| Popis: |
During the IGY continuous vertical incidence ionosonde records were obtained at Terre Adelie by the Expeditions Polaires Francaises in collaboration with the Group Ionosphere of CNET. Excellent hourly and, during World Days, quarter hourly, ionograms were obtained during the entire twenty-four month period from January, 1957 to December, 1958. From an examination of the numerous ionograms, the occurrences of complete blackouts was noted at Terre Adelie, which is well within the southern auroral zone and only a few hundred kilometers from the south magnetic pole. Correlation of these high absorption periods was sought with other geophysical phenomena; e.g. local and planetary magnetic indices, cosmic ray fluctuations, proton events, solar radio and ultraviolet bursts and with ionospheric blackouts found at northern high latitude stations. Several conclusions were found: (a) the occurrence, duration and intensity of blackouts in Terre Adelie correlates rather poorly with local magnetic character figures as deduced from the station magnetograms; (b) observed blackouts correlate much better with planetary magnetic character figures, Kp or Ap; (c) good correlation exists with cosmic ray intensity fluctuations both the total component (recorded at Limeil-Brevannes) or the nucleonic component (recorded at Pic du Midi and Kerguelen). Antarctic blackouts in most cases coincide with the main, negative, phase of cosmic ray storms. It was also found that a definite relationship exists between the few proton events which we investigated and the most intense blackouts; the proton events occurred prior to the blackouts. An excellent correlation was noted between the blackouts found at Terre Adelie and those observed at Little America, Thule, Barrow, Churchill, Ottawa, etc. Thus, with the exception of partial absorption of small duration, polar blackouts seem to be global polar phenomena being particularly intense in the auroral zones. Suggestions are made regarding the probable mechanism responsible for producing the polar high absorption periods and their precursors. |
