|dc.description.abstract||This thesis deals with the development of automatic methods for nding pulsation events
in time series produced by the radars in the SuperDARN network. These methods are then
applied to the detection and analysis of pulsation events illustrating the relative usefulness
of radar data for the study of global pulsation dynamics.
Each of the SuperDARN radars produces 1200 Doppler velocity records every hour. If
backscatter is present, and there is a pulsation occurring in the same region as the scatter,
the pulsation can be measured as periodic changes in the Doppler velocity of that record.
There are over 85 million Doppler velocity data records for 2004. In order to identify
pulsations in these data, an automated pulsation nder was developed. All records with
signi cant peaks in the FFT spectra were tagged as having a pulsation present.
If a record had less than 20% data missing it was termed a clean record as it was suitable
for use with the automated pulsation nder. As pulsations can only be observed if there
are scatter, an investigation into scatter characteristics are presented. It is shown that the
occurrence of clean records is most strongly in
uenced by IMF Bz, and the underlying
spatial structure of the SuperDARN network.
The results for the automated pulsation nder for 2004 are then presented. It was found
that the average daily distribution of pulsation events, shown as a function of pulsation
frequency, followed 1/f distribution with no distinct peaks. It was also found, however,
that the standard deviation of the average showed peaks close to the "magic" frequencies
indicating that on average there is more variation at these frequencies that any of the
other pulsation frequencies measured.
The occurrence of pulsations followed the clean scatter statistics both temporally and directionally
telling us that the network is not suited for studying global pulsation dynamics
because the variations in scatter dominated any variations in pulsation occurrence.
Data from a few events identi ed by the pulsation nder are then presented to illustrate
the advantages and disadvantages of using SuperDARN data for pulsation event studies.
The events show a pulsation that occurs at its fundamental and third harmonics, an
aliased pulsation, a pulsation, interrupted by sounding frequency changes, that shows
how ionospheric scatter was tagged as ground scatter and how data from two overlapping
pulsations in di erent radars can be merged to give the poloidal and toroidal characteristics
of the event.||en