131 research outputs found
Studying internal and external magnetic fields in Japan using MAGSAT data
Examination of the total intensity data of CHRONIT on a few paths over Japan and its neighboring sea shows MAGSAT is extremely useful for studying the local magnetic anomaly. In high latitudes, the signatures of field aligned currents are clearly recognized. These include (1) the persistent basic pattern of current flow; (2) the more intense currents in the summer hemisphere than in the winter hemisphere; (3) more fluctuations in current intensities in summer dawn hours; and (4) apparent dawn-dusk asymmetry in the field-aligned current intensity between the north and south polar regions
Japanese Magsat Team. A: Crustal structure near Japan and its Antarctic Station. B: Electric currents and hydromagnetic waves in the ionosphere and the magnetosphere
Efforts continue in compiling tapes which contain vector and scalar data decimated at an interval of 0.5 sec, together with time and position data. A map of the total force field anomaly around Japan was developed which shows a negative magnetic anomaly in the Okhotsk Sea. Examination of vector residuals from the MGST model shows that the total force perturbation is almost ascribable to the perturbation parallel to the main geomagnetic field and that the contribution from the perturbation transverse to the main field to the total force perturbation is negligibly small. The influences of ionospheric current with equatorial electroject and of the magnetospheric field aligned current on the dawn-dusk asymmetry of daily geomagnetic variations are being considered. The total amount of electric current flowing through the plane of the Magsat orbit loop was calculated by direct application of Maxwell's equation. Results show that the total electric current is 1 to 5 ampheres, and the current direction is either sunward or antisunward
Report of investigation from Japanese MAGSAT Team
Progress in the data processing and data acquisition of computer compatible MAGSAT tapes is reported. Investigations focused on the crustal structure near Japan and its Antarctic station, and electric currents and hydrodynamic waves in the ionosphere and the magnetosphere. The magnetization of the crust in the northwestern Pacific region is discussed
Japanese MAGSAT team
Construction of a model of the regional magnetic field and investigation of the local magnetic anomalies and their origin were approaches used in attempts to study the crustal structure near Japan and its Antarctic bases. Spatial properties of the regional magnetic field and comparison of the regional model with that derived from MAGSAT data are discussed. Possible causes of the magnetic anomalies, and results of aeromagnetic surveys incorporating gravity and seismic data are explored. Ionospheric and magnetospheric contributions to geomagnetic variations, field-aligned currents, magnetic geomagnetic pulsations, and hydromagnetic waves by analysis of MAGSAT data are also examined
Slow magnetic Rossby waves in the Earth's core
The westward drift component of the secular variation is likely to be a signal of waves riding on a background mean flow. By separating the wave and mean flow contributions, we can infer the strength of the “hidden” azimuthal part of the magnetic field within the core. We explore the origin of the westward drift commonly seen in dynamo simulations and show that it propagates at the speed of the slow magnetic Rossby waves with respect to a mean zonal flow. Our results indicate that such waves could be excited in the Earth's core and that wave propagation may indeed play some role in the longitudinal drift, particularly at higher latitudes where the wave component is relatively strong, the equatorial westward drift being dominated by the mean flow. We discuss a potential inference of the RMS toroidal field strength within the Earth's core from the observed drift rate
On the existence and structure of a mush at the inner core boundary of the Earth
It has been suggested about 20 years ago that the liquid close to the inner
core boundary (ICB) is supercooled and that a sizable mushy layer has developed
during the growth of the inner core. The morphological instability of the
liquid-solid interface which usually results in the formation of a mushy zone
has been intensively studied in metallurgy, but the freezing of the inner core
occurs in very unusual conditions: the growth rate is very small, and the
pressure gradient has a key role, the newly formed solid being hotter than the
adjacent liquid. We investigate the linear stability of a solidification front
under such conditions, pointing out the destabilizing role of the thermal and
solutal fields, and the stabilizing role of the pressure gradient. The main
consequence of the very small solidification rate is the importance of
advective transport of solute in liquid, which tends to remove light solute
from the vicinity of the ICB and to suppress supercooling, thus acting against
the destabilization of the solidification front. For plausible phase diagrams
of the core mixture, we nevertheless found that the ICB is likely to be
morphologically unstable, and that a mushy zone might have developed at the
ICB. The thermodynamic thickness of the resulting mushy zone can be
significant, from km to the entire inner core radius, depending on
the phase diagram of the core mixture. However, such a thick mushy zone is
predicted to collapse under its own weight, on a much smaller length scale
( km). We estimate that the interdendritic spacing is probably
smaller than a few tens of meter, and possibly only a few meters
An investigation into the remote triggering of the Oita earthquake by the 2016 Mw 7.0 Kumamoto earthquake using full wavefield simulation
Introduction to the special section on the 2007 Chuetsu-Oki, Niigata, Japan, Earthquake
Highly efficient and broadband Si homojunction structured near-infrared light emitting diodes based on the phonon-assisted optical near-field process
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