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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 199 records · Page 11
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NASA NTRS1983

The kinetic temperature and CH3CCH column density profiles in SGR B2, Orion, and Dr 21

Kinetic temperatures, T(kin), are presently estimated by means of a technique employing the intensities of the adjacent rotational transitions of symmetric top molecules, under the assumptions that the metastable levels are thermalized, and that the excitation temperature connecting the upper level of the observed transition to the lowest level in the K ladder is the same for the both adjacent transitions. The method is applied to observations of the J = 5-4 and J = 6-5 transitions of CH3CCH obtained at 1-arcmin intervals along a NS-EW cross that centered on Orion KL, Sgr B2, and Dr 21. The technique's application to CH3CN lines from the central positions of Sgr B2 and Orion produces T(kin) values that are in good agreement with other determinations. The fact that these lines are broader than those of CH3CCH is interpreted in terms of a model in which CH3CN emission is confined to small and warm core region while CH3CCH emission is dominated by a more extensive, almost isothermal and cooler halo region in Orion KL and Sgr B2.

Churchwell, E.↗
NASA NTRS1983

The GLE-associated flare of 21 August, 1979

A variety of ground-based and satellite measurements is to identify the source of the ground level event (GLE) beginning near 06:30 UT on 21 August, 1979 as the 2B flare with maximum at about 06:15 UT in McMath region 16218. This flare differed from previous GLE-associated flares in that it lacked a prominent impulsive phase, having a peak about 9 GHz burst flux density of only 27 sfu and a greater than 10 keV peak hard X-ray flux of less than about 3 x 10 to the -6th ergs/sq cm/s. Also, McMath 16218 was magnetically less complex than the active regions in which previous cosmic-ray flares have occurred, containing essentially only a single sunspot with a rudimentary penumbra. The flare was associated with a high speed mass ejection observed by the NRL white light coronagraph aboard P78-1 and a shock accelerated (SA) event observed by the low frequency radio astronomy experiment on ISEE-3.

Cliver, E. W.↗
NASA NTRS1985

Wind-tunnel evaluation of a 21-percent-scale powered model of a prototype advanced scout helicopter

An exploratory wind tunnel investigation of a 21 percent scale powered model of a prototype advanced scout helicopter was conducted in the Langley 4 by 7 Meter Tunnel. The investigation was conducted to define the overall aerodynamic characteristics of the Army Helicopter Improvement Program (AHIP), to determine the effects of the rotor on the aerodynamic characteristics and to evaluate the effect of a mast mounted sight on the aircraft stability characteristics. Tests covered a range of thrust coefficients, advance ratios, angles of attack and angles of sideslip and were run for both rotor on and rotor off configurations. Results of the investigation showed that the prototype configuration was longitudinally unstable with angle of attack for all configurations tested. The instability was due to unfavorable interference effects between the horizontal tail and the wake shed from the engine pylon and rotor hub, which caused a loss of horizontal tail effectiveness. The addition of the mast mounted sight had little effect on the stability of the model, but it caused an alteration in the rotor lift distribution that resulted in substantial interference drag for the sight.

Phelps, A. E., III↗
NASA NTRS1985

Solar and interplanetary particles at 2 to 4 MEV during solar cycles 21, solar cycle variations of event sizes, and compositions

In This paper 2 to 4 MeV/nucleon protons, alpha particles, and medium (CNO) nuclei in the near-Earth interplanetary medium during the years 1974 to 1981 are studied. This period contains both the solar activity minimum in 1976, and the very active onset phase of Solar Cycle 21. Characteristic compositional differences between the solar minimum and solar maximum ion populations have been investigated. Previous studies of interplanetary composition at these energies have concentrated on well-defined samples of the heliospheric medium. During flare particle events, the ambient plasma is dominated by ions accelerated in specific regions of the solar atmosphere; observation of the proton/alpha and alpha/medium ratios for flare events shows that there is marked compositional variability both during an event and from event to event suggesting the complicated nature of flare particle production and transport.

