Space weather manifests in power networks as quasi‐DC currents flowing in and out of the power system through the grounded neutrals of high‐voltage transformers, referred to as geomagnetically induced currents. This paper presents a comparison of modeled geomagnetically induced currents, determined using geoelectric fields derived from four different impedance models employing different conductivity structures, with geomagnetically induced current measurements from within the power system of the eastern states of Australia. The four different impedance models are a uniform conductivity model (UC), one‐dimensional n‐layered conductivity models (NU and NW), and a three‐dimensional conductivity model of the Australian region (3DM) from which magnetotelluric impedance tensors are calculated. The modeled 3DM tensors show good agreement with measured magnetotelluric tensors obtained from recently released data from the Australian Lithospheric Architecture Magnetotelluric Project. The four different impedance models are applied to a network model for four geomagnetic storms of solar cycle 24 and compared with observations from up to eight different locations within the network. The models are assessed using several statistical performance parameters. For correlation values greater than 0.8 and amplitude scale factors less than 2, the 3DM model performs better than the simpler conductivity models. When considering the model performance parameter, P, the highest individual P value was for the 3DM model. The implications of the results are discussed in terms of the underlying geological structures and the power network electrical parameters.

It has been found that goethite acquires a thermoremanent magnetization (TRM) when cooled in the presence of a magnetic field from 120°C. It is believed that this TRM is due to the presence of antiferromagnetism in goethite with a Nee1 temperature of 120°C. A few spins have no mates because of small grain size or the presence of imperfections and impurities.Similarly, hematite acquires a TRM at its Nee1 temperature which is due to unbalanced spins. In addition hematite is known to have a ' parasitic ferromagnetism '. Hematite derived from heating goethite above 350°C showed two different types of behaviour. Hematite composed of particles less than +,i diameter showed no spontaneous magnetization, but did show a weak thermoremanence whereas hematite composed of larger particles developed a spontaneous magnetization. These observations indicate that parasitic ferromagnetism exists only in graiiis larger than +p.This TRM is related to antiferromagnetism.

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Goethite, known to be antiferromagnetic, acquires thermoremanent magