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At least 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

External control of planetary radio emission

Recent studies using data from Voyagers 1 and 2 to correlate variations in the Saturn kilometric radiation (SKR) with changes in solar-wind properties are summarized and illustrated with graphs. Best SKR correlations have been obtained with the solar-wind ram pressure and the related kinetic energy flux. It is pointed out that the related phenomenon on earth, the auroral kilometric radiation, occurs mainly in the nightside auroral region (as opposed to the dayside cleft region for SKR) and is best correlated with solar-wind velocity and inverted-V electron-precipitation events, implying a different stimulation process. The evidence for solar-wind control of the non-Io-related decametric radiation of Jupiter is also reviewed.

Rucker, H. O.↗
NASA NTRS1986

The relationship of storm severity to directionally resolved radio emissions

The objective was to provide continuous observation of atmospheric electrical activity occurring in association with tropical storms in the Gulf of Mexico. The observations were to include the location of all detected intracloud and cloud-to-ground lightning activity occurring in the storm. To provide synoptic scale coverage, a phase linear interferometer high frequency direction finder (HFDF) system was constructed and developed at Marshall Space Flight Center (MSFC). This was used in concert with the existing HFDF interferometer at the southwest research institute to provide lightning location data through triangulation. Atmospheric electrical events were synchronized through the use of satellite receivers at each site. The intent of the data analysis was to correlate the location of electrical centers of activity with radar and satellite imagry to identify areas of intense convection within the tropical storm system. Analysis of the hurricane Alicia data indicate a center of atmospheric electrical activity associated with the vortex of the storm. The center appears to rotate from the Northern side of the vortex to the Southern side during the period of observation. An analysis of the atmospheric electrical burst rates associated with hurrican Alicia indicates that the electrical activity appears to maximize at the time of greatest storm intensity, i.e., maximum winds and lowest central pressure.

Johnson, R. L.↗
NASA NTRS1986

Radio emission of cataclysmic variable stars

Eight cataclysmic variable stars were observed at 6 cm wavelength using the Very Large Array (VLA). The objects were: CN-Ori, SS-Aur, YZ-Cnc, SU-Uma, Z-Cam, V603-Aql, EM-Cyg, and RZ-Sge. Most of these objects were in optical high stage, but none were detected beyond flux limits between 0.1 and 0.3 mJy.

Fuerst, E.↗
NASA NTRS1986

Relativistic dispersion modifications to the cyclotron maser theory of planetary radio emissions

The effects of relativistic dispersion on the electron-cyclotron maser instability are investigated by linear theory, electromagnetic particle simulation, and quasilinear theory. When vsq/csq greater than or = omega pesq/Omega sq for the energetic electrons, the instability is localized just below k c/Omega e = 1, and the growth rate is strongly peaked for emission at 90 deg to the magnetic field. Saturation of the instability is due to perpendicular diffusion in momentum space, and the saturation level increases as omega pe/Omega e is decreased. Applications of the maser instability to the generation of the Earth's auroral kilometric radiation are discussed.

Pritchett, P. L.↗
NASA NTRS1986

Relativistic dispersion modifications to the cyclotron maser theory of planetary radio emissions

The effects of relativistic dispersion on the electron-cyclotron maser instability are investigated by means of linear theory, electromagnetic particle simulation, and quasilinear theory. Saturation of the instability is due to perpendicular diffusion in momentum space, and the saturation level increases as the plasma frequency/electron cyclotron ratio is decreased. Applications of the maser instability to the generation of the the earth's auroral kilometric radiation are discussed.

Pritchett, P. L.↗
NASA NTRS1986

The relationship of shock-associated kilometric radio emission with metric type II bursts and energetic particles

Shock-associated (SA) events from 1978 to 1982 are compared with metric type II bursts and solar energetic particle (SEP) events. Most metric type II bursts are not obviously associated with SA events at 1980 kHz. Metric type II bursts associated with magnetically well connected flares and SA emission are well correlated with SEP events; those without SA emission are poorly correlated with SEP events. The largest SEP events from flares at any longitude are well correlated with SAs. These results are consistent with the hypothesis that the escaping electrons giving rise to SA emission are accelerated in coronal shocks.

Kahler, S. W.↗
NASA NTRS1987

The discovery of nonthermal radio emission from magnetic Bp-Ap stars

In a VLA survey of chemically peculiar B- and A-type stars with strong magnetic fields, five of the 34 stars observed have been identified as 6 cm continuum sources. Three of the detections are helium-strong early Bp stars (Sigma Ori E, HR 1890, and Delta Ori C), and two are helium weak, silicon-strong stars with spectral types near A0p (IQ Aur = HD 34452, Babcock's star = HD 215441). The 6 cm luminosities L6 (ergs/s Hz) range from log L6 = 16.2 to 17.9, somewhat less than the OB supergiants and W-R stars. Three-frequency observations indicate that the helium-strong Bp stars are variable nonthermal sources.

Drake, Stephen A.↗
NASA NTRS1987

Radio emission from coronal and interplanetary shocks

Observational data on coronal and interplanetary (IP) type II burst events associated with shock-wave propagation are reviewed, with a focus on the past and potential future contributions of space-based observatories. The evidence presented by Cane (1983 and 1984) in support of the hypothesis that the coronal (metric) and IP (kilometric) bursts are due to different shocks is summarized, and the fast-drift kilometric events seen at the same time as metric type II bursts (and designated shock-accelerated or shock-associated events) are characterized. The need for further observations at 0.5-20 MHz is indicated.

