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 the electron phase-space holes are roughly spherical for Omega(e)/omega(p) > 1, and become more oblate (with the perpendicular scale larger than the parallel scale) with decreasing Omega(e)/omega(p). A scaling argument based upon electron gyrokinetic theory is proposed as a possible explanation for the observed scaling. The data indicate that the ratio of the parallel dimension (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 Geotail measurements in the deep magnetotail, where Omega(e)/omega(p) much less than 1, and the FAST measurements in the low altitude auroral zone, where Omega(e)/omega(p) much greater than 1.