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|Title:||Periodicities and spread-F associated with large-scale travelling ionospheric disturbances|
|Authors:||Bowman, G G|
|Abstract:||Spread-F associated with large-scale travelling ionospheric disturbances (LS-TIDS) has been discussed and examined by considering fixed-frequency phase-path information for an event on October 24/25, 1990 at Bribie Island, near Brisbane, Australia. The results suggest that radiowave reflections from the titled isoionic surfaces, which are produced by LS-TIDs with certain periodicities, are not responsible for the spread. Instead, it seems likely that the wave amplitudes of medium-scale travelling ionospheric disturbances (MS-TIDs), which are also present at these times, are enhanced when the LS-TID macroscale height changes occur. It is suggested that these wave amplitudes are sufficiently enhanced (due to lower neutral densities) to allow the significant off-vertical reflections which are responsible for the spread. Also, during the equinoctial periods of some sunspot-maximum years, it is shown using phase-path rates of change of the main trace of the F2 layer that the LS-TIDs have preferred periodicities of 35 and 17 min.|
|ISSN:||0975-105X (Online); 0367-8393 (Print)|
|Appears in Collections:||IJRSP Vol.25(2) [April 1996]|
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