Engineering topics

Mayr, H. G.

Publications and source records attributed to Mayr, H. G..

At least 127 records · Page 7

NASA NTRS1979

CO2 and CO electron vibrational cooling rates

Electron cooling rates for electron vibrational excitation of CO2 and CO and rotational excitation of CO are calculated. Results of the calculation are expressed as closed form analytic relations that are both convenient for numerical calculations and valid over a wide range of electron and neutral temperatures. It is found that the cooling rates and their temperature dependences differ significantly from other calculations. For CO2, these differences are related mainly to the assumptions about the approach to equilibrium and not to the actual cross-section choices. For electron temperatures below 1000 K and gas temperatures near 300 K (representative of conditions in the Venus atmosphere, where collisional cooling of the electrons dominates), the CO2 cooling rate is as much as an order of magnitude larger than previously considered in ionospheric models.

Porter, H. S.↗

NASA NTRS1979

Empirical models of the electron temperature and density in the nightside Venus ionosphere

Empirical models of the electron temperature and density of the late afternoon and nightside Venus ionosphere based on the Pioneer Venus measurements are presented. They describe the ionosphere conditions near 18 deg latitude between 150 and 700 km altitude for solar zenith angles of 80 to 180 deg, with a 10-fold decrease beyond 90 deg and a gradual decrease between 120 and 180 deg. The nightside electron density profile, the ion transport process, and electron precipitation are discussed. The high nocturnal temperatures and the well defined nightside ionopause suggest that energetic processes occur across the top of the entire nightside ionosphere, maintaining elevated temperatures.

Brace, L. H.↗

NASA NTRS1979

Energy and mass transport in the thermosphere

Examples illustrating the effects of large scale energy and mass transport in the thermosphere discussed include: (1) The seasonal variations reveal temperature, composition, and ionospheric anomalies involving energy exchange between the thermosphere and mesosphere. (2) The midnight temperature maximum in the thermosphere is interpreted as a signature of tidal waves emanating from the mesosphere and momentum coupling associated with ion drag. (3) The ionospheric storm in the F region illustrates the intricate effects of large scale atmospheric winds driven by magnetospheric energization processes. (4) Atmospheric signatures of Joule heating and electric field momentum coupling are markedly different.

Mayr, H. G.↗

NASA NTRS1979

The midnight temperature maximum in the earth's equatorial thermosphere

The paper reports in situ direct measurements of regularly observed thermosphere neutral particle (i.e., N2) temperature maxima that occur predominantly after midnight. The measurements were made using the Neutral Atmosphere Temperature Instrument aboard Atmosphere Explorer-E in circular orbit (inclination 19 deg) at about 275 km. Hundreds of midnight temperature maxima were observed, some having values exceeding the well-known afternoon maximum. Simultaneous in situ direct measurements of the wind component normal to the orbit plane have also been obtained and observed to correlate in a systematic way with the temperature maxima.

Spencer, N. W.↗

NASA NTRS1979

Tides and the midnight temperature anomally in the thermosphere

Spectral analysis of the midnight temperature anomaly observed on Atmosphere Explorer-E indicates that the phenomenon can be adequately represented with wave numbers between 1 and 5. Results from a multiconstituent circulation model suggest that this feature and associated variations in composition are the result of a complex interaction between the semidiurnal tide generated in the lower atmosphere and ion-neutral momentum coupling associated with the diurnal variation of the ion density which, in turn, also generates higher order tidal models.

Mayr, H. G.↗

NASA NTRS1979

F-region dynamics

The U.S. research efforts in the last four years, relating to an understanding of upper atmosphere or thermosphere and F-region dynamics are reported. Simultaneous measurements of atmospheric parameters from the Atmosphere Explorer satellites were used in photochemistry and photoenergetics studies. Studies of the magnetosphere as a major source of energy and momentum for the thermosphere are outlined. Time-dependent ionosphere models which describe the thermal structure, composition, photoelectron spectrum, and airglow emissions in F-regions are discussed. Solar tides, magnetic disturbances, and gravity waves in the thermosphere are considered. It is noted that planetary explorations will help to understand scientific problems of the space environment.

Mayr, H. G.↗

NASA NTRS1978

Some properties of upper atmosphere dynamics

A unifying description is provided of some important dynamic properties of the upper atmosphere in composition and temperature characteristic of a variety of phenomena, including diurnal and seasonal tides, magnetic storms, and momentum coupling with the magnetosphere. A theoretical multiconstituent model is used which can link the large-scale variations of composition and temperature to the dynamics and energetics of the thermosphere. Global mean properties of the thermosphere are reviewed, and an attempt is made to convey some understanding of the dynamic properties of energy and diffusive mass transport in the thermosphere. Attention is given to sources of energy for the thermosphere, the transport processes involved in the solar diurnal tide of the thermosphere, energy and particle sources for the annual tide, feedback from composition changes to wind-field and temperature variations, energy deposition in the thermosphere during magnetic storms and substorms, and momentum source signatures in the thermosphere.

