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At least 343 records · Page 19
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NASA NTRS1971

Correlation between convection electric fields in the nightside magnetosphere and several wave and particle phenomena during two isolated substorms.

Correlation of several magnetoionospheric wave and particle phenomena previously linked observationally to magnetospheric substorms and inferred to involve convection electric fields with whistler measurements of convection activity during two relatively isolated substorms. The events occurred at about 0600 UT on July 15, 1965, and about 0500 UT on Oct. 13, 1965. The correlated phenomena include cross-L inward plasma drifts near midnight within the plasmaphere, diffuse auroral radar echoes observed near the dusk meridian, IPDP micropulsations (intervals of pulsations of diminishing period) in the premidnight sector, apparent contractions and expansions of the plasma sheet at about 20 earth radii in the magnetotail, and Pc 1/Pi 1 micropulsation events near or before midnight. Two new vlf phenomena occurred during the October 13 event - a noise band within the plasmasphere associated with a convecting whistler path, and ?hisslers,' falling-tone auroral-hiss forms repeated at intervals of about 2 sec.

Carpenter, D. L.↗
NASA NTRS1971

Rocket measurements of ion and electron densities in the D-region during sunrise.

Results from two rockets launched near sunrise at White Sands, N. Mex., when positive ion and electron densities were measured in the D-region for solar zenith angles of 91 and 79 deg. The measurements cover the height range 80 to 110 km and complement previous vlf observations and rocket measurements of electron density. It is shown that the majority of negative ions in this height range are detached near to after ground sunrise. On the basis of these measurements it is possible to discuss electron affinity of negative ions and ion production functions during twilight.

Pedersen, A.↗
NASA NTRS1972

Ogo 4 observations of extremely low frequency hiss.

Analysis of ELF and VLF data from the Stanford University experiment on Ogo 4 revealed an ELF hiss band with characteristics not previously identified. The band, referred to as band-limited ELF hiss, is seen from low to medium latitudes. On the basis of wave-propagation properties, it is proposed that the BLH is generated at large wave normal angles in the equatorial region near L = 4. This model can be used to explain the characteristics of the BLH. Two mechanisms for the generation of BLH based on radiation from energetic electrons are considered.

Muzzio, J. L. R.↗
NASA NTRS1972

Ogo 5 observations of LHR noise, emissions, and whistlers near the plasmapause at several earth radii during a large magnetic storm.

On May 15, 1969, Ogo 5 crossed the plasmapause during a major storm that produced severe geomagnetic disturbances (Kp up to 8-), large and rapid variations in ring-current intensity (as measured by Dst), intense low-latitude aurora, and persistent SAR arcs. Near the highly structured plasmasphere boundary, the electric- and magnetic-field sensors on Ogo 5 detected lower-hybrid-resonance noise bursts, whistlers, ELF hiss, and other discrete signals or emissions. Some LHR noise bursts were associated with whistlers, and these high-altitude phenomena resembled the corresponding ionospheric ones. This report contains a description of the VLF observations. We also show that intense ULF magnetic signals were present near the plasmapause, and we attempt to relate these observations to the predictions of various theories of proton ring-current decay and SAR-arc formation.

Scarf, F. L.↗
NASA NTRS1972

Plasma waves in the dayside polar cusp. I - Magnetospheric observations.

General survey of the Ogo 5 plasma-wave measurements for the dayside polar-cusp encounters of Nov. 1, 1968, and detailed analysis of the observations at the low-altitude (r approximately 3 to 5 earth radii) cusp boundaries. The survey section contains an overall discussion of the ULF magnetic-field wave levels and the VLF electric-field amplitude ranges measured from perigee out to 9 earth radii on Nov. 1, 1968. These cusp-associated observations are compared with those made on Oct. 27 and Nov. 6, 1968, when Ogo 5 traversed the dayside magnetosphere without encountering the cusp. It is shown that at the November 1 low-altitude cusp boundaries intense wave levels were detected over a broad spectral region at the steep gradients in cusp plasma density and thermal energy. The results are interpreted in terms of drift instabilities for low-beta plasmas with hot ions, and associated wave-particle and wave-wave interactions are briefly discussed.

Scarf, F. L.↗
NASA NTRS1972

Sideband growth in nonlinear Landau wave-particle interaction.

The distortion of the electron velocity distribution caused by a large amplitude Landau wave is determined analytically for the initial-value problem. The resulting stability of electrostatic perturbations impressed on the evolving plasma is studied. Narrow sidebands of the applied frequency experience consecutive growths of large magnitude during the early stages of the nonlinear wave-particle interaction. The significance of the derived results to both wave propagation experiments and triggered VLF emissions in the magnetosphere is discussed.

Brinca, A. L.↗
NASA NTRS1972

Type III solar noise observed below 100 kHz on OGO 3.

Type III solar noise bursts have been observed in the frequency range 25-100 kHz with the VLF detector on OGO 3. The bursts decrease in frequency from 100 kHz (the highest frequency of observation) to as low as 25 kHz in approximately 45 min. The intensity at 100 kHz increases for about 20 min then decays over a period of approximately 1 hr. The variation of the intensity with time becomes less regular at lower frequencies. Bursts are predominantly associated with west-limb flares. Their commencement at 100 kHz tends to follow type III bursts observed at 2-4 MHz by about 10 min. Observed drift rates and decay times correspond roughly to those extrapolated from higher frequency measurements.

Dunckel, N.↗
NASA NTRS1972

The light ion trough, the main trough, and the plasmapause

Extensive observations of mid-latitude depletions in electron and total ion density by both direct and indirect techniques, have prompted numerous studies of the possible association between these troughs, observed in the F-region, the topside ionosphere, and the plasmapause. One basic problem arises, in that while the plasmapause was detected as a global phenomenon both by VLF and ion composition measurements, the electron and ion density troughs were identified primarily as nightside features. This problem, as well as the difficulty in explaining various inconsistencies in relating the position of the plasmapause and the ionization trough, is explained by a close examination of the ion composition. In particular, ion composition results from the polar orbiting OGO satellites identify the persistence of a pronounced light ion trough in H(+) and He(+) identified by order of magnitude decreases in the light ion concentrations.

Taylor, H. A., Jr.↗
NASA NTRS1973

A step in time: Changes in standard-frequency and time-signal broadcasts, 1 January 1972

An improved coordinated universal time (UTC) system has been adopted by the International Radio Consultative Committee. It was implemented internationally by the standard-frequency and time-broadcast stations on 1 Jan. 1972. The new UTC system eliminates the frequency offset of 300 parts in 10 to the 10th power between the old UTC and atomic time, thus making the broadcast time interval (the UTC second) constant and defined by the resonant frequency of cesium atoms. The new time scale is kept in synchronism with the rotation of the Earth within plus or minus 0.7 s by step-time adjustments of exactly 1 s, when needed. A time code has been added to the disseminated time signals to permit universal time to be obtained from the broadcasts to the nearest 0.1 s for users requiring such precision. The texts of the International Radio Consultative Committee recommendation and report to implement the new UTC system are given. The coding formats used by various standard time broadcast services to transmit the difference between the universal time (UT1) and the UTC are also given. For users' convenience, worldwide primary VLF and HF transmissions stations, frequencies, and schedules of time emissions are also included. Actual time-step adjustments made by various stations on 1 Jan. 1972, are provided for future reference.

Chi, A. R.↗
NASA NTRS1972

The plasmapause period of magnetic recovery. Combined study of OGO 4, OGO 5 data and of grounded whistler reception

The equatorial structure and dynamics of the plasmasphere during the period of magnetic recovery, lasting from the 13 to 23 of September 1968, are studied. The H(+) ions density profiles measured in the night and afternoon sectors by the excentered orbital satellite OGO 5 and L sub p positions of the plasmapause deduced from the VLF records of the polar orbital satellite OGO 4, are included. Electron densities are calculated from the whistlers received at Kerguelen (L approximately 3, 7) and Byrd (L approximately 7), ground stations 150 degrees of longitude apart.

Corcuff, P.↗
NASA NTRS1972

Banded whistlers observed on OGO-4

Inspection of broadband VLF records from OGO-4 shows that some whistlers exhibit a banded structure in which one or more bands of frequencies are missing from the whistler's spectrum. The phenomenon is commonly observed by satellites on midlatitude field lines at all local times and at various longitudes around the world. The dispersion of banded whistlers (BW) is of several tens of sec to the 1/2 power, indicating that they originated in the opposite hemisphere and are propagating downward at the satellite. BW are generally spread in time (tenths of seconds) rather than sharply defined and tend to occur at random. The frequency spacing of the bands may be either uniform or irregular, and may vary radically between successive events. Several possible explanations for BW are considered. In particular, an analysis of the interaction of plane electromagnetic waves traveling in an anisotropic plasma with a field aligned slab of enhanced ionization is presented with promising results.

Paymar, E. M.↗
NASA NTRS1972

Earth's magnetospheric processes; Proceedings of the Symposium, Cortina, Italy, August 30-September 10, 1971.

New data obtained by satellites, rockets, aircraft, and ground-based observations are interpreted in papers dealing with the magnetospheric structure and processes, particle distributions, magnetic and electric fields, plasma convection, particle acceleration and diffusion mechanisms, and substorm phenomena. Attention is given to particle populations in different magnetospheric regions, auroral particle precipitation patterns, effects of electric fields on plasma convection, VLF phenomena, a high-energy proton model for the inner radiation belt, substorm behavior of plasma sheet particles, and interpretations of magnetic field variations during substorms. Individual items are announced in this issue.

Mccormac, B. M.↗
NASA NTRS1972

OMEGA time transmissions and receiver design.

This document gives a short history of the development of dual VLF time-transmission technique. The theory of time recovery from the relative phase of the dual-frequency transmission is presented. The transmission and receiving requirements for cycle identification and cycle ambiguity resolution are described. Finally, a prototype OMEGA timing receiving design is described.

Chi, A. R.↗
NASA NTRS1973

Observation of a current-driven plasma instability at the outer zone-plasma sheet boundary.

Several spacecraft experimenters have reported on the detection of large temporal variations in trapped electron fluxes near L = 5 to 6 at midlatitudes in the night hemisphere. In this report we describe in detail the particle, wave, and field changes measured when Ogo 5 traversed an outer-zone trapping boundary of this type on September 7, 1968. It is shown that thermal proton concentrations and E greater than 50-keV electron fluxes abruptly decreased when electrons with (1-4) keV mean energy were detected. It is also shown that currents flowed along the average geomagnetic field direction near the plasma boundaries and that these were accompanied by intense VLF electrostatic waves. It is proposed that turbulent resistivity produced by current-driven plasma instabilities allows parallel dc electric fields to develop along this boundary.

Scarf, F. L.↗
NASA NTRS1973

The Pioneer 9 electric field experiment. III - Radial gradients and storm observations.

We present a detailed analysis of the Pioneer 9 VLF electric field observations for 20 selected storm periods covering a heliocentric range extending from 0.754 AU to 0.99 AU. Although data from only two low frequency channels are available, the results of the present study tend to confirm the preliminary speculation by Scarf and Siscoe (1971) that the turbulent E-field spectrum in the disturbed solar wind has a significant radial gradient.

Scarf, F. L.↗
NASA NTRS1973

Pioneer 8 observations and interpretations of sixteen interplanetary shock waves observed in 1968.

A study has been made of 16 interplanetary shock waves observed in 1968 by Pioneer 8 at large distances from earth. A comparison with the shapes of interplanetary shock fronts obtained by De Young and Hundhausen (1971) suggests that in general the ejection of flare gas occurs within a cone of half-angle between 30 and 60 deg. For near-earth events a deflection of the shock front has been observed, possibly owing to an interaction with the bow shock. The average duration of the postshock perturbation is about 20 hours. Strong magnetic fields and rapid fluctuations occur during the first 6 to 12 hours. Electric field perturbations in the VLF band are also noted during these periods. There is limited evidence for one corotating shock in these data.

Bavassano, B.↗
NASA NTRS1973

Electron concentrations calculated from the lower hybrid resonance noise band observed by Ogo 3.

A noise band at the lower hybrid resonance (LHR) is often detected by the VLF and ELF receivers on Ogo 3, using the electric antenna. In some cases the noise band is at the geometric mean gyrofrequency as measured by the Goddard Space Flight Center (GSFC) magnetometer, and local LHR in a dense H(+) plasma is indicated; in such cases, electron concentration can be calculated, if it is assumed that heavy ions are negligible. Observations at midlatitudes and altitudes of a few earth radii show local concentrations as low as 1.4 electrons/cu cm. In one case the concentrations obtained from the LHR noise band agree with those measured simultaneously by the GSFC ion mass spectrometer within a factor of 2. In another case the concentration is observed to fall by a factor of 2 in 150 km and then to decrease roughly as R to the minus fourth power, in agreement with whistler measurements outside the plasmapause.

Burtis, W. J.↗