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  • 1
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    High resolution gravity models combining terrestrial and satellite data (1992)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: Spherical harmonic expansions to degree 360 have been developed that combine satellite potential coefficient information, terrestrial gravity data, satellite altimeter information as a direct tracking data type and topographic information. These models define improved representations of the Earth's gravitational potential beyond that available from just satellite or terrestrial data. The development of the degree 360 models, however, does not imply a uniform accuracy in the determination of the gravity field as numerous geographic areas are devoid of terrestrial data or the resolution of such data is limited to, for example, 100 km. This paper will consider theoretical and numerical questions related to the combination of the various data types. Various models of the combination process are discussed with a discussion of various correction terms for the different models. Various sources of gravity data will be described. The new OSU91 360 model will be discussed with comparisons made to previous 360 models and to other potential coefficient models that are complete to degree 50. Future directions in high degree potential coefficient models will be discussed.
    Keywords: GEOPHYSICS
    Type: In: From Mars to Greenland: Charting gravity with space and airborne instruments - Fields, tides, methods, results (A93-55951 24-46); p. 93-106.
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  • 2
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    Dynamics Explorer measurements of particles, fields, and plasma drifts over a horse-collar auroral pattern (1992)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: As shown from ground-based measurements and satellite-borne imagers, one type of global auroral pattern characteristic of quiet (usually northward IMF) intervals is that of a contracted but thickened emission region of a pattern referred to as 'horse-collar' aurora (Hones et al., 1989). In this report we use the Dynamics Explorer data set to examine a case in which this horse-collar pattern was observed by the DE-1 auroral imager, while at the same time DE-2, at lower altitude, measured precipitating particles, electric and magnetic fields, and plasma drifts. Our analysis shows that, in general, there is close agreement between the optical signatures and the particle precipitation patterns. In many instances, over scales ranging from tens to a few hundred kilometers, electron precipitation features and upward field-aligned currents are observed at locations where the plasma flow gradients indicate negative V-average x E. The particle, plasma, and field measurements made along the satellite track and the 2D perspective of the imager provide a means of determining the configuration of convective flows in the high-latitude ionosphere during this interval of northward IMF. Recent mapping studies are used to relate the low-altitude observations to possible magnetospheric source regions.
    Keywords: GEOPHYSICS
    Type: Journal of Geomagnetism and Geoelectricity (ISSN 0022-1392); p. 1225-1237.
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  • 3
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    Ozone and temperature trends in the lower stratosphere (1992)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: It is shown that the pattern of temperature trend with height in the upper troposphere and lower stratosphere is consistent with that calculated from a model incorporating the observed ozone changes. The magnitude of the observed temperature decrease is less than that determined from the numerical model. It is found that the obverse ozone-temperature relationship does not hold. If the temperature at 20 km decreases, this by itself would result in an increase in the ozone values through the inverse temperature sensitivity of the chemical reactions. In the lower stratosphere a positive correlation between ozone and temperature tends to exist through the dynamics. Ozone-rich air moving downward undergoes an increase in temperature through adiabatic compression and vice-versa. That the temperature trends indicate no apparent variation with latitude suggests a nondynamic cause.
    Keywords: GEOPHYSICS
    Type: In: Conference on the Middle Atmosphere, 8th, Atlanta, GA, Jan. 5-10, 1992, Preprints (A93-49361 21-47); p. 70-73.
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  • 4
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    Lateral variations in lower mantle seismic velocity (1992)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: To obtain a theoretical model which provides a rationale for the observed high values of velocity variations, the effect of a 0.1 to 0.2 percent partially molten volatile-rich material in various geometries which are heterogeneously dispersed in the lower mantle is examined. Data obtained indicate that, depending on aspect ratio and geometry, 0.1-0.2 percent partial melting in conjunction with about 100 K thermal anomalies can explain the seismic variations provided the compressibility of the melt differs by less than about 20 percent from the surrounding solid.
    Keywords: GEOPHYSICS
    Type: ; : Analysis of optica
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  • 5
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    Anomalous plasma diffusion and the magnetopause boundary layer (1992)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: An overview of the current state of anomalous diffusion research at the magnetopause and its role in the formation of the magnetopause boundary layer is presented. Plasma wave measurements in the boundary layer indicate that most of the relevant unstable wave modes contribute negligibly to the diffusion process at the magnetopause under magnetically undisturbed northward IMF conditions. The most promising instability is the lower hybrid drift instability, which may yield diffusion coefficients of the right order if the highest measured wave intensities are assumed. It is concluded that global stationary diffusion due to wave-particle interactions does not take place at the magnetopause. Microscopic wave-particle interaction and anomalous diffusion may contribute to locally break the MD frozen-in conditions and help in transporting large amounts of magnetosheath plasma across the magnetospheric boundary.
    Keywords: GEOPHYSICS
    Type: IEEE Transactions on Plasma Science (ISSN 0093-3813); 20; 6; p. 833-842.
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  • 6
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    Acoustic double layers in multispecies plasma (1992)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: The formation of acoustic double layers in the presence of two ion species is examined via a particle simulation in a 1D bounded system. The effect of having two ion components, an H(+) and an O(+) beam, on double-layer evolution from ion acoustic turbulence driven by an electron drift relative to the H(+) beam of about 0.5 u sub e, where u sub e is the electron thermal speed, is examined. It is found that acoustic double layers form in either ion species on a time scale of about 100 omega sub ps exp -1, where omega sub ps is the ion plasma frequency for species 's' and s = H or O, and for drifts relative to the electrons lower than that required for double layer formation in simulations of single ion component plasma.
    Keywords: GEOPHYSICS
    Type: IEEE Transactions on Plasma Science (ISSN 0093-3813); 20; 6; p. 745-755.
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  • 7
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    An analysis of differential impact melt-crater scaling and implications for the terrestrial impact record (1992)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: The volume of impact melt relative to that of the transient cavity is known to increase with the magnitude of the impact event. This paper investigates the influence of that phenomenon on the nature of terrestrial impact craters. A model of impact melting was used to estimate the volume of melt produced during the impact of chondritic projectiles into granite targets at velocities of 15, 25, and 50 km per sec. The results were compared with observed melt volumes at terrestrial craters, which were collated from the literature and paired with the transient-cavity diameters of their respective craters. Results show that the record on terrestrial craters is not inconsistent with the predictions of the model.
    Keywords: GEOPHYSICS
    Type: Meteoritics (ISSN 0026-1114); 27; 5; p. 526-538.
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  • 8
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    Evidence from coupled (Sm-147)-(Nd-143) and (Sm-146)-(Nd-142) systematics for very early (4.5-Gyr) differentiation of the earth's mantle (1992)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: Evidence for early differentiation of the earth's mantle is presented based on measurements of Nd-143/Nd-144 and Nd-142/Nd-144 ratios in an approximately 3.8 Gyr-old supracrustal rock from Isua, West Greenland. Coupled (Sm-146,147)-(Nd-142,143) systematics suggest that the fractionation of Sm/Nd took place 4.44-4.54 Gyr ago, due to extraction of a light rare earth element-enriched primordial crust.
    Keywords: GEOPHYSICS
    Type: Nature (ISSN 0028-0836); 360; 6406; p. 728-732.
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  • 9
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    Mirror and ion cyclotron anisotropy instabilities in the magnetosheath (1992)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: The kinetic properties of the ion cyclotron anisotropy and the mirror instabilities are investigated using one-dimensional hybrid simulations. It is found that, for moderate values of the ion beta and the proton temperature anisotropy, the two instabilities produce similar levels of turbulence. For high values of beta or temperature anisotropy, the ion cyclotron instability produces higher fluctuation levels of turbulence than does the mirror instability.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 97; A12; p. 19,421-19,432.
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  • 10
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    On the formation and evolution of plasmoids - A survey of ISEE 3 Geotail data (1992)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: The magnetic and plasma properties of plasmoids, their evolution with distance downtail, and the effect of the direction of the IMF on the plasmoid magnetic configuration were investigated by examining the ISEE 3 magnetometer and electron plasma measurements of the 1983 ISEE 3 Geotail Mission. Both data sets were systematically examined for the presence of bipolar magnetic signatures that occur while ISEE 3 was in the plasma sheet. Results revealed 366 events consistent with this signature while ISEE was in the plasma sheet. It was found that plasmoids are characterized by high-speed plasma flow and that many of them have a well-defined magnetic core field characterized by a field strength maximum at the center of the pass through the structure. Once completely formed, plasmoids are relatively stable. It was found that the size, velocity, magnetic core strength, and Bz field amplitude of plasmoids do not depend on the distance downtail beyond -100 R(E).
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 97; A12; p. 19,259-19,282.
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