Precession of the whistler polarisation plane normal observed on Freja

Abstract

[1] We have observed that the normal to the polarisation plane of a whistler precesses around the geomagnetic field. Magnetic field observations by the Freja spacecraft have been used. These results were made possible by the use of an analysis which estimates the instantaneous polarisation properties of waves. During one event, the instantaneous normal of the polarisation plane precesses around the direction antiparallel to the geomagnetic field with an average deviation of 6°. In total, the normal precesses four times around this direction as the whistler frequency decreases from 2 to 0.4 kHz in about 0.2 s. Available theoretical understanding can not unambiguously explain the precession. We show that the precession of whistler wave vectors can be observed, and suggest to use this new observable parameter to put new constraints on the theories of whistler propagation. Citation: Karlsson, R. L., T.

Propagation of unducted whistlers from their source lightning: A case study

“…On the other hand, the subprotonospheric whistlers at ϕ around 180° have wave vectors inclined from B 0 toward the Earth in the same plane. We find no signs of the precession of the polarization plane, as was observed for another case by Karlsson et al [2005].…”

“…This is also true for weak subprotonospheric whistlers immediately following the fractional‐hop whistler but propagating with different wave vectors. Again, we find no indications of the precession of the polarization plane observed by Karlsson et al [2005].…”

“…On the basis of the results of backward ray tracing of the observed fractional‐hop whistlers we are able to show that their wave vector directions are very close to vertical just after they penetrate upward into the ionosphere, consistent with a simple model of planar discontinuity at the level of the bottomside of the ionospheric F layer. No effects similar to observations of precession of the normal to the polarization plane [ Karlsson et al , 2005] are found in the analyzed cases. The lightning detection data allow us to compare the obtained ray traces with the positions of their source lightning strokes.…”

“…Direct ionospheric measurements of wave vector directions of downgoing whistlers by a rocket experiment [ Iwai et al , 1974] yielded contradictory results, with wave vector directions widely distributed around a broad peak at ≈20° with respect to the vertical and at ≈40° with respect to B 0 . More recently, Karlsson et al [2005] analyzed multicomponent measurements of a low‐orbiting spacecraft. They found that the normal to the polarization plane of a whistler precesses around the geomagnetic field which again seems to be inconsistent with a simple ionospheric propagation pattern.…”

“…Most of these past studies used forward ray tracing of whistlers from their source to simulate observed spectrograms [e.g., Kimura , 1985; Holzworth et al , 1999; Shklyar and Jiricek , 2000; Shklyar et al , 2004; Platino et al , 2005] or wave vector directions [e.g., James , 1972]. Only a few studies in the past were based on determination of wave vector or Poynting vector directions of whistlers using spacecraft measurements [ Gurnett et al , 1971; James , 1972; Santolík and Parrot , 1999; Karlsson et al , 2005].…”