ONE-DIMENSIONAL TRANSIENT-RESPONSE OF THE INNER MAGNETOSPHERE AT THE MAGNETIC EQUATOR .2. ANALYSIS OF WAVE-FORMS

Under a model of altitude distribution of the Alfven speed VA, one-dim ensional transient response of the inner magnetosphere at the magnetic equator to earthward propagating impulse- and step-like MHD disturban ces is considered. The waveforms of transient compressional oscillatio ns due to these disturbances at some L shells are directly simulated b y a numerical inversion of the Laplace transform with orthonormal Lagu erre functions. The present paper concentrates on the analysis of wave forms. Then, it is verified that the compressional oscillations are du e to the poles of the system under consideration. The oscillation aris ing from the cavity resonance all over the inner magnetosphere is most dominant. However, its amplitude becomes smaller as the characteristi c time scale T of an incident disturbance grows large, and it is negli gibly small for T greater than several times of eigen-period of the re sonance. On the other hand, when T is relatively small (e.g., T less t han or similar to 10 s), the oscillations due to the cavity resonances trapped around the trough in V-A are outstanding. It is also found th at the relative phase between the cavity-mode oscillations all over th e inner magnetosphere at the earth's surface and another L shell incre ases monotonically with L when the inner magnetosphere has no strong g radient or a strong positive gradient of VA at its outer boundary. How ever, the relative phase is nearly zero and nearly 180 degrees inside and outside a specific L shell, respectively, when the inner magnetosp here has a strong negative gradient at its outer boundary. The one-dim ensional cavity-mode type resonance of the inner magnetosphere is cert ainly a cause of equatorial Pi2 pulsations. However, some constituents of the Pi2's may be not cavity-mode oscillations but quasi-steady-sta te oscillations forced by some damped sinusoidal waves incident on the outer boundary of the inner magnetosphere.