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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Equatorial ion composition, 140-200 km, based on Atmosphere Explorer E data

We have used in situ measurements of ion composition and horizontal winds, taken from equatorial orbiting Atmosphere Explorer E in eccentric orbit during 1975-1976 to investigate the bottomside ionosphere at altitudes 140-200 km. Representative daytime altitude profiles of ionization were stable against wide variations in horizontal wind patterns. Special features that sometimes appeared in the structured nightside ionization were apparent ion composition waves, intermediate layers of enhanced ionization, and ionization depletions similar to equatorial ionization bubbles. Apparent ion composition waves displayed a horizontal wave length of about 650 km. Enhanced layers of ionization appeared to be newly separated from the bottomside midnight F layer; its ions were primarily NO(+) and O2(+) without significant densities of metallic ions, an indication that metallic ions are not required to produce the layers at altitudes above 140 km. Equatorial ionization depletions were observed at lower altitudes than previously reported and displayed molecular ion depletions as well as O(+) depletions.

Miller, N. J.↗
NASA NTRS1976

A study of the conditions necessary for the onset of mid-latitude spread F

Ionospheric conditions associated with the initiation of spread F in the mid-latitude ionosphere were observed. The morphology of spread F at Puerto Rico was investigated. Data from 7 nights was examined for Arecibo, five with spread F and two without. The relative height of the F layer maximum and the vertically integreted Pedersen conductivity, the relation between E and F region conductivities, the coupling lengths between the E and F regions, and vertical and horizontal gradients of electron density were examined. At Millstone Hill 13 nights were examined for all of which spread F was observed. The EW and NS velocities and the vertical velocities and the electric ion temperature ratio were examined.

Zinchenko, G. N.↗
NASA NTRS1977

Magnetic storm effects on the tropical ultraviolet airglow

Ogo 4 measurements of the UV equatorial airglow made during a period which included a major magnetic storm are analyzed and used as an indicator of wind direction and velocity as well as ExB drift magnitude and phase. Some features of the airglow intensity and distribution are explained in terms of storm-induced changes in vertical drift velocity, neutral composition, or both. The observations are shown to be consistent with an eastward neutral wind that transports ionization from the Southern to the Northern Hemisphere while raising the F layer in the South and lowering it in the North. Theoretical modeling of the low-latitude F-region ionosphere indicates that an eastward wind with velocity approaching 300 m/s at 2100 LT can qualitatively produce the observed hemispheric asymmetries in airglow emission rates.

Gerard, J.-C.↗
NASA NTRS1977

Vertical lifting of ionization during geomagnetic storms from satellite measurements of ion composition

Magnetic-storm phenomena at low latitudes are discussed based on ion-composition /O(+), H(+), He(+)/ and electron- and ion-temperature measurements from the OGO-4 and Isis-2 satellites. For the moderately severe storms considered, the effects of changes in the neutral composition and in the neutral and plasma temperatures are discussed, and it is shown that these changes would not produce the observed O(+) increase during storms at low latitudes. It is suggested that the observed increase in O(+) in the topside region is a manifestation of the vertical lifting of ionization of the F-layer. The argument in favor of vertical lifting is further substantiated by the observed changes in the F-region critical frequency and the height parameters.

Goel, M. K.↗
NASA NTRS1999

Extremely Low Ionospheric Peak Altitudes in the Polar-Hole Region

Vertical electron-density (N (sub e)) profiles, deduced from newly-available ISIS-II digital ionospheric topside-sounder data, are used to investigate the "polar-hole" region within the winter, nighttime polar cap ionosphere during solar minimum. The hole region is located around 0200 MLT near the poleward side of the auroral oval. Earlier investigations had revealed very low N (sub e) values in this region (down to 200/cu cm near 300 km). In the present study, such low N, values (approx. 100/cu cm) were only found near the ISIS (International Satellite for Ionospheric Study)-II altitude of 1400 km. The peak ionospheric concentration below the spacecraft remained fairly constant (approx. 10 (exp 5)/cu cm across the hole region but the altitude of the peak dropped dramatically. This peak dropped, surprisingly, to the vicinity of 100 km. These observations suggest that the earlier satellite in situ measurements, interpreted as deep holes in the ionospheric F-region concentration, could have been made during conditions of an extreme decrease in the altitude of the ionospheric N (sub e) peak. The observations, in combination with other data, indicate that the absence of an F-layer peak may be a frequent occurrence at high latitudes.

Benson, Robert F.↗
NASA NTRS1985

Universal time dependence of nighttime F region densities at high latitudes

Coincident auroral-zone experiments using three incoherent-scatter radars at widely spaced longitudes are reported. The observational results demonstrate that, during the night, the F layer electron density is strongly dependent on the longitude of the observing site. Ionization patches were observed in the nighttime F region from the Chatanika and EISCAT radars, while densities observed from the Millstone radar were substantially smaller. The electron density within these maxima is larger at EISCAT than at Chatanika. When observed in the midnight sector auroral zone, these densities had a peak density at a high altitude of 360-475 km. The density was maximum when EISCAT was in the midnight sector and minimum when Millstone was in the midnight sector. A minimum in insolation in the auroral zone occurs at the UT when Millstone is in the midnight sector.

De La Beaujardiere, O.↗
NASA NTRS1980

F region airglow - Are ground-based observations consistent with recent satellite results

The Atmosphere Explorer photochemistry is used to interpret simultaneous observations made at the Arecibo Observatory of the OI (6300 A) and NI (5200 A) airglow surface brightness and electron density and temperature profiles measured by incoherent scatter radar. It was found that the theory and the experiment agree for the 5200-A emission; however, it was not possible to obtain to a complete agreement for the 6300-A nightglow. It is suggested that the source of the discrepancy results from one of the parameters used to calculate the production rate of O(lD); the data show evidence of an asymmetrical behavior of the ionosphere between times when the F layer is descending and when it is ascending, with asymmetry probably reflecting the effects of transport on molecular ion densities in the bottom side of the F region.

