Dynamic spectral study of Pc 3-5 magnetic pulsations observed in the north polar cusp region

Dynamic spectral characteristics of magnetic pulsations in the frequency range from Pc 3 to Pc 5 are examined on the basis of simultaneous observations at Cambridge Bay in the north polar cusp region and Fort Smith in the auroral zone. Both stations are located at almost the same longitude. In the dynamic spectra observed at both stations two predominant spectral bands are generally seen in the frequency ranges of Pc 3 (20-80mHz) and Pc 4/5 (3-10mHz). Although spectral peaks in the Pc 3 and Pc 4/5 bands are shown at almost the same frequencies for both stations, sharpness (Q value) of the peaks is very different between the stations. The spectral peaks at Fort Smith are much sharper than those at Cambridge Bay. These observed features are discussed in the light of propagation and resonance mechanism of Pc 3 and Pc 4/5 waves in the magnetosphere

Characteristics of magnetic field fluctuations as observed in the magnetosheath

Magnetic data obtained by the ISEE-1 and -2 satellites during twelve months from July to December, 1978 and 1979,are analyzed to clarify characteristics of low-frequency hydromagnetic fluctuations near the bow shock in the magnetosheath. Characteristics of the magnetic field fluctuations are examined by means of the spectral MEM and the minimum variance methods. The dynamic spectrum indicates that the spectral peaks appear in the frequency range from 0.01 to 0.05Hz. The spectral power of the component parallel to the average magnetic field tends to be larger than those perpendicular to the field. The angles between the wave normal vector and the average magnetic field are almost restricted within 60°-90°, i. e., the wave normal vector is directed nearly perpendicular to the magnetic field. Therefore, these characteristics strongly signify that the magnetic field fluctuations in the magnetosheath tend to be compressional mode

A multi-satellite study of magnetic pulsations associated with a storm sudden commencement (SSC) as observed at syochronous orbit

Oscillation characteristics of ultra-low frequency (ULF) hydromagnetic waves at synchronous orbit in response to a storm sudden commencement (SSC) are studied on the basis of the magnetic field observed on March 23,1975,simultaneously by the three synchronous satellites, SMS-1,SMS-2 and ATS-6,20 degrees apart from one another in longitude. The oscillations exhibited dampedtype, quasi-sinusoidal oscillations. They were purely transverse and azimuthally polarized, indicating a toroidal mode oscillation. The characteristics of the pure toroidal mode oscillation were emphasized with a drastic change of the oscillation component of the magnetic field perturbation from the radial (V) to the azimuthal (D) direction in association with the SSC. The oscillations appeared as a harmonic structure in the frequency. The dominant harmonics were odd ones, i. e. 1st, 3rd, etc. Furthermore, the frequencies of the harmonics observed at each satellite showed a clear local time dependence. In conclusion, the present study verifies that the ULF waves in association with the SSC on March 23,1975 in the afternoonside of the magnetosphere behaved as a clear standing oscillation of toroidal mode of the field line resonance excited by the SSC