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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 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
NASA NTRS1971

Observations on pulsating auroras

Infrasonic pulsations of optical auroral luminosity in 3914 A positive molecular nitrogen ion and 5577 A O I emission measurement by double photometer system

Miller, R. E.↗
NASA NTRS1973

Direct comparison between satellite electric field measurements and the visual aurora

Electric field data from two passes of the Injun 5 satellite, one corresponding to magnetically quiet conditions and one corresponding to substorm conditions, are compared with simultaneous all-sky-camera data from College, Alaska. In each case, a significant deviation of the electric field from the expected V x B field (where V is the satellite velocity) was evident and a distinct electric field reversal could be identified. In the region of substantial electric field equatorward of the electric field reversal a diffuse auroral arc was observed during the magnetically quiet pass and auroral patches were observed during the substorm pass. The motion of the auroral patches was consistent with the general direction and magnitude of the E x B drift computed from the satellite electric field measurements. In the substorm case the electric field reversal occurred very near a discrete auroral arc at the poleward side of the diffuse arcs and patches. Comparison of the quiet time and substorm cases suggests that the convection electric field penetrates deeper into the magnetosphere during a substorm.

Swift, D. W.↗
NASA NTRS1974

Laboratory studies on the excitation and collisional deactivation of metastable atoms and molecules in the aurora and airglow

The aeronomy group at the University of Pittsburgh is actively engaged in a series of coordinated satellite, sounding rocket, and laboratory studies designed to expand and clarify knowledge of the physics and chemistry of planetary atmospheres. Three major discoveries have been made that will lead ultimately to a complete and dramatic revision of our ideas on the ionospheres of Mars, Venus, and the Earth and on the origin of their vacuum ultraviolet airglows. The results have already suggested a new generation of ionosphere studies which probably can be carried out best by laser heterodyning techniques. Laboratory studies have also identified, for the first time, the physical mechanism responsible for the remarkable nitric oxide buildup observed in some auroral arcs. This development is an important break-through in auroral physics, and has military ramifications of considerable interest to the Department of Defense. This work may also shed some light on related NO and atomic nitrogen problems in the mesosphere.

Zipf, E. C.↗
NASA NTRS1974

The aurora as a source of planetary-scale waves in the middle atmosphere

Photographs of global scale auroral forms taken by scanning radiometers onboard weather satellites in 1972 show that auroral bands exhibit well organized wave motion with typical zonal wave number of 5 or so. The scale size of these waves is in agreement with that of well organized neutral wind fields in the 150- to 200-km region during the geomagnetic storm of May 27, 1967. Further, the horizontal scale size revealed by these observations are in agreement with that of high altitude traveling ionospheric disturbances. It is conjectured that the geomagnetic storm is a source of planetary and synoptic scale neutral atmospheric waves in the middle atmosphere. Although there is, at present, no observation of substorm related waves of this scale size at mesospheric and stratospheric altitudes, the possible existence of a new source of waves of the proper scale size to trigger instabilities in middle atmospheric circulation systems may be significant in the study of lower atmospheric response to geomagnetic activity.

Chiu, Y. T.↗
NASA NTRS1973

Direct comparison between satellite electric field measurements and the visual aurora

Electric field data from two passes of the Injun 5 satellite, one corresponding to magnetically quiet conditions and one corresponding to substorm conditions, are compared with simultaneous all-sky camera data from College, Alaska. In each case, a significant deviation of the electric field from the expected V x B field (where V is the satellite velocity) was evident, and a distinct electric field reversal could be identified. In the region of substantial electric field equatorward of the electric field reversal, a diffuse auroral arc was observed during the magnetically quiet pass, and auroral patches were observed during the substorm pass. In the substorm case, the electric field reversal occurred very near a discrete auroral arc at the poleward side of the diffuse arcs and patches. Comparison of the quiet time and substorm cases suggests that the convection electric field penetrates deeper into the magnetosphere during a substorm.

Swift, D. W.↗
NASA NTRS1973

Electron excitation of a Jovian Aurora

Because Jupiter possesses a magnetic field, auroral activity is very likely. The auroral emissions due to electron precipitation are estimated for a model atmosphere with and without helium. The incident primary electrons, which are characterized by representative spectra, are degraded in energy by applying the continuous slow down approximation. All secondaries, tertiaries, and higher generation electrons are assumed to be absorbed locally. A compilation of excitation, dissociation, and ionization cross section data for H, H2, and He are used to model all aspects of the energy deposition process. Volume emission rates are calculated from the total direct excitation rates, and appropriate corrections for cascading are applied. Helium emissions are relatively small because the majority of electrons are absorbed above the region of maximum He concentration.

