The polarisation of whistlers received on the ground near L = 4

The observed polarisation of the horizontal magnetic components of whistler mode signals received at Halley, Antarctica (L≈ 4.3), is in many cases that expected from a simple model of the transionospheric and sub-ionospheric propagation in the southern hemisphere; i.e. right-hand elliptical (field vectors rotate clockwise, looking towards the source) for ionospheric exit points close to the receiver, tending towards linear for more distant exit points. This suggests it may be possible to use the observed polarisation to estimate the propagation distance. However, in other cases, in certain frequency ranges, left-hand elliptically polarised signals have been observed. More realistic models do predict polarisation reversals at certain frequencies and exit point to receiver distances, but not over such a wide frequency range as has sometimes been observed. Also, in some cases, signals with nearly right-hand circular polarisation have been observed for exit points at large distances where linear polarisation would be expected.