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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 91 records · Page 5
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NASA NTRS1981

Dynamic variations observed in thermal and superthermal ion distributions in the dayside ionosphere of Venus

In-situ measurements of the ion composition and concentration of the ionosphere of Venus are obtained with the Bennett RF ion mass spectrometer (OIMS) on the Pioneer Venus Orbiter (PVO). Dayside ion profiles exhibit considerable variability in the height of the ionopause as well as the scale heights of the ion constituents, which reflect the compression and expansion of the ionosphere in response to solar wind variations. Near the dayside upper boundary of the thermal O+ distribution, super-thermal ions are detected by the OIMS, presenting a complication for identifying the ion signature of the ionopause. Correlated with the presence of the superthermal ions, the ac electric field detector (OEFD) detects regions of intensified signals, with peak response in the 100 Hz frequency channel. It is expected that further analysis of the superthermal ion-electric field signatures will contribute to a clearer understanding of the physical processes underlying the formation of the ionopause.

Taylor, H. A., Jr.↗
NASA NTRS1989

Solar activity influence on climatic variations of stratosphere and mesosphere in mid-latitudes

The direct modulation of temperature of the mid-latitude mesosphere by the solar-cycle EUV variation, which leads to greater heat input at higher solar activity, is well established. Middle atmosphere temperature modulation by the solar cycle is independently confirmed by the variation of reflection heights of low frequency radio waves in the lower ionosphere, which are regularly monitored over about 30 years. As explained elsewhere in detail, these reflection heights depend on the geometric altitude of a certain isobaric surface (near 80 k), and on the solar ionizing Lyman-alpha radiation flux. Knowing the solar cycle variation of Lyman-alpha how much the measured reflection heights would be lowered with the transition from solar minimum to maximum can be calculated, if the vertical baric structure of the neutral atmosphere would remain unchanged. An discrepancy between expected and observed height change must be explained by an uplifting of the isobaric level from solar minimum to maximum, caused by the temperature rise in the mesosphere. By integrating the solar cycle temperature changes over the height region of the middle atmosphere, and assuming that the lower boundary (tropopause) has no solar cycle variation, the magnitude of this uplifting can be estimated. It is given for the Lidar-derived and for the rocket-measured temperature variations. Comparison suggests that the real amplitude of the solar cycle temperature variation in the mesosphere is underestimated when using the rocket data, but probably overestimated with the Lidar data.

Taubenheim, J.↗
NASA NTRS2008

Lessons Learned from Previous Space-Borne Sounders as a Guide to Future Sounder Development

Space-borne radio sounding is considered to be the gold standard for electron-density (N(sub e)) measurements compared to other techniques even under low-density conditions, such as N(sub e) < 1/cu cm, when other techniques are known to experience difficulties. These reliable measurements are not restricted to in-situ N(sub e) determinations since a spaceborne sounder can provide vertical N(sub e) profiles (N(sub e)(h)) from the spacecraft altitude to the altitude of maximum N(sub e). Near-conjunction studies involving the International Satellites for Ionospheric Studies (ISIS) satellites in the topside ionosphere and Dynamics Explorer 2 (DE 2) near the altitude of the F-region peak density have verified that, even at the greatest distance from the sounder, the ISIS-derived N(sub e)(h) profiles agree with the DE-2 Langmuir-probe measurements to within about 30% over a density range of more than two decades. Space-borne sounders can also provide N(sub e) profiles along the magnetic-field B, by inverting echoes that are ducted along field-aligned irregularities (FAI), and can provide information about the terrain beneath the satellite by examining surface reflections in the frequency range above the ionospheric penetration frequency. Many nations have launched rocket and satellite radio sounders in geospace over more than 4 decades and there have been sounders on space-probes and in orbit around other planets. Here we will summarize some of the lessons learned from these accomplishments by analyzing data from radio sounders on the Alouette and ISIS satellites and the OEDIPUS and other rockets in the terrestrial ionosphere, the IMAGE satellite in the terrestrial magnetosphere, the Ulysses space probe in Jupiter's 10 plasma torus and the MARSIS satellite in orbit around Mars. The emphasis will be on information deduced concerning (1) fundamental plasma processes and gradients in N, and B in the vicinity of the sounders from sounder-stimulated plasma resonances and short-range echoes involving ion as well as electron motions, (2) the importance of the antenna orientation relative to B for the detection of different plasma resonances, (3) sounder-stimulated plasma phenomena, including FAI, when special plasma conditions are satisfied, (4) the minimum power required for long-range echoes, as indicated by echoes from frequency components of the transmitted pulse and by multiple ducted echoes, and (5) the terrain beneath the satellite from surface reflections. Knowledge of these results should enable the optimum design of a future sounder to satisfy specific science requirements with minimal spacecraft resources.

