Pi B pulsations

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

Introduction

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.)

Source

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

upgoing field aligned currents and ionospheric electric fields (Wilhelm et al., 1977; Bösinger et al., 1981)
enhanced E layer conductivity and electrojet currents (Heacock and Hunsucker, 1981)
auroral luminosity pulsations (Troitskaya, 1961; Grant and Burns, 1995)
pulsations in cosmic noise; see riometers (Heacock and Hunsucker, 1977)

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.

References

Arnoldy, R. L., J. L. Posch, M. J. Engebretson, H. Fukunishi, and H. J. Singer, Pi1 magnetic pulsations in space and at high latitudes on the ground, J. Geophys. Res., 103, 23581-23591, 1998.
Bösinger, T., K. Alanko, J. Kangas, H. Opgenoorth, and W. Baumjohann, Correlation between Pi B type magnetic micropulsations, auroras and equivalent current structures during two isolated substorms, J. Atmos. Terr. Phys., 43, 933-945, 1981.
Bösinger, T., and A. G. Yahnin, Pi1B type magnetic pulsations as a high time resolution monitor of substorm development, Ann. Geophysicae, 5, 231-238, 1987.
Campbell, W. H., and M. H. Rees, A study of auroral coruscations, J. Geophys. Res., 66, 41, 1961.
Grant, I. F. and G. B. Burns, Observations and modeling of correlated Pi B magnetic and auroral luminosity pulsations, J. Geophys. Res., 100, 19387-19404, 1995.
Heacock, R. R., Two subtypes of Pi micropulsations, J. Geophys. Res., 72, 3905, 1967.
Heacock, R. R., and R. D. Hunsucker, A study of concurrent magnetic field and particle precipitation pulsations, 0.0005 to 0.5 Hz, recorded near College, Alaska, J. Atmos. Terr. Phys., 39, 487, 1977.
Heacock, R. R., and R. D. Hunsucker, Type Pi 1/2 magnetic field pulsations, Space Sci. Rev., 28, 191, 1981.
Knecht, D. J., and H. J. Singer, Multistation observations of simultaneous Pi1 and Pi2 pulsations at substorm onsets, abstract in Eos Trans. AGU, 62, 358, 1981.
Lysak, R. L., Theory of auroral zone PiB pulsation spectra, J. Geophys. Res., 93, 5942, 1988.
Troitskaya, V. A., Pulsations of the Earth's electromagnetic field with periods of 1 to 15 seconds and their connection with phenomena in the high atmosphere, J. Geophys. Res., 66, 5, 1961.
Wilhelm, K., J. W. Munch, and G. Kremser, Fluctuations of the auroral zone current system and geomagnetic pulsations, J. Geophys. Res., 82, 2705, 1977.