Aurora and associated VLF phenomena.

Abstract

Observations have been made at Sanae (gm. lat. -63,71°) on

occurring auroral forms, (diffuse and pulsating aurora), and

simultaneous occurring VLF phenomena, (whistlers and auroral hiss) .

Two studies are presented in this thesis.

(a) A comparison of the positions of auroral forms and the

positions of field lines, along which whistlers propagate, is made and it is found that:

(i) Diffuse aurora occurs on closed field lines and indirect evidence shows that this is also the case for pulsating aurora.

(ii) For two periods of data the separation of diffuse

aurora from the plasmapause ranges from < 0,9 L

to < 0,2 L but during a third period, the diffuse

aurora lies, at least partially, within the plasmasphere.

(b) An investigation into the association between pulsating

aurora and pulsating auroral hiss is made and it is

shown that:

(i) A common identical pulsation period of 0,75 s and

high coherency exists between the light intensity

of an auroral patch and the intensity of the associated

pulsating auroral hiss. This suggests a wave-particle

interaction as a common modulation mechanism.

(ii) Cyclotron instability (gyroresonance) or Cerenkov

radiation mechanisms occurring in the equatorial

plane do not account for the time delays, typically

between 0,90 s and 0,157 s, found to be present between,

the two phenomena, where the incident auroral electrons,

responsible for the auroral patch light intensity,

are observed to arrive before the auroral hiss

emissions.

The results of the analysis in (a) are reported in The Journal

of Atmospheric and Terrestrial Physics, 39, 1429, 1977.