Engineering topics
Publications and source records attributed to Smith, L. G..
A full-wave analysis of the reflection coefficient is developed and applied to electron-density profiles of midlatitude sporadic-E layers observed by rocket-borne probes. It is shown that partial reflection from the large electron-density gradients at the upper and lower boundaries of sporadic-E layers does not account for the partial transparency observed by ionosondes.
The electron density and positive-ion composition above Wallops Island were measured on August 12, 1976, about 12 hours after the maximum of the Perseid shower. At launch time, 4.5 MHz was recorded for fbEs, corresponding to an electron density of 2.4 x 10 to the 5th power per cu cm. Electron profile and ion composition measurements confirmed the presence of a sporadic E-layer with two maxima at 101.3 and 105.4 km. The electron density was measured with a pair of boom-mounted probes at fixed potential. The positive ion composition above 77 km was measured with a magnetic mass spectrometer employing a liquid He cryopump. Some of the salient results of the (still incomplete) analysis are discussed.
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The design of a rocket-borne photometer to measure the airglow emission of ionized molecular nitrogen in the 391.4 nm band is presented. This airglow is a well known and often observed phenomenon of auroras, where the principal source of ionization is energetic electrons. It is believed that at some midlatitude locations energetic electrons are also a source of nighttime ionization in the E region of the ionosphere. If this is so, then significant levels of 391.4 nm airglow should be present. The intensity of this airglow will be measured in a rocket payload which also contains instrumentation to measured in a rocket payload which also contains instrumentation to measure energetic electron differential flux and the ambient electron density. An intercomparison of the 3 experiments in a nightime launch will allow a test of the importance of energetic electrons as a nighttime source of ionization in the upper E region.
The partially transparent echo from midlatitude sporadic E layers was recorded by ionosondes between the blanketing frequency and the maximum frequency. The theory that the midlatitude sporadic E layers are not uniform in the horizontal plane but contain localized regions of high electron density was evaluated using data obtained by incoherent scatter radar and found to provide a satisfactory explanation. The main features of midlatitude sporadic E layers are consistent with the convergence of metallic ions as described by the wind shear theory applied to gravity waves and tides. The interference of gravity waves with other gravity waves and tides can be recognized in the altitudes of occurrence and the structure of the layers. Small scale horizontal irregularities are attributed in some cases to critical level effects and in others to fluid instabilities. The convergence of a meteor trail can, under some circumstances, account for localized enhancement of the electron density in the layer.
By using rocket-borne Langmuir probes, electron temperature profiles have been obtained in five mid-latitude sporadic E layers. The data show the electron temperature within the layers to be lower than the electron temperature at the adjacent altitudes. This is consistent with the layers' being maintained by a vertical redistribution of ionization. The magnitude of the observed electron temperature variation is, however, larger than expected.
Observations of the electron density profile and flux of energetic electrons obtained in two rocket flights at Wallops Island near midnight are presented. The ionization rates of the upper E region deduced from the electron density profiles are found to support the dependence on Kp established in previous observation. Calculations of the ionization rates using the observed electron fluxes show agreement with the values derived from the electron density profiles.
The behavior of two types of Langmuir probes, one with electrodes made of low-sulfur stainless steel and one with electrodes made of aluminum coated with Aquadag, has been compared on two rocket flights. Each rocket payload included one Langmuir probe of each type. The electron temperatures measured with the stainless-steel electrodes were about 15% higher than the electron temperatures measured with the Aquadag-coated electrodes at 150 km on ascent and about 10% higher at 180 km. These results imply that the use of Aquadag coated electrodes or electrodes of other carefully chosen materials permits greater reliability in the measurement of electron temperatures in the ionosphere by the Langmuir probe technique.
The investigation reported is concerned with a model considered by Whitehead (1972). The partial transparency of the sporadic-E layer observed on certain occasions is attributed to regions of high electron density embedded in the layer. Observations obtained with an incoherent scatter radar facility are presented. Taking into account all factors, it is concluded that the partial transparency of sporadic-E layers, on the occasions of these observations, are explained by the Whitehead model.
