Engineering topics

Desch, M. D.

Publications and source records attributed to Desch, M. D..

115 records · Page 7

NASA NTRS1979

Latitudinal beaming of Jupiter's low frequency radio emissions

By comparing RAE-1 and IMP-6 satellite measurements of Jupiter's radio emission near 1MHz with recent Voyager-1 and 2 observations in the same frequency range, the properties of the low frequency radiation pattern over a 10 deg range of latitudes with respect to the Jovian rotation equator can be studied. These observations, which cover a wider latitudinal range than is possible from the earth, are consistent with many aspects of earlier ground-based measurements used to infer a sharp beaming pattern for the decameter wavelength emissions. Marked, systematic changes are found in the statistical occurrence probability distributions with system 3 central meridian longitude as the jovigraphic latitude of the observer changes over this range. Simultaneous observations by the two Voyager spacecraft suggest that the instantaneous beam width may be no more than a few degrees at times. The new hectometer-wave results can be interpreted in terms of a narrow, curved sheet at a fixed magnetic latitude into which the emission is beamed to escape the planet.

Alexander, J. K.↗

NASA NTRS1978

Modulation of the Jovian emission below 8 MHz

RAE-1 data on Jovian decametric emission between 1 and 8 MHz are analyzed to investigate modulation of the emission with respect to the rotation phase of the planet and Io phase as well as a possible variation with flux density of the rotation-phase and Io-phase control below 8 MHz. Attention is given to the observing interval, identification of Jovian emission, orbital-phase constraint, and calculated emission occurrence probabilities. Five frequencies are selected for the analysis (6550, 4700, 3930, 2200, and 1310 kHz), and System III coordinates are used to illustrate the rotation-phase behavior. The spectral distribution of peak flux density is examined along with the overall occurrence probability, the individual modulations, theoretical implications of invariance of active Io phases, and possible modulation by Europa. The results show that Io exerts a suprisingly high degree of control at the low frequencies, that rotation-phase control is only marginal, and that the manner in which Io control is found to vary with flux density is consistent with previous findings at higher frequencies.

Desch, M. D.↗

NASA NTRS1978

Io-phase motion and jovian decametre source locations

A second-order effect in the relationship between jovian decameter storms and the departure of Io from superior geocentric conjunction is explained on the basis of latitudinal variations in the earth-Jupiter viewing geometry. These variations are defined by the 12-year cycle in the jovicentric declination of the earth. In addition, it is found that the emission of the jovian decameter storm source Io-B (Io-C) is beamed from the northern (southern) magnetic latitudes. These conclusions are compatible with source positions derived from polarimetry and from considerations of planetary-limb shadowing.

Desch, M. D.↗

NASA NTRS1978

Jovian S-burst observations at 32 MHz

Drift rates for S-burst emissions from Jupiter are studied. The burst spectra, recorded in the frequency range near 32 MHz, provide a qualitative illustration of the behavior of electron bunches shortly after injection into the Io-associated magnetic flux tube. The morphology of the spectra may be taken as support for the hypothesis of an ionospheric acceleration mechanism influencing the flow of electrons.

Desch, M. D.↗

NASA NTRS1976

Recent decametric and hectometric observations of Jupiter

Observational results on Jupiter's high-frequency radiation, for the range 1-35 MHz (10 to 100 m), obtained over the past six years with the aid of orbited telescopes, are surveyed. Spectral distributions, periodic effects, burst waveforms and dynamic spectra of storms, polarization effects, high-resolution interferometry, and possible correlations with solar activity are discussed. Related spacecraft experiments are described. Close attention is given to long-term accumulation of occurrence probability data as functions of time and frequency (synoptic monitoring) on Jovian HF emission, and to dominating effects of the Jovian satellite Io, as well as modulation of periodicities by the 11.9-year orbital motion period of Jupiter. Possible effects of the other four Jovian satellites immersed in the Jovian magnetosphere are also taken into consideration. Absence of a Jovian Faraday effect and polarization of fine burst structure are discussed.

Carr, T. D.↗

NASA NTRS1975

Observations of Jupiter at 26.3 MHz using a large array

A 640 element phase-steerable dipole array has been used to make highly sensitive observations of the planet Jupiter during the 1973 apparition. The satellite Io is found to have very little influence at the low flux levels, whereas the definition of sources A and B appears to be relatively flux independent. A two-dimensional analysis of the data in the Jupiter-Io plane has revealed considerable source B activity at low intensities which is not influenced by Io.

Desch, M. D.↗

NASA NTRS1974

Dekametric and hectometric observations of Jupiter from the RAE-1 satellite

Analysis of RAE-1 satellite data has revealed the presence of radio bursts from Jupiter in the frequency range from 4700 kHz to 450 kHz. Variations in the activity with respect to the planet's system III longitude are presented at seven frequencies. A merge of ground-based and satellite-acquired data indicates that the long-sought-for peak in Jupiter's low-frequency flux spectrum occurs at about 8 MHz.

Desch, M. D.↗