Alouette Topside Research Articles

Electon density profiles of the topside ionosphere

The existing uncertainties about the electron density profiles in the topside ionosphere, i.e., in the height region from h,F2 to - 2000 km, require the search for new data sources. The ISIS and Alouette topside sounder satellites from the sixties to the eighties recorded millions of ionograms but most were not analyzed in terms of electron density profiles. In recent years an effort started to digitize the analog recordings to prepare the ionograms for computerized analysis. As of November 2001 about 350000 ionograms have been digitized from the original 7-track analog tapes. These data are available in binary and CDF format from the anonymous ftp site of the National Space Science Data Center. A search site and browse capabilities on CDAWeb assist the scientific usage of these data. All information and access links can be found at http://nssdc.gsfc.nasa.gov/space/isis/isis- status.htm1. This paper describes the ISIS data restoration effort and shows how the digital ionograms are automatically processed into electron density profiles from satellite orbit altitude (1400 km for ISIS-2) down to the F peak. Because of the large volume of data an automated processing algorithm is imperative. The TOPside Ionogram Scaler with True height algorithm TOPIST software developed for this task is successfully scaling - 70% of the ionograms. An > is available to manually scale the more difficult ionograms. The automated processing of the digitized ISIS ionograms is now underway, producing a much-needed database of topside electron density profiles for ionospheric modeling covering more than one solar cycle.

Preliminary results of comparison between Thomson scatter and topside sounder measurements

Ionic compositions are derived by combining Alouette topside electron density profiles with electron and ion temperatures measured by the bistatic Thomson scatter sounder at St. Santin. Data from only four passes in 1967 are available, so that the results are still tentative.

The seasonal behaviour of the topside ionosphere

Alouette topside sounder data acquired over North America during the solstice periods of 1962 and 1963 indicate that, over a wide range of middle latitudes, the midday electron concentration values at various fixed heights (400, 600, 800 and 1000 km) are always substantially greater, by a factor of about two, at midsummer than at midwinter. This behaviour is in complete contrast with that of the F2-layer critical frequencies observed at corresponding times and localities; these latter data exhibit the usual seasonal anomaly in which the summer ƒ 0F2 values are smaller than the winter ones.

Correlation of plasma scale height withKpin the topside ionosphere

Correlation of geomagnetic index and plasma scale height in topside ionosphere observed from Alouette topside sounder and planetary geomagnetic data

Remote Cyclotron Resonance Phenomenon observed by the Alouette Satellite

A NOVEL cyclotron resonance phenomenon associated with the second harmonic of the electron gyrofrequency 2fH is sometimes observed on Alouette topside ionograms. The phenomenon occurs remote from the satellite and will consequently be called the ‘remote resonance’. The cyclotron resonances which occur in the vicinity of the satellite, and which are responsible for the cyclotron spikes, have been discussed by previous authors1,2.

Ion distribution and temperature in the topside ionosphere obtained from the Alouette satellite

Electron-density distributions are obtained from Alouette topside soundings recorded at Stanford University. Plasma scale height profiles are then determined, from which information can be deduced about relative ion concentrations, electron temperature, and ion temperature. Results are obtained for dip latitudes between 48° and 78°N, and altitudes from 400 to 900 km. The lower-latitude nighttime data can be interpreted in terms of a three-constituent (O+, He+, H+) diffusive equilibrium model with an (O+) - (He+, H+) transition occurring at about 550 km in the summer and 500 km in the winter. The variation of the transition altitude with local time and with latitude is obtained. The transition level is found to rise with increasing latitude, rising above 900 km at about 62° dip latitude. It is also observed to rise very quickly at local sunrise and to descend quickly at local sunset. The data suggest that the (O+) - (He+, H+) transition is at least as high as 1000 km during the day. Under these conditions the daytime scale heights at all observed latitudes and the nighttime scale heights at dip latitudes north of 63° can be interpreted in terms of temperature variations in an O+ ionosphere.

Theory of collective spikes observed by the Alouette topside sounder

A theory is advanced to explain the spikes at the plasma frequency ωp and the Pythagoras frequency [(ωp2 + ωb2)1/2] observed in ionograms of the Alouette topside sounder. It is based on the properties of Green's function for a uniform magnetoplasma, which may be cold or warm, and it disregards possible sheath effects. The theory predicts the absolute strength of the observed signal, its asymptotic time behavior, and its dependence on the orientation of the satellite antenna, but the present experimental data are insufficient to make detailed comparisons.

Alouette topside sounder satellite - experiments, data, and results

Covers advancements in spacecraft and tactical and strategic missile systems, including subsystem design and application, mission design and analysis, materials and structures, developments in space sciences, space processing and manufacturing, space operations, and applications of space technologies to other fields.

Electron density at the Alouette orbit

Alouette topside soundings recorded at Stanford University have been used to determine the diurnal, seasonal, and latitudinal variations of electron density at the orbit of the satellite (∼1000 km) over a wide range of latitudes. The electron density is larger in summer than in winter by a factor of approximately 2 at the level of the satellite. The derived latitudinal distributions of electron density at the base of the exosphere are important to the theory of electron and positive ion distributions in the exosphere discussed in the companion paper by Angerami and Thomas.

Cyclotron harmonic signals received by the Alouette topside sounder

It is proposed that the long-lived returns (spikes) at multiples of the electron cyclotron frequency, often observed in Alouette ionograms, may be due to the action of the antenna field on the electrons in the antenna sheath, whose motions are influenced by the steady nonuniform electric field of the sheath and the ambient magnetic field. It remains to be seen whether this mechanism or that of Lockwood is the more effective. (Lockwood's mechanism invokes nonuniformities in the oscillating antenna field to produce bunches of electrons moving in circular orbits.) Starting from a model of the sheath, we outline the steps of a detailed calculation that is apparently necessary to determine which theory is correct. It is suggested that laboratory work on induced emission may provide useful information.

Spread-Fobservations by the Alouette Topside Sounder Satellite

Ionograms recorded by the Alouette topside sounder satellite exhibit a variety of spread-F echo configurations. The observed echoes are found to be consistent with three qualitative radio-propagation models involving aspect-sensitive scattering by thin magnetic-field-aligned irregularities, ducting along broad irregularities, and refraction within large-scale reductions of electron density. A large number of Alouette ionograms were examined for the three types of spread F to determine their frequency of occurrence. Spread F appeared on 54 per cent of the topside ionograms; the three types exhibit markedly different patterns of occurrence in geomagnetic latitude and local time.

Simultaneous rocket and satellite measurements of the topside ionosphere

Charged-particle profiles of upper ionosphere from alouette topside satellite sounding, compared with rocket- & ground-based backscatter measurements

Plasma resonances in the upper ionosphere

Plasma resonances, detected in the upper atmosphere with the Alouette topside sounder satellite, have been examined. The resonant frequencies have been found to be fN and (fN2+fH2)1/2, where fN is the plasma frequency and fH is the electron gyrofrequency. The two resonances are attributed to electron oscillations along and across the earth's magnetic field respectively.

Radio Propagation along Magnetic Field-Aligned Sheets of Ionization Observed by the Alouette Topside Sounder

Radio Propagation along Magnetic Field-Aligned Sheets of Ionization Observed by the Alouette Topside Sounder

Radio propagation along magnetic field-aligned sheets of lonization observed by the Alouette Topside Sounder

Radio propagation along magnetic field-aligned sheets of lonization observed by the Alouette Topside Sounder