We analyzed the A-X(0-0) band of CH, which appears in high-resolution spectra of comet Austin (1990 V), in order to understand fluorescence and collisional processes that influence the rotational structure of the A-X(00) band. Some of the weak lines of the A-X (0-0) band are clearly resolved, which have not been previously resolved with relatively low-resolution spectroscopy. We unambiguously confirmed the B-X (0-0) band lines around 3890 Å, which had been suspected previously, but it had not been clearly identified because of strong adjacent CN and C₃ bands. In order to analyze the cometary spectra we have conducted two different fluorescence calculations: a single-cycle fluorescence and fluorescent equilibrium. The fluorescent equilibrium model includes infrared and ultraviolet fluorescence processes as well as electron and neutral collisional effects, and therefore the model is a function of cometocentic distance. We found that single-cycle fluorescence models with a Boltzmann distribution in the X state fit the observed spectra better than the fluorescent equilibrium models. However, single-cycle fluorescence models with two different temperatures (130 K for F1 state and 250 K for F2 state) in the X state fit the Austin spectra significantly better than the single-cycle fluorescence model with the same temperature (150 K) for F1 and F2 states. This suggests that we are observing two different Boltzmann distributions of nascent, short-life CH radicals right after they were produced by photodissociations of parent molecules. We presented g-factors of the A-X (0-0) and B-X (0-0) bands as a function of heliocentric velocity based on single-cycle fluorescence models with a 150 K distribution in the X state. We have calculated the expected intensity of the fundamental band (v' = 1 → 0) of CH and discussed the detectability of this band near 2730 cm^-1. We also discussed possible parent molecules of CH and long lifetimes of the parent molecules, which may explain extensive emissions of CH up to 10⁵km from the nucleus despite its short lifetime.

View full abstract

Several ssc were recorded simultaneously at the low-latitude longitudinal and along the 210° magnetic meridian networks. The considered ULF wave phenomena stimulated by the ssc comprise main and preliminary impulses, Psc 3 pulsations, ssc-related Pc 3 and cavity-like oscillations. The analysis of observed ssc shows that the preliminary impulse is still not able to explain invoking by the existing theory. It is also found some problems concerning the interpretation of features of other ssc-associated wave phenomena. Further specially coordinated observations at a world-wide magnetometer network with high precision of time synchronization are required to understand these unresolved problems.

View full abstract

Unmanned magnetometer network observation was carried out near Syowa Station, Antarctica from early spring to summer seasons of 1988. The network consisted of three remote stations, H100 (80 km south of Syowa Station), Skarvsnes (50 km south-west of Syowa Station), and site F22 (20 km east of Syowa Station). From a cross-correlation analysis of Pc 5 events observed during the magnetometer operation, we found an unusual phase characteristics in vertical component of F22-Syowa pair, which can not be interpreted by a Pc 5 incidence for the ground conductivity with horizontally uniform distribution. We carried out a numerical simulation of Pc 5 incidence for the ground conductivity with a local conductivity anomaly, and based on that model calculation, we can infer a possible effect of local earth currents that may appear in the cross-correlation analysis for such a short separation.

View full abstract

During the early decades of the 19th century variations of the geomagnetic field at geomagnetic observatories were observed visually only. The most widely used method to observe changes of variometer magnets was Poggendorff's mirror-and-scale system aided with a telescope. Readings were made typically 1 ... 12 times per hour. For observations of the horizontal field, Gauss' bifilar H-variometer was in use at geomagnetic observatories. At the Helsinki observatory, founded in 1838, Gauss' bifilar instrument was continuously in operation for more than 60 years. During that time about 1, 000, 000 readings of H were accumulated. Most of the data are still unreduced and are available in original observational notebooks only. The quality of the H-data, at least in the period 1844-1848 studied here, seems to be reliable. Comparisons between Helsinki H-results and the present day Nurmijarvi observatory data, reveal similar daily variation curves at both observatories. In long-term changes, with varying number of annual sunspots, the daily range of H follows the same linear relationship as H at Nurmijarvi. We believe that the Helsinki H-data series is reliable and homogeneous and thus suitable for detailed studies of changes of the geomagnetic horizontal field component in the mid 19th century.

View full abstract

Paleomagnetic and rock magnetic investigations have been carried out for the late Carboniferous-Permian Pyeongan Supergroup, exposed in the Yeongwol area in eastern South Korea. A total of 228 independently oriented core samples was drilled from thirteen sites for the study. The mean direction after bedding correction (D/I = 202.7°/-24.6°, k = 2.4, α₉₅ = 36.9°) is more dispersed than the in-situ mean direction (D/I = 175.3°/-58.9°, k = 69.0, α₉₅ = 5.3°), indicating that the fold test is negative at 95% confidence level. In addition, the stepwise unfolding of the characteristic remanent magnetization (ChRM) reveals a maximum value of k at 0% unfolding. Furthermore, authigenic magnetite and hematite grains are identified by the electron microscope observations. These results collectively imply that the ChRM directions were acquired after tilting of the strata by a chemical remanent magnetization when the secondary authigenic magnetic minerals formed. The ChRM directions of the Supergroup, however, pass the reversal test at 95% confidence level suggesting that the remagnetization occurred during the period including both normal and reversed polarity intervals. Because the paleomagnetic pole position (39.4°E, 85.6°N. A₉₅ = 8.9°) of the Pyeongan Supergroup calculated from the mean site directions of the ChRMs is close to that of the Tertiary period of the Korean Peninsula, it is interpreted that the remagnetization in this area occurred during the Tertiary. However, it is also plausible that the study area might be rotated about 30° anticlockwise after the remagnetization at the end of the Daebo Orogeny, in the beginning of the Cretaceous period.

View full abstract

Low-temperature experiments document changes in magnetic mineralogy in Pleistocene hemipelagic sediments at ODP Holes 976D and 977A. The Verwey transition was observed only for samples below ∼1.3 mbsf, which suggests depth-limited appearance of stoichiometric magnetite in the sediment column. Primary magnetite is interpreted to be covered with a maghemite skin as a result of in situ low-temperature oxidation on the sea floor. The oxidized maghemite skin gradually dissolves with depth, and the Verwey transition is observed below ∼1.3 mbsf. This depth matches the iron redox boundary inferred on the basis of a sediment color change from tan to green.

View full abstract

The signal amplitudes in the Hx component of magnetic pulsations undergo significant enhancement at the dip equator during intervals of Equatorial Electrojet (EEJ), the enhancement attaining a peak value during prenoon hours. On the other hand, it is shown in this study, that the enhancement peak which occurs during prenoon hours on EEJ days shifts towards noon hours on major counter electrojet (CET) days. The observed shift of the peak towards noon hours is interpreted to indicate corresponding change in the diurnal variation of ionospheric conductivity during the CET days.

View full abstract