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The need for accurate assessment of the geomagnetic hazard to power systems is driving a requirement to model geomagnetically induced currents (GIC) in multiple voltage levels of a power network. The Lehtinen–Pirjola method for modelling GIC is widely used but was developed when the main aim was to model GIC in only the highest voltage level of a power network. Here we present a modification to the Lehtinen–Pirjola (LP) method designed to provide an efficient method for modelling GIC in multiple voltage levels. The LP method calculates the GIC flow to ground from each node. However, with a network involving multiple voltage levels, many of the nodes are ungrounded, i.e. have infinite resistance to ground, which is numerically inconvenient. The new modified Lehtinen–Pirjola (LPm) method replaces the earthing impedance matrix [ Ze ] with the corresponding earthing admittance matrix [ Ye ] in which the ungrounded nodes have zero admittance to ground. This is combined with the network admittance matrix [ Yn ] to give a combined matrix ([ Yn ] + [ Ye ]), which is a sparse symmetric positive definite matrix allowing efficient techniques, such as Cholesky decomposition, to be used to provide the nodal voltages. The nodal voltages are then used to calculate the GIC in the transformer windings and the transmission lines of the power network. The LPm method with Cholesky decomposition also provides an efficient method for calculating GIC at multiple time steps. Finally, the paper shows how software for the LP method can be easily converted to the LPm method and provides examples of calculations using the LPm method. [ABSTRACT FROM AUTHOR]

The DI-flux, consisting of a fluxgate magnetometer coupled with a theodolite, is used for the absolute manual measurement of the magnetic field angles in most groundbased observatories worldwide. Commercial solutions for an automated DI-flux have recently been developed by the Royal Meteorological Institute of Belgium (RMI) and are practically restricted to the AutoDIF and its variant, the GyroDIF. In this article, we analyze the pros and cons of both instruments in terms of its suitability for installation at the partially manned geomagnetic observatory of Livingston Island (LIV), Antarctica. We conclude that the GyroDIF, even if it is less accurate and more power demanding, is more suitable than the AutoDIF for harsh conditions due to the simpler infrastructure that is necessary. Power constraints in the Spanish Antarctic Station Juan Carlos I (ASJI) during the unmanned season require an energy-efficient design of the thermally regulated box housing the instrument as well as thorough power management. Our experiences can benefit the geomagnetic community, which often faces similar challenges. [ABSTRACT FROM AUTHOR]

Solar flare effects (Sfe's) are rapid magnetic variations related to the enhancement of the amount of radiation produced during solar flare events. For several minutes, the ionosphere is activated and electron densities, electrical conductivities and electric currents are enhanced. The magnetic signature of a flare is visible in the illuminated hemisphere, and sometimes it shows up as small crochet-like movements in the magnetograms. However, regarding their detection using an automatized procedure, they have been very elusive because their small amplitude, which is close to the level of noise produced by other natural phenomena, and their highly variable irregular shapes make it extremely difficult to apply predesigned patterns. In this paper, we summarize the difficulties that Sfe detection presents and explain a line of work we initiated to overcome these difficulties with the goal of achieving a system capable of performing automatic detection. Some properties of Sfe's, including spherical symmetry around the vortex and different time durations between Sfe's and other natural variations, were used to construct an index allowing us to detect Sfe's. [ABSTRACT FROM AUTHOR]

The geophysical observatory in the Antarctic Spanish Station, Juan Carlos I (ASJI), on Livingston Island, has been monitoring the magnetic field in the Antarctic region for more than fifteen years. In 2004, a vertical incidence ionospheric sounder completed the observatory, which brings a significant added value in a region with low density of geophysical data. Although the ASJI is only operative during the austral summer, the geomagnetic station records the data throughout the year. A High Frequency (HF) transmission system was installed in 2004 in order to have the geomagnetic data available during the whole year. As the power supply is very limited when the station is not operative, we had to design a low-power HF transceiver with a very simple antenna, due to environmental aspects. Moreover, the flow of information was unidirectional, so the modulation had to be extremely robust since there is no retransmission in case of error. This led us to study the main parameters of the ionospheric channel and to design new modulations specially adapted to very low signal to noise scenarios with high levels of interference. In this paper, a review of the results of our remote geophysical observatory and associated transmission system in Antarctica during the last decade is presented. [ABSTRACT FROM AUTHOR]

Spherical Elementary Current Systems (SECS) is an equivalent source method aimed at explaining the observed ground magnetic variations in terms of its current sources, flowing either at the Earth's ionosphere or at the subsurface. This technique has contributed valuable results for magnetic interpolation purposes, as well as for modeling equivalent currents in their source region, thus distinguishing between their external and internal origin. Its outcome gives a realistic picture of the ongoing electrodynamic processes on the occasion of severe Space Weather (SW) events, with applications in the field of geomagnetically induced currents (GIC). Although different modalities of SECS exist (either 1D, 2D or 3D) depending on the number of space dimensions involved, the method is limited to providing a sequence of instantaneous pictures of those source currents. The extension presented hereby consists in introducing a temporal dependence in the formulation based on a cubic B-splines expansion. The technique thus adds one dimension, becoming 4D in general (e.g., 3D + t). Its reliability is demonstrated by comparing the modeled currents with those obtained for different snapshots using the traditional spatial version of SECS. However, its range of application is extended to cases of heterogeneous geomagnetic datasets which could hardly be treated otherwise, such as those containing gaps, different sampling rates or diverse data sources, especially common in the past decades before the gradual standardization of the geomagnetic observations worldwide. Tests so far in this sense reveal results that are consistent with known upper atmospheric processes. [ABSTRACT FROM AUTHOR]