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  • 1
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    Lower thermospheric density fluctuations during the time period of Typhoon Dinah (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: 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.
    Keywords: GEOPHYSICS
    Type: AIAA PAPER 89-0854
    Format: text
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  • 2
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    Ionospheric remote sensing of medium-scale gravity waves and tornadic storms (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Gravity waves associated with severe storms are investigated on the basis of ionospheric sounding using a ground-based Doppler system. Reverse-group ray tracing computations are used to determine the origin of over 20 gravity waves detected within 800 km of Huntsville, Alabama in association with a group of tornadoes, isolated tornadoes in the presence of a squall line, and isolated tornadoes in the absence of a squall line. Gravity waves associated with tornadoes are found either to be generated by thunderstorms with enhanced convection embedded in a squall line, or in an isolated cloud with enhanced convection. The computed wave sources are observed in all cases to be located near the points where the tornadoes touched down more than an hour after wave excitation. Results show that gravity waves play an important role in troposphere-ionosphere coupling during times of intense convection associated with tornadic storm activity.
    Keywords: GEOPHYSICS
    Type: Nuovo Cimento C; vol. 4C
    Format: text
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  • 3
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    Combustion-related pollutants of polydisperse single-composition aerosols and advection fog formation (1982)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The most noticeable effect of air pollution on the properties of the atmosphere is the reduction in visibility, with and without the occurrence of condensation, which frequently accompanies polluted air. The present study concerns the formation of advection fog associated with aerosols, due to combustion-related pollutants, with a polydisperse population distribution and a single composition model. The results show that an aerosol population with high particle concentration-shifted distribution provides a more favorable condition for the formation of dense fog than an aerosol population with a low particle concentration-shifted distribution if the value of the mass concentration of the aerosols is kept constant.
    Keywords: GEOPHYSICS
    Format: text
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  • 4
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    Propagation of acoustic modes in the transitional ionosphere (1975)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Continuum theory is unsatisfactory for describing wave propagation in the transitional ionosphere, since the mean free path is of the same order as the characteristic length (i.e., Knudsen number in this region is of the order of unity). Therefore a transition model in which isotropic electrons behave as a fluid while the ions are governed by the kinetic equation modified by ion-electron collision effects is proposed to study acoustic wave propagation in the upper atmosphere in the altitude region from 500 to 2000 km. The results show that the dissipation of acoustic waves by electrons is through the viscous and thermal conduction effects, and the dissipation of acoustic waves by ions is through Landau damping. Comparisons of the characteristics of acoustic mode propagation and wave dissipation mechanisms in the collision-dominated, transitional from collisional to collisionless, and collisionless media are also discussed.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research; 80; Nov. 1
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  • 5
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    Observation of acoustic-gravity waves in the upper atmosphere during severe storm activity (1975)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A nine-element continuum wave spectrum, high-frequency, Doppler sounder array has been used to detect upper atmospheric wave-like disturbances during periods with severe weather activity, particularly severe thunderstorms and tornadoes. Five events of severe weather activity, including extreme tornado outbreak of April 3, 1974, were chosen for the present study. The analysis of Doppler records shows that both infrasonic waves and gravity waves were excited when severe storms appeared in the north Alabama area. Primarily, in the case of tornado activity, S-shaped Doppler fluctuations or Doppler fold-backs are observed, while quasi-sinusoidal fluctuations are more common in the case of thunderstorm activity. A criterion for the production of Doppler fold-backs is derived and compared with possible tornado conditions.
    Keywords: GEOPHYSICS
    Type: NASA-CR-144293
    Format: application/pdf
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  • 6
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    Gravity wave initiated convection (1990)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The vertical velocity of convection initiated by gravity waves was investigated. In one particular case, the convective motion-initiated and supported by the gravity wave-induced activity (excluding contributions made by other mechanisms) reached its maximum value about one hour before the production of the funnel clouds. In another case, both rawinsonde and geosynchronous satellite imagery were used to study the life cycles of severe convective storms. Cloud modelling with input sounding data and rapid-scan imagery from GOES were used to investigate storm cloud formation, development and dissipation in terms of growth and collapse of cloud tops, as well as, the life cycles of the penetration of overshooting turrets above the tropopause. The results based on these two approaches are presented and discussed.
    Keywords: GEOPHYSICS
    Type: NASA-CR-186868 , NAS 1.26:186868
    Format: application/pdf
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  • 7
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    Multifluids description of dynamics of upper atmosphere (1975)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A multifluids model to investigate ionospheric dynamics was established on kinetic theory. Its resultant equations are used to examine the following dynamic problems in the gamma region of 80-2000 Km of the ionosphere: (1) propagation of acoustic modes in the 500-2,000 Km of the ionosphere (two fluid model); (2) the relation between the cross field plasma drift instabilities and type I and type II ionospheric irregularities; and (3) time dependent neutral wind structure and horizontal pressure gradient.
    Keywords: GEOPHYSICS
    Type: NASA-CR-143930 , UAH-RR-175
    Format: application/pdf
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  • 8
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    Propagation of hydromagnetic waves in the upper F2-region (1973)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: The theory of hydromagnetic-wave in the upper F2-region, in which electrons are in a transitional regime from collisional to collisionless conditions and ions are in a collisionless state, is examined. Derivation of the governing equations is based on the fact that the isotropic electrons are fluid-like, and the anisotropic ions follow kinetic equations modified by ion-electron collisions. Magneto-acoustic waves of a period of from about 0.2 to 10 sec are dissipated by ion Landau damping and electron thermal conduction and viscosity. Numerical solutions under ionospheric conditions show that the dissipation of hydromagnetic waves is insufficient to modify the large scale heating of the ionosphere.
    Keywords: GEOPHYSICS
    Type: Planetary and Space Science; 21; Dec. 197
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  • 9
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    Double scattering of the plasma streams in a bithermal ionosphere. (1968)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Double scattering of plasma streams by interactions with large moving bodies in bithermal ionosphere with and without magnetic field
    Keywords: GEOPHYSICS
    Type: ; ADEMIE DES SCIENCES
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  • 10
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    Infrasonic waves in the ionosphere during severe thunderstorms (1974)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The coupling between the lower and upper atmosphere during severe weather and thunderstorms is investigated from the ionospheric Doppler frequency fluctuations recorded using a three dimensional CW Doppler sounder array. Two events typical of the severe thunderstorms that occurred on May 26, 1973 and March 20, 1974, are chosen for our investigation. The CW Doppler records show a wave-like disturbance with a periodicity of 3 to 5 minutes that persisted for 3 to 4 hours. A possible explanation, based on a theoretical model is presented. There is good agreement between the experimental observations and the model.
    Keywords: GEOPHYSICS
    Type: International Symposium on Solar-Terrestrial Physics; Jun 17, 1974 - Jun 22, 1974; Sao Paulo; Brazil
    Format: text
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