On the perpendicular scale of electron phase-space holes

The perpendicular scale of electron phase-space holes is investigated using electric field data from the Polar Plasma Wave Instrument. We show that th e electron phase-space holes are roughly spherical for Omega(e)/omega(p) > 1, and become more oblate (with the perpendicular scale larger than the par allel scale) with decreasing Omega(e)/omega(p). A scaling argument based up on electron gyrokinetic theory is proposed as a possible explanation for th e observed scaling. The data indicate that the ratio of the parallel dimens ion (L-parallel to) to the perpendicular dimension (L-perpendicular to) is such that L-parallel to/L-perpendicular to similar or equal to (1 + rho(e)( 2)/lambda(D)(2))(-1/2). Our results provide a connection between the Geotai l measurements in the deep magnetotail, where Omega(e)/omega(p) much less t han 1, and the FAST measurements in the low altitude auroral zone, where Om ega(e)/omega(p) much greater than 1.