Search NASA⌕ Search

SEARCH · Search NASA

Results for “IONOSPHERIC DRIFT”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Fe/+/ ions in the high latitude F-region

Ion mass-spectrometer measurements on Atmosphere Explorer C orbits from December 1974 to December 1976 were surveyed poleward of + or - 30 deg for instances in which the Fe(+) number density exceeded the spectrometer threshold sensitivity of 30/cu cm. The occurrences of Fe(+) within the altitude range covered by the orbit, 220 to 320 km, revealed a distinct pattern apparently associated with regions of upward plasma transport. At night a band of such events occurred between 50 and 60 deg invariant latitude, which typically corresponded to the location of the main ionospheric trough. In this region large upward ion drifts due to the drag of an equatorward-blowing neutral wind are expected. The Fe(+) band extends past 0600 MLT to about 1100 MLT during the summer, but is not observed in the afternoon. The dayside distributions possibly result from the upward drifts of F-region ions detected by backscatter techniques after dawn during summer. At higher latitudes patches of Fe(+) were detected in regions where strong plasma drifts often prevail and hence where poleward E x B drift motions and atmospheric expansion through Joule heating can lift the ions upwards.

Grebowsky, J. M.↗
NASA NTRS1983

Mapping electrostatic potentials from the ionosphere to the magnetosphere

Techniques for mapping observed ionospheric-potential distributions into the magnetosphere are discussed and illustrated using published Millstone Hill and Chatanika incoherent-scatter-radar data. It is shown that the mapping of a given field line to the equator is subject to strong diurnal and seasonal variations (attributed to the combination of internal and tail-current magnetic-field sources at auroral latitudes and the diurnal variation of solar declination in dipole coordinates) and longitude-dependent differences in ionospheric geometry. A mapping based on the tilt-dependent model of Olson and Pfitzer (1977) and using an empirical ionospheric-potential distribution derived from Chatanika plasma-drift measurements produces a relativity uniform magnetospheric electric field in the tail region. The field at 12 earth radii (Re) is found to be between 1 and 2 kV/Re; at the dawn-dusk meridian beyond the plasmasphere it is as high as 5 kV/Re. The plasmasphere is shown to have a dusk bulge in its equipotential structure and to be almost symmetric about the dawn-dusk meridian.

Sojka, J. J.↗
NASA NTRS1992

Anisotropic ion heating and parallel O(+) acceleration in regions of rapid E x B convection

A numerical solution to the 20-moment set of transport equations has been found in order to study subauroral ionospheric outflows during periods of enhanced perpendicular ion drifts. The numerical model solves the time-dependent O(+) density, momentum, and both the parallel and perpendicular energy and heat flow equations in the 200-6000 km altitude range. Assuming perpendicular drifts of 3 km/s relative to the neutral atmosphere, we have found that anisotropic heating of O(+) (a result of ion-neutral collisions) leads to a temperature anisotropy, with perpendicular temperatures exceeding 8000 K and parallel temperatures greater than 5000 K (near 200 km altitude). Above approximately 2000 km, transport processes dominate the effects of collisions and wavelike oscillations in O(+) velocity, temperature and heat flux were noted.

Korosmezey, A.↗
NASA NTRS1992

The Harang discontinuity and magnetospheric forecasting

This paper describes the physics of the Harang discontinuity and its application to forecasting of the magnetospheric environment. Gradient/curvature depletion of energetic ions from earthward drifting flux tubes results in upward Birkeland currents. Ionospheric closure rotates the dawn-dusk convection electric field resulting in the Harang reversal. This physical mechanism has been incorporated into the Rice Convection Model (RCM) and can serve as a fundamental part of the forecasting of the magnetospheric system. The inclusion of this physics within the RCM results in a physical picture of the Harang discontinuity which did not previously exist. Model results are close to observations and represent a significant improvement in predicted electric field and Birkeland current patterns.

