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Walker, J. C. G.

Publications and source records attributed to Walker, J. C. G..

At least 55 records · Page 3
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NASA NTRS1976

Recombination of O2/+/ in the ionosphere

In spite of the excellent agreement between various laboratory measurements of the recombination rate of O2(+) with electrons, it is still questionable whether the laboratory results apply in the ionosphere, because although the radiative lifetime of vibrating O2(+) is not well known, indications are that it may be very long. Whether the laboratory results apply in the atmosphere depends on whether the recombination rate is dependent on the vibrational state of the O2(+) ion and on whether the ions are deactivated (or not) in both the laboratory experiments and the atmosphere prior to recombination. To obtain reliable answers to these questions, the present study was carried out to determine the recombination of O2(+) in the ionosphere from in situ measurements of the relevant temperatures and densities made by the open source mass spectrometer carried by the AE-C satellite. The photochemistry involved is discussed. The results show that the ionospheric determination of the recombination rate of O2(+) with electrons agrees with the laboratory measurements of Walls and Dunn (1974) for electron temperatures between 1200 and 2000 K.

Torr, D. G.↗
NASA NTRS1976

Global characteristics of 0.2 to 26 keV charged particles at F region altitudes

Measurements have been made by the low energy electron experiment (LEE) on the Atmosphere Explorer-C satellite (AE-C) of electrons and protons in the energy range 0.2 to 26 keV. Data taken in the altitude range 250 to 300 km during the period 15 December 1973 to 25 May 1975 are analyzed. Measurements were made over a range of magnetic latitudes extending from the equator to 80 deg. The average electron flux at midlatitudes at night is found to be about (1-5) x 10 to the -4 ergs/sq cm/s, and increases by about an order of magnitude during the day. The upper limit for the nighttime and daytime proton energy flux is about 1 x 10 to the -4th ergs/sq cm/s. The total nighttime energy flux will result in a production rate of .3 to 10 ions/cu cm/s at the base of the F region and in the D region, respectively, and should constitute an important source of ionization in the nocturnal ionosphere.

Torr, D. G.↗
NASA NTRS1976

The penetration of soft electrons into the ionosphere

Calculations are presented of energy spectra and angular and spatial distributions of electron fluxes in the ionosphere resulting from precipitation of monoenergetic (E = 25, 50, and 100 eV) electrons. The incident electrons are assumed to be isotropic over the downward direction. It is found that the resulting steady-state electron fluxes above ca. 300 km are highly anisotropic and that the pitch-angle distribution is energy dependent. About 15% of the incident electrons are backscattered elastically to the protonosphere. A much larger number of electrons escapes after they have deposited part of their energy in the atmosphere. The mean energy of the escaping electrons is about half that of the incident electrons. About 50% of the incident energy is absorbed in the atmosphere, the remainder being returned to the protonosphere. The rate of energy absorption is a maximum at heights between 300 and 400 km. Most of the energy is absorbed in ionization and excitation of atomic oxygen; an appreciable amount is absorbed as heat by the ambient electron gas. Altitude profiles are presented for the rates of ionization, excitation, and electron heating caused by soft-electron precipitation.

Mantas, G. P.↗
NASA NTRS1976

Recombination of NO/+/ in the ionosphere

Simultaneous nighttime measurements of ion and neutral concentrations and temperatures made by the Atmosphere Explorer-C satellite were used to determine the recombination rate coefficient of NO(+) as a function of electron temperature. The results agree in shape and absolute magnitude to within one standard deviation with those of Walls and Dunn (1974), indicating that NO(+) ions in the ionosphere may be in the ground vibrational state.

Torr, D. G.↗
NASA NTRS1976

Metastable 2D atomic nitrogen in the mid-latitude nocturnal ionosphere

The only source at night at midlatitudes of N(2D) in the F region is the dissociative recombination of the positive NO ion, and the only important sinks are quenching by atomic oxygen and electrons. Ground-based measurements of the 5200 angstrom emission line resulting from the transition from N(2D) to N(4S) combined with satellite observations of neutral and ion densities and temperatures and the shape of the 5200 angstrom profile are used to relate the rate of quenching by atomic oxygen and the efficiency of production of N(2D) to the rate of quenching by electrons. A rate of quenching by atomic oxygen of 1.5-2.5 x 10 to the minus 12th cu cm/s and an efficiency of (0.8-1.0) plus or minus 30% for the production of N(2D) are obtained.

