Search NASA⌕ Search

Engineering topics

Kokubun, S.

Publications and source records attributed to Kokubun, S..

43 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Field-aligned current signatures in the near-tail region. I - ISEE observations in the plasma sheet boundary layer

Field-aligned currents in the near-tail region are examined using ISEE magnetometer data. Two substorms (the 1054 UT and the 1436 UT substorms on March 22, 1979) were examined, demonstrating the consistency of the current polarity and intensity with observations at lower altitudes, which suggests that field-aligned currents in the plasma sheet boundary layer are parts of the large-scale current system, the region-1 system. An examination of the steplike changes of the magnetic field direction, which correspond to the spacecraft crossing of a net field-aligned current, showed that the field-aligned currents in the plasma sheet boundary layer have the same polarity as the region-1 system.

Ohtani, S.↗
NASA NTRS1981

Substorm signatures at synchronous altitude

The signatures of magnetospheric substorms near 6.6 earth radii are statistically examined using data obtained on board ATS 6 by magnetic field and energetic particle measurements. It is confirmed that the configuration change toward a tail-like field in the dusk-to-midnight sector typically begins about one hour before the onset of the expansion phase of a substorm. Configuration changes before the onsets of moderate substorms are characterized by a directional change of magnetic field at magnetic latitude of approximately 10 deg, rather than by a change in the field magnitude. It is found during storm periods that the magnetic field orientation occasionally becomes almost parallel to the magnetic equator before expansion phase onsets. Here, the field magnitude usually increases above background levels. These facts are seen as strongly suggesting that a tail-like configuration is caused by an intensification and earthward motion of the cross-tail current system, often close to 6.6 earth radii, rather than by development of diamagnetic ring current.

Kokubun, S.↗
NASA NTRS1979

Harmonics of 60 Hz in power systems caused by geomagnetic disturbances

Simultaneous VLF/ULF observations carried out near Winnipeg, Manitoba show that geomagnetic disturbances control the behavior of harmonics of 60 Hz man-made electric power. The harmonics of 60 Hz detected by the VLF receiver are at multiples of 180 Hz, indicating that they originated from a 3 phase ac power system. Under geomagnetically quiet conditions, only odd harmonics of 70 Hz were detected. In disturbed conditions, both odd and even harmonics were excited. The strength of each harmonic changed concurrently with geomagnetic pulsation (ULF) activity. These findings seem to indicate that a portion of telluric currents shunted into the power line system through the neutrals of the Y-connected transformers give rise to a dc bias to the transformer core materials and that it distorts their hysteresis loops, activating harmonics of 60 Hz power. A mathematical proof is given that a hysteresis loop having a point of symmetry generates odd harmonics only, whereas loops lacking in point-symmetry generally give rise to both odd and even harmonics. A general formula was obtained to calculate the strength of each harmonic based on the shape of the hysteresis loop.

Hayashi, K.↗
NASA NTRS1977

OGO 5 observations of Pc 5 waves - Particle flux modulations

An investigation is conducted concerning the modulations of particle fluxes associated with Pc 5 waves in the region beyond the plasmapause. A study of thermal flux modulations indicates that some of the density enhancements observed are not spatial structures but are spurious features caused by temporal flux variations associated with hydromagnetic waves. A resonance model of the energetic particle flux modulations is discussed. Energetic particle modulations are also considered. The reported observations reveal that modulations are dominant at energies of about 100 keV for electrons and at 100 keV to 1 MeV for protons. This may indicate that the bounce resonance interaction is not important for Pc 5 waves.

Kokubun, S.↗
NASA NTRS1977

Triggering of substorms by solar wind discontinuities

The probability of triggering of polar substorms by a large-scale magnetospheric compression associated with a discontinuity in the solar wind has been examined statistically using ground magnetogram data, AE index data and satellite geomagnetic data on 125 sudden storm commencements observed during 1967-1970. The triggering probability was found to depend on the amplitude of the sudden storm commencement and on the degree of preceding AE activity. In almost all cases the triggering occurred when the B-Z component of the interplanetary magnetic field was negative or decreasing during the 30 min before the passage of the discontinuity. Transient geomagnetic responses with a time scale of Alfven wave propagation in the polar cap also depend on interplanetary magnetic field conditions.

Kokubun, S.↗
NASA NTRS1976

The ground signatures of the expansion phase during multiple onset substorms

The paper examines the signatures of multiple-expansion-phase substorm onsets in night-time magnetograms as well as in recordings of auroral activity and energetic electron precipitation. Individual onsets of Pi2 magnetic pulsations observed at three widely spaced stations are used to define and time each onset accurately in order to distinguish between local variations in bay activity and fully developed substorm onsets; this method is equivalent to defining each new onset in terms of the brightening of an auroral arc and the formation of a westward-travelling surge. It is found that the formation of multiple auroral surges appears to be a fundamental feature of multiple-onset substorms, that each surge seems to be associated with a localized field-aligned current system which moves westward with the surge and perturbs the preexisting current wedge, and that this gives rise to the multiple-onset signatures observed on subauroral and low-latitude magnetograms. Since certain findings contradict existing models of multiple-onset events, an alternative model is proposed which is based on the fundamental role of surge activity and localized current wedges.

Pytte, T.↗