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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 217 records · Page 12
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NASA NTRS1987

Six reasons why thermospheric measurements and models disagree

The differences between thermospheric measurements and models are discussed. Sometimes the model is in error and at other times the measurements are, but it also is possible for both to be correct, yet have the comparison result in an apparent disagreement. These reasons are collected for disagreement, and, whenever possible, methods of reducing or eliminating them are suggested. The six causes of disagreement discussed are: actual errors caused by the limited knowledge of gas-surface interactions and by in-track winds; limitations of the thermospheric general circulation models due to incomplete knowledge of the energy sources and sinks as well as incompleteness of the parameterization which must be employed; and limitations imposed on the empirical models by the conceptual framework and the transient waves.

Moe, Kenneth↗
NASA NTRS1987

The normal modes of the thermosphere

The linearized momentum, energy, and continuity equations for the thermosphere can be reduced to a form that gives the vertical structure for each horizontal wave mode. The vertical structure equation can be described in terms of the normal modes, or eigenmodes, of the thermosphere. The latter are obtained by using a 27-layer model that includes a realistic temperature profile and the effects of the Lorentz force, viscosity, and heat conduction. The normal modes have one real eigenfrequency for every two complex conjugate eigenfrequency values. The real modes have a dominant rotational wind component and are nonpropagating. The complex modes have comparable divergent and rotational wind components. The complex eigenvalues give vertically propagating modes, primarily associated with the transient response to forcing, and are significantly affected by the dissipation in the upper E region and F region. Results show that the rotational wind component dominates in the steady state when the forcing is due to the two-cell convection pattern at high latitudes and that the normal modes explain the large shears and large winds speeds that are typically observed in the high-latitude E region. The vertical energy flux for the normal modes is also calculated. The results show that the flux is upward above 130 km but downward in the lower E region for the total solution. The downward energy flux is a contribution from the real eigenmode structure.

Larsen, M. F.↗
NASA NTRS1987

Global excitation of wave phenomena in a dissipative multiconstituent medium. III - Response characteristics for different sources in the earth's thermosphere

A linear trasnfer function model of the earth's thermosphere which includes the electric field momentum source is used to study the differences in the response characteristics for Joule heating and momentum coupling in the thermosphere. It is found that, for Joule/particle heating, the temperature and density perturbations contain a relatively large trapped component which has the property of a low-pass filter, with slow decay after the source is turned off. The decay time is sensitive to the altitude of energy deposition and is significantly reduced as the source peak moves from 125 to 150 km. For electric field momentum coupling, the trapped components in the temperature and density perturbations are relatively small. In the curl field of the velocity, however, the trapped component dominates, but compared with the temperature and density its decay time is much shorter. Outside the source region the form of excitation is of secondary importance for the generation of the various propagating gravity wave modes.

Mayr, H. G.↗
NASA NTRS1987

Circulation of the polar thermosphere during geomagnetically quiet and active times as observed by Dynamics Explorer 2

The effects of geomagnetic activity on the circulation of the high-latitude neutral thermosphere were studied for the periods of November 1981 through January 1982 and November 1982 through January 1983, using neutral wind measurements obtained by the Fabry-Perot interferometer and the wind and temperature spectrometer on the Dynamics Explorer 2. Results for the Northern Hemisphere show evidence of two-cell circulation of the thermosphere at high latitudes during both quiet and active geomagnetic periods at solar maximum; the dusk cell was always dominant. In the Southern Hemisphere, only a single circulation cell existed for both quiet and active periods associated with the dusk cell of ionospheric convection. In both hemispheres, the cell sizes decreased when geomagnetic activity was reduced.

Mccormac, F. G.↗
NASA NTRS1987

On the interconnection of dynamic processes in the lower thermosphere with meteorological phenomena in the tropostratosphere

Nowadays the atmosphere is considered a single dynamic system governed by inner and other factors, the separate layers (troposphere, strato-mesosphere, thermosphere) of which are in a state of interaction though they differ physically from one another in thermal stratification and energetic processes. Observational data of thermodynamic parameter connections in these layers height range are presented. The interconnection between the temperature field disturbances in the tropo-stratosphere and the dynamic regime in the lower thermosphere in winter and summer is defined as revealed by observational data.

Fakhrutdinova, A. N.↗
NASA NTRS1987

On the dependence of the lower thermospheric wind regime on the solar cycle

The lower thermosphere occupies the intermediate position between the overlying thermospheric layers, for which direct correlation of its parameters with solar variety variations is well established, and the underlying ones, where this correlation is mainly of an indirect character. Therefore, for understanding the mechanism of solar terrestrial correlation it is important to investigate the dependence of different atmospheric parameters in the lower troposphere, and of wind regime parameters in particular, on the solar activity. Several series of observations were used which include the results of meteor radar wind velocity measurements carried out in Obninsk complemented by the data obtained using the same technique at Jodrell Bank from 1953 to 1958 and in Kharkov from 1960 to 1963. The interannual variations of values averaged over these periods for prevailing wind velocities and semidiurnal harmonic amplitudes and also results for some months are presented. These results are discussed.

