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  • GEOPHYSICS  (13)
  • 1980-1984  (13)
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  • 1
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    Calculated stormtime variations in plasmaspheric thermal ion composition (1983)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: Model calculations describing stormtime variations in the earth's dayside plasmasphere are used to examine variations in ion composition. The model storm is initiated by high-latitude thermospheric heating that generates meridional winds that carry neutral species, momentum, and energy equatorward. The thermosphere acts on the plasmasphere through collisional transfer of momentum and through chemical reactions between neutral species and ions. Over latitudes near the region of thermospheric heating, the thermosphere-plasmasphere coupling processes cause enhancement in the density of oxygen ions while protons are being lost. Meanwhile, densities of oxygen ions and protons near the equator are increasing together, almost in phase. The largest enhancements in ion density develop at latitudes near 45 deg invariant for both oxygen and hydrogen.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 88; 10233-10
    Format: text
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  • 2
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    Global excitation of wave phenomena in a dissipative multiconstituent medium. I - Transfer function of the earth's thermosphere. II - Impulsive perturbations in the earth's thermosphere (1984)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: A transfer function approach is taken in constructing a spectral model of the acoustic-gravity wave response in a multiconstituent thermosphere. The model is then applied to describing the thermospheric response to various sources around the globe. Zonal spherical harmonics serve to model the horizontal variations in propagating waves which, when integrated with respect to height, generate a transfer function for a vertical source distribution in the thermosphere. Four wave components are characterized as resonance phenomena and are associated with magnetic activity and ionospheric disturbances. The waves are either trapped or propagate, the latter becoming significant when possessing frequencies above 3 cycles/day. The energy input is distributed by thermospheric winds. The disturbances decay slowly, mainly due to heat conduction and diffusion. Gravity waves appear abruptly and are connected to a sudden switching on or off of a source. Turn off of a source coincides with a reversal of the local atmospheric circulation.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 89; 10929-10
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  • 3
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    An analytic formulation for heating source memory in the thermospheric composition (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Numerical calculations from a spectral circulation model are utilized to construct an analytic Green's function formulation describing the meridional, time-dependent thermospheric composition and temperature response during magnetic storms. The purpose is to develop a formulation that embodies source memory while being sufficiently simple to serve as a heuristic guide for empirical modeling. By passing from the discrete Fourier series representation, utilized for the numerical circulation model, to a continuous Fourier integral representation, explicit waves are obtained for the thermospheric response times. The response times are altitude and species dependent and can exceed two days below 200 km. Thus, for certain storm scenarios, pronounced source memory signatures for the composition and temperature are predicted. Response times obtained from the formulation are shown to give a response consistent with previously published neutral composition data from AE-C for the February 1974 storm when an ap dependent heat source is employed.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research; 86; May 1
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  • 4
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    Semiempirical modeling of thermospheric magnetic storms (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: An improved formulation for empirical modeling of magnetic storm effects in neutral thermospheric composition and temperature is utilized in a study of two disturbed periods. The formulation, which incorporates the prior history of the heat input rather than a single phase delay, is based on a Fourier integral representation of an existing theoretical model. This results in an improved representation of the detailed time variations and a better carry-over of model parameters from one storm to the other and provides a basis for theoretical interpretation.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research; 86; May 1
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  • 5
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    A magnetospheric signature of some F layer positive storms (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Calculations of electron density distributions in the global thermosphere-ionosphere system perturbed by high-latitude thermospheric heating are presented which indicate a link between the heating and magnetospheric plasma disturbances near the equator. The calculations were made using a self-consistent model of the global sunlit thermosphere-ionosphere system describing the evolution of equatorial plasma disturbances. The heat input is found to cause electron density enhancements that propagate along magnetic field lines from the F2 maximum over mid-latitudes to the equator in the magnetosphere and which correspond to the positive phase of an F layer storm. The positive phase is shown to be generated by the induction of equatorward winds that raise the mid-latitude F layer through momentum transfer from neutral atoms to ionospheric ions, which ions pull electrons with them. Model results are used to identify plasma signatures of equatorward winds and an intensified magnetospheric electric field in Explorer 45 and Arial 4 measurements taken during the positive phase of an F layer storm.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research; 86; May 1