Erickson, G. M.↗
NASA NTRS1983

Cold streams of ionospheric oxygen in the plasma sheet during the CDAW-6 event of March 22, 1979

During magnetospheric substorm events, the plasma and ion composition experiments in the ISEE-1 and 2 satellites detected cold ionospheric O+ streams, moving tailwards in the near Earth magnetotail. Flow is parallel to the magnetic field lines, with drift velocity in agreement with the electric field topology obtained by mapping the model ionospheric field along the magnetic field lines. Fluctuations of the flow velocity of the streams can be related to magnetotail movements. Oscillations of the flow direction and speed with periods ranging from 5 to 10 min that suggest the presence of waves are observed. The streams are observed at all distances between 15 and 6 Re from the Earth. When averaged over 360 deg, the streams show up as a low energy peak, superimposed on the distribution of isotropic plasma sheet ions. This double-peak structure of the energy spectrum seems typical of the disturbed plasma sheet.

Orsini, S.↗
NASA NTRS1985

Cold streams of ionospheric oxygen in the plasma sheet during the CDAW 6 event of March 22, 1979

During magnetospheric substorm events, the plasma and ion composition experiments in the ISEE-1 and 2 satellites detected cold ionospheric O+ streams, moving tailwards in the near earth magnetotail. Flow is parallel to the magnetic field lines, with drift velocity in agreement with the electric field topology obtained by mapping the model ionospheric field along the magnetic field lines. Fluctuations of the flow velocity of the streams can be related to magnetotail movements. Oscillations of the flow direction and speed with periods ranging from 5 to 10 min that suggest the presence of waves are observed. The streams are observed at all distances between 15 and 6 Re from the earth. When averaged over 360 deg, the streams show up as a low energy peak, superimposed on the distribution of isotropic plasma sheet ions. This double-peak structure of the energy spectrum seems typical of the disturbed plasma sheet.

Orsini, S.↗
NASA NTRS1984

Effects of line-of-sight velocity on spaced-antenna measurements, part 3.5A

Horizontal wind velocities in the upper atmosphere, particularly the mesosphere, have been measured using a multitude of different techniques. Most techniques are based on stated or unstated assumptions about the wind field that may or may not be true. Some problems with the spaced antenna drifts (SAD) technique that usually appear to be overlooked are investigated. These problems are not unique to the SAD technique; very similar considerations apply to measurement of horizontal wind using multiple-beam Doppler radars as well. Simply stated, the SAD technique relies on scattering from multiple scatterers within an antenna beam of fairly large beam width. The combination of signals with random phase gives rise to an interference pattern on the ground. This pattern will drift across the ground with a velocity twice that of the ionospheric irregularities from which the radar signals are scattered. By using spaced receivers and measuring time delays of the signal fading in different antennas, it is possible to estimate the horizontal drift velocities.

Royrvik, O.↗
NASA NTRS2011

Observations of Low-Latitude Plasma Density Enhancements and their Associated Plasma Drifts

Plasma density structures are frequently encountered in the nighttime low-latitude ionosphere by probes on the Communication/Navigation Outage Forecasting System (C/NOFS) satellite. Of particular interest to us here are plasma density enhancements, which are typically observed +/- 15 deg away from the magnetic equator. The low inclination of the C/NOFS satellite offers an unprecedented opportunity to examine these structures and their associated electric fields and plasma velocities, including their field-aligned components, along an east-west trajectory. Among other observations, the data reveal a clear asymmetry in the velocity structure within and around these density enhancements. Previous observations have shown that the peak change in drift velocity associated with a density enhancement occurs simultaneously both perpendicular and parallel to the magnetic field, while the 1results in this paper show that the peak change in parallel fl ow typically occurs 25-100 km to the east of the peak perpendicular ow. We discuss this and other aspects of the observations in relation to the characteristics of the plasma depletions formed near the magnetic equator detected by the same probes on the C/NOFS satellite and to previous observations and theories.

Klenzing, J. H.↗
NASA NTRS1978

Effect of diffusion-thermal processes on the high-latitude topside ionosphere

The extent to which diffusion-thermal heat flow affects H(+) temperatures in the high-latitude topside ionosphere is studied. Such a heat flow occurs whenever there are H(+)-O(+) relative drifts. From our study we have found that at high-latitudes, where H(+) flows up and out of the topside ionosphere, diffusion-thermal heat flow acts to reduce H(+) temperatures by 500-600 K at altitudes above about 900 km.