Torr, M. R.↗
NASA NTRS1976

Atomic nitrogen densities in the thermosphere

Recently atomic nitrogen densities of about one million per cu cm were measured at 400 km by the open source mass spectrometer on the Atmosphere Explorer-C satellite (AE-C). Daytime N densities about 50 million per cu cm at 160 km have also been inferred from airglow and other measurements on AE-C. It is shown that atomic nitrogen densities of this magnitude result in significantly lower values for the O2(+) concentration than those measured on AE-C over the altitude range to 160 to 200 km, because of the removal process O2(+) + N k3 yields NO(+) + O. The discrepancy can be explained in terms of latitudinal variations in both the N and O2 densities. Evidence is presented which indicates that k3 could be as low as 0.1 billionth per cu cm at ionospheric temperatures. K3 is the rate constant for the reaction of O2(+) with N(4-S).

Torr, D. G.↗
NASA NTRS1975

Stratospheric ozone - The possible effects of tropospheric-stratospheric feedback

The existence of tropospheric-stratospheric feedback mechanisms affecting variations in stratospheric ozone indicates the need to model the complete tropospheric-stratospheric system. For instance, a decrease in stratospheric ozone results in increased photolytic destruction of nitrous oxide in the troposphere and thereby reduced production of nitric oxide in the stratosphere. Estimates indicate that this mechanism will result in a recovery in atmospheric ozone of about 6 to 13 percent of the initial perturbation.

Chameides, W. L.↗
NASA NTRS1975

Effects of atomic nitrogen on the nocturnal ionosphere

Recently, atomic nitrogen densities of 50-500 million/cu cm were inferred in the daytime thermosphere from studies of the NI(2D-4S) 5200 A emission and from the photochemistry of various ion species using data measured by the Atmosphere Explorer-C satellite. In this paper we use the photochemistry of NO(+) and O2(+) at night to determine nocturnal N(4S) densities in the thermosphere. We present evidence for a missing source of NO(+) and a missing sink for O2(+) at night and show that this can be adequately supplied by the reaction O2(+) + N yields NO(+) + O if the N density at 200 km is about 7 million/cu cm. The atomic nitrogen has an important effect on studies of the 6300 A airglow. The omission of N in calculations of O(1D) using ground-based data results in an overestimate of the rate coefficient for quenching of O(1D) by N2.

Torr, M. R.↗
NASA NTRS1975

Time markers in interstellar communication

The chances that two civilizations establish contact with each other by means of interstellar radio communication are exceedingly small in the absence of time markers which will tell the two civilizations when to search for one another. In the case of binary stars, suitable time markers are provided by the apastron and the periastron. Single star civilization would transmit signals to binaries at the observation of apastron and periastron and the binary star civilization would scan single stars at the proper time for the reception of these signals.

Pace, G. W.↗
NASA NTRS1975

Electron density decrease in SAR arcs resulting from vibrationally excited nitrogen

A study is made of the effect on theoretical electron-density profiles of vibrational enhancement in the rate of the reaction O(+) + N2 yields NO(+) + N. It is shown that the F-region electron-density depression that is observed in stable auroral red (SAR) arcs may be caused by vibrational excitation of molecular nitrogen.

Newton, G. P.↗
NASA NTRS1975

Metastable 2P oxygen ions in the daytime thermosphere

Dayglow radiation at 7319 A has been measured by the visible airglow experiment on Atmosphere Explorer C. The overhead surface brightness measured at 15.4 hours local solar time on January 27, 1974, was 250 plus or minus 10 R. The volume emission rate had a peak value of 20 photons per cu cm per sec at a height of about 210 km. The data show clear evidence of quenching by collisons with thermal electrons at the higher altitudes and with neutral particles at lower altitudes. Quenching by neutral particles occurs at nearly the gas kinetic rate.

