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  • Other Sources  (11)
  • 1990-1994  (11)
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  • 1
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    Thermosphere and F-region plasma dynamics in the equatorial region (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The dynamics of the equatorial thermosphere and the F-region plasma are reviewed, highlighting some features observed with the San Marco satellite, the AE-E, and the DE-2, as well as with ground-based facilities at Arecibo and Jicamarca. Particular attention is given to the midnight temperature maximum and related phenomena, and to results on zonal neutral and plasma flows at F-region heights.
    Keywords: GEOPHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 13; 1, Ja
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  • 2
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    Dynamical interactions between the middle atmosphere and thermosphere (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Based on modeling some interactions between the middle atmosphere and thermosphere are presented. The interactions studied include the thermospheric circulations driven by radiative and auroral heating affecting the O concentration and temperature of the upper mesosphere through the exchange of chemical energy. Considering Kellog's mechanism, an interaction between the mesosphere and thermosphere that is driven by Joule heating is discussed.
    Keywords: GEOPHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 12; 10, O
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  • 3
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    What maintains the zonal circulation in planetary atmospheres? (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The latest Voyager observations have shown large zonal velocities in Neptune's atmosphere, with some indication of alternating jets. Similar wind velocities have also been observed on Venus and are characteristic of planetary atmospheres in general, which is remarkable considering that the available solar or internal heating varies by more than a factor of 1000. A simplified model of the planetary circulation which provides some qualitative understanding is discussed. The basic assumption is that the source driving the circulation is also generating the dissipating eddies which are simulated by diffusion. Thus, the magnitude and structure of the zonal circulation are independent both of the source and the dissipation rate. The zonal velocities are related to the speed of sound and are of comparable magnitude in different atmospheres; although the available heating varies by a large factor, and the planetary parameters vary over a wide range. The alternating jets are described by a convective eigenmode which develops when energy transport out of the planetary interior is important, as is the case on Jupiter, Neptune, and Saturn.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 367; 361-366
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  • 4
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    Mars ionopause during solar minimum - A lesson from Venus (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The ion densities measured by the Viking landers (Hanson et al., 1977) do not show an abrupt falloff with height, giving the false impression that Mars has no ionopause. On the basis of knowledge gained from the solar wind interaction at Venus during solar minimum, it is demonstrated that the observed O2 profile above about 160 km on Mars is a distributed photodynamical ionosphere and can produce an ionopause at around 325 km, similar to that observed on Venus during solar minimum. It is concluded that the solar wind interacts directly with the Mars ionosphere, suggesting that the planet does not have an intrinsic magnetic field of any consequence.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 8265-826
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  • 5
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    An equatorial temperature and wind anomaly (ETWA) (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Data obtained from the WATS (Wind and Temperature Spectrometer) and LP (Langmuir Probe) experiments on board DE-2 (Dynamic Explorer) during high solar activity show evidence of anomalous latitudinal variations in the zonal winds and temperature at low latitudes. The zonal winds exhibit a broad maximum centered around the dip equator, flanked by minima on either side around 25 degrees; while the temperature exhibits a pronounced bowl-shaped minimum at the dip equator which is flanked by maxima. The two minima in the zonal winds and the corresponding maxima in the temperature are nearly collocated with the crests of the well known Equatorial Ionization Anomaly (EIA). The maximum in the zonal winds and the minimum in the gas temperature are collocated with the trough of the EIA. The differences between the maxima and minima in temperature and zonal winds, on many occasions, are observed to exceed 100 K and 100 m/s, respectively. The characteristics of this new phenomenon have eluded present day empirical models of thermospheric temperature and winds. The connection among these variables can be understood from the ion-neutral drag effect on the motions of the neutrals that in turn affect their energy balance.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 18; 1193-119
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  • 6
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    Thermospheric gravity waves - Observations and interpretation using the transfer function model (TFM) (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: This paper presents some numerical experiments performed with the TFM to study the various wave components excited in the auroral regions that propagate through the thermosphere and lower atmosphere, and to demonstrate the properties of realistic source geometries. The model is applied to the interpretation of satellite measurements, and gravity waves seen in the thermosphere of Venus are discussed. Gravity waves are prominent in the terrestrial thermosphere polar region and can be excited by perturbations in Joule heating and Lorentz force due to magnetospheric processes. Observations from the Dynamics Explorer-2 satellite are used to illustrate the complexity of the phenomenon and to review the TFM that is utilized.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Space Science Reviews (ISSN 0038-6308); 54; 297-375
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  • 7
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    The dynamo of the diurnal tide and its effect on the thermospheric circulation (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A theoretical multiconstituent model (including O, N2, and O2) which describes the interactions between neutral winds, dynamo electric fields, and ion drifts is used to interpret observations that revealed a dominance of the fundamental diurnal tide in the upper thermosphere and at equatorial latitudes, and its effect on the thermospheric circulation. The model is shown to reproduce reasonably well the magnitudes of the neutral winds, ion drift velocities, and the ratio between the two. A solution for the neutral winds in which the dynamo electric field is forced to zero shows that the dynamo-induced ion drift is very important in accelerating the neutral atmosphere at higher altitudes. The dynamo interaction primarily affects the curl component of the field; its effect on the temperature and density perturbations is small.