Cogger, L. L.↗
NASA NTRS1983

Ionospheric plasma bubble encounters or F region bottomside traversals?

Data from in situ Atmospheric Explorer (AE) measurements and ground-based ionosonde measurements of the ion composition and concentration in the equatorial plasma bubbles are analyzed. The ionosonde produced data on the bottomside electron density (NE) profiles and aided in ascertaining the satellite measurements as being in the topside or bottomside of the F layer. The AE data were taken during low latitude evening conditions at various altitudes, and revealed ion compositions consistent with plasma bubbles originating at the altitude of the steep F region bottomside ionization gradient. The lifetimes of NO ions were observed to be short even if the ions were dominant in the regions where the bubbles form. Vertical distortions of tens of kilometers in the equatorial F region occurred in the unstable postsunset period to the extent that the bubble formation area and the bottomside plasma region became virtually indistinguishable.

Benson, R. F.↗
NASA NTRS1979

The equatorial total electron content and shape factor

The diurnal variations of electron content and shape factor observed at an equatorial station during sunspot minimum are shown to be consistent with the electron density profiles observed at Jicamarca during sunspot minimum. The rapid increase in electron content and the shape factor at sunrise results from the EUV production of ionization in the E and F regions. Day-to-day variations in daytime electron content are observed to be quite small at the equator. The evening decrease in the shape factor results from an upward drift of the F region at sunset and the evening decay of the E and bottomside F regions. The nighttime peak or plateau in the shape factor is produced by the slow downward drift of the electron density profile. The deep predawn dip in the shape factor is caused by the main peak of the F layer reaching low altitudes where high loss rates cause a large reduction in ionization below 300 km and very flat electron density profile.

Donnelly, R. F.↗
NASA NTRS1982

Coordinated airborne and satellite measurements of equatorial plasma depletions

A series of experiments conducted in December 1979 to investigate the structure of plasma depletions in the low latitude, nighttime ionosphere is discussed. Density biteouts of about one order of magnitude in the dominant ion, O(+), are mapped to lower altitudes along magnetic field lines for comparison with 6300-A and 7774-A O I airglow depletions. Owing to the different airglow production mechanisms (dissociative recombination of O2(+) for 6300 A and radiative recombination of O(+) for 7774 A), the 6300-A depletions reflect plasma depletions near the bottomside of the F layer, while those at 7774 A are located near the peak of the layer. The O(+) biteouts map directly into the 7774-A airglow depletions in the same hemisphere and also when traced into the opposite hemisphere, which suggests magnetic flux tube alignment over north-south distances of approximately 2220 km. The 6300-A (bottomside) depletions are found to be wider in longitude than the 7774-A (F-peak) depeletions near the equatorward edge of the Appleton anomaly.

Weber, E. J.↗
NASA NTRS1977

A refracting radio telescope

Observations of extraterrestrial radio sources at the lower end of the radio frequency spectrum are limited by reflection of waves from the topside ionosphere and by the large size of antenna apertures necessary for the realization of narrow beamwidths. The use of the ionosphere as a lens is considered. The lens is formed by the release of chemicals such as H2 and H2O at the F2-layer peak. These chemicals promote dissociative recombination of O(+) in the ionosphere resulting in a local reduction in plasma density. Gradients in electron density in the vicinity of the gas release tend to focus rays propagating through the depleted region. Preliminary calculations indicate that a lens capable of focusing cosmic radio waves in the 1 to 10 MHz frequency range may be produced by the release of 100 kg of H2 at the peak of the nighttime F layer. The beamwidth of a refracting radio telescope using this lens may be less than 1/5 degree.

Bernhardt, P.↗
NASA NTRS1988

Case study of polar cap scintillation modeling using DE 2 irregularity measurements at 800 km

High-resolution in situ Dynamics Explorer 2 data on thermal plasma densities are used here to study the small-scale irregularity structure of the F layer patches. It is shown that spatially discrete density structures associated with polar cap patches can be detected fairly high in the topside by an in situ irregularity sensor and that they correspond to temporally discrete scintillation patches. It is also shown that it is possible to model phase and amplitude scintillation occurrence from a knowledge of irregularity amplitude at a satellite altitude of about 800 km provided that independent measurements of the peak density and scale height of the F region are available.

Basu, Sunanda↗
NASA NTRS1997

Gravity Wave Seeding of Equatorial Plasma Bubbles

Some examples from the Atmosphere Explorer E data showing plasma bubble development from wavy ion density structures in the bottomside F layer are described. The wavy structures mostly had east-west wavelengths of 150-800 km, in one example it was about 3000 km. The ionization troughs in the wavy structures later broke up into either a multiple-bubble patch or a single bubble, depending upon whether, in the precursor wavy structure, shorter wavelengths were superimposed on the larger scale wavelengths. In the multiple bubble patches, intrabubble spacings vaned from 55 km to 140 km. In a fully developed equatorial spread F case, east-west wavelengths from 690 km down to about 0.5 km were present simultaneously. The spacings between bubble patches or between bubbles in a patch appear to be determined by the wavelengths present in the precursor wave structure. In some cases, deeper bubbles developed on the western edge of a bubble patch, suggesting an east-west asymmetry. Simultaneous horizontal neutral wind measurements showed wavelike perturbations that were closely associated with perturbations in the plasma horizontal drift velocity. We argue that the wave structures observed here that served as the initial seed ion density perturbations were caused by gravity waves, strengthening the view that gravity waves seed equatorial spread F irregularities.

Singh, Sardul↗