Benson, Robert F.↗
NASA NTRS2007

Estimation of the Total Electron Content of the Martian Ionosphere using Radar Sounder Surface Echoes

The Martian ionosphere's local total electron content (TEC) and the neutral atmosphere scale height can be derived from radar echoes reflected from the surface of the planet. We report the global distribution of the TEC by analyzing more than 750,000 echoes of the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS). This is the first direct measurement of the TEC of the Martian ionosphere. The technique used in this paper is a novel 'transmission-mode' sounding of the ionosphere of Mars in contrast to the Active Ionospheric Sounding experiment (AIS) on MARSIS, which generally operates in the reflection mode. This technique yields a global map of the TEC for the Martian ionosphere. The radar transmits a wideband chirp signal that travels through the ionosphere before and after being reflected from the surface. The received waves are attenuated, delayed and dispersed, depending on the electron density in the column directly below the spacecraft. In the process of correcting the radar signal, we are able to estimate the TEC and its global distribution with an unprecedented resolution of about 0.1 deg in latitude (5 km footprint). The mapping of the relative geographical variations in the estimated nightside TEC data reveals an intricate web of high electron density regions that correspond to regions where crustal magnetic field lines are connected to the solar wind. Our data demonstrates that these regions are generally but not exclusively associated with areas that have magnetic field lines perpendicular to the surface of Mars. As a result, the global TEC map provides a high-resolution view of where the Martian crustal magnetic field is connected to the solar wind. We also provide an estimate of the neutral atmospheric scale height near the ionospheric peak and observe temporal fluctuations in peak electron density related to solar activity.

magnetic field↗
NASA NTRS1997

Achieving Zero Current for Polar Wind Outflow on Open Flux Tubes Subjected to Large Photoelectron Fluxes

In this study we investigate how the condition of zero current on open flux tubes with polar wind outflow, subjected to large photoelectron fluxes, can be achieved. We employ a steady state collisionless semikinetic model to determine the density profiles of O(+), H(+), thermal electrons and photoelectrons coming from the ionosphere along with H(+), ions and electrons coming from the magnetosphere. The model solution attains a potential distribution which both satisfies the condition of charge neutrality and zero current. For the range of parameters considered in this study we find that a 45-60 volt discontinuous potential drop may develop to reflect most of the photoelectrons back toward the ionosphere. This develops because the downward flux of electrons from the magnetosphere to the ionosphere on typical open flux tubes (e.g. the polar rain) appears to be insufficient to balance the photoelectron flux from the ionosphere.

Wilson, G. R.↗
NASA NTRS1979

The magnetospheric electric field and convective processes as diagnostics of the IMF and solar wind

Indirect measurements of the convection field as well as direct of the ionospheric electric field provide a means to at least monitor quanitatively solar wind processes. For instance, asymmetries in the ionospheric electric field and ionospheric Hall currents over the polar cap reflect the solar wind sector polarity. A stronger electric field, and thus convective flow, is found on the side of the polar cap where the y component of the IMF is parallel to the y component of the geomagnetic field. Additionally, the magnitude of the electric field and convective southward B sub Z and/or solar wind velocity, and thus may indicate the arrival at Earth of an interaction region in the solar wind. It is apparent that processes associated with the convention electric field may be used to predict large scale features in the solar wind; however, with present empirical knowledge it is not possible to make quantitative predictions of individual solar wind or IMF parameters.

Kaye, S. M.↗
NASA NTRS1977

The large-scale ionospheric electric field - Its variation with magnetic activity and relation to terrestrial kilometric radiation

Four days of simultaneous auroral zone electric field measurements on balloons flown from six sites spanning 180 deg of magnetic longitude have been analyzed. The average electric field behavior during this magnetically quiet epoch is consistent with earlier single-point measurements, although the average auroral zone electric field was more affected by corotation effects than it was during more disturbed times. When these data, which primarily reflect the large-scale (several hundred kilometer) ionospheric electric field, are mapped to the equator, a steady dawn to dusk component is apparent only on the average, while instantaneously the field is quite variable. The ionospheric electric field during isolated substorms is shown to have differing signatures east and west of 2200 LT. A worldwide positive correlation is shown to exist between the auroral zone electric field strength and the intensity of terrestrial kilometric radiation.