Walker, J. C. G.↗
NASA NTRS1975

Particle precipitation in the South Atlantic geomagnetic anomaly

A simple model of the motion of charged particles in the closed-field-line magnetic field for L less than about 4.5 is used together with Injun 3 measurements of 40-keV precipitated electrons made in the northern hemisphere to estimate theoretically the extent of electron precipitation, the energy input, and the 3914-A airglow in the South Atlantic geomagnetic anomaly. Using average values of the northern hemisphere precipitated electron flux, two regions of significantly enhanced electron precipitation are found in the southern hemisphere. The results show a gradual increase in precipitation for near sunspot minimum conditions on the western side of the anomaly followed by a rapid increase and sudden cut-off in precipitation within a few degrees west of minimum B. The flux on L = 2 reaches a spike in the southern hemisphere about 35 times greater than the average flux precipitated on L = 2 in the northern hemisphere. This increase in precipitation arises from the loss of trapped particles to the atmosphere where the mirror heights are lowest.

Torr, D. G.↗
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

Vibrationally excited nitrogen in stable auroral red arcs and its effect on ionospheric recombination

The time-dependent continuity equations, including diffusion, were solved for the first six energy levels of molecular nitrogen for conditions in the thermosphere corresponding to stable auroral red (SAR) arcs. The results show that molecular nitrogen is excited vibrationally to the degree that the rate constant for the ionospheric loss process, O(+) + N2 yields NO(+) + N, is increased by as much as a factor of 7.6 at F2 region altitudes. It was found that deviations from the energetically equivalent Boltzmann distribution were large, causing the rate constant to be as much as 1.6 times the rate constant calculated for the Boltzmann distribution. These results indicate that SAR arc intensities as small as 58 R can produce noticeable increases in the ionosphere ion-atom interchange reaction rate and hence in the rate of loss of ionospheric electrons. It is suggested that the observed decrease of electron density in the F2 region in SAR arcs can probably be explained by enhanced reaction rates for ion-atom interchange between O(+) and N2 caused by vibrational excitation of molecular nitrogen by electron impact.

Newton, G. P.↗
NASA NTRS1973

A photochemical theory of tropospheric ozone

We present a photochemical theory for tropospheric ozone in which the methane oxidation chain constitutes a large local source. This source produces about one trillion odd oxygen molecules per square centimeter per second and implies a photochemical lifetime for ozone of about 1 day, much shorter than characteristic mixing times. The photochemical model reproduces the altitude and seasonal dependence of ozone at 30 deg N. It also gives qualitative agreement with observed day-to-day variations of the ozone density.

Chameides, W.↗
NASA NTRS1973

Theoretical ion densities in the lower ionosphere

We have solved the coupled momentum and continuity equations for NO(+), O2(+), and O(+) ions in the E- and F-regions of the ionosphere. This theoretical model has enabled us to examine the relative importance of various processes that affect molecular ion densities. We find that transport processes are not important during the day; the molecular ions are in chemical equilibrium at all altitudes. At night, however, both diffusion and vertical drifts induced by winds or electric fields are important in determining molecular ion densities below about 200 km. Nitric oxide plays an important role in determining the NO(+) to O2(+) ratio in the E-region, particularly at night. Nocturnal sources of ionization are required to maintain the E-region through the night. Vertical velocities induced by expansion and contraction of the neutral atmosphere are too small to affect ion densities at any altitude.

Schunk, R. W.↗
NASA NTRS1973

The visible-airglow experiment on Atmosphere Explorer.

The visible-airglow experiment is an airglow photometer designed to measure various thermospheric emission features during the day and night both at low latitudes and in auroras. The photometer has two distinct optical channels, a high-sensitivity channel with a large field of view and a low-sensitivity channel with a narrow field of view to resolve small features. The system is protected by a combination attenuator and cathode back-biasing scheme which allows measurements of maximum sensitivity within a fraction of a second of viewing the sun. This experiment will be a part of the scientific payload on all three Atmosphere Explorer missions.

Hays, P. B.↗