Engineering topics

Hanson, W. B.

Publications and source records attributed to Hanson, W. B..

At least 127 records · Page 7

NASA NTRS1975

An auroral F-region study using in situ measurements by the Atmosphere Explorer-C satellite

The ion densities observed as the Atmosphere Explorer-C satellite passed through an aurora at F-region altitudes are compared to those calculated from photochemical theory using in situ measurements of atmospheric parameters (ionic and neutral composition; electron flux; neutral temperature; ion temperature) along the satellite track together with current values for reaction rates. Good agreement is obtained for the ions O2(+), NO(+), and N2(+). The atomic nitrogen densities calculated from the observed NO(+)/O2(+) ratio are found to account for about 60% of the N(+) production through electron impact on N and the resonant charge exchange of O(+)(2P) with N(4S). The N density at about 280 km, the region of the most intense electron fluxes (20 erg/sq cm/sec), is between 20 and 70 million/cu cm.

Torr, M. R.↗

NASA NTRS1974

Is the red arc a good indicator of ionosphere-magnetosphere conditions

Weak red arcs were observed on the two consecutive nights of July 12-13 and July 13-14, 1969, at Richland, Washington, whereas no red arcs were detectable on the nights preceding and following the observations. Satellite (Ogo 6) data of electron temperature and density, low-frequency ac electric field, and suprathermal electron flux corresponding to the conjugate region of Richland show no significant variations during these days. The data show elevated electron temperatures and enhanced low-frequency ac noise levels at the expected red arc position in the neighborhood of the density trough, as indicated by previous observations. The data appear to indicate that the optical criterion of red arc occurrence would lead to the conclusion of significantly different ionosphere-magnetosphere conditions during these four nights, whereas the more detailed in situ data show that the conditions were very similar.

Nagy, A. F.↗

NASA NTRS1974

A comment on plasma 'pile-up' in the F-region

At ionospheric heights, the geomagnetic field is virtually incompressible. In consequence, an electromagnetic drift can only compress the F-region plasma by moving it in a direction in which the field becomes stronger. This paper examines the rate of compression at mid-latitudes for three different assumptions about the ion motion.

Rishbeth, H.↗

NASA NTRS1974

In situ measurements of the spectral characteristics of F region ionospheric irregularities

The retarding potential analyzer aboard Ogo 6 has provided high-resolution observations of the ion concentration along the satellite path. Changes in ion concentration as small as 0.03% and at times as small as 0.01% could be measured. Spatial resolution varied from 35 to 380 m. Samples of data have been analyzed to determine the spectral properties of the F region irregularities observed. The most common frequency spectrum observed suggests that the responsible irregularities result from the turbulent dissipation of larger irregularities. At the equator, the larger irregularities are probably produced by convective electric fields. At high latitudes, electric fields may also be involved, but other factors such as precipitating particles may contribute to, or be primarily responsible for, the production of large irregularities. Examples of other types of spectra associated with wavelike irregularities and with 'ground glass' (high-frequency noise) irregularities are also shown.

Dyson, P. L.↗

NASA NTRS1973

A catalog of ionospheric F region irregularity behavior based on Ogo 6 retarding potential analyzer data

Review of in situ data obtained with the aid of the retarding potential analyzer on board Ogo 6 which reveal the nature of ionospheric irregularities in the total ion concentration above 400 km. Except for the high-latitude regions, the ionosphere is usually observed to be very smooth in the daytime, but considerable structure is observed at night, particularly near the equator and at Atlantic longitudes. Although most of the irregularities observed appear to be stochastic in nature, many nearly monochromatic waveforms are observed near the equator. The topics discussed include the midlatitude scintillation boundary, large-amplitude equatorial irregularities, the fluctuation spectrum of typical F-region irregularities, the lower edge of the equatorial F region, sinusoidal waveforms, ground glass irregularities, breaking wave irregularities, and regions of smooth and irregular ionization inside the polar cap.

Mcclure, J. P.↗

NASA NTRS1973

Effects of interhemisphere transport on plasma temperatures at low latitudes.

