Browsing by Author "Magnus, Lindsay Gerald."

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An analysis of Pc5 pulsations observed in the SuperDARN radar data.
(2009) Magnus, Lindsay Gerald.; Rash, Jonathan Paul Stuart.; Walker, Anthony David Mortimer.
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.
Mapping of magnetospheric electric fields from Cluster into ionospheric convection from SuperDARN using the Tsyganenko field model.
(2010) Maphaha, Fulufhelo Kenneth.; Pillay, Sadhasivan Rangan.; Magnus, Lindsay Gerald.
The data from Super Dual Auroral Radar Network (SuperDARN) radar and Cluster was used to investigate whether the processes observed by SuperDARN radar in the highlatitude ionosphere leads to the processes that take place in the magnetosphere. SuperDARN is a global network of high-frequency coherent-scatter radars operating in the northern and southern hemispheres and these radars are capable of observing backscatter from ionospheric irregularities. The Tsyganenko T96 field model was used to map the footprint of the Cluster spacecraft into the ionosphere. The SuperDARN radar data analysis software was used to generate time series, fi eld of view and convection plots. The data from Syowa South, Syowa East SuperDARN radars, Advance Composition Explorer (ACE) and Cluster spacecrafts was used in this study. Two events were found and discussed, an event on 09 August 2002 and another event on 30 September 2002. The SuperDARN radar and Cluster data for these events were compared. When a change in electric field was observed by Cluster, SuperDARN radar observed a change in the convection flow. There was a time delay between the change in the electric fi eld and the change in convection flow.