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  • 1
    Electronic Resource
    Electronic Resource
    The effect of anisotropic permeability on free convective boundary layer flow in porous media (1995)
    Springer
    Transport in porous media 19 (1995), S. 79-92 
    Details
    ISSN: 1573-1634
    Keywords: Porous medium ; convection ; boundary layer ; anisotropy ; permeability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract The effect of an anisotropic permeability on thermal boundary layer flow in porous media is studied. The convective flow is induced by a vertical, uniformly heated surface embedded in a fluid-saturated medium. A leading-order boundary layer theory is presented. It is shown that the thickness of the resulting boundary layer flow is different from that obtained in an isotropic porous medium. In general, an anisotropic permeability induces a fluid drift in the spanwise direction, the strength of which depends on the precise nature of the anisotropy. Conditions are found which determine whether or not the boundary layer flow is three-dimensional.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00716050
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Non-Darcy natural convection from a vertical wavy surface in a porous medium (1995)
    Springer
    Transport in porous media 20 (1995), S. 223-234 
    Details
    ISSN: 1573-1634
    Keywords: Porous medium ; convection ; boundary layer ; nonsimilarity ; inertia ; surface waves
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract We examine the combined effect of spatially stationary surface waves and the presence of fluid inertia on the free convection induced by a vertical heated surface embedded in a fluid-saturated porous medium. We consider the boundary-layer regime where the Darcy-Rayleigh number, Ra, is very large, and assume that the surface waves have O(1) amplitude and wavelength. The resulting boundary-layer equations are found to be nonsimilar only when the surface is nonuniform and inertia effects are present; self-similarity results when either or both effects are absent. Detailed results for the local and global rates of heat transfer are presented for a range of values of the inertia parameter and the surface wave amplitude.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01073173
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  • 3
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    Optical observations of the AMPTE artificial comet from the Northern Hemisphere (1986)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The AMPTE artificial comet of Dec. 27, 1984, developed a well-defined core (maximum size about 160 x 100 km) of cold barium ions, surrounded by a diffuse coma, 500 km in diameter, consisting of ions extracted from the core. A plasma tail extended from the core, mainly directed away from the sun. The plasma tail and diffuse coma consisted of energetic ions (above 200 eV). Confounding predictions, the artificial comet survived for barely five minutes, and the core of the comet moved southward, rather than in the direction of the solar wind.
    Keywords: GEOPHYSICS
    Type: Nature (ISSN 0028-0836); 320; 704-708
    Format: text
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  • 4
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    Observations of a gradual transition between Ps 6 activity with auroral torches and surgelike pulsations during strong geomagnetic disturbances (1988)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: This paper describes a long-lasting large-amplitude pulsation event, which occurred on January 10, 1983 in the ionosphere and magnetosphere and was characterized by Steen and Rees (1983). Over the 4-h period (0200-0600 UT), the characteristics of the pulsations in the ionosphere changed from being Ps 6 auroral torches toward substorms and back to Ps 6. At GEO, the corresponding characteristics were a modulation of the high-energy particle intensity and plasma dropouts. Based on the ideas presented by Rostoker and Samson (1984), an interpretation of the event is offered, according to which the pulsations are caused by the Kelvin-Helmholtz instability during an interval of strong magnetospheric convection. On the basis of this explanation, a new interpretation of the substorm time sequence is proposed.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 93; 8713-873
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  • 5
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    Observations of the dynamics of the polar thermosphere (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The dynamics of the polar thermosphere are examined by using observations made from the Dynamics Explorer 2 satellite. The results used in this study were obtained primarily from the Fabry-Perot interferometer (FPI) and the wind and temperature spectrometer (WATS) during the time period from September 1981 through January 1982. Two primary geophysical conditions were examined: these were the southern summer and the northern winter polar regions. The results support the conclusion that above 60 degrees of latitude the neutral winds are strongly controlled by ion/neutral frictional momentum transfer resulting from magnetospheric convection. This implies that the natural coordinate system within which to display the neutral winds in the high polar thermosphere is magnetic. The collected observations of this study were used to assess the validity of two of the large thermospheric general circulation models. The result of this assessment was that the models reasonably represent the vector winds at high altitudes but do not, at present, accurately simulate the thermodynamics of that regime.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 89; 5597-561
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  • 6
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    The westward thermospheric jet-stream of the evening auroral oval (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Ground-based and satellite measurements of the thermospheric wind in jet-streams during the evening auroral oval are analyzed, in order to study the geophysical mechanisms of thermospheric wind generation. Numerical simulations using a global, three-dimensional, time-dependent model of thermospheric dynamics were compared with the satellite data, and the results are discussed in detail. The wind distribution during the storm is shown in a series of color plates.
