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Volume 47, Issue 12
Displaying 1-7 of 7 articles from this issue
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IAGA Division V, Working Group 81995 Volume 47 Issue 12 Pages 1257-1261
Published: December 20, 1995
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESSDownload PDF (885K) -
A. W. P. Thomson1995 Volume 47 Issue 12 Pages 1263-1275
Published: December 20, 1995
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESSSolar coronal holes are magnetically open and may give rise to an enhanced solar wind velocity with significance for geomagnetic activity. From a database of coronal hole observations covering 1970-1991 we have obtained a probabilistic relationship between hole central meridian passage (CMP) and subsequent geomagnetic activity. The mean lag between CMP of both equatorial holes and equatorward extensions of polar holes and the onset of geomagnetic activity, measured by the Ap index, is 3-4 days, depending slightly on cycle phase. The peak Ap at this lag and the number of geomagnetically “active” days, post-CMP, similarly follow the solar cycle. Weak relationships are noted between individual hole parameters, for example, latitude and area and Ap. However this is put into context in a correlation study, over 1982-1986, of hole CMP, interplanetary field and plasma data, and Ap. Relatively high cross-correlations (maximum ≤ 0.5) are found between daily-averaged, near-earth, solar wind velocity and Ap. Only weak cross-correlations (≤0.15) are obtained between hole CMP and Ap and this emphasises the significance of the interplanetary environment in modulating the energy transfer.View full abstractDownload PDF (2537K) -
Shigeru Fujita, Karl-Heinz Glassmeier1995 Volume 47 Issue 12 Pages 1277-1292
Published: December 20, 1995
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESSWe discuss the condition for the presence of a magnetospheric global oscillation having the properties of a cavity resonance oscillation by using a numerical method and assuming that the magnetopause is not a perfect reflector. The cavity resonance oscillation occurs when there is a plasmaspheric trough of the Alfvén speed. The plasmaspheric cavity resonance oscillation is evanescent in the outer magnetosphere, where the Alfvén speed is larger than in the plasmasphere. The plasmaspheric mode is not completely confined within the plasmasphere, but can tunnel into the outer magnetosphere and have finite amplitude at the magnetopause. The nonzero electromagnetic field perturbation at the magnetopause leads to leakage of the Poynting flux across the magnetopause, and the plasmaspheric cavity resonance oscillation is damped by the escaping flux. The perturbations of the damped cavity resonance oscillation exhibit phase shift toward the magnetopause, which does not imply propagation of the wave.View full abstractDownload PDF (3140K) -
L. N. Baransky, A. W. Green, E. N. Fedorov, N. A. Kurneva, V. A. Pilip ...1995 Volume 47 Issue 12 Pages 1293-1309
Published: December 20, 1995
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESSThe methods of an unambiguous determination of the parameters of the magnetospheric resonator (resonance frequency, its meridional gradient, and width of the resonance) by studying the spatial structure of ULF waves, in the Pc3-4 frequency range, are summarized and reviewed. The methods considered are the gradient technique (synchronous measurements of ULF field at two nearby stations) and the polarization method (multicomponent observations atone station). Both methods are experimentally tested using the data from an experiment at low latitude (L ≅ 1.5). Taking into account modifications of the structure of the ULF magnetic field due to geoelectric inhomogeneities, both methods demonstrate consistent results and are in a qualitative agreement with theoretical predictions. These methods should provide a useful tool for monitoring resonant frequencies and the distribution of plasma in the magnetosphere.View full abstractDownload PDF (3193K) -
Antonio L. Padilha1995 Volume 47 Issue 12 Pages 1311-1323
Published: December 20, 1995
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESSSeveral MT soundings carried out in different sites at the South Atlantic Magnetic Anomaly region in Brazil are distorted by severe incoherent noise. Apparent resistivity curves are displaced downwards showing local minima in frequencies around 0.1 Hz. On the other hand, power spectra analyses of pulsations in the Pc1-2 range observed at a ground station in the same region indicate the presence of linearly polarized Pi-bursts. These events may be related to the intensification of particle precipitation at localized low L values of the anomaly during magnetic disturbed periods with the characteristic polarization being probably associated with a local ionospheric current system driven by middle atmospheric ionization enhancement. It is speculated here that the mechanisms responsible for the Pi-bursts generation can introduce local spatial inhomogeneities in the external inducing field in the anomaly area generating the observed distortions in MT curves.View full abstractDownload PDF (2674K) -
Hugo Gabriel Nami1995 Volume 47 Issue 12 Pages 1325-1332
Published: December 20, 1995
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESSPaleomagnetic data from a section of a sedimentary sequence at Mylodon Cave (Seno de Ultima Esperanza, Chile) are reported. According to previous 14C data, the sediments have dates between 13, 500 and 5, 360 y.b.p. The section that is analyzed here is younger than 12, 000 y.b.p. Natural Remanent Magnetization (NRM) was measured from 39 successive cores, and stability of the NRM was analyzed by thermal demagnetization. Only five samples were rejected because they did not carry a characteristic remanent magnetization. Analysis of the rest of samples shows that the upper part of the section (younger than 10, 000 y.b.p.) recorded directions far removed from the present magnetic field, probably corresponding to a field excursion. Two areas where transitional VGP are concentrated were noticed: one in Africa and the other near Australia.View full abstractDownload PDF (1335K) -
N. Hasebe, K. Kondoh, M. Kobayashi, Y. Mishima, T. Doke, J. Kikuchi, T ...1995 Volume 47 Issue 12 Pages 1333-1338
Published: December 20, 1995
Released on J-STAGE: April 03, 2007
JOURNAL FREE ACCESSInterplanetary ions in a few MeV/n energies were observed by the GEOTAIL spacecraft at 1 AU during the period from December 1993 to April 1994. The measurements were performed with the HEP-particle telescopes onboard the GEOTAIL. We have examinedthe correlation between the interplanetary ion events and cosmic ray modulation. It is found that the variation of counting rates of neutron monitor is well correlated with the flux variation of low energy ions. The corotating interaction regions formed in the interplanetary space significantly affect the intensities not only of low energy galactic cosmic rays (GCRs) but also of high energy GCRs. It implies that corotating streams cause the decrease of GCR flux because they act as barriers that impede the flows of GCRs toward the Sun.View full abstractDownload PDF (1349K)
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