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Sechrist, C. F., Jr.

Publications and source records attributed to Sechrist, C. F., Jr..

36 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Ionospheric D and E regions

Some areas of D and E region research are examined, with particular reference to the photochemistry and transport of minor neutral constitutents in the mesosphere and lower thermosphere. The review shows that the D and E regions become more complex physical and chemical systems as research progresses, so that some previous views on these regions have to be revised. In particular, the lower ionosphere appears to be hydrodynamically coupled to the lower atmosphere and electrodynamically coupled to the magnetosphere.

Sechrist, C. F., Jr.↗
NASA NTRS1975

An investigation of the solar zenith angle variation of D-region ionization

Model calculations are carried out with a view to interpreting the solar zenith angle variation of D-region ionization. A model is developed for the neutral chemistry including the transport terms relating to molecular and eddy diffusion. The diurnal behavior is described of the minor neutral constituents formed in an oxygen-hydrogen-nitrogen atmosphere, in the height interval between 30 and 120 km. Computations carried out for two cases of the eddy diffusion coefficients models indicate that the constituents which are important for the D-region positive-ion chemistry do not show a significant variation with zenith angle for values up to 75 deg over the D-region heights. In the ion chemistry model, ion-pair production rates are calculated for solar X-rays between 1 A and 100 A, EUV radiations from 100 A up to the Lyman-alpha line, precipitating electrons, and galactic cosmic rays. The solar zenith angle variation of the positive-ion composition, negative-ion composition, and the electron densities are described up to 75 deg zenith angle, in the height interval between 60 and 100 km.

Ratnasiri, P. A. J.↗
NASA NTRS1974

Comparisons of techniques for measurement of D-region electron densities

This paper reviews the ground-based and rocket techniques that are presently being used to determine electron density profiles in the ionospheric D region. Ground-based techniques include VLF, LF, and MF sounding; differential absorption and differential phase measurements using partial reflections; wave interaction; and incoherent scatter. Rocket techniques include differential absorption and Faraday rotation in association with high-resolution dc probes calibrated by means of the radio measurements. The characteristics of the aforementioned techniques are presented, including time and height resolution, accuracy estimates, preferred height ranges, and problems encountered. Electron density profiles obtained with these techniques are presented for comparable solar zenith angles and undisturbed solar and geophysical conditions.

Sechrist, C. F., Jr.↗
NASA NTRS1972

Electron loss coefficients for the D-region of the ionosphere from rocket measurements during the eclipses of March 1970 and November 1966.

Observation that recombination-like electron loss coefficients measured during the March 1970 eclipse coincide with those from the November 1966 eclipse and range from 2 x 10 to the minus 7th power cu cm/sec at Z sub zero + 6 km to 0.00005 cu cm/sec at Z sub zero -2 km, where Z sub zero is the altitude of the steep gradient of electron concentration. During totality, Z sub zero was 82.5 km in 1970, and 86.8 km in 1966. For full-sun conditions, Z sub zero was 84 km on both eclipse days. Attachment-like electron loss coefficients from both eclipses are in good agreement below Z sub zero, and have a nearly constant value of about 0.008 per sec. Below Z sub zero, attachment-like loss rates agree with production rates - i.e., electron concentration is proportional to electron production.

Mechtly, E. A.↗
NASA NTRS1972

Differential phase measurements of D-region partial reflections

Differential phase partial reflection measurements were used to deduce D region electron density profiles. The phase difference was measured by taking sums and differences of amplitudes received on an array of crossed dipoles. The reflection model used was derived from Fresnel reflection theory. Seven profiles obtained over the period from 13 October 1971 to 5 November 1971 are presented, along with the results from simultaneous measurements of differential absorption. Some possible sources of error and error propagation are discussed. A collision frequency profile was deduced from the electron concentration calculated from differential phase and differential absorption.

Wiersma, D. J.↗
NASA NTRS1971

Partial reflection data collection and processing using a small computer

Online data collection of the amplitudes of circularly polarized radio waves, partially reflected from the D region of the earth's ionosphere, has enabled the calculation of an electron-density profile in the height region 60-90 km. A PDP 15/30 digital computer with an analog to digital converter and magnetic tape as an intermediary storage device are used. The computer configuration, the software developed, and the preliminary results are described.

Birley, M. H.↗
NASA NTRS1970

An investigation of the ionospheric D region at sunrise

The growth over sunrise of the C and D layers of the ionosphere is investigated. The model which is analyzed includes the negative ion species O(-), O2(-), O3(-), O4(-), NO3(-), CO3(-), and CO4(-). Ionization sources due to galactic cosmic rays, precipitated electrons, ionization of NO by scattered Lyman alpha radiation, and the direct solar radiation ionization are also included. The photodetachment of most of the negative ions is discussed, as well as the time variation of these parameters. The time variations of the electron, negative ion, and positive ion densities are calculated over sunrise. From these data, the mesospheric C and D layer development is plotted. Several model parameters are varied until the best agreement with experimentally determined electron densities is obtained. The results are discussed in light of several atmospheric parameters including the O and NO concentrations and the electron-ion recombination coefficient.

Turco, R. P.↗
NASA NTRS1966

VLF studies

Very low frequency experiment and theory, and full-wave solutions of coupled wave equations

VERY LOW FREQUENCY↗
NASA NTRS1966

Partial reflection experiment

Increasing pulse repetition rate of transmitter to meet system gain requirements for partial ionospheric reflection sounder

POWER GAIN↗