    Keywords: GEOPHYSICS
    Type: Planetary and Space Science (ISSN 0032-0633); 33; 425-443
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  • 7
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    Midlatitude measurements of the ionospheric electric field during the ALADDIN programme (1980)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: Three measurements of ionospheric electric field were made during the 24-h ALADDIN rocket program at Wallops Island on June 29-30, 1974. The first of these used a double probe instrument, flown at 1500 Local Solar Time, and the second and third measurements were made by barium cloud releases at evening and morning twilight. These three electric field vectors have been compared with the predictions of a number of models of electric field due to the dynamo effects of various atmospheric tides, and also of a possible magnetospheric origin. On the assumption that the measurements were made at a location equatorward of the afternoon convergence and poleward of the morning divergence in the electric field patterns related to the Sq current system, Stening's (1973) model of the diurnal variation of the electric field induced by the (1, -2) tidal model at the time of the summer solstice correctly predicts the directions of the observed electric field. Forbes and Lindzen's (1976, 1977) model, incorporating the three major propagating tidal modes as well as the evanescent (1, -2) mode, also bears an acceptable relationship to the ALADDIN electric field directions. The ALADDIN E-field magnitudes are comparable with those obtained by ground-based observations from Millstone Hill and from Saint Santin but are about half of Stening's model values, and three times those of Forbes and Lindzen. Saint Santin E-field directions, at the same latitude but 75 deg difference in longitude, are distinctly different from ALADDIN, implying that longitudinal differences are significant.
    Keywords: GEOPHYSICS
    Type: Journal of Atmospheric and Terrestrial Physics; 42; June 198
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  • 8
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    A comparison of wind observations of the upper thermosphere from the Dynamics Explorer satellite with the predictions of a global time-dependent model (1983)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: Experimental and theoretical investigations of high-latitude circulation in the upper thermosphere are reported. Vector-wind plots constructed by combining remotely sensed meridional-wind and in situ zonal-wind data obtained during four south-polar and three north-polar passes of the NASA Dynamics Explorer satellite in October and December, 1981, are presented and analyzed, taking the geomagnetic activity level and local solar time into account. The results are then compared with the predictions of 3D time-dependent global models of thermospheric neutral winds (Fuller-Rowell and Rees, 1980, 1981, 1983) adjusted to account for both solar-UV/EUV heating and ionization effects and quiet (Kp from 1 to 2) or moderately disturbed (Kp from 3 to 4) geomagnetic conditions (models Q and MD). An MD model incorporating a self-consistent description of the high-latitude ionosphere and a Q model excluding high-latitude effects are found to give the most accurate predictions for the respective geomagnetic conditions.
    Keywords: GEOPHYSICS
    Type: Planetary and Space Science (ISSN 0032-0633); 31; 1299-131
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  • 9
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    The composition, structure, temperature and dynamics of the upper thermosphere in the polar regions during October to December 1981 (1985)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Observational data obtained by the Dynamics Explorer-2 (DE-2) spacecraft were compared with global model simulations in order to study the composition, structure, temperature, and dynamics of the upper thermosphere in polar regions during the period October-December 1981. A UCL three-dimensional model was used to simulate the seasonal, diurnal, and geomagnetic response of the neutral thermosphere and to follow the major features of the solar and geomagnetic inputs during the late 1981 period. Overall agreement was obtained between the simulations and the DE-2 data for thermospheric wind structure at high latitudes, and for the combined thermal and compositional structure in both hemispheres. Computer-generated line drawings of the variations in thermospheric structure are given, as well as a series of color graphic illustrations of the DE-2 data.
    Keywords: GEOPHYSICS
    Type: Planetary and Space Science (ISSN 0032-0633); 33; 617-666
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  • 10
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    Observations of barium ion jets in the magnetosphere using Doppler imaging systems and very sensitive imaging systems using imaging photon detectors (1985)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Observations of four shaped charge releases from rockets launched from Alaska are described. Results demonstrate that imaging and Doppler imaging instruments, based on exploiting the imaging photon detector, provide additional insight into the motion and development of low intensity targets such as the fast ion jets produced by shaped charge releases. It is possible to trace the motion of fast ion jets to very great distances, of the order of 50,000 km, outward along the Earth's magnetic field, when the conditions are suitable for the outward (upward) motion and/or acceleration of such ion jets. It is shown that ion jets, which fade below the lower sensitivity threshold of previous instruments, do not always disappear. There is no evidence of an abrupt field-aligned shear-type acceleration.
    Keywords: GEOPHYSICS
    Type: Stockholm Univ. Proceedings of 12th Annual Meeting on Atmospheric Studies by Optical Methods; p 15-38
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