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Volume 32 (1980)
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Volume 31, Issue 6
Displaying 1-4 of 4 articles from this issue
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L. THOMAS1979 Volume 31 Issue 6 Pages 567-583
Published: 1979
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSA positive-ion model of the D region is used to examine the causes of enhanced electron concentrations measured with rocket-borne experiments at S. Uist during conditions of anomalous radio-wave absorption in winter. A coordinated measurement of ion composition has indicated that the photoionization of nitric oxide by solar Lyman-α radiation represents the main source of ionization, and the model is concerned with the formation of water cluster ions in this situation. Particular attention is paid to the influence of changes in concentrations of mesospheric nitric oxide and water vapour, and to the role of temperature variations, in attempts to reproduce the changes observed in the electron density distributions and ion composition. It is found that the major effects arise from enhancements in nitric oxide concentrations but increases in temperature can also play a significant role; by comparison the effects of variations in water vapour concentrations are small.View full abstractDownload PDF (1578K) -
T. J. ROSENBERG, L. J. LANZEROTTI, C. G. MACLENNAN, C. EVANS1979 Volume 31 Issue 6 Pages 585-597
Published: 1979
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSCosmic radio noise data, acquired with a fast-response 30MHZ riometer at Siple Station, Antarctica (L≈4), show evidence of weak impulsive quasiperiodic variations in ionospheric absorption. Significant amplitude variations approaching 0.02dB, approximately the statistical noise limit of the measurement, have been measured. An event typically will consist of 3 to 5 cycles of oscillation (-60 to 90sec period) and can occur during locally disturbed or quiet geomagnetic conditions. Usually the oscillations are not related closely to magnetic field fluctuations as measured on the ground at Siple or in the conjugate area. Conjugate bremsstrahlung X-ray data, available for one event, suggest that these absorption variations are caused by the impact on the ionosphere of a modulated flux of energetic electrons from the magnetosphere. Limited statistics on the location of the plasmapause suggest that these events occur close to, but on either side of, the boundary of the plasmasphere. These absorption oscillations may be another manifestation of the process that produces short-term intensity and phase variations in fixedfrequency sub-ionospheric LF and VLF wave propagation. Further studies of this unique modulated precipitation/absorption phenomenon and its relationship to hydromagnetic wave disturbances in the magnetosphere will be conducted with a set of riometer and magnetometer stations appropriately sited in a latitude array.View full abstractDownload PDF (1227K) -
W. NIENABER, H. W. DOSSO, L. K. LAW, F. W. JONES, V. RAMASWAMY1979 Volume 31 Issue 6 Pages 599-613
Published: 1979
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSThe results of geomagnetic measurements at field stations on Vancouver Island, British Columbia, and the nearby mainland are found to be in close agreement with measurements for a laboratory analogue model which employs a horizontal inducing field over a simple model including only the conducting ocean and a uniform earth. A transfer function and hypothetical event analysis of the field station measurements is used to compare field station and an alogue model vertical magnetic fields. The field station results show that for frequencies greater than -0.0006Hz (30min period) the fields are strongly affected by channelling of telluric current in the seawater channel between the island and the continent. As well, this study demonstrates that, for a coastal region, model studies can aid in selecting magnetotelluric stations minimally affected by the coast, and thus optimum for studying the tectonics of the region.View full abstractDownload PDF (1504K) -
Edward R. BENTON, Lorant A. MUTH, Michael STIX1979 Volume 31 Issue 6 Pages 615-626
Published: 1979
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSContour maps of the northward, eastward, and downward components of the main geomagnetic field and of the field intensity at the surface of earth's liquid core are presented and compared with similar maps at earth's surface. The mantle is assumed to be an insulator for purposes of the extrapolation. Maximum values of the individual field components are found to be amplified by factors of order 10-20 and the maximum field intensity by 12 over the value at earth's surface and the increase in small scale structure is evident. By comparing maps of places where Br=0 at different truncation levels, we find that even for a recent magnetic model which best fits the data quite well, contours of the field extrapolated to the core are quite sensitive to truncation level. This suggests a need to develop nonlinear data-fitting procedures if one's interest is in precise location of field contours rather than in estimating field values.View full abstractDownload PDF (1376K)
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