Armstrong, T. P.↗
NASA NTRS1984

Energetic ion mass composition as observed at near-geosynchronous and low altitudes during the storm period of February 21 and 22, 1979

Mass composition data acquired during the storm period of February 21 and 22, 1979 are presented and analyzed. Near-geosynchronous data from the SCATHA spacecraft are described, giving the data in spectrogram format. Low-altitude data from the S3-3 spacecraft are presented, and it is shown that they raise questions concerning the evolution of the low-altitude, 0.5-16 keV/q plasma population after the main phase of magnetic storms. The importance of convection as an explanation of the signatures found in the low-altitude S3-3 data is considered. Some work concerning steady state convection models is summarized, pointing out those aspects of the theory relevant to the S3-3 data. Results from the theory are applied to those data, which are also displayed in spectrogram format. The results are discussed, using the geosynchronous composition data as a monitor of the source of the injected plasma.

Strangeway, R. J.↗
NASA NTRS1985

The galactic cosmic ray intensity minimum in the inner and outer heliosphere in solar cycle 21

The occurrence of the cosmic ray intensity minimum during solar cycle 21 at widely separated locations in the heliosphere is investigated. The data include in situ measurements by cosmic-ray detectors on the earth-orbiting satellite IMP 8, on the Voyagers 1 and 2 spacecraft, and on the Pioneers 10 and 11 spacecraft, located at distances from 1 to 27 AU. It is noted that Pioneer 10 and the other three spacecraft (Pioneer 11 and Voyagers 1 and 2) are on the opposite sides of the sun, with the latter moving toward the tail of the heliosphere. The data used in the study have been suitably corrected by removing solar flare particle contributions, Forbush decreases, and contamination by the radioisotope thermoelectric generator. It is evident that there exists a time delay in the occurrence of the cosmic ray intensity minimum registered by the IMP 8 and Pioneer 10 detectors, the latter being located at approximately 27 AU. It is shown that the data from the four spacecraft in deep space are on an average consistent with the IMP 8 data at 1 AU when suitably corrected, using 3 percent/AU for the radial gradient and 500 km/s for the average speed of propagation. An overview of the intensity profiles reveals reasonable agreement among them. However, specific intensity features appear at times to propagate with speeds in excess of the average value of about 500 km/s.

Venkatesan, D.↗
NASA NTRS1985

Thermospheric and ionospheric structure of the Southern Hemisphere polar cap on October 21, 1981, as determined from Dynamics Explorer 2 satellite data

For a number of years, satellites have been employed to measure auroral particles and fields within the high-latitude thermosphere. In the present paper, data from orbit 1174 of the Dynamics Explorer 2 satellite on October 21, 1981, are utilized to calculate the structure of the ionosphere and thermosphere below the satellite altitude down to about 80 km. Attention is given to details regarding the DE 2 measurements, a satellite track model, the calculated ionospheric structure, and the calculated neutral gas heating rates. The investigation demonstrates that the technique of deriving characteristics of the ionosphere and atmosphere below a satellite track promises to be very fruitful for defining the characteristics of the lower thermosphere for use in large numerical models of the thermosphere and ionosphere.

Emery, B. A.↗
NASA NTRS1985

The response of ozone to solar proton events during solar cycle 21 - The observations

It is pointed out that during a solar proton event (SPE), large numbers of high-energy protons penetrate the earth's mesosphere and upper stratosphere and perturb the normal chemistry by ionizing molecules and changing the balance of odd nitrogen, oxygen, and hydrogen. Changes in ozone caused by an SPE are produced very rapidly, typically in a matter of hours, and are confined to a limited geographic area, the region above 60 deg geomagnetic latitude. In this paper, an analysis is reported of the response of ozone to the significant SPE's in solar cycle 21 from the Nimbus 7 launch in October 1978 to date, using data from the solar backscattered ultraviolet instrument (SBUV). Ozone data during 15 SPE's were examined. It was found that ozone depletion occurred during SPE's on at least five dates.