Mayr, H. G.↗

NASA NTRS1978

Effect of anomalous transport coefficients on the thermal structure of the storm time auroral ionosphere

By analyzing an observed storm time auroral electron temperature profile it is shown that anomalous transport effects strongly influence the thermal structure of the disturbed auroral ionosphere. Such anomalous transport effects are a consequence of plasma turbulence, the existence of which has been established by a large number of observations in the auroral ionosphere. The electron and composite ion energy equations are solved with anomalous electron thermal conductivity and parallel electrical resistivity coefficients. The solutions are parameterized with respect to a phenomenological altitude-dependent anomaly coefficient A and are compared with an observed storm time electron temperature profile above Chatanika. The calculated temperature profile for the classical case (A = 1) disagrees considerably with the measured profile over most of the altitude range up to 450 km. It is shown that an anomaly coefficient with a sharp peak of the order of 10,000 centered around the F2 peak is consistent with observations.

Fontheim, E. G.↗

NASA NTRS1978

Diffusion model for the upper atmosphere of Venus

On the basis of a linear theory it is shown that wind-induced diffusion associated with large-scale circulation in the Venus atmosphere leads to nighttime bulges in O, He, and H. The effect on He is very large with a 243-day rotation period of the atmosphere, yielding an upper limit for the maximum/minimum diurnal density ratio of approximately 1000. This ratio is much smaller for H (max/min of about 4) due to the greater importance of exospheric flow, which acts (as for He) as a damping mechanism. For the faster rotation period of 4 days consistent with the motions of the cloud tops, the diurnal variation of O is significantly reduced, contributing to an increase by a factor of two in the horizontal wind velocity. The same effect significantly reduces the He variations to an increase by a factor of 7 from day to night. The results suggest that composition and wind measurements provide valuable information on the rotation rate of the Cytherean thermosphere.

Mayr, H. G.↗

NASA NTRS1978

Global circulation and distribution of hydrogen in thermosphere of Venus

The global density distribution of atomic H in the upper atmosphere of Venus is determined in terms of a global circulation model. It is shown that H produced on the dayside is efficiently advected to the nightside by the major gas CO2 where it is then convected to lower altitudes and recombines. A maximum night/day H density ratio of about 5 is derived, in which case exospheric return flow from night to day strongly limits the nightside density enhancement. A previously postulated constraint connecting the eddy diffusion coefficient with the escape flux of H in one dimensional models is no longer required when global circulation of H is considered.

Hartle, R. E.↗

NASA NTRS1978

Some characteristics of electric field momentum coupling with the neutral atmosphere

A three-dimensional model has been developed to describe momentum coupling between high-latitude electric fields, neutral winds, temperature, and composition. The Hall drag is found to be the main source for atmospheric winds and the small divergence component of winds is due to the Pedersen drag and the Hall drag. Adiabatic heat transfer is responsible for the back pressure which damps the divergence field and for the reversal in circulation of the divergence field at higher altitudes. Back pressure causes a decrease in total wind velocity of about 10% at exospheric heights and by a factor of about 2 at 120 km. The wind field with the pressure feedback may be simulated by neglecting pressure variations and the Coriolis force. Density variations of Ar, N2, O, and He, induced by the momentum source, are in phase above 120 km and out of phase with the temperature amplitude above 150 km. The electrostatic field momentum source is ineffective for directly inducing density and temperature variations in the upper thermosphere.

Mayr, H. G.↗

NASA NTRS1978

Direct evidence of transport processes in the thermospheric diurnal tide

Measurements of neutral composition and temperature obtained between December 6, 1975, and September 17, 1976, with instruments aboard the near-equatorial AE-E satellite are analyzed to determine the diurnal variations at altitudes from 145 to 295 km. The general trends, including the shift in oxygen phase from afternoon at high altitudes to morning at low altitudes, are reproduced by circulation theories. The oxygen and helium variations show small departures from diffusive equilibrium below 200 km that are consistent with wind-induced diffusion and provide the first direct evidence of transport processes in the diurnal tide of the thermosphere.

Hedin, A. E.↗

NASA NTRS1978

The signature of H/+/ in the equatorial anomaly - An empirical model

Ion composition data from the OGO-6 satellite are used to develop an empirical model of the H(+) signature in the equatorial anomaly. The empirical model is an attempt to represent the generally repeatable details of the satellite data by a parameterized numerical model accounting for such variables as the altitude, local time and longitude of the observations. Although the resulting model is in general agreement with past findings on the variability of the equatorial anomaly phenomenon, there appears to be a complexity of short-term or narrowly localized variations which cannot be adequately understood on the basis of data from a single satellite.

Taylor, H. A., Jr.↗

NASA NTRS1978

Momentum source signatures in thermospheric neutral composition

Perturbations in the structure of the neutral atmosphere were measured in narrow latitude bands near the dayside polar cusp by mass spectrometers aboard the S3-1 and Esro 4 satellites. The disturbances are characterized by an in-phase variation of both the lighter and the heavier species. They are observed to occur in latitude bands of about 5-10 deg extent in the altitude region of 200 km during periods of increased geomagnetic activity. It is suggested that thermospheric winds driven by momentum sources associated with ion convection are the predominant cause for these disturbances. The narrow structure features associated with the momentum source are superimposed on the thermospheric changes caused by Joule heating. Both effects may be present simultaneously, resulting in a complex response pattern of the neutral gas composition in the thermosphere.

Trinks, H.↗

NASA NTRS1977

Observations of neutral composition and related ionospheric variations during a magnetic storm in February 1974

The neutral-atmosphere composition experiment on Atmosphere Explorer C measured N2, O, Ar, and He densities during a magnetic storm at altitudes down to about 160 km. At latitudes above 45 deg N, N2 and Ar densities generally increase during the storm, while He and O densities decrease. Below 45 deg N all densities tend to increase during the storm. The density increases at perigee indicate that density- or temperature-profile changes are taking place below 160 km. The return to prestorm conditions is very slow, demonstrating the integrating effect of the atmospheric response. A recent theoretical model incorporating thermospheric circulation and diffusion effects reproduces the longitudinally averaged data, including latitude trends and the asymmetry about the storm maximum. Comparison with the mass-spectrometer and incoherent-scatter empirical model shows qualitative agreement with latitude trends but not with storm asymmetry, while the earlier J71 model based on total mass density is not in agreement with observed latitudinal trends. A close correlation is found between in situ O/N2 measurements and in situ and ground-based ionosonde measurements of electron density.

Hedin, A. E.↗

NASA NTRS1977

Spherical asymmetry in thermospheric magnetic storms

It is suggested that spherical asymmetries in heat-input distribution during magnetic storms could be important in moving the center of thermospheric circulation toward the equator. Circumstantial evidence from neutral-composition data obtained by two satellites during a series of strong geomagnetic substorms is shown to suggest a pronounced hemispherical asymmetry in magnetic-storm-related energy deposition and to support the circulation concept. Ground-based observations of the F2 peak density in both hemispheres are used to complement the composition data and to confirm the concept of hemispherical asymmetry. The composition data are analyzed quantitatively on the basis of a linear circulation model for the cases of a zero heat source in the Northern Hemisphere, factor-of-two differences between the heat sources in the Northern and Southern Hemispheres, and identical heat sources in both hemispheres. The results are found to be in qualitative agreement with the suggestion of pronounced asymmetry in thermospheric circulation.

Mayr, H. G.↗

NASA NTRS1977

Diurnal variations in the thermosphere. II - Temperature, composition, and winds

The fundamental diurnal component of temperature, composition and wind fields is discussed for the thermosphere, the results delineated in terms of energy sources in the lower atmosphere, mesosphere and thermosphere, illustrating their relative significance. The diurnal component in the composition of H, He, O, O2 and Ar has been analyzed in terms of effects from thermal expansion in diffusive equilibrium and transport processes associated with chemistry, wind circulation, exospheric flow and escape. Next to thermal expansion, wind-induced diffusion is the single most important process; it dominates the diurnal variations of He and prevails in the variations of O, O2 and Ar below 200 km.

Mayr, H. G.↗

NASA NTRS1977

A global thermospheric model based on mass spectrometer and incoherent scatter data MSIS. II - Composition

Measurements of O, He, and Ar from neutral gas mass spectrometers on four satellites (Ogo 6, San Marco 3, Aeros A, and AEC-C) and inferred oxygen and hydrogen densities from an ion mass spectrometer on AE-C have been combined with a neutral temperature and nitrogen density model to produce a global model of thermospheric composition in terms of inferred variations at 120 km. The data set covers the time period from mid-1969 to mid-1975. The MSIS (mass spectrometer and incoherent scatter data) model is compared with the Ogo 6 model (Hedin et al., 1974). Ar variations at 120 km tend to be in phase with temperature variations and inverse to the He, O, and H variations.

Hedin, A. E.↗