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Volume 45, Issue 10
Displaying 1-6 of 6 articles from this issue
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W. Sun, Y. Kamide, J. R. Kan, S.-I. Akasofu1993 Volume 45 Issue 10 Pages 1151-1157
Published: October 20, 1993
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESSAn improved method is developed to invert a one-dimensional east-west electrojet from the H component of the geomagnetic disturbances measured along a meridian chain of magnetometer stations. This nonlinear inversion method is based on the flexible tolerance method. The main difference between this new method and the previous methods is that the height, the width and the location of the auroral electrojet current are determined together from the data by the flexible tolerance method, rather than assumed or calculated independently as in the previous methods. It should be noted also that the method presented in this paper is fast enough to allow a real-time display of the inverted electrojet current distribution by a workstation.View full abstractDownload PDF (16436K) -
F. W. Menk, B. J. Fraser, H. J. Hansen, P. T. Newell, C.-I. Meng, R. J ...1993 Volume 45 Issue 10 Pages 1159-1173
Published: October 20, 1993
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESSGeomagnetic pulsations with frequencies in the range 0.1-2.5 Hz have been recorded with a six station Antarctic magnetometer array ranging in latitude from -62.3 to -80.6° invariant. The observed spectral characteristics were compared with the cusp and boundary layer locations for selected days in November and December, 1986, and July, 1990, in order to determine wave source regions. Specific pulsation features have been identified with different magnetospheric regions. The cusp is characterised by intense unstructured 0.15-0.45 Hz noise which diminishes rapidly away from this region. These signals are likely to result from a mixture of ion-cyclotron, Kelvin-Helmholtz and drift-wave instabilities. Narrowband unstructured Pc2 emissions typically around 0.2 Hz and short discrete Pc1 packets or bursts with frequencies below 0.4 Hz, occur in the local morning at boundary layer latitudes, accompanied by generally enhanced power levels between about 0.1 and 0.5 Hz. These emissions are probably due to ion-cyclotron waves generated near or below the He+ gyrofrequency on boundary layer field lines. Propagation of such signals into the polar cap via the ionospheric waveguide is uncommon, perhaps due to the existence of severe ionospheric irregularity features near the dayside auroral oval. Structured and quasi-structured emissions such as hydromagnetic chorus are recorded at the foot of plasmatrough field lines and are consistent with ion-cyclotron wave generation and propagation on closed field lines in the outer magnetosphere.View full abstractDownload PDF (49594K) -
V. V. Kuznetsov, V. V. Plotkin, I. I. Nesterova, N. I. Izraileva1993 Volume 45 Issue 10 Pages 1175-1179
Published: October 20, 1993
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESSIn this paper the universal diurnal variation of f0F2 is suggested to be used as the characteristic of the global ionosphere condition. The method was elaborated to obtain the universal diurnal variation of f0F2 by means of the Fourier series. This method allows us to use the small number of the observatories for the analysis. The possibility to distinguish the universal diurnal variation of f0F2 by the described method is shown as an example for December 1988 data (the period of the International Program SUNDIAL).View full abstractDownload PDF (11989K) -
Y. Iwasaka, M. Hayashi, Y. Kondo, M. Koike, S. Koga, M. Yamato, P. Aim ...1993 Volume 45 Issue 10 Pages 1181-1192
Published: October 20, 1993
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESSElectron microscopic observation of individual particles collected in the winter Arctic stratosphere (Sweden, Kiruna, January 31, 1990) with a balloon borne impactor showed that the layer of particles containing NO3- ion (possibly Type-I PSCs: nitric acid trihydrate particles) formed on the background sulfate aerosol layer. The nitrate particle layer was well corresponding to the region where atmospheric temperature was lower than the frost point of Type-I PSCs. Two different type nitrate particles were identified in the nitrate particle layer, which may be due to the difference in nucleation processes of Type-I PSCs, from the analysis of morphology of particles producing nitron nitrate crystals on the surface of nitron thin film. Type “A” nitrate particles having large disk structure in its center were frequently observed in the lower region of the nitrate particle layer, and type “B” nitrate particles were major in the upper region of the nitrate layer.View full abstractDownload PDF (46524K) -
S. Yang, J. Shaw, T. Rolph1993 Volume 45 Issue 10 Pages 1193-1207
Published: October 20, 1993
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESSArchaeointensities were determined by the Thellier method from about 60 ceramic samples from Peru, with ages ranging from 1200 B.C. to 1800 A.D. The stability of NRM was analyzed for each sample using stepwise thermal demagnetisation. Partial TRM (PTRM) checks were used to detect any chemical change due to the laboratory heating. Anisotropy of both magnetic susceptibility and TRM were measured but found to be very small. The mineral magnetic properties of the samples were investigated using several techniques, including Curie temperatures, susceptibility variations from low temperature (about -200°) to room temperature, and hysteresis measurements, and the results were used to estimate magnetic mineralogy and successfully select samples suitable for archaeointensity measurements. Finally a secular variation curve covering the past 3000 years was obtained for Peru.View full abstractDownload PDF (32745K) -
Francois H. Chamalaun, Charles E. Barton1993 Volume 45 Issue 10 Pages 1209-1212
Published: October 20, 1993
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESSA widely-spaced array of three-component recording magnetometers has been used to make a natural geomagnetic induction reconnaissance of the whole Australian continent. The coast effect is well observed, as are two major continental electrical conductivity anomalies known previously. While there may be considerable small-scale detail yet to be mapped, the gross electrical conductivity structure of the continent appears relatively simple. Taking into account the known geology, the regions of high electrical conductivity appear to be associated with the sedimentary basins that separate major continental cratonic blocks. The two previously known conductors may be electrically connected to form a major continent-wide “Australian intercratonic conductivity zone”.View full abstractDownload PDF (10644K)
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