Heaps, M. G.↗
NASA NTRS1974

The aurora and the magnetosphere - The Chapman Memorial Lecture

Review of recent progress in magnetospheric physics, in particular, in understanding the magnetospheric substorm. It is shown that a number of magnetospheric phenomena can now be understood by viewing the solar wind-magnetosphere interaction as an MHD dynamo; auroral phenomena are powered by the dynamo. Also, magnetospheric responses to variations of the north-south and east-west components of the interplanetary magnetic field have been identified. The magnetospheric substorm is entirely different from the responses of the magnetosphere to the southward component of the interplanetary magnetic field. It may be associated with the formation of a neutral line within the plasma sheet and with an enhanced reconnection along the line. A number of substorm-associated phenomena can be understood by noting that the new neutral line formation is caused by a short-circuiting of a part of the magnetotail current.

Akasofu, S.-I.↗
NASA NTRS1975

Jovian proton aurora

Auroral and polar cap emissions in a model Jovian atmosphere are determined for proton precipitation. The incident protons, which are characterized by representative spectra, are degraded in energy by applying the continuous slowing down approximation. All secondary and higher generation electrons are assumed to be absorbed locally and their contributions to the total emissions are included. Volume emission rates are calculated from the total direct excitation rates with corrections for cascading applied. Results show that most molecular hydrogen and helium emissions for polar cap precipitation are below the ambient dayglow values. Charge capture by precipitating protons is an important source of Lyman alpha and Balmer alpha emissions and offers a key to the detection of large fluxes of low energy protons.

Heaps, M. G.↗
NASA NTRS1975

Neutral hydrogen flux measured at 100- to 200-km altitude in an electron aurora

Neutral hydrogen fluxes were measured at altitudes of 120-200 km by a rocket payload that also measured electron and proton fluxes and vector magnetic fields. An intense electron arc was crossed, while an upper limit to the flux of 0.5- to 20-keV protons was 1,000,000 per sq cm s sr keV. A neutral flux of 50,000,000 per sq cm s sr was observed, assuming hydrogen with greater than 1-keV energy, with greater north-south extent than the electron flux. Its pitch angle distribution was peaked toward 90 deg, tending toward isotropy in the center. This is fitted to a model describing spreading of an initial proton arc above 500 km.

Iglesias, G. E.↗
NASA NTRS1975

The aurora as a source of planetary-scale waves in the middle atmosphere

Photographs of global-scale auroral forms taken by scanning radiometers onboard U.S. Air Force weather satellites in 1972 show that auroral bands exhibit well-organized wave motion with typical zonal wave number of 5 or so. The scale size of these waves is in agreement with that of well-organized neutral wind fields measured by the 1967-50B satellite in the 150- to 220-km region during the geomagnetic storm of May 27, 1967. The horizontal scale size revealed by these observations is in agreement with that of high-altitude traveling ionospheric disturbances. It is conjectured that the geomagnetic storm is a source of planetary and synoptic scale neutral atmospheric waves in the middle atmosphere. The possible existence of a source of waves of the proper scale size to trigger instabilities in middle atmospheric circulation systems may be significant in the study of lower atmospheric response to geomagnetic activity.

Chiu, Y. T.↗
NASA NTRS1975

A measurement of perpendicular current density in an aurora

A Nike Tomahawk sounding rocket was launched into a 400-gamma auroral substorm from Esrange, Kiruna, Sweden. The rocket instrumentation included a split Langmuir-probe plasma-velocity detector and a double-probe electric-field detector. Above 140-km altitude, the electric field deduced from the ion-flow velocity measurement and the electric field measured by the double probe agree to an accuracy within the uncertainties of the two measurements. The difference between the two measurements at altitudes below 140 km provides an in situ measurement of current density and conductivity. Alternatively, if values for the conductivity are assumed, the neutral-wind velocity can be deduced. The height-integrated current was 0.11 A/m flowing at an azimuth angle of 276 deg. The neutral winds were strong, exhibited substantial altitude variation in the east-west component, and were predominantly southward.

Bering, E. A.↗