Electron temperatures and electron densities measured on four rocket flights have been used to deduce electron heating rates in the E and lower F regions. Above 150 km, heating rates at midday are found to be in good agreement with calculated values. Anomalies are found in the heating rates at sunrise which are attributed to a source, such as joule heating, which does not produce ionization.
Midlatitude sunrise electron density profiles have been analyzed in order to determine nitric oxide concentrations in the range 100-160 km. In general, the determinations are restricted to heights for which the ionization of nitric oxide by direct solar Lyman-alpha radiation is the main contribution to the growth of the E region. The concentrations obtained are larger, by factors of approximately 3 to 4, than those obtained from the midlatitude airglow measurements of other workers. Concentrations have been obtained from one sunset measurement and these are significantly lower than the sunrise values. The results also give a clear indication of increasing nitric oxide concentrations above 120 km with increasing solar activity.
In the analysis existing measurements of nighttime E-region electron densities are separated in two groups. The first group includes a series of five rocket measurements which were taken during the night of February 22, 1968. The second group consists of a collection of rocket measurements taken near midnight at Wallops Island, Virginia, under varying conditions of geomagnetic activity. Information is obtained about the ionization production as well as the dynamics in the nighttime E region.
Investigations of the ionosphere, in the rocket program of the Aeronomy Laboratory, include a propagation experiment, the data from which may be analyzed in several modes. This report considers in detail the differential absorption experiment. The sources of error and limitations of sensitivity are discussed. Methods of enhancing the performance of the experiment are described. Some changes have been made in the system and the improvement demonstrated. Suggestions are made for further development of the experiment.
An explanation was developed for the formation, near midnight at midlatitudes, of a broad electron density layer extending approximately from 120 to 180 km and usually referred to as the intermediate E layer. The responsible mechanism is believed to be the converging vertical ion drifts resulting from winds of the solar semidiurnal tide. Numerical solutions of the continuity equation appropriate to the intermediate layer is described for particular models of ion drift, diffusion coefficents, and ionization production. Analysis of rocket observations of the layer show that the ionization rate is highly correlated with the planetary geomagnetic index, K sub p. Particle flux measurements support the idea that energetic electrons are the principal source of this ionization. A semiconductor spectrometer experiment for investigation of the particle flux, spectrum, and angular properties was designed and successfully flown on a Nike Apache rocket. A detailed description of the theory, design, and calibration of the experiment and some preliminary results presented.
An analysis of electron density profiles in the upper E region near midnight at Wallops Island is shown to indicate that the ionization rate is very strongly correlated with geomagnetic activity. This suggests that energetic electrons are the principal source of ionization at midlatitudes in the upper E region near midnight, even under rather quiet geomagnetic conditions.
Measurements of O2 number density obtained from rocket observations of the absorption profile of solar Lyman alpha (1216 A) have been compared with values derived from nearly simultaneous measurements of atmospheric density from other rocket techniques: grenades, falling sphere, and Pitot tube. All launches were from Wallops Island, Virginia. The atmospheric density derived from the absorption spectroscopy data is found to be about 20% less than that from the other techniques when a constant value of the absorption cross section of 1.0 times 10 to the minus 20th sq cm is used. The agreement is worse when the cross section is allowed to vary across the width of the solar line. The data in the altitude range 70-90 km are interpreted as showing that the effective value of the absorption cross section at Lyman alpha for O2 at 200 K and negligible pressure is about 0.8 times 10 to the minus 20th sq cm.
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It is shown that the absorption cross section for molecular oxygen at Lyman alpha is about 0.8 times 10 to the minus twentieth power sq cm. It is pointed out that, for application of absorption spectroscopy to the measurement of molecular oxygen density in the atmosphere, no correction for the variation of cross section with wavelength is necessary.