Multi-station observation of IPDP micropulsations - Two-dimensional distribution and evolution of the source regions.

Abstract

Short period geomagnetic pulsations called IPDP (intervals of pulsations of diminishing periods) are investigated, using ground data obtained at 35 campaign stations in the northern polar region. Comparison of the frequency-time (f-t) spectrograms of data from the stations shows that the internal structures of f t pattern of IPDP pulsations vary with a small separation between stations. The variability of the internal structures suggests that "an IPDP event" consists of many discrete wave packets each of which comes from individual sources. Spatial-temporal developments of IPDP wave power are also examined. The two-dimensional distribution of IPDP power is both highly structured in space, suggesting presence of discrete source regions, and also highly variable with time, indicating characteristic dynamic features of the source regions. The source regions are located in the dusk half of the magnetosphere in a range of L value from 4 to 10. Three types of dynamics of the source regions are found; 1) fast westward motion consistent with magnetic-drift velocity of 60-70keV protons in the magnetosphere, 2) quasi-stationary sources, which are almost stationary in the magnetospheric frame for periods longer than 10 minutes, 3) evolution of the IPDP region toward the night and earthward with increase in center frequency. When the westward moving sources arrive at the location of the stationary sources, they merge with them and do not go further westward beyond the stationary sources. These time developments of the IPDP source regions comprehensively explain most of the IPDP characteristics so far obtained from observations in a limited area. Not only well-defined IPDP's but also 583

Temporal development of irregular magnetic pulsations occurring during low‐latitude auroras

“…Particles injected along the injection boundary encounter the duskside bulge region of the plasmapause. It is believed that the IPDP plasma wave event is generated by an ion-cyclotron instability process in the region where the westward drifting energetic protons (--•50 keV) encounter the duskside bulge region of the plasmapause [Fukunishi, 1969;Horita et al, 1979;SOraas et al, 1980;Hayashi et al, 1988;Hayakawa et al, 1992]. However, Baishev and Solovyev [1994] pointed out that the region of the maximum intensity of the IPDP plasma wave event was located lø-2 ø south of the eastward electrojet and near the region of subauroral ion drift (SAID).…”

Range finding of Alfvén oscillations and direction finding of ion-cyclotron waves by using the ground-based ULF finder

“…Measurement at one observation point thus tells us nothing about the location of this end. The problem has been solved by several methods such as triangulation direction of arrival (Frazer and Wawrzyniak, 1978), directional analysis (Chetaev, 1978), dispersion and group delay (see Feygin et al 1979 and references therein) and by using the measurements from a dense network of magnetometers (Hayashi et al, 1982(Hayashi et al, , 1988. In addition to these methods we present here an independent technique for the measurement of azimuth u of the Pc 1 propagation (see Fig.…”

Global aurora dynamics campaign, 1985-1986.

“…An example of the source distribution of IPDP pulsations is reproduced in Fig. 7 from HAYASHI et al (1988). This figure shows distribution of source regions of IPDP emissions at three frequencies, 0.1, 0.3 and 0.5Hz, obtained from the network stations in the CanadaAlaska area.…”

“…This inference is supported by the fact that the ULF waves observed by a satellite in the magnetosphere are usually in a narrow frequency band while the concurrent IPDP pulsations on the ground show frequency-time structures in a wide frequency band. The waves observed by a satellite probably correspond to a single component of the internal sub-structures, since what a satellite could observe are the waves which are generated just in a single source located along the common field line (see HAYASHI et al, 1988, for detail).…”