Abstract
Geomagnetic storms are space weather events that result in a temporary disturbance of the earth’s magnetosphere caused by a solar wind that interacts with the earth’s magnetic field. We examined more closely how some southern African magnetic observatories responded to the Saint Patrick’s Day storm using local K-indices. We show how this network of observatories may be utilised to model induced electric field, which is useful for the monitoring of geomagnetically induced anomalous currents capable of damaging power distribution infrastructure. We show an example of the correlation between a modelled induced electric field and measured geomagnetically induced currents in southern Africa. The data show that there are differences between global and local indices, which vary with the phases of the storm. We show the latitude dependence of geomagnetic activity and demonstrate that the direction of the variation is different for the X and Y components.
 Significance:
 
 The importance of ground-based data in space weather studies is demonstrated.
 We show how SANSA’s geomagnetic network may be utilised to model induced electric field, which is useful for the monitoring of geomagnetically induced anomalous currents capable of damaging power distribution infrastructure.
 
 Open data set: 
 http://www.intermagnet.org/data-donnee/download-eng.php
Highlights
Geomagnetic storms can affect communication satellites, interrupt radio communication by changing the status of the ionosphere, induce low frequency electric currents in long conductors like power lines and disrupt power grids
We look at how South African National Space Agency (SANSA)’s magnetic network responded to this magnetic storm using local K-indices and show how magnetotelluric stations can be used for the mapping of electric fields and for studying geomagnetically induced currents (GICs) in power networks in southern Africa
The geomagnetic observation network of SANSA in southern Africa plays a crucial role in the proper identification and characterisation of the spatial distribution of disturbance effects resulting from geomagnetic storms
Summary
Geomagnetic storms can affect communication satellites, interrupt radio communication by changing the status of the ionosphere, induce low frequency electric currents in long conductors like power lines and disrupt power grids. The magnetotelluric instrument, a LEMI-417 device (Lviv Center of Institute of Space Research, http://www.isr.lviv.ua/lemi417.htm), of which several are installed in this region, is composed of three magnetic channels to measure the X, Y and Z components of the magnetic field at 1-s intervals, and two electric channels to measure the horizontal components of the electric field at the same location with the same cadence This network of magnetotelluric stations allows researchers to use measurements of natural geomagnetic and geo-electrical field variations at the earth’s surface to model the subsurface electrical conductivity over southern Africa and apply the conductivity to calculate GICs in power grids. The physical locations of these magnetometers and magnetotelluric stations are given in Table 1 and Figure 1
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