Schunk, R. W.↗
NASA NTRS2010

Dst Index in the 2008 GEM Modeling Challenge - Model Performance for Moderate and Strong Magnetic Storms

The GEM 2008 modeling challenge efforts are expanding beyond comparing in-situ measurements in the magnetosphere and ionosphere to include the computation of indices to be compared. The Dst index measures the largest deviations of the horizontal magnetic field at 4 equatorial magnetometers from the quiet-time background field and is commonly used to track the strength of the magnetic disturbance of the magnetosphere during storms. Models can calculate a proxy Dst index in various ways, including using the Dessler-Parker Sckopke relation and the energy of the ring current and Biot-Savart integration of electric currents in the magnetosphere. The GEM modeling challenge investigates 4 space weather events and we compare models available at CCMC against each other and the observed values of Ost. Models used include SWMF/BATSRUS, OpenGGCM, LFM, GUMICS (3D magnetosphere MHD models), Fok-RC, CRCM, RAM-SCB (kinetic drift models of the ring current), WINDMI (magnetosphere-ionosphere electric circuit model), and predictions based on an impulse response function (IRF) model and analytic coupling functions with inputs of solar wind data. In addition to the analysis of model-observation comparisons we look at the way Dst is computed in global magnetosphere models. The default value of Dst computed by the SWMF model is for Bz the Earth's center. In addition to this, we present results obtained at different locations on the Earth's surface. We choose equatorial locations at local noon, dusk (18:00 hours), midnight and dawn (6:00 hours). The different virtual observatory locations reveal the variation around the earth-centered Dst value resulting from the distribution of electric currents in the magnetosphere during different phases of a storm.

Rastaetter, Lutz↗
NASA NTRS1993

Small-scale density irregularities in the nightside Venus ionosphere - Comparison of theory and observations

The theory of the lower-hybrid-drift instability is compared with observations of plasma density irregularities. Marginal stability boundaries (gamma = 0) for the lower-hybrid-drift instability and the occurrence of small-scale density fluctuations are presented as a function of magnetic field B and density n. For plasma density gradient scale lengths in the range 2-10 km, 80-85 percent of the density fluctuations lie in the unstable B/n parameter regime (gamma greater than 0). Stability boundaries for the onset of instability at a wavelength for which the Pioneer Venus Orbiter could measure a Doppler-shifted frequency of 100 Hz are presented. The conditions on B and n for instability in this situation are more stringent than those for marginal stability, especially at low densities (n less than or equal to 5000/cu cm). In general, the instability is most likely to be active in regions of low beta: high magnetic field strength and low density, as found in ionospheric holes or troughs.

Huba, J. D.↗
NASA NTRS1993

Model of superthermal ions in the Venus ionosphere

A model is presented that simulates the behavior of superthermal ions previously reported in the dayside ionosphere of Venus. The model considers effects of ExB and gradient drifts, charge exchange and collisions with the ambient neutral atmosphere and the possible effects of a wave-particle (anomalous) scattering process. Results indicate that scattering processes are required if superthermal ions are the explanation for the observed 'missing pressure' component in the day-side Venus ionosphere. The scattering scale length required to match the 'missing pressure' distribution is similar to the scale length previously predicted for growth of a lower hybrid beam instability.

Kramer, Leonard↗
NASA NTRS1985

ELF wave production by an electron beam emitting rocket system and its suppression on auroral field lines - Evidence for Alfven and drift waves

Orthogonal probes on a free-flying plasma diagnostics payload are used to study ELF electric disturbances in the auroral ionosphere that are due to the injection of powerful electron beams. Frequency spectrograms are presented for various pitch angles, pulsing characteristics, and other properties of the injected beams; the large scale DC ionospheric convection electric field is measured, together with auroral particle precipitation, visual auroral forms, and ionospheric parameters. In view of the experimental results obtained, it is postulated that the observed ELF waves are in the Alfven and drift modes, and are generated by the positive vehicle potential during beam injection.

