

Optical Reflection Spectroscopy of GEO Objects

We report on optical reflection spectroscopy of geosynchronous (GEO) objects in the US Space Surveillance Network (SSN) catalog. These observations were obtained using imaging spectrographs on the 6.5-m Magellan telescopes at the Las Campanas Observatory in Chile. Our goal is to determine the composition of these objects by comparing these spectral observations with ground-based laboratory measurements of spacecraft materials. The observations are all low resolution (1 nm after smoothing) obtained through a 5 arcsecond wide slit and using a grism as the dispersing element. The spectral range covered was from 450 nm to 800 nm. All spectra were flux calibrated using observations of standard stars with the exact same instrumental setup. An effort was made to obtain all observations within a limited range of topocentric phase angle, although the solar incident angle is unknown due to the lack of any knowledge of the attitude of the observed surface at the time of observation.

Seitzer, Patrick↗
NASA NTRS1985

Comparative magnetospheric/ionospheric studies using Dynamics Explorer spacecraft and ground-based radars

Coincident observations between the Dynamics Explorer 1 and 2 spacecraft with Chatanika and Arecibo ground-based radar are briefly reviewed. Ionospheric-magnetospheric coupling processes in the plasmasphere, main trough, auroral zone, and polar cap are inferred from the density, temperature, composition, and angular distributions of the low-energy plasma observed from the E-region ionosphere out into the magnetosphere to an altitude of 2.5 earth radii (Re). From the polar cap to the inner plasmasphere, parallel and perpendicular electric fields, polar wind flow, and equilibrium diffusion appear to be involved in the ionospheric-magnetospheric coupling of the low energy plasma.

Green, J. L.↗
NASA NTRS1995

Multiband VLBI Observations of CTA102

The source CTA102, known to exhibit low frequency variability, has been observed at six epochs (three at lambda 32 cm, two at lambda 18 cm, and one at lambda l.3 cm) with intercontinental VLBI arrays. On the basis of the changes observed in the structure, we believe that the flux density variations at these wavelengths are due to intrinsic processes and not due to interstellar scintillation. This source exhibits behaviour suggestive of being expanding with a very high apparent transverse velocity.

Rantakyro, F. T.↗
NASA NTRS1996

Multiband VLBI Observations of CTA102

The source CTA102, known to exhibit low frequency variability, has been observed at six epochs (three at labmda32cm, two at lambda18cm, and one at lambda1.3cm) with intercontinental VLBI arrays. On the basis of the changes observed in the structure, we believe that the VLBI arrays at these wavelengths are due to intrinsic processes, and not due to interstellar scintillation. This source exhibits behaviour suggestive of being expanding with a very high apparent transverse velocity.

galaxies↗
NASA NTRS1976

The acceleration of energetic particles in the interplanetary medium by transit-time damping

Transit time damping is examined as a possible means for accelerating low energy particles in co-rotating streams and interstellar ions. Data show that: the protons in co-rotating streams may be accelerated by transient-time damping the small-scale variations in the field magnitude that are observed at a low level in the inner solar system. The interstellar ions may be accelerated by transit time damping large-scale field variations in the outer solar system.

Fisk, L. A.↗
NASA NTRS2022

Multisensor Machine Learning to Retrieve High Spatiotemporal Resolution Land Surface Temperature

Climate change is making heat waves more frequent, long-lasting, and severe. While multiple satellite types provide data to monitor surface temperature, geostationary (GEO) sensors provide near-continuous, continental-scale observations which can better capture the diurnal variability of land surface temperature (LST) than intermittent observations from low-earth orbit (LEO) sensors. However, standard products from GEO satellites are available at coarsened spatial and temporal resolutions compared to the native sensor resolution. Using datasets from the NASA Earth Exchange, we leveraged co-located, co-temporal observations from LEO and GEO satellites to learn a data-driven mapping using a convolutional neural network. The resulting NASA Earth eXchange Artificial Intelligence LST (NEXAI-LST) achieved a mean absolute error of 1.73 K relative to the target LEO product and improves on both spatial and temporal resolution [2 km, 10 minute] compared to the GEO full disk standard product [10 km, hourly]. In validation against measurements from a ground-based sensor network, NEXAI-LST achieves similar or better fit than both LEO and GEO standard products, while depending none of the prior knowledge of land surface and atmospheric states required by physical-statistical models. Further, application of the model to unseen LEO and GEO satellites demonstrates robust generalization of the model across spatial region, time of day, and sensor. In support of NASA’s open-source science initiative, we make our NEXAI-LST product, model, and codes available to facilitate data exploration and further studies.

Kate Marie Duffy↗
NASA NTRS1976

Low-energy-proton regime in the geomagnetic tail at lunar distance

The reported investigation makes use of data obtained with the aid of the suprathermal ion detector experiment (SIDE) that is being conducted with instruments which were placed on the moon during the Apollo lunar landings. The moon traverses the geomagnetic tail once each month. Observations of a new low-energy plasma regime in the tail are presented. It is pointed out that the new regime lies within the magnetosphere, but outside the plasma sheet. According to the mass analyzer data of SIDE, the observed low-energy fluxes could consist entirely of protons. However, there might be an admixture of ions of greater mass.

Hills, H. K.↗
NASA NTRS2011

Modeling the Oxygen K Absorption in the Interstellar Medium: An XMM-Newton View of Sco X-1

We investigate the absorption structure of the oxygen in the interstellar medium by analyzing XMM-Newton observations of the low mass X-ray binary Sco X-1. We use simple models based on the O I atomic cross section from different sources to fit the data and evaluate the impact of the atomic data in the interpretation of astrophysical observations. We show that relatively small differences in the atomic calculations can yield spurious results. We also show that the most complete and accurate set of atomic cross sections successfully reproduce the observed data in the 21 - 24.5 Angstrom wavelength region of the spectrum. Our fits indicate that the absorption is mainly due to neutral gas with an ionization parameter of Epsilon = 10(exp -4) erg/sq cm, and an oxygen column density of N(sub O) approx. = 8-10 x 10(exp 17)/sq cm. Our models are able to reproduce both the K edge and the K(alpha) absorption line from O I, which are the two main features in this region. We find no conclusive evidence for absorption by other than atomic oxygen.

Garcia, J.↗
NASA NTRS1966

1961-1964 balloon observations of cosmic rays.

Low energy galactic cosmic radiation studies by high altitude balloon flights carrying nuclear emulsions, including solar activity, energy and intensity spectra, etc

GALACTIC RADIATION↗
NASA NTRS1973

Azimuthal propagation of low-energy solar flare protons - Interpretation of observations

The major conclusions reached by McKibben (1972) in a report of fluxes and spectra of solar flare protons in the approximate energy range from 10 to 30 MeV are reviewed. The observations had been made with cosmic ray telescopes on board the deep space probes Pioneer 6 and Pioneer 7 and the earth satellite Imp 4 during nine solar flare proton events occurring in the period from December 1967 to August 1968. The interpretation of the observations is discussed, giving attention to the stochastic field model of Jokipii and Parker (1969). Aspects of interplanetary diffusion are considered together with observations of corotating events.

Mckibben, R. B.↗