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 Ωep > 1, and become more oblate (with the perpendicular scale larger than the parallel scale) with decreasing Ωep. 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) to the perpendicular dimension (L) is such that L/L ≃ (1 + ρe²/λD²)−1/2. Our results provide a connection between the Geotail measurements in the deep magnetotail, where Ωep ≪ 1, and the FAST measurements in the low altitude auroral zone, where Ωep ≫ 1.