Pi B pulsations

spaceweb@oulu.fi - last update: 7 January 1999, 1300 UT (RR)


ULF range, broadband, bursty geomagnetic pulsations occurring in the Pi 1 and Pi 2 frequency ranges (2 mHz - 1 Hz; sometimes frequencies above 1 Hz are also seen) are called PiB pulsations (Heacock, 1967). Typically the two different frequency bands are marked as Pi1B and Pi2B. It has been argued that the often seen enhancement of power near 3 sec period is not related to the PiB (see PiC).

The PiB bursts are closely related with substorms (Troitskaya, 1961; Campbell and Rees, 1961). More precicely, they relate to the breakup auroral arc that forms the auroral bulge (e.g., Bösinger and Yahnin, 1987), and are thus good indicators of substorm onset time. Because of the higher frequencies observed, the onset time can be defined more accurately using a PiB event than a more traditional Pi 2 event. However, this is not always true, as the Pi 2 pulsations extend to much larger geographical area than PiB, and are thus easier to observe. Note also that typical magnetometers with 10-20 second sampling period are not good enough for proper PiB identification. (See also Posch et al., AGU Fall Meeting 1998.)


Most PiB pulsation events are associated with fluctuations in the ionospheric current system caused by electron precipitation and related conductivity variability. This can be seen from the close relationship between them and

However, Knecht and Singer (1981) have reported that, at midlatitudes, Pi1B are often occurring simultaneously practically over the entire nightside hemisphere, indicating an additional source for some events. Arnoldy et al. (1998) suggest that although part of the PiB pulsations are indeed related to ionospheric currents, they are also propagating down from the equatorial current disruption region (see SCW). In the ionosphere, they are ducted horizontally to cover wider latitudinal and longitudinal region.

Lysak (1988) have suggested that PiB could also relate to the IAR.


See also: