ULF Waves Associated to the Energetic Ions Foreshock at WIND and GEOTAIL
D. Berdichevsky (Raytheon STX Corporation at NASA/GSFC, e-
mail: istp::berdi), R. Fitzenreiter (NASA/GSFC, Greenbelt, MD 20771), G.
Thejappa (Dept. of Astr., Univ. of Maryland, College Park, MD 20742), D.
Williams, R.W. McEntire (JHU/ Applied Physics Laboratory), R. P. Lin (Dept. of
Phys., Univ. of California, Berkeley), S. Kokubun (Solar-Terrestrial
Environment Laboatory, Nagoya University, Toyokawa, Ai-chi 442, Japan), T.
Yamamoto (Institute of Space and Astronautical Science, Sagamihara,
Kanagawa 229, Japan), R. Lepping (NASA/GSFC, Greenbelt, MD 20771)
We present several energetic ion (EI) events observed simultaneously by WIND
GEOTAIL spacecraft. During these observations, WIND was located near the
Lagrangian point one or it was in its wide orbit with apogee at X-GSE
approximately equal to 110 Re, whereas GEOTAIL was skimming the magnetosheath
its orbit around the Earth with its apogee toward the Sun (March to August
1995). During these periods the EI show a similar characteristic exponential
energy spectrum at GEOTAIL and WIND. In all cases we observe at GEOTAIL the
signature of energetic scattered ions in the near foreshock region, i.e. a
comparable EI flow toward, from, in the dawn, and dusk direction with respect
the Earth's position. We give the spacecraft positions, average general
conditions of the SW interplanetary magnetic field and plasma, at the time of
these simultaneous EI observations. For three cases we study the associated ULF
waves and the ratio of transverse to compressible wave amplitudes and modes. We
show that both at GEOTAIL and WIND several excited ULF wave modes coexist, and
investigate the overall associated polarization. We present the implications of
these observations for the structure of the ion foreshock regions and the role
of wave particle interactions.