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  • 6
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    The semidiurnal and terdiurnal tides in the equatorial thermosphere from AE-E measurements (1980)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: Measurements of neutral composition and temperature aboard the near-equatorial AE-E satellite are analyzed to determine the semidiurnal and terdiurnal variations from 145 to 295 km. The amplitudes and phases of the semidiurnal variation are approximately the same for N2, O, He, and Ar at the lowest altitude, and the amplitude increases with decreasing altitude. Except for He, the phase undergoes a 180 deg shift around 200 km. The behavior of the terdiurnal variation is in many respects similar to the behavior of the semidiurnal variation. These characteristics suggest that the semidiurnal tide and (to a lesser extent) the terdiurnal tide have an origin primarily in the lower thermosphere or below.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research; 85; Apr. 1
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  • 7
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    Latitudinal (seasonal) variations in the thermospheric midnight temperature maximum - A tidal analysis (1983)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: The temperature variations of the neutral gas in the thermosphere are considered as a function of local time and season, taking into account the latitude range from -17.5 deg to +17.5 deg and the altitude range from about 250 km to about 400 km. The temperature measurements were conducted in situ with the Neutral Atmospheric Temperature Experiment (NATE) on the Atmospheric Explorer E (AE-E) spacecraft during the time between December 1976 and January 1979. The altitude of the circular orbit of the spacecraft was gradually increased during this period from 250 to 400 km. A significant result of the reported analysis is the latitudinal (seasonal) variation observed in the semidiurnal and terdiurnal tides during solstice. It is found that this variation is responsible for the seasonal behavior of the midnight temperature maximum.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 88; Sept. 1
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  • 8
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    The earth's thermospheric superrotation from Dynamics Explorer 2 (1984)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: Neutral thermospheric zonal winds measured from the Wind and Temperature Experiment on Dynamics Explorer 2 have been analyzed to provide a measure of the superrotation of the neutral thermosphere. The data were averaged in local time in 10 degree bands from the equator to 40 degrees latitude. The results show an average wind velocity on the order of 18 m/s to the East at the equator and a westward wind of the same magnitude at mid latitudes. Within the range of altitudes of the data base (200 to 700 km) no evidence of any significant altitude dependence was found. Averaging our data over the latitude bands studied indicates a net corotation of the thermosphere. This result is not in agreement with the superrotation value reported by King-Hele and Walker on the basis of satellite drag analysis.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 11; 531-533
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  • 9
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    A zonally symmetric model for volcanic influence upon atmospheric circulation (1984)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: The effects of volcanic activity upon zonal wind flow in a model atmosphere are considered. A low latitude volcanic eruption could lower the tropospheric pole to equator temperature difference and thereby affect the atmospheric motions. When the temperature contrast decreases, the zonal wind velocities at high altitudes are reduced. To conserve angular momentum, the velocities in the lower atmosphere near the surface must increase, thus providing a momentum source for ocean currents. It is suggested that this momentum source may have played a role as a trigger for inducing the 1982-83 anomalous El Nino and possibly other climate changes.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 11; 303-306
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  • 10
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    Thermospheric superrotation revisited (1984)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: The characteristics of thermospheric superrotation and accompanying latitudinal variations in temperature and composition are examined theoretically. Superrotation was measured by the Dynamics Explorer 2 satellite, which provided data for the atmospheric rotational velocity with respect to that of the planet for all seasons for 300-350 km altitudes. Zonally averaged circulation is described with momentum equations. A spectral model covers the superrotation, and account is taken of symmetric radiative and auroral components, asymmetric ion drag, an asymmetric pressure gradient and a viscous component. The horizontal wind field of the diurnal tide and diurnal variations in ion density which produce a momentum source are the largest contributors to superrotation at low and midlatitudes.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 89; 5613-562
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