Engineering topics

Atreya, S. K.

Publications and source records attributed to Atreya, S. K..

96 records · Page 6

NASA NTRS1976

Electron temperatures in the Jovian ionosphere

The daytime electron temperature profile of the Jovian ionosphere was calculated, taking into account the effects of thermal conduction and heat inflow from the plasmasphere. The photoelectron fluxes and electron heating rates were determined by using the two-stream approach of Banks and Nagy (1970) and Nagy and Banks (1970). The calculated electron temperatures were found to follow the neutral temperature up to an altitude slightly above the electron density peak, while at higher altitudes they were significantly enhanced above the assumed neutral temperature value.

Nagy, A. F.↗

NASA NTRS1976

Ultraviolet stellar occultation measurement of the H2 and O2 densities near 100 km in the earth's atmosphere

Results are presented for an experimental study designed to measure the density of H2 near 100 km in the earth's atmosphere from occultation of a star, Gamma Vel, by the earth's atmosphere at several wavelengths near the H2 absorption line at 1108.128 A by a spectrometer on an orbiting astronomical observatory. Measurement of the O2 density between 95 and 123 km is also reported. Attention is focused on testing the predictions of a model of the distribution of hydrogen constituents, H, H2, H2O, CH4, OH, and H2O in the upper atmosphere related to a theory of hydrogen escape developed by Hunten and Strobel (1974) and by Liu and Donahue (1974). The measured H2 densities are found to be in good agreement with recent theoretical predictions, whereas the measured O2 density profile generally agrees with the models except for a wavelike structure in the range 104-114 km.

Atreya, S. K.↗

NASA NTRS1976

Model ionospheres of Jupiter

The principal concepts presently involved in modeling the Jovian ionosphere are reviewed. A model ionosphere is developed on the basis of our present knowledge of atmospheric composition, relevant chemical and ion-molecule reactions, with their associated rate constants. The shortcomings of this model are discussed when it is compared with the electron density profile obtained from the Pioneer 10 radio occultation data. It is demonstrated that the apparent great extent of the observed topside ionosphere may imply a hot thermosphere, as if Jupiter sustained a corona. Some of the layers observed in the electron density profile may be due to sporadic-E like clustering of protons and other ions.

Atreya, S. K.↗

NASA NTRS1975

A model of the Venus ionosphere

Results of model calculations of the Venus ionosphere from 120 to 300 km are presented. The chemical scheme and reaction rates used are the same as given by Kumar and Hunten (1974) except that the electron temperature dependence of the dissociative recombination rates is taken into account. Calculations are made for low and high atomic oxygen models in which the O/CO2 ratios are 0.4% and 4% respectively at 140 km, and the results agree well in shape and magnitude with the Mariner 5 and 10 occultation results in the chemically controlled region. Reasonable agreement is obtained at higher altitudes if diffusive equilibrium and high vertical flow velocities (10 km/s) are assumed as upper boundaries for the Mariner 5 and 10 conditions respectively, although solar wind-ionosphere interactions are considered to be the controlling mechanism for the Mariner 10 results.

Nagy, A. F.↗

NASA NTRS1974

Jupiter's ionosphere - Prospects for Pioneer 10

Model Jovian ionospheres are constructed for comparison with Pioneer 10 results. Electron density maxima are predicted at a level approximately 220 kilometers above an assumed reference height where the hydrogen density is 10 to the 16-th power molecules per cubic centimeter. It may be possible to use observations of the electron density to locate the turbopause. Attention is drawn to a possible strong source of ionized sodium from Io which might lead to large electron densities at low altitudes.

Atreya, S. K.↗

NASA NTRS1971

The influence of thermospheric winds on the auroral red-line profile of atomic oxygen.

Discussion of the effect of thermospheric winds on the emission profile of lambda 6300. It is shown that meridional winds play a significant role in determining the shape of this emission and that the conventional diffusion of O(super 1 D) hypothesis, although important, is not adequate to explain the observed features completely.

Hays, P. B.↗