Winckler, J. R.↗
NASA NTRS1994

Ionospheric footprint of magnetosheathlike particle precipitation observed by an incoherent scatter radar

We have examined Sondrestrom incoherent scatter radar observations of ionospheric plasma density and temperature distributions and measurements of F region ion drifts that were made during a prenoon pass of the Defense Meteorological Satellite Program (DMSP)-F7 satellite through the radar field of view. The spacecraft traversed a region of intense electron precipitation with a characteristic energy below approximately 200 eV. Particles with such low characteristic energies are believed to be directly or indirectly of magnetosheath origin. The precipitation region had a width about 2 deg invariant latitude and covered the low-latitude boundary layer (LLBL), the cusp, and the equatorward section of the plasma mantle (PM). The corotating radar observed a patch of enhanced electron density and elevated electron temperature in the F2 region between about 10.5 and 12 magnetic local time in the same invariant latitude range where DMSP-F7 detected the soft-electron flux. The ion drift pattern, also obtained by radar, shows that it is unlikely that the plasma patch was produced by solar radiation and advected into the radar field of view. We suggest that the radar observed modifications of the ionospheric plasma distribution, which resulted from direct entry of magnetosheath electrons into the magnetosphere and down to ionospheric altitudes. Model calculations of the ionospheric response to the observed electron precipitation support our interpretation. The spectral characteristics of the electron flux in the LLBL, cusp, and equatorward section of the PM were in this case too similar to allow to distinguish between them by using incoherent scatter radar measurements only.

Watermann, Jurgen↗
NASA NTRS1973

Spatial resonance in the ionosphere.

When the phase velocity of an internal gravity wave equals the natural drift of an ionization irregularity, then a spatial resonance results. If the ionization irregularity has been produced by the gravity wave then it is possible to obtain simple quantitative relations to describe this effect. They indicate this spatial resonance will only occur when the horizontal electric field is westward (i.e., at night), and for tropospherically launched waves it will only affect the ionization at the valley of the equatorial electron density profile.

Beer, T.↗
NASA NTRS1992

Theory of small-scale density and electric field fluctuations in the nightside Venus ionosphere

Recently, it has been reported that small-scale (lambda about 0.1-2 km) density irregularities occur during 100-Hz electric field bursts in the nightside ionosphere of Venus. This paper provides a detailed analysis of the lower-hybrid-drift instability as a mechanism to generate the observed irregularities. A fully electromagnetic theory is developed that is relevant to the finite beta plasma in Venus's ionosphere and includes collisional effects (e.g., electron-ion, electron-neutral, and ion-neutral collisions). The key features of the analysis that favor this instability are the following: (1) it is a flute mode and propagates orthogonal to the ambient magnetic field; (2) it is a relatively short wavelength mode and the Doppler-shifted frequency can be greater than about 100 Hz; (3) it can produce both electric field and density fluctuations, as well as magnetic field fluctuations in a finite beta plasma; and (4) it is most unstable in low-beta plasmas so that it is likely to occur in the low-density, high-magnetic-field ionospheric holes. These features are consistent with observational results.

Huba, J. D.↗
NASA NTRS1972

Synthesis of Jicamarca data during the great storm of March 8, 1970.

Continuous measurement of electron temperature and electron concentration during the great magnetic storm of Mar. 8, 1970, when the F2 peak rose as high as 800 km. Continuous measurements of the vertical component of E x B drift were made from 1130 to 1730 LT. A synthesis of the observed electron concentrations was made using a model that solved the time-dependent electron-ion continuity equation for O(+) and the molecular ions; the latter chemistry was included to improve the solutions at lower heights. It was found, using the observed values of vertical drift, that most of the observed features of the F2-region ionosphere were synthesized by the model. An interpretation of the synthesis that emphasizes the importance of horizontal diffusion at the equator is given. Observations are presented for Mar. 7, 8, and 9, 1970, including the Huancayo magnetograms, which display a close correlation with the drift measurements.

Woodman, R. F.↗