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  • GEOPHYSICS  (6)
  • 2005-2009
  • 1985-1989  (2)
  • 1980-1984  (4)
  • 1960-1964
  • 1950-1954
  • 1
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    Simultaneous VHF and UHF radar observation of the mesosphere at Arecibo during a solar flare: A check on the gradient-mixing hypothesis (1986)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The results of a two wavelength (VHF and UHF) mesosphere experiment performed at the Arecibo Observatory on January 5, 1981 are discussed. The 46.8-MHz VHF radar (3.21 m Bragg scale) was operated to provide spectral measurements of signals scattered from refractivity fluctuations due to turbulence. Other physical parameters such as radial velocities, scattered signal power, and Doppler spread due to turbulence can be derived from signal spectra. The 430-MHz UHF radar (0.36 m Bragg scale) was used for D-region electron-density measurements using the incoherent scatter technique with a comparable height resolution. The radars were pointed symmetrically about the vertical with a beam spacing of 5.5 degree in the meridional plane. Occurrence of a type 4 solar flare during the experiment produced enhanced D-region electron-density gradients. This was a unique circumstance that provided the possibility of testing the basic premises of the turbulent gradient-mixing hypothesis.
    Keywords: GEOPHYSICS
    Type: International Council of Scientific Unions, Middle Atmosphere Program. Handbook for MAP, Vol. 20; 8 p
    Format: application/pdf
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  • 2
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    Usefulness of multifrequency MST radar measurements, part 2.6B (1984)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Scattering of radio waves from atmospheric refractive-index irregularities induced by turbulence was invoked almost four decades ago to explain the characteristics of signals received on VHF/UHF ionospheric and tropospheric forward-scatter links. Due to the bistatic geometry of these links a slender, horizontally extended, common volume or cell is formed in space. The principal contribution to scattering arises from refractive-index fluctuations in this volume at the Bragg wave number K approx. sub B = K approx. sub i -k approx. sub s vectors. It has been surmised that the use of more than one frequency in probing the middle-atmosphere regions should help resolve several issues pertaining to the scattering mechanism. These issues are briefly re-examined in this note. The implications of the radar equation are discussed. The problems arising due to layered structure of turbulence and the choice of frequencies most suitable for multifrequency measurements are considered.
    Keywords: GEOPHYSICS
    Type: International Council of Scientific Unions Middle Atmosphere Program: Handbook for MAP. Vol. 14; p 121-125
    Format: application/pdf
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  • 3
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    Some aspects of metallic ion chemistry and dynamics in the mesosphere and thermosphere (1987)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The relationship between the formation of sporadic layers of metallic ion and the dumping of these ions into the upper mesosphere is discussed in terms of the tidal wind, classical (i.e., windshear) and other more complex, perhaps highly nonlinear layer formation mechanisms, and a possible circulation mechanism for these ions. Optical, incoherent scatter radar, rocket, and satellite derived evidence for various layer formation mechanisms and for the metallic ion circulation system is reviewed. The results of simple one dimensional numerical model calculations of sporadic E and intermediate layer formation are presented along with suggestions for more advanced models of intense or blanketing sporadic E. The flux of metallic ions dumped by the tidal wind system into the mesosphere is estimated and compared with estimates of total particle flux of meteoric origin. Possible effects of the metallic ion flux and of meteoric dust on D region ion chemistry are discussed.
    Keywords: GEOPHYSICS
    Type: International Council of Scientific Unions, Middle Atmosphere Program. Handbook for MAP, Volume 25; p 228-254
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  • 4
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    Observations of the Ca/+/ twilight airglow from intermediate layers of ionization (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Optical and incoherent scatter radar techniques are applied to detect the presence of Ca(+) in lower thermospheric intermediate layers over Arecibo. The Arecibo 430 MHz radar is used to measure electron densities, and the altitude distribution and density of the calcium ion is inferred from the variation of twilight resonant scattering with solar depression angle. Ca(+) and electron column densities are compared, and results indicate that the composition of low-altitude intermediate layers is 2% Ca(+), which is consistent with rocket mass spectrometer measurements. Fe(+) and Mg(+) ultraviolet resonance lines are not detected from the ground due to ozone absorbing all radiation short of 3000 A, and measurements of the neutral iron resonance line at 3860 A show that an atmospheric continuum may result in overestimations of emission rates at high solar depression angles.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research; 86; Sept. 1
    Format: text
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  • 5
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    Observations of neutral iron emission in twilight spectra (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A method is presented for the analysis of twilight airglow spectra that may be contaminated by atmospheric continuum emission of unknown brightness. The necessity of correcting for this continuum emission when measuring weak airglow features in twilight is illustrated by application of the method to the neutral iron line at 3860 A.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research; 86; June 1
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  • 6
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    Incoherent Scatter Radar Studies of the Mesosphere (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: All current incoherent backscatter radars can make mesospheric or D region measurements under at least some conditions. The conditions under which measurements are possible are derived and shown for each radar. Conditions examined include overall system sensitivity, electron and ion spectral line widths and power distributions, and time/height averaging effects. The radar equations is derived and calibrations of the radar system is discussed. Total power only and combined total power and ion line spectral measurements are described in terms of ease of use, applicability to various radars, and parameters of aerodynamic interest derivable from the measurements.
    Keywords: GEOPHYSICS
    Type: International Council of Scientific Unions Middle Atmosphere Handbook, Vol. 13; p 135-154
    Format: text
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