The thermal balance of the equatorial plasma between 300 and 800 km is examined. Steady state nighttime calculations are made for O+, H+, and electrons. The following features are included: collisional heat transfer between ions, electrons, and neutrals; ion and electron thermal conduction along the field lines; curvature of the field lines; nonlinear advection due to field-aligned ion and electron motions; and convective compression or expansion due to field-aligned and E x B motions. The ion velocities necessary to calculate the effects of convection are obtained from the work of Moffett and Hanson, who include a meridional wind across the magnetic equator in their calculations. It is shown that field-aligned interhemisphere plasma flows appreciably affect the plasma temperatures.

Bailey, G. J.↗

NASA NTRS1973

OGO-6 experiment F-03

The results obtained with the retarding potential analyzer on the OGO-6 satellite are discussed. The information obtained during the OGO-6 flight concerned the following subjects: (1) measurement of electron flux density in the plasmasphere, (2) latitudinal variations of ion temperature, (3) heating in the nighttime ionosphere by conjugate photoelectrons, (4) longitudinal variation in equatorial ion temperature at low altitude, and (5) identification of heavy ions in the upper F region.

Hanson, W. B.↗

NASA NTRS1973

On the cause of equatorial spread F.

It is suggested that convective electric fields in the equatorial ionosphere are generated by neutral winds (zonal or meridional) which act on regions having structure in their field aligned Pedersen conductivity integrals. The conductivity structure is presumably caused by long-lived metallic ions concentrated irregularly below the F layer at altitudes where their collision and gyrofrequencies are comparable. The resulting plasma convection leads to large-scale irregularities and sets up gradients in the electric field that drive other instability mechanisms to produce small-scale irregularities. The mechanism proposed requires a different velocity above and below 200 km for winds in the magnetic east-west direction, but for winds in the magnetic meridian direction, an altitude gradient is not required.

Hanson, W. B.↗

NASA NTRS1973

The Atmosphere Explorer mission.

Summary of the general scientific objectives of the Atmosphere Explorer (AE) mission. The overall purpose of the AE mission is shown to be the performance of simultaneous measurements needed for cause and effect studies that are to provide a detailed understanding of the physical processes governing the lower thermosphere and ionosphere.

Dalgarno, A.↗

NASA NTRS1973

The magnetic ion-mass spectrometer on Atmosphere Explorer.

The magnetic ion-mass spectrometer is designed to measure the abundances of the ambient positive ions in the ionosphere. It will be calibrated in flight against the retarding-potential analyzer and the cylindrical electrostatic probe to give absolute concentration data for the ion species detected. These parameters can be measured to approximately plus or minus 10% in well-behaved regions where concentrations are above 1000/cu cm. However, in highly structured polar regions, some degradation in accuracy may be expected. Three mass ranges, covered simultaneously by the scan of the instrument, 1 to 4, 4 to 16, and 16 to 64 amu, permit measurement of the entire mass range, 1 to 64 amu, in 1 sec in the main (peaks) mode. An alternate mode, analog-long, will extend the mass range to 90 amu with a 9-sec period.

Hoffman, J. H.↗

NASA NTRS1973

The retarding-potential analyzer on Atmosphere Explorer.

A planar retarding-potential analyzer will be included in each of the Atmosphere Explorer (AE) payloads. The primary functions of the instrument are to supply ion-temperature and ion-concentration data, which it will do at least once every 40 km of flight path in the region of interest with an expected accuracy of better than 2%. In addition, the instrument will determine ion-drift velocities and energy spectra of both the thermal and suprathermal electrons. During eclipse, negative-ion concentrations greater than 0.3/cu cm can be detected, though the normal positive-ion sensitivity is approximately 1.5 ions per cu cm. Changes in the ion concentration along the flight path greater than 0.1% can be monitored with a spatial resolution of less than 40 m.

Hanson, W. B.↗

NASA NTRS1973

Large ion concentration gradients below the equatorial F peak.

Very large vertical and longitudinal gradients in the ion concentrations are observed below the F peak near the magnetic equator with the retarding potential analyzer on Ogo 6. Ion concentration 'bite outs' of up to a factor of 1000 are observed above 400 km. They appear to be associated with the bottomside of the nighttime F layer. The ion composition in the minima may contain large fractions of ions heavier than O(+) (e.g., NO(+) and Fe(+)). It is suggested that convective electric fields associated with spread F steepen the bottomside of the F layer and also introduce longitudinal irregularities in the vertical ion concentration profiles.

Hanson, W. B.↗

NASA NTRS1973

Calculated distributions of hydrogen and helium ions in the low-latitude ionosphere.