Mcpeters, R. D.↗
NASA NTRS1985

The response of ozone to solar proton events during solar cycle 21 - A theoretical interpretation

The effects associated with the solar proton events (SPE) during solar cycle 21 are examined. The only SPE documented to cause an ozone depletion below 45 km (approximately 2 mbar) was the event which occurred on Aug. 4, 1972. The ozone decreases associated with this event follow approximately the theoretically predicted behavior discussed by Heath et al. (1977) and Reagan et al. (1981). Ozone decreases during the July 13, 1982 and the Dec. 8, 1982, SPEs also follow approximately their theoretically predicted behavior between 60 and 85 km. Attention is given to the energy deposition by solar protons and electrons, photochemistry, model descriptions, model results, the solar zenith angle effect, three solar proton events during solar cycle 20, sensitivity studies, and temperature effects.

Jackman, C. H.↗
NASA NTRS1986

The production rate of cosmogenic 21-Ne in chondrites deduced from 81-Kr measurements

Cosmogenic Ne-21 is used widely to calculate exposure ages of stone meteorites. In order to do so, the production rate P(21) must be known. This rate, however, is dependent on the chemical composition of the meteorite as well as the mass of, and position within, the meteoroid during its exposure to the cosmic radiation. Even for a mean shielding the production rates determined from measurments of different radionuclides vary by a factor of two. A method that can be used to determine exposure ages of meteorites that avoids shielding and chemical composition corrections is the -81-Kr-Kr-method. However, for chondrites, in many cases, the direct determination of production rates for the Kr isotopes is prevented by the trapped gases and the neutron effects on bromine. Therefore, this method was applied to four eucrite falls and then their 81-Kr-83-Kr-ages were compared to their cosmogenic Ne-21 and Ar-38 concentrations. The eucrites Bouvante-le-Haut, Juvinas, Sioux County, and Stannern were chosen for these measurements because of their similar chemical composition regarding the major elements.

Schultz, L.↗
NASA NTRS1985

Photometric lightcurves of 21 asteroids

Forty-three light curves of 21 asteroids obtained during 1968-1978 are presented and briefly discussed. The light curves were obtained to increase the data base for studies in shapes, spin periods, and the orientation of the rotation axes.

Vesely, C. D.↗
NASA NTRS1985

Low-energy and medium-energy gamma rays from PSR 0531 + 21

Results are presented from the Crab Pulsar PSR 0531 + 21 for energies of 0.3-30 MeV. For energies of 1-30 MeV, the absolute phase and separation of the first and second pulses 12.9 + or - 0.3 ms, widths of the pulses 2.2 + or - 0.5 ms FWHM, and 1.6 + or - 0.4 ms FWHM, ratio of the counts in the second to the first pulse 0.64 + or - 0.33 and ratio of counts in the interpulse region to the total pulsed counts 0.17 + or - 0.30 are compared to te results vor energies, E greater than 50 MeV and their variations with time. Values from the phase plots for E greater than 0.3 MeV are compared with low-energy gamma rays during 1970 through 1980 from several experiments with energies from about 20 to 360 keV. The above suggest different production mechanisms for low- and high-energy gamma rays with a transition at about 1 MeV. Derived fluxes from 0.3 to 30 MeV confirm a previously derived power law.

White, R. S.↗
NASA NTRS1986

The interplanetary magnetic field during solar cycle 21 ISEE-3/ICE observations

Temporal variations in the IMF during solar cycle 21 are investigated using magnetic field observations collected by the vector helium magnetometer on the ISEE-3/ICE spacecraft. Analysis of the observations reveal that the IMF magnitude, which had declined to 4.7 nT in 1976, peaked in late 1982 (two years after solar maximum) at 9.0 nT and rapidly decreased during 1983-1984 to an intensity of 6.2 nT in early 1985. The IMF intensities are compared with the auroral AE index; the observed peak in strength during 1981-1983 is related to a 50 percent increase in substorm activity levels. A decrease in Parker spiral angle, revealing the existence of high-speed streams is detected in the declining phase of the solar cycle. Variations in the intensity of the IMF correlate with Mt. Wilson magnetograph measurements of full disk magnetic flux. Source regions for the evolution of solar wind and the IMF are proposed.