Holzworth, R. H.↗
NASA NTRS1997

Experimental Verification of Ocean Bounced GPS Signals and Analysis of their Application to Ionospheric Corrections for Satellite Altimetry

An algorithm is presented which uses observations of Global Positioning System (GPS) signals reflected from the ocean surface and acquired by a GPS receiver onboard an altimetric satellite to compute the ionospheric delay present in the altimeter measurement. This eliminates the requirement for a dual frequency altimeter for many Earth observing missions. A ground-based experiment is described which confirms the presence of these ocean-bounced signals and demonstrates the potential for altimeter ionospheric correction at the centimeter level.

Axelrad, P.↗
NASA NTRS1992

Electron beams and their interactions with the ionosphere - A review of the E parallel B series

A review is presented of results from a series of experiments which began with an attempt to reflect electrons from the potential change which is thought to generate the aurora. In order to understand the experiment, this series then expanded to study beam-plasma interactions in the laboratory as well as in the ionosphere. Results from the electron reflection experiment, as well as in situ and ground-based observations of the waves generated by beam-plasma interactions will be reviewed. Measurements bearing on modifications of the ambient plasma by the beam-emitting rocket will be presented.

Kellogg, P. J.↗
NASA NTRS1982

DE-2 cusp observations - Role of plasma instabilities in topside ionospheric heating and density fluctuations

Observations by the low altitude Dynamics Explorer satellite (DE-2) in the polar cusp show the ionospheric plasma electron temperature and the ratio of electron to ion temperature to be increased, and the electron density fluctuations to be enhanced. Also, downward fluxes of energetic eletrons and ions increase in the cusp, and the magnetic field structure are consistent with the existence of a field-aligned current. Simultaneously, there is characteristic broadband electrostatic noise (BEN) with amplitudes of 1-10 mV/m, peaking in the cusp but extending into the polar cap. These emissions range from far below the local 0(+) gyrofrequency F sub O(+) to the vicinity of the proton gyrofrequency, but below the oxygen lower hybrid frequency. The BEN observations are compared to the predictions of several theories. The amplitude of these waves is shown to be far too small to contribute significantly to the observed ionospheric heating or density fluctuations by local wave-particle interactions. Rather, the observed spatial variations are attributed to nonlocal field aligned heating processes and reflect the nonuniformity of the magnetosheath plasma's penetration into the ionosphere.

Curtis, S. A.↗
NASA NTRS1979

Electromagnetic noise and radio wave propagation below 100 kHz in the Jovian atmosphere. I - The equatorial region

The Galileo satellite program includes the delivery of an entry probe to the Jovian equatorial atmosphere in mid-1985. Optical and RF sensors for a lightning detection system are included as a part of the probe experimental payload. In this paper, calculations of the RF wave propagation and reflection characteristics of the equatorial Jovian atmosphere and ionosphere for frequencies less than 100 kHz are presented. It is shown that wave propagation is limited to line-of-sight and one-hop from the ionosphere. Results are also presented of a statistical treatment of the RF wave power densities for the case of a finite number of events and for the case of a uniformly distributed source. The results can be applied to specific RF experiment configurations concerned with establishing the statistical characteristics of Jovian lightning.

Rinnert, K.↗
NASA NTRS1983

Saturn's ionosphere: Inferred electron densities

During the two Voyager encounters with Saturn, radio bursts were detected which appear to have originated from atmospheric lightning storms. Although these bursts generally extended over frequencies from as low as 100 kHz to the upper detection limit of the instrument, 40 MHz, they often exhibited a sharp but variable low frequency cutoff below which bursts were not detected. We interpret the variable low-frequency extent of these bursts to be due to the reflection of the radio waves as they propagate through an ionosphere which varies with local time. We obtain estimates of electron densities at a variety of latitude and local time locations. These compare well with the dawn and dusk densitis measured by the Pioneer 11 Voyager Radio Science investigations, and with model predictions for dayside densities. However, we infer a two-order-of-magnitude diurnal variation of electron density, which had not been anticipated by theoretical models of Saturn's ionosphere, and an equally dramatic extinction of ionospheric electron density by Saturn's rings.