    Keywords: GEOPHYSICS
    Type: Planetary and Space Science (ISSN 0032-0633); 38; 301-309
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  • 8
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    Polar thermospheric Joule heating, and redistribution of recombination energy in the upper mesosphere (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Kellogg (1961), suggested that transport of atomic oxygen from the summer into the winter hemisphere and subsequent release of energy by three body recombination, O+O+N2 yields O2+N2+E, may contribute significantly to the so-called mesopause temperature anomaly. Earlier model calculations have shown that Kellogg's mechanism produces about a 10-percent increase in the temperature from summer to winter at 90 km. This process, however, is partly compensated by differential heating from absorption of UV radiation associated with dissociation of O2. In the auroral region of the thermosphere, there is a steady energy dissipation by Joule heating causing a redistribution and depletion of atomic oxygen due to wind-induced diffusion. With the removal of O, latent chemical energy normally released by three body recombination is also removed, and the result is that the temperature decreases by almost 2 percent near 90 km. Through dynamic feedback, this process reduces the depletion of atomic oxygen by about 25 percent and the temperature perturbation in the exosphere from 10 to 7 percent at polar latitudes. Under the influence of the internal dynamo interaction, the prevailing zonal circulation in the upper thermosphere changes direction when the redistribution of recombination energy is considered.
    Keywords: GEOPHYSICS
    Type: Journal of Atmospheric and Terrestrial Physics (ISSN 0021-9169); 52; 103-112
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  • 9
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    Accuracy of the O(+)-O collision cross-section deduced from ionosphere-thermosphere observations (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Aeronomic observations applied to the empirical derivation of the ion-neutral collision cross-section -- a basic parameter governing the mutual interaction between the neutral and plasma components in the Earth's upper atmosphere -- have given values considerably larger than those derived from theory. The empirical scheme uses the plasma velocities obtained with the Incoherent Scatter Radar and the neutral winds obtained with the Fabry-Perot Interferometer. It is shown here that such an analysis overestimates the collision cross-section due to the effects of errors in the observables. The effect may be sufficiently large to bring about agreement with theory, and calls for a re-analysis of the aeronomic data using methods which minimize the bias caused by measurement errors.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 21; 22; p. 2429-2432
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  • 10
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    Properties of thermospheric gravity waves on earth, Venus and Mars (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: A spectral model with spherical harmonics and Fourier components that can simulate atmospheric perturbations in the global geometry of a multiconstituent atmosphere is presented. The boundaries are the planetary surface where the transport velocities vanish and the exobase where molecular heat conduction and viscosity dominate. The time consuming integration of the conservation equations is reduced to computing the transfer function (TF) which describes the dynamic properties of the medium divorced from the complexities in the temporal and horizontal variations of the excitation source. Given the TF, the atmospheric response to a chosen source distribution is then obtained in short order. Theoretical studies are presented to illuminate some properties of gravity waves on earth, Venus and Mars.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Chapman Conference; Jun 04, 1990 - Jun 08, 1990; Balatonfured; Hungary
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