Cane, H. V.↗
NASA NTRS1989

The source location and beaming of broadband bursty radio emissions from Uranus

A rotationally-dependent occurrence pattern is identified for the b-bursty emissions observed with Voyager 2 during its 1986 encounter with Uranus. Certain features of this pattern, such as its extension to the highest frequencies and a 40-min signal gap, were sometimes recognizable on individual rotations despite the bursty character of the signals. This pattern is interpreted in terms of Voyager's passing from the inside of a broad, hollow emission cone coming from the southern hemisphere to the outside, and then back in, as a result of planetary rotation. The emission gap then corresponds to the times when Voyager was outside the cone.

Farrell, W. M.↗
NASA NTRS1988

Does solar radio emission trigger SKR?

Using Voyager I data, a preliminary search has been made for evidence of both triggering and enhancement of Saturn Kilometric Radiation (SKR) by solar type III bursts. The interval from September 1, 1980 to September 30,1980 was examined at a frequency near the spectral peak of the SKR (385 kHz). The investigation compared emission levels before and after the arrival of Type III bursts at Saturn by subjecting the data to both superposed epoch analysis and intensity distribution analysis. Strong SKR associated with the arrival of a high-density solar wind stream at Saturn was removed to avoid possible masking of a weak triggering effect. No evidence of triggering or of enhancement of SKR due to the arrival of Type III bursts at Saturn could be found.

Desch, Michael D.↗
NASA NTRS1988

Ray tracing planetary radio emissions

Planetary ray tracing calculations of free escaping electromagnetic waves are presented, with special attention given to calculations of the earth's auroral kilometric and continuum radiations and of the Jovian decametric and kilometric radiation. The technique is used to study the composition and propagation effects causing multiion resonances and shadow zones. Although results obtained for Jovian broadband kilometric radiation have been used to estimate the location of the source region, no unique solutions are obtained.

Green, James L.↗
NASA NTRS1989

Shock-associated kilometric radio emission and solar metric type II bursts

New criteria are used here to select and study the properties of shock-associated (SA) kilometric bursts. Nearly half of all intense metric type II bursts were temporally associated with 1980 kHz emission which was not attributable to metric type III bursts. A quarter of all intense type II bursts are not associated with any significant 1980 kHz emission and another quarter are accompanied by 1980 kHz emission presumed due to type II bursts. The SA bursts are generally not well correlated with microwave flux-density profiles but compare more closely with the most intense and structured parts of the profiles of metric type II bursts. These results imply that the SA emission is due primarily to energetic electrons accelerated at the associated shock.

Kahler, S. W.↗
NASA NTRS1990

Ray tracing of broadband bursty radio emissions from Uranus

To determine the source position of the broadband bursty emission, rays of X-mode emissin were traced from source positions along magnetic field lines with footprints that form a large grid centered approximately on the south magnetic pole of Uranus. For large wave normal angles, source regions different from those producing b-smooth emission were found. The emission observed prior to closest approach has a source along field lines that are distinct from those which generate emissions observed after closest approach.

Curran, D. B.↗
NASA NTRS1991

The lower subsidiary diffuse plasma resonances and the classification of radio emissions below the plasma frequency

Using previusly published data and newly scaled ionograms from the Alouette 2 and ISIS 1 experiments, the diffuse ionospheric resonances Dn, stimulated by topside sounders Dn, are classified. The classification also includes the lower subsidiary resonances Dn(-) (n = 1, 2, 3, and 4). It is shown that the Dn(-) frequencies are related to f(Dn) and f(H) by the expression f(Dn)- = sq rt of (f(Dn)-squared - f(H)-squared).

Osherovich, Vladimir A.↗
NASA NTRS1994

Dynamics and efficiency of type III solar radio emission

Existing calculations of nonlinear coupling coefficients for fundamental and harmonic emission via three-wave interactions are refined and used to calculate the conversion efficiency of Langmuir energy into electromagnetic waves when the Langmuir waves have the observed bursty form. Resulting field strengths for harmonic emission are found to be consistent with typical International Sun Earth Explorer 3 (ISSE 3) observations at 1 AU. Fundamental emission at 1 AU is found to proceed only when stimulated by the presence of a source of ion sound waves. However, it is argued that electrostatic decay of Langmuir waves can supply the necessary waves provided the driving electron beam is sufficiently fast. Under these conditions, the predicted fundamental field strengths can account for both the highest and typical fields observed; they also dominate the predicted harmonic fields, consistent with observations. This mechanism is also consistent with previous observations that fundamental emission generally occurs early in type III events, when the beam is fastest. For typical parameters it is shown that neither fundamental nor harmonic emission saturates its respective source instability, contrary to previous assumptions. However, saturation cannot be ruled out under particularly favorable conditions.

Robinson, P. A.↗
NASA NTRS1997

The Contribution of Ionizing Stars to the Far-Infrared and Radio Emission in the Galaxy

This is the first report of a new contract. However, this project represents ongoing work, so there are completed tasks as well as newly started tasks to report. The project involves the completion of the IRAS Galaxy Atlas (IGA), a large image database produced using data from the Infrared Astronomical Satellite (IRAS). In this phase, the project switches from the production and characterization of the IGA to its use in astronomical research studies of massive star formation. The research utilizes the IGA as well as two other large data sets being produced by research partners.

Cao, Yu↗