Kaiser, M. L.↗
NASA NTRS1984

Saturn's ionosphere - Inferred electron densities

During the two Voyager encounters with Saturn, radio bursts were detected which appear to have originated from atmospheric lightning storms. Although these bursts generally extended over frequencies from as low as 100 kHz to the upper detection limit of the instrument, 40 MHz, they often exhibited a sharp but variable low frequency cutoff below which bursts were not detected. We interpret the variable low-frequency extent of these bursts to be due to the reflection of the radio waves as they propagate through an ionosphere which varies with local time. We obtain estimates of electron densities at a variety of latitude and local time locations. These compare well with the dawn and dusk densities measured by the Pioneer 11 Voyager Radio Science investigations, and with model predictions for dayside densities. However, we infer a two-order-of-magnitude diurnal variation of electron density, which had not been anticipated by theoretical models of Saturn's ionosphere, and an equally dramatic extinction of ionospheric electron density by Saturn's rings. Previously announced in STAR as N84-17102

Kaiser, M. L.↗
NASA NTRS2012

Improving the Automatic Inversion of Digital Alouette/ISIS Ionogram Reflection Traces into Topside Electron Density Profiles

The topside sounders of the International Satellites for Ionospheric Studies (ISIS) program were designed as analog systems. The resulting ionograms were displayed on 35 mm film for analysis by visual inspection. Each of these satellites, launched between 1962 and 1971, produced data for 10 to 20 years. A number of the original telemetry tapes from this large data set have been converted directly into digital records. Software, known as the Topside Ionogram Scalar With True-Height (TOPIST) algorithm, has been produced and used for the automatic inversion of the ionogram reflection traces on more than 100,000 ISIS-2 digital topside ionograms into topside vertical electron density profiles Ne(h). Here we present some topside ionospheric solar cycle variations deduced from the TOPIST database to illustrate the scientific benefit of improving and expanding the topside ionospheric Ne(h) database. The profile improvements will be based on improvements in the TOPIST software motivated by direct comparisons between TOPIST profiles and profiles produced by manual scaling in the early days of the ISIS program. The database expansion will be based on new software designed to overcome limitations in the original digital topside ionogram database caused by difficulties encountered during the analog-to-digital conversion process in the detection of the ionogram frame sync pulse and/or the frequency markers. This improved and expanded TOPIST topside Ne(h) database will greatly enhance investigations into both short- and long-term ionospheric changes, e.g., the observed topside ionospheric responses to magnetic storms, induced by interplanetary magnetic clouds, and solar cycle variations, respectively.

Benson, Robert F.↗
NASA NTRS1971

Partial reflection data collection and processing using a small computer

Online data collection of the amplitudes of circularly polarized radio waves, partially reflected from the D region of the earth's ionosphere, has enabled the calculation of an electron-density profile in the height region 60-90 km. A PDP 15/30 digital computer with an analog to digital converter and magnetic tape as an intermediary storage device are used. The computer configuration, the software developed, and the preliminary results are described.

Birley, M. H.↗
NASA NTRS1973

The correlation of VLF propagation variations with atmospheric planetary-scale waves

Variations in the received daytime phase of long distance, cesium-controlled, VLF transmission were compared to the height variations of the 10-mb isobaric surface during the first three months of 1965 and 1969. The VLF phase values are also compared to height variations of constant electron densities in the E-region and to variations of f-min which have been shown to be well correlated with planetary-scale variations in the stratosphere by Deland and Cavalieri (1973). The VLF phase variations show good correlation with these previous ionospheric measurements and with the 10-mb surfaces. The planetary scale waves in the stratosphere are shown to be travelling on the average eastward in 1965 and westward in 1969. These correlations are interpreted as due to the propagation of travelling planetary scale waves with westward tilted wave fronts. Upward energy transport due to the vertical structure of those waves is also discussed. These correlations provide further evidence for the coupling between the lower ionosphere at about 70 km altitude (the daytime VLF reflection height and the stratosphere, and they demonstrate the importance of planetary wave phenomena to VLF propagation.

Cavalieri, D. J.↗
NASA NTRS1982

Dynamics of magnetosphere-ionosphere coupling including turbulent transport

A two dimensional two-fluid MHD model including anomalous resistivity was used to investigate the dynamics of magnetosphere-ionosphere coupling. When a field-aligned current is generated on auroral field lines, the disturbance propagates towards the ionosphere in the form of a kinetic Alfven wave. When the current exceeds a critical value, microscopic turbulence is produced, which modifies the propagation of the Alfven wave. This process is modeled by a nonlinear collision frequency, which increases with the excess of the drift velocity over the critical value. Turbulence leads to absorption and reflection of the Alfven wave, partially decoupling the generator from the ionosphere. The approach to a steady-state is strongly dependent on the presence or absence of the turbulence. The current is self-limiting, since a current in excess of critical causes a diffusion of the magnetic field perturbation and a reduction of current.

Lysak, R. L.↗