Slavin, J. A.↗
NASA NTRS1985

Ozone depletion during solar proton events in solar cycle 21

Ozone profile data from the Solar Backscattered Ultraviolet Instrument on Nimbus 7 from 1979 to the present and clear cases of ozone destruction associated with five sudden proton events (SPEs) on June 7, 1979, August 21, 1979, October 13-14, 1981, July 13, 1982, and December 8, 1982 are found. During the SPE on July 13, 1982, the largest of this solar cycle, no depletion at all at 45 km is observed, but there is a 15 percent ozone depletion at 50 km increasing to 27 percent at 55 km, all at a solar zenith angle of 85 deg. A strong variation of the observed depletion with solar zenith angle is found, with maximum depletion occurring at the largest zenith angles (near 85 deg) decreasing to near zero for angles below about 70 deg. The observed depletion is short lived, disappearing within hours of the end of the SPE.

Mcpeters, R. D.↗
NASA NTRS1986

Measurement of radial and latitudinal gradients of cosmic ray intensity during the decreasing phase of sunspot cycle 21

The cosmic ray radial and latitudinal gradients during the 1981-1984 decreasing phase of sunspot cycle 21 are investigated based on data from Voyagers 1 and 2, with a detector threshold of not less than 70 MeV/nuc, and IMP-8, with a detector threshold of not less than 35 MeV/nuc. During the interval, the heliolongitudinal separation between the Voyager spacecraft changed from about 4 to 26 deg, and comparison of the 26-day means of the cosmic ray intensities obtained show that the data is consistent on the average with a long-term zero latitudinal gradient. Comparison at 1 AU of Voyager and IMP-8 data illustrate that the radial gradient decreased over this period at the rate of about 0.4 percent per AU per year, reaching a value of about 2.0 percent/AU between 16 and 22 AU, and a value of about 0.6 percent/AU between 16 and 22 AU, a pattern which would locate both Voyagers during 1977 outside the principal cosmic ray modulation at solar minimum within 22 AU.

Venkatesan, D.↗
NASA NTRS1986

Evidence against chromospheric evaporation from the 21 May 1980 flare

Antonucci et al. (1985) have presented observations of the large two-ribbon flare of May 21, 1980 and interpreted the Ca XIX X-ray line profiles, hard X-ray observations, and X-ray images to support the standard model of electron-beam-driven chromospheric evaporation. Here it is shown that an active filament which erupted at flare onset can also explain the observations, and that a closer look at the evidence of Antonucci et al. leads to discrepancies with the chromospheric evaporation model.

Batchelor, David A.↗
NASA NTRS1987

Simulations of the sun's polar magnetic fields during sunspot cycle 21

Regarding new bipolar magnetic regions as sources of flux, the evolution of the radial component of the solar photospheric magnetic field is simulated during 1976-1984, and the corresponding evolution of the line-of-sight polar fields as seen from earth is derived. The observed timing and strength of the polar-field reversal during cycle 21 can be accounted for by supergranular diffusion alone, for a diffusion coefficient of 800 sq km/sec. For an assumed 300 sq km/sec rate of diffusion, on the other hand, a poleward meridional flow with a moderately broad profile and a peak speed of 10 m/s reached at about 5 deg latitude is required to obtain agreement between the simulated and observed fields. Such a flow accelerates the transport of following-polarity flux to the polar caps, but also inhibits the diffusion of leading-polarity flux across the equator. For flows faster than about 10 m/s, the latter effect dominates, and the simulated polar fields reverse increasingly later and more weakly than the observed fields.

Devore, C. Richard↗