Physics
Scientific paper
Apr 1965
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1965jatp...27..499h&link_type=abstract
Journal of Atmospheric and Terrestrial Physics, vol. 27, no. 4, pp. 499-502, IN2-IN8, 503-512
Physics
2
Scientific paper
The direction of arrival of the v.l.f.-emission in the 8 kc/s bands has been studied using two crossed loops with their planes lying in EW and NS directions, and by switching the loops alternately to the same amplifier channel. The v.l.f.-noise level was higher in the EW than in the NS direction, and this higher EW noise level was maintained during day and night for a year and also independently at two observing places lying 35 km apart. The vEl.f.-bursts came in on both frames with amplitudes of the same order of magnitude. It is concluded that Tromsø is lying within an area of arrival of the v.l.f.-emissions, and that the energy is coming in from all directions. This point of view is confirmed by the polarization studies. The v.l.f.-emissions were picked up on two crossed frames, each of which was connected to identical amplifiers and displayed on the pairs of X, Y-plates on an oscillograph. Ordinary broad and irregular v.l.f.-bursts showed an irregular oscillograph pattern with changing amplitudes and irregularly appearing reversals of the sense of rotation. The oscillograph patterns are to be explained by the simultaneous arrival of several v.l.f.-noise trains which are uncorrelated. In some few cases when a sudden and single, sharp burst appeared the oscillograph pattern was different, the pattern was almost circular and the sense of rotation was always in the same direction. In this case it is assumed that the emission came down vertically along the field lines, circularly polarized, and only in the extraordinary mode. Examples of amplitude distribution are demonstrated in which a strong v.l.f.-emission is being built up by a series of sudden, discrete trains of bursts which gradually merge together into a continuous emission. The frequency-analysis of a number of bursts in the range 5-13 kc/s is demonstrated. It seems to be a general rule that at the start of a burst the higher frequency amplitudes on 12-10 kc/s are stronger, while at the end of a burst the lower frequency 6-5 kc/s is the strongest. A possible explanation of this effect is the gradual building-up of an absorption in the E-layer during a disturbance, which in the beginning will influence the higher frequencies more strongly than the lower. The mechanism of generation of the continuous band-emission, Cerenkov- and gyroradiations, are discussed, and it is concluded that the observations do not give any decisive proof for either of the two hypothesesE It is pointed out that the diurnal curve of occurrence of the v.l.f.-emissions at Tromsø (the appearance being limited to the interval 1800-2400 hours M.E.T.) is difficult to explain and some more extended series of observations are needed at various places along the auroral zone.
Harang Leiv
Hauge Knut N.
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