The simultaneous time-dependent continuity equations for O(+), H(+) and He(+) in the low latitude F-region are solved. Account is taken of E x B drift, a meridional neutral wind, and ion-ion and ion-neutral drag. The calculated profiles of O(+) and H(+) concentrations at 1630 LT are in fair agreement with the observations of Hanson et al. The He(+) field-aligned velocity is almost matched to the O(+) field-aligned velocity and, above the chemical equilibrium region and around the He(+) peak, the He(+) concentration is determined largely by production and transport. There is disagreement between the theoretical vertical He(+) profile and the profile observed by Hanson et al. Satisfactory agreement is obtained with Taylor's satellite results at fixed height for O(+) and H(+). It is found that the He(+) concentration is greater in the winter hemisphere than in the summer hemisphere, even if the neutral helium distribution is symmetrical about the Equator. The He(+) results are consistent with Taylor's results.

Moffett, R. J.↗

NASA NTRS1973

Ogo 6 measurements of supercooled plasma in the equatorial exosphere.

Plasma measurements performed on Ogo 6 reveal electron and ion temperature values that on occasion appear to be well below the expected neutral gas temperature. The phenomenon is observed only at night above 500 km near the magnetic equator. It is suggested that the expansion cooling of the plasma is accomplished by downward motions of the F region plasma induced by winds or diffusion, by outward E x B drift, or more probably by the upward flow of plasma during interhemisphere transport along magnetic field lines. It is also suggested that preferential cooling of electrons because of their greater thermal conductivity should tend to give ion temperatures greater than electron temperatures during the postsunset cooling of the plasmasphere when photoelectrons are absent.

Hanson, W. B.↗

NASA NTRS1973

Comparison of Te and Ti from Ogo 6 and from various incoherent scatter radars.

Langmuir probe and retarding potential analyzer (RPA) data on the electron and ion temperatures Te and Ti obtained from Ogo 6 are compared with Te and Ti values obtained from the incoherent scatter network. The satellite to radar temperature ratio TeS/TeR is 1.15 on the average for these comparisons. This discrepancy is larger than the uncertainties usually placed on the probe and radar Te values. The ion temperature ratio TiS/TiR approximately 1.0, independent of the particular radar examined. This comparison serves as an intercalibration of the incoherent scatter network.

Mcclure, J. P.↗

NASA NTRS1972

Source and identification of heavy ions in the equatorial F layer.

Further evidence is presented to show that the interpretation of some Ogo 6 retarding potential analyzer (RPA) results in terms of ambient Fe+ ions is correct. The Fe+ ions are observed only within dip latitudes of plus or minus 30 deg, and the reason for this latitudinal specificity is discussed in terms of a low-altitude source region and F region diffusion and electrodynamic drift. It is shown that the polarization field associated with the equatorial electrojet will raise ions to 160 km out of a chemical source region below 100 km but it will do so only in a narrow region centered on the dip equator. Subsequent vertical ExB drift, coupled with motions along the magnetic fields, can move the ions to greater heights and greater latitudes. There should be a resultant fountain of metallic ions rising near the equator that subsequently descends back to the E and D layers at tropical latitudes.

Hanson, W. B.↗

NASA NTRS1972

Molecular ions in the F2 layer.

Data on ion concentrations at heights of 400-500 km, obtained by the OGO VI satellite, suggest that the O(+) and molecular ion concentrations are sometimes anticorrelated. To assist in explaining this phenomenon, a table of the chemical reactions most likely to control the molecular ion concentrations is drawn up, and its validity tested with the aid of data from rocket-borne mass spectrometers at heights of 220-400 km. The anticorrelation of O(+) and NO(+) ions by day is thought to be due to the importance of a reaction between N2(+) ions and O atoms; the main source of N2(+) above 300 km is probably charge-exchange between N2 and O(+), the latter being produced by photoionization. However, at night another source of NO(+) ions is required, which may be N(+) ions that are either stored in the magnetosphere or are produced from He(+) and N2.

Rishbeth, H.↗

NASA NTRS1972

Satellite and ground-based observations of a red arc.

The results of simultaneous satellite and ground-based observations carried out during the red-arc period of August 8-9, 1970, are discussed in the light of present day theory. The formation of the arc at the electron temperature peak and density trough seems to support the thermal-conduction theory of red-arc formation.

Nagy, A. F.↗