Djachenko, V. A.↗
NASA NTRS1987

Mesoscale density variability in the mesosphere and thermosphere: Effects of vertical flow accelerations

A mechanistic one dimensional numerical (iteration) model was developed which can be used to simulate specific types of mesoscale atmospheric density (and pressure) variability in the mesosphere and the thermosphere, namely those due to waves and those due to vertical flow accelerations. The model was developed with the idea that it could be used as a supplement to the TGCMs (thermospheric general circulation models) since such models have a very limited ability to model phenomena on small spatial scales. The simplest case to consider was the integration upward through a time averaged, height independent, horizontally divergent flow field. Vertical winds were initialized at the lower boundary using the Ekman pumping theory over flat terrain. The results of the computations are summarized.

Revelle, D. O.↗
NASA NTRS1987

Into the thermosphere: The atmosphere explorers

The need to study the lower thermosphere with the new instrument, data handling, and spacecraft technology available in the 1960s led to the formulation and establishment of the Atmospheric Explorer program. This book provides an overview of this program with particular emphasis on the AE3, AE4, and AE5 satellites, which represent early examples of problem-dedicated missions. Both the satellites and their instrumentation on the one hand and the experimental and scientific considerations in studying the thermosphere on the other are discussed.

Burgess, Eric↗
NASA NTRS1988

Ionosphere-thermosphere momentum coupling at solar maximum and solar minimum from DE-2 and AE-C data

DE-2 and AE-C measurements of plasma and neutral densities were used to derive time constants for momentum transfer (MT) to neutrals from ions in the high-latitude thermosphere. The MT time constants for solar cycle maximum (DE-2) and for solar cycle minimum (AE-C) were averaged and binned according to geomagnetic latitude and LT to provide a quantitative measure for the tightness of ion-neutral momentum coupling (MC) in the 250-350-km altitude range. Comparisons with results obtained using the Chiu and MSIS-83 empirical models have provided an indication of the accuracy with which thermospheric general circulation models quantitatively reproduce the MC between ions and neutrals in the high-latitude F-region.

Ponthieu, J. J.↗
NASA NTRS1988

Heating efficiencies in the thermosphere of Venus reconsidered

Heating efficiencies less than 10 percent are required by recent models of the low neutral temperatures in the daytime thermosphere of Venus. It is considered here whether such values are justifiable from a molecular point of view. The primary uncertainty in a calculation of the heating efficiency is the fraction of energy, f sub v, that appears as vibrational excitation of product molecules in quenching, photodissociation, and exothermic chemical reactions. The current state of knowledge of energy partitioning in chemical reactions is discussed and a range of likely values for f sub v is deduced. The calculated heating efficiencies fall in the range 16-25 percent over the altitude range from 115 to 200 km. It is suggested that the heating efficiency should not be taken as a free parameter and that the cold Venus thermosphere has not yet been satisfactorily explained.

Fox, J. L.↗
NASA NTRS1988

Empirical global model of upper thermosphere winds based on atmosphere and dynamics explorer satellite data

Thermospheric wind data obtained from the Atmosphere Explorer E and Dynamics Explorer 2 satellites have been used to generate an empirical wind model for the upper thermosphere, analogous to the MSIS model for temperature and density, using a limited set of vector spherical harmonics. The model is limited to above approximately 220 km where the data coverage is best and wind variations with height are reduced by viscosity. The data base is not adequate to detect solar cycle (F10.7) effects at this time but does include magnetic activity effects. Mid- and low-latitude data are reproduced quite well by the model and compare favorably with published ground-based results. The polar vortices are present, but not to full detail.

Hedin, A. E.↗
NASA NTRS1989

Effects from the coupling from below on the lower thermosphere dynamics

Results of wind measurements at the midlatitude ionospheric D region are presented. The wind regime of the lower thermosphere is rather sensitive to stratospheric temperature variations, especially to sudden stratospheric warmings. The longitudinal effect in D region dynamics was revealed on the basis of simultaneous wind measurements at some points located practically at the same latitude but in different climatic regions. The distance differences are observed in the statistical distributions of wind parameters, during winter the average zonal wind speed over East Siberia was about twice that over Central Europe, and the semidiurnal zonal tide is weaker over East Siberia. The data on the seasonal reconstruction of circulation and the response of the D region wind field to the stratospheric warmings depend on the intensity and locations of stratospheric disturbances in relation to the observatory. These experimental facts are interpreted as a meteorological control of the D region and as a dependence of the lower thermosphere dynamics on the conditions of dissipation of internal waves propagating from the troposphere and stratosphere.

Kazimirovsky, E. S.↗
NASA NTRS1988

Wavelike perturbations observed in the neutral thermosphere of Venus

Wavelike perturbations are evident in the neutral thermosphere measurements of He, N, O, N2, and CO2 by the Pioneer Venus orbiter neutral mass spectrometer. In the wavelength range from 100 to 600 km, the amplitudes of the various species are comparable in magnitude, with CO2 having the largest amplitude, and with helium out of phase with respect to the heavier species. On the dayside, the small-scale variations of CO2 and N2 increase with increasing altitude from 170 to 210 km, with CO2 having the largest slope. Simple and complex wave structures are observed, including wave trains and pulselike events. There is more activity during nighttime than during daytime, and larger values of the activity occur in the vicinity of the predawn and postdusk terminator sectors. Below 160 km, the standard deviation of the CO2 density on the nightside is 12 percent, about 3 times the daytime value. The data are consistent with the interpretation that the density perturbation are due to gravity waves propagating upward from the lower thermosphere.

Kasprzak, W. T.↗
NASA NTRS1988

Atomic oxygen modeling in the upper thermosphere

Empirical models of atomic oxygen in the earth's thermosphere are discussed, and calibration problems in satellite drag and in situ mass spectrometer measurements are reviewed. Models based on drag data and mass spectrometer data are found to agree on average to within 15 percent, suggesting that the absolute values are reasonably well known in the upper thermosphere. Comparison of different models with various data sources show residuals of at least 15 percent which are the results of unmodeled magnetic storm, EUV, and geographical variations and smaller scale variations caused by gravity waves.

Hedin, A. E.↗
NASA NTRS1988

Thermosphere dynamics - Recent contributions from Dynamics Explorer-2

This paper discusses results obtained during the period between August 1981, and February 1983, by the instruments aboard the Dynamic Explorer-2 (DE-2) mission, with emphasis placed on the data obtained through the direct measurements of thermospheric vector neutral winds and ion drifts. The DE-2 instrumentation used to obtain the vector neutral-wind observations is described together with the information obtained on the dynamics of the thermosphere. Special consideration is given to the theoretical model development and the ongoing data-theory comparative studies. The progress made during the first five years of the DE mission is summarized.

Killeen, T. L.↗
NASA NTRS1988

On the structure and circulation of the polar thermosphere under magnetically quiet conditions

A theoretical study of the thermospheric circulation and composition at polar latitudes is presented. It is suggested that the observed motions and density perturbations in N2, O and He can be understood in terms of electric field momentum coupling, Joule heating, and interactions between these two processes. It is found that the vortex type double cell polar circulation is primarily driven by collisional momentum transfer from electric field induced ion convection. Because of the thermospheric low pass filter, a large time independent component is produced by Joule heating. Due to wind induced diffusion, the N2 is concentrated where the O and He are depleted and vice versa. The electric field driven vortex circulation redistributes the mass and energy in the time independent density and temperature variations, producing primarily diurnal variations in the temperature and composition near the pole and at auroral latitudes.

Mayr, H. G.↗
NASA NTRS1989

Lower thermospheric density fluctuations during the time period of Typhoon Dinah

High frequency Doppler sounder arrays were used to study the thermospheric density fluctuations caused by Typhoon Dinah in August, 1987. The results show that the maximum density fluctuations caused by the typhoon at altitudes of 150 to 350 km were close to + or - 30 percent deviation from the quiet background. The time-dependent density fluctuations were in phase with the horizontal phase velocity of major gravity waves excited by the storm. It is suggested that the study demonstrates the use of HF Doppler sounder measurement of gravity waves, horizontal wind velocity in the direction of gravity wave propagation, and density perturbations at thermospheric heights.

Hung, R. J.↗
NASA NTRS1988

In situ measurements of thermospheric composition, temperature, and winds by mass spectrometry

Mass spectrometry, in which a beam of electrons ionizes a sample of atmospheric gas and then analyses the ions thus produced to determine the concentration of each species in the sample, is presently evaluated as a basis for the study of earth atmosphere and other planetary atmospheres' properties. Recent applications of in situ mass spectrometry have measured thermospheric neutral gas composition, temperatures, and winds, with a spatial resolution sufficiently high to reveal previously unsuspected atmospheric variability. It is expected that analyses of these data will lead to a more detailed understanding of the deposition processes governing the thermosphere's highly variable structure.

Spencer, N. W.↗