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In a relatively rare occurrence, three African-born women have together published breakthrough research in the field of space physics.
A study by Dr Judy Stephenson, Dr Zama Katamzi-Joseph and Ms Tsige Atilaw titled: Multitaper Analysis of an MSTID Event Above Antarctica on 17 March, 2013, has been published in the peer-reviewed journal Polar Science.
Their research is focused on the analysis of a Medium-Scale Travelling Ionospheric Disturbance (MSTID) event they observed simultaneously from both the South African National Antarctic Expedition (SANAE) and Halley SuperDARN radars located in Antarctica. Their analysis employed a multiple windowing method, also known as the Multitapering method, which is a sophisticated spectral technique. Their publication includes the first estimation of energy dissipation by Joule heating due to an MSTID event.
Stephenson, who was born in Malawi, holds a PhD in Atmospheric/Solar Physics from UKZN. She is currently a full time research associate and data manager for the South African SuperDARN radar at UKZN where she supervises postgraduate students and is also a Magnetospheric Physics lecturer.
South African Katamzi-Joseph, who holds a PhD in Ionospheric Physics from Bath University in the United Kingdom, is currently a researcher at the South African National Space Agency (SANSA) as well as a research associate at Rhodes University and a lecturer in Ionospheric Physics at UKZN.
Atilaw, who was born in Ethiopia, is currently pursuing her PhD in Magnetospheric Physics through Rhodes University.
Stephenson and her co-authors used the SuperDARN radars at SANAE and Halley base to observe a Travelling Ionospheric Disturbances (TID) event for their research. SuperDARN is an acronym for a network of radars which form one of the most important international experiments in space physics. These radars receive returns from within the ionosphere, the layer of the earth’s atmosphere which contains a high concentration of ions and free electrons and is able to reflect radio waves. In the polar regions, the ionosphere acts like a screen onto which space weather phenomena are projected. This is due to the unique configuration of the Earth’s magnetic field in these locations. When the data from the 35 or so SuperDARN radars are combined, space weather maps over both north and south polar regions can be created. Furthermore, each individual radar can also observe smaller scale phenomena, such as TIDs, which are wave-like structures of electron density enhancements – basically ripples in the ionosphere caused by some disturbance.
The data the researchers collected from the radars is of sufficient quality both in time and space as it allowed them to calculate quite accurately the wavelength and velocity of the TID. By using sophisticated spectral analysis of the radar data combined with neutral wind models, they were able to make an estimate of the energy dissipated by the TID as the TID wave “broke” in the ionosphere. It was estimated to have an upper limit of 55 kW, which is more or less the energy required to boil a kettle 20 times. This is the first published estimate that the researchers know of and makes TIDs a significant energy transporter.
‘The disturbance, or source, of the TID can be external to the earth’s atmospheric layers as is the case when an active Sun induces currents in the ionosphere,’ said Stephenson. ‘The heating input by these currents can cause an instability to be set up, in this case, a TID. Or, the source may come from below the ionosphere, in the form of atmospheric gravity waves which are set up by winds passing over obstacles such as mountain ranges or sudden heating in the neutral atmosphere from the onset of solar radiation. This energy estimation implies that TIDs are a key component in understanding and assessing the global climate as TIDs play a critical role in atmospheric dynamics. In particular, they significantly affect global circulation through their ability to transport and redistribute energy and momentum vertically through the different layers of the atmosphere and horizontally across the globe.’
Stephenson said in addition it was well known that TIDs also posed a potential problem for the world, in high, and ultra-high, frequency band communication. ‘More so they can have a negative impact on communication with satellites. The distortion of the signal can cause satellite communication problems and GPS positioning errors.
‘The study of TIDS has a twofold relevance within the space physics field due to the fact that they affect the accuracy of the navigation and communication systems that depend on the ionosphere for propagation and due to their role in global energy distribution.’
The co-authors noted that a better understanding of the ionosphere, such as irregular change in the electron density caused by TIDs, would lead to better ionospheric model predictions, which in turn help to minimise ionospheric errors in communication and accuracy in global energy budgets.
Words: Nicole Chidzawo