Browsing by Author "Mtumela, Zolile."

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Development of near real time and cumulative GIC proxy indices.
(2021) Essop, Abu-Bakr.; Mtumela, Zolile.; Lotz, Stefan.
Geomagnetic storms are phenomena which can give rise to geomagnetically induced currents (GICs), which have an adverse effect on technology in that they can cause anomalous low frequency currents that damage critical infrastructure. The problems with quantifying the damage in the absence of accurate GIC data (which can show the level of damage) are twofold, namely, for near real-time applications and the other for long-term applications respectively. Since GIC data is not easily available due to power utilities either not having measuring devices or not allowing its dissemination readily, other methods of quantifying damage as unambiguously as possible using data from more attainable sources such as local magnetometer stations, are necessary improvements that can be made. Attempts are made in this work, using an algorithm similar to that of Wintoft et al. [1], to address these problems via the creation of two GIC proxies to, in the case of near-real time applications, track damage, and in the long-term case, by combining ideas from Yu and Ridley [2] as well as Lotz and Danskin [3], to indicate damage incurred during storms. Using these algorithms, results are acquired by making use of Pearson’s correlation and graphical methods, although the data set is too small to draw statistically significant conclusions. The results from the short-term index show that the index works well with the best indicators of shortterm behaviour available as well as GIC data from power stations in South Africa. The results from the long-term index corroborates with the literature, in that damage done in long, yet less intense events can can be as significant as damage done by short-term, yet highly intense events, as reported by Lotz and Danskin [3].
An investigation of high velocity flows in HF radar data during northward interplanetary magnetic field, non-substorm intervals.
(2010) Mtumela, Zolile.; Rash, Jonathan Paul Stuart.; Sutcliffe, Peter Roy.
Several previous studies, including one using early Sanae radar data, have found examples of high speed ionospheric plasma flows on the nightside, mapping to the magnetospheric tail, during periods which were magnetically quiet. These high speed flows were interpreted to be associated with the release of energy from a rapid reconfiguration of tail magnetic field lines due to reconnection. Such events are now known as ‘TRINNIs’ or ‘tail reconnection during IMF northward, non-substorm intervals’. The purpose of this study was to identify further TRINNI events, using SuperDARN data from both hemispheres. In situations where the y-component of the Interplanetary Magnetic Field dominates over the z-component, the directions of both the high speed flows and the underlying convection pattern depend on the direction of the y-component. Some examples of likely TRINNI events for cases where the y-component was positive and negative are presented and discussed. The assumption of a non-substorm interval is justified by magnetometer and GOES satellite data, and the observations are discussed in relation to magnetic reconnection in the magnetotail.
An investigation of the nature of Pc5 pulsations using SuperDARN and magnetometer data.
Mtumela, Zolile.; Stephenson, Judy Ann Elizabeth.; Walker, Anthony David Mortimer.
Pc5 pulsations are global magnetohydrodynamic events in the magnetosphere. We employed an Automated Pulsation Finder program to identify significant Pc5 pulsation events in SuperDARN data. Those events for which a resonance of similar frequency band was observed in more than one HF radar were selected. The three events presented here are such that a similar resonance was observed in Goose Bay, Saskatoon and Pykkvibaer HF radars, located in the northern polar region. One event was isolated in which the resonance was observed at the conjugate hemisphere at Sanae, Antarctica. Those events have a good data from magnetometer chains within the field of view of HF radars are chosen for analysis. These two instruments complement each other. We combined these two instruments to investigate the nature of the pulsation, determining its qualitative polarization characteristics. Observations of a resonance that extend over a large fraction of the polar region are rarely reported. A complex demodulation technique was employed to determine the amplitude and phase relationship between field components observed by the radars and magnetometer chains, this in turn, affords resolution of other characteristics of pulsations such as wave number and phase velocity. We present results in a graphical form and discuss them in the context of MHD theory of magnetic pulsations, speculating on their generation mechanism.