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NASA NTRS1988

Plasma wave observations with the Dynamics Explorer 1 spacecraft

This paper reviews the results from the plasma wave instrument on the Dynamics Explorer 1 (DE-1) spacecraft. The DE-1 spacecraft was launched on August 3, 1981, into an elliptical polar orbit with initial perigee and apogee radial distances of 1.09 and 4.65 earth radii. In the roughly six years since the launch of the spacecraft, DE-1 has provided basic new information on a wide variety of magnetospheric plasma wave phenomena. These include auroral kilometric radiation, auroral hiss, Z mode radiation, narrow-band electromagnetic emissions associated with equatorial upper hybrid waves, whistler mode emissions, wave-particle interactions stimulated by ground VLF transmitters, equatorial ion-cyclotron emissions, ion Bernstein-mode emissions, and electric field turbulence along the auroral field lines. A brief review of the basic plasma wave modes that can exist in the equatorial and polar regions of the magnetosphere is first given. After the basic terminology is established, each of the above areas of plasma wave research is discussed in detail, first by reviewing the state of knowledge at the time of the DE-1 launch, and then by describing the contribution made by DE-1 in the six years since the spacecraft was launched.

Gurnett, D. A.↗

NASA NTRS1988

Longitudinal differences in electron precipitation near L = 4

The origin of the significant differences revealed in data on electron precipitation characteristics obtained above Siple Station, Antarctica, and Kerguelen Islands was investigated. The two stations are both in the Southern Hemisphere at nearly the same magnetic latitude (L=4) and at longitudes that place them roughly at equal distances east and west of the center of the South Atlantic magnetic anomaly. The primary data used in the study were counting rates from rocket-borne parachute-deployed scintillation counters and VLF data from ground-based and rocket-borne receivers. The two locations were found to differ in two major respects: (1) the precipitation background at Kerguelen Islands is very low, with high levels of wave activity being required to produce any detectable precipitation, and (2) X-ray microbursts, very common at Siple, were found to be essentially absent at Kerguelen. This observation supports models of the microburst generation process which predict maximum pitch angle scatterings of only a few tenths of a degree.

Bering, E. A., III↗

NASA NTRS1988

Pulsed electron beam emission in space

During the Spacelab-2 mission of July 1985, electron beams (1 keV, 50-150 mA) pulsed at ELF and VLF frequencies were emitted from the Space Shuttle Orbiter. The wave fields generated by the beam were monitored by a Plasma Diagnostics Package which was released as a free-flying subsatellite during a six hour period. Measurements of the Orbiter potential and the return current during beam emissions were obtained from a Charge and Current Probe mounted in the payload bay.

Neubert, T.↗

NASA NTRS1989

Whistler-triggered emissions observed by ISIS satellites

A statistical examination has been conducted of the ducted and nonducted whistler-triggered emissions (WTEs) observed by the ISIS satellites in the 1979-1981 period. Most WTEs are observed with simultaneous lower hybrid resonance in the topside ionosphere. The VLF emissions triggered by ducted whistlers frequently occur at L of 2-3, while those triggered by nonducted whistlers occur in the wider latitudinal regions at L of 2.2-4.3.

Nakamura, Y.↗

NASA NTRS1989

Source locations for impulsive electric signals seen in the night ionosphere of Venus

A mapping of the rate of occurrence of impulsive VLF noise bursts in Venus' dark low altitude ionosphere, which increases rapidly with decreasing altitude, as a function of latitude and longitude indicates enhanced occurrence rates over Atla. In a 30-sec observing period, there are impulsive signals 70 percent of the time at 160 km in the region of maximum occurrence; the occurrence rates, moreover, increase with decreasing latitude, so that the equatorial rate is of the order of 1.6 times that at 30 deg latitude. These phenomena are in keeping with lightning-generated wave sources.

Russell, C. T.↗

NASA NTRS1989

Influence of non-stationary field of magnetospheric convection on the D-region

Perturbations of F region electron density caused by the extension of magnetospheric convection electric field to middle latitudes are already well known. For the D region of the first observations are believed to be reported by Eliseyev, Kashpar and Nikitin (1988). On several occasions, following the southward turning of the Bz-component of interplanetary magnetic field (IMF) small disturbances of the D region electron density were detected at night by steep-incidence VLF sounding, which may be attributed to the influence of the penetrated convection electric field (CEF). Some evidence is given of a local time dependence of the CEF effect in the D region and a rather good correlation is demonstrated at the initial stage of disturbance between high latitude magnetic field variations and simultaneous perturbation of the midlatitude ionospheric reflection height.

Eliseyev, A. YU.↗

NASA NTRS1990

Ionospheric signatures of cusp latitude Pc 3 pulsations

Search coil magnetometer, riometer, photometer, and ELF-VLF receiver data obtained at South Pole Station and McMurdo, Antarctica during selected days in March and April 1986 are compared. Narrow-band magnetic pulsations in the Pc 3 period range are observed simultaneously at both stations in the dayside sector during times of low IMF cone angle, but are considerably stronger at South Pole, which is located at a latitude near the nominal foot point of the dayside cusp/cleft region. Pulsations in auroral light at 427.8 nm wavelength are often observed with magnetic pulsations at South Pole, but such optical pulsations are not observed at McMurdo. The observations suggest that precipitating magnetosheathlike electrons at nominal dayside cleft latitudes are at times modulated with frequencies similar to those of upstream waves. These particles may play an important role, via modification of ionospheric currents and conductivities, in the transmission of upstream wave signals into the magnetosphere and in the generation of dayside high-latitude Pc 3 pulsations.

Engebretson, M. J.↗

NASA NTRS1990

Electron beam injection during active experiments. I - Electromagnetic wave emissions

The wave emissions produced in Echo 7 experiment by active injections of electron beams were investigated to determine the properties of the electromagnetic and electrostatic fields for both the field-aligned and cross-field injection in such experiments and to evaluate the sources of free energy and relative efficiencies for the generation of the VLF and HF emissions. It is shown that, for typical beam energies in active experiments, electromagnetic effects do not substantially change the bulk properties of the beam, spacecraft charging, and plasma particle acceleration. Through simulations, beam-generated whistlers; fundamental z-mode and harmonic x-mode radiation; and electrostatic electron-cyclotron, upper-hybrid, Langmuir, and lower-hybrid waves were identified. The characteristics of the observed wave spectra were found to be sensitive to both the ratio of the electron plasma frequency to the cyclotron frequency and the angle of injection relative to the magnetic field.

Winglee, R. M.↗

NASA NTRS1990

Method and apparatus for determining return stroke polarity of distant lightning

A method is described for determining the return stroke polarity of distant lightning for distances beyond 600 km by detecting the electric field associated with a return stroke of distant lightning, and processing the electric field signal to determine the polarity of the slow tail of the VLF waveform signal associated with the detected electric field. The polarity of the return stroke of distant lightning is determined based upon the polarity of the slow tail portion of the waveform.

Blakeslee, Richard J.↗

NASA NTRS1990

A correlative investigation of the propagation of ULF wave power through the dayside magnetosphere

Three different ULF wave phenomena (azimuthally polarized Pc 3 pulsations, radially polarized Pc 4 pulsations, and solitary Pc 5 pulsations related to solar wind pressure pulses) were studied. The main problems covered are: (1) how do magnetospheric Pc 3-4 pulsations, which appear to originate in the solar wind, enter the magnetosphere, and how is this wave energy transported throughout the magnetosphere once it enters; (2) what is the ULF response of the outer dayside magnetosphere to solar wind pressure pulses; and (3) how do Pc 3-4 pulsations modulate ELF-VLF emissions in the dayside magnetosphere.

Engebretson, Mark J.↗

NASA NTRS1990

Lightning observations from space shuttle

The experimental program of the Earth Sciences and Applications Division at NASA/MSFC includes development of the Lightning Imaging Sensor (LIS) for the NOAA Earth Observing System (EOS) Polar Platform. The research plan is to use existing lightning information to generate simulated data for the LIS experiment. Navigation algorithms were used to transform pixel locations to latitude and longitude values. The simulated data would then be used to test and develop algorithms for the analysis of LIS data. Individual frames of video imagery obtained from Space Shuttle Missions provide the raw data for the simulation. Individual video frames were digitized to get the pixel locations of lightning flashes. The pixel locations will be used to locate the geographical position of the event. Because of a lack of detailed knowledge of camera orientation with respect to the Space Shuttle, video scenes that contain identifiable city lights were chosen for analysis. A method for locating the payload bay camera axis was developed and tested. Two measurements are needed: the pixel location of the apparent horizon and a timed siting of a known location passing the principal line of the image. Individual video frames were navigated and lightning illuminated clouds were located on the map. Satisfactory agreement in location was achieved for cities and LLP lightning locations. Ground truth measurements were compared to satellite observations. A vertical lightning event was identified on the horizon. Very low frequency (VLF) transmission on this particular occassion shows a strong response to negative cloud to cloud flashes.

Boeck, William L.↗

NASA NTRS1990

Precise frequency calibration using television video carriers

The availability of inexpensive and quick precise frequency calibration methods is limited. VLF and GPS do offer precise calibration. However, antenna placement, cost of equipment, and calibration time place many restrictions on the user. The USNO maintained line-10 television Time of Coincidence (TOC) of station WTTG, channel 5, Washington, DC requires a frequency stable video carrier. This video carrier, 77.24 MHz is controlled by the same cesium beam standard controlling the TOC of line-10. Excellent frequency comparisons against this video carrier have been accomplished at 95 miles (153 km). With stable propagation and a three foot wire antenna, a part in 10(exp 9) can be determined in a few minutes. Inexpensive field equipment with a synthesized 1 kHz offset from the video carrier offers parts in 10(exp 11) calibrations in a few minutes using an oscilloscope as a phase comparator.

Burkhardt, Edward E.↗

NASA NTRS1991

Investigation of the structure of the electromagnetic field and related phenomena, generated by the Active Satellite

The altitude dependencies of the moduli of the electric field E in the VLF and LF frequency bands (f sub B much less than F less than f sub B) and in the altitude range of the ionosphere Z equals (400 to 2500) km up to Z equals 6000 km (the bottom of the magnetosphere) were calculated by the linear theory. The amplitudes of the field have large maxima in four regions: the axis field (E sub o) close to the direction of the Earth's magnetic field line B sub o, beta approximately 0 degrees, the fields (E sub St), (E sub RevSt) and (E sub Res) in the Storey, Reversed Story and Resonance cones, beta approximately (0 approaches 20) degrees. Their maxima are very pronounced close to the low hybrid frequency F sub L. The nonlinear heating of the magnetoplasma under the action of an electric field Ee (sup iwt) was recently expanded by the macroscopic theory by the author. The velocities, collision frequencies and temperatures of all the constituents of a magnetoplasma - electrons, ions, and neutral particles - are taken into account. Formulae and numerical results are presented for the ionosphere in the frequency band F equals (1 to 10 exp 4) kHz and altitude range Z approximately (100 - 1000) km. Some results of calculations by the self consistent solution of the basis system of equations are also discussed.

Alpert, Yakov L.↗

NASA NTRS1991

Anomalous optical events detected by rocket-borne sensor in the WIPP campaign

This paper describes the instruments used in the Wave Induced Particle Precipitation campaign in 1987, in which one rocket and four balloons were launched near thunderstorms from the NASA Wallops Flight Facility. Examples of both the lightning events and the anomalous optical events (AOEs) detected on July 31, 1987 are presented. It is shown that the signatures of these AOEs differ from those of well-known optical sources in the atmosphere. It was found that AOEs were sometimes associated with subionospheric VLF signal perturbations (Trimpi events), suggesting a possibility that AOEs might be linked to a disturbance of the electron concentration in the high-altitude atmosphere or lower ionosphere.

Li, Ya QI↗

NASA NTRS1991

Venus lightning

Although it is not unanimously accepted, many independent observations lead to the conclusion that lightning is prevalent on Venus. The EM signals detected by all four Venera landers are most readily explained as generation by lightning. The Venera 9 spectrometer appears to have observed a lightning storm on one occasion. The Pioneer Venus plasma-wave instrument detects waves both below the electron gyrofrequency (that may be due to lightning) and signals above the electron gyrofrequency but at very low altitudes (that may be due to the near field of the lightning). The VLF observations suggest that Venus lightning must be an intracloud phenomenon which is most frequent in the afternoon and evening sector. The occurrence rate is likely to be greater than on earth.

Russell, C. T.↗

NASA NTRS1991

Harmonic H(+) gyrofrequency structures in auroral hiss observed by high-altitude auroral sounding rockets

Two recent sounding rocket experiments have yielded VLF wave data with spectral structures ordered by the hydrogen gyrofrequency. The spectral structures occur near and above the lower hybrid frequency in association with auroral hiss. These structures are observed within and near regions of auroral electron precipitation and transverse ion acceleration. They are accompanied by auroral hiss but are anticorrelated with spectral peaks at the lower hybrid frequency. They are typically found above 500 km altitude, have no measurable magnetic component, and are at least occasionally short wavelength. Because the spectral structures appear to be electrostatic, are ordered by the hydrogen gyrofrequency, and are short wavelength, the structures are interpreted as modes which connect the lower hybrid mode with the hydrogen Bernstein modes. A study of the plasma wave mode structure in the vicinity of the lower hybrid frequency is presented to substantiate this interpretation. These results imply that these waves are a common feature of the auroral zone ionsphere above 500 km altitude and exist any time that auroral hiss exists. The absence of previous satellite observations of this phenomenon can be explained by Doppler broadening.

Kintner, P. M.↗

NASA NTRS1991

Laboratory experiments on the electrodynamic behavior of tethers in space

The transient current systems between tethered plasmas in a large magnetoplasma are investigated experimentally for extrapolation to electrodynamic tethers in space. The studies measure the perturbed magnetic fields and the current density associated with pulsed currents to electrodes in three-dimensional space and time. The electrodes excite electron whistlers because they produce fields that dominantly couple to electrons, allowing pulsed currents to propagate and disperse as whistler wave packets. The wave packets evolve into force-free, flux-ropelike field configurations, and a whistler 'wedge' is formed in the plasma due to 'eddy' currents caused by insulated tethers with dc currents. Substantial radiation into the whistler mode happens with moving VLF antennas as well as tethers, and the wave spread within the ray cone is the most significant characteristic event. The wave spread widens the current channel, incites current closure, and is also associated with a 'phantom loop' phenomenon.

Stenzel, Reiner L.↗

NASA NTRS1991

Wave mode identification of electrostatic noise observed with ISEE 3 in the deep tail boundary layer

The characteristics of the VLF electrostatic noise observed with ISEE 3 in the low-latitude boundary layer of distant geomagnetic tail are examined using a display format for the wave dynamic spectra different from that used by Scarf et al. (1984). It is shown that the observed noise is composed of impulsive bursts. The results of the detailed analysis of the noise parameters are used to develop a model of plasma wave behavior in the plasma rest frame. A hypothesis is proposed that the wide frequency extent of the noise spectra is composed of Doppler effects of waves propagating nearly omnidirectionally within the plasma rest frame, which is moving with the electron bulk speed. On the basis of this hypothesis, the wavelength of the observed waves were determined from the width of the frequency extent and the measured electron bulk speed. It is shown that the wavelength ranges from 2 to 8 times the plasma Debye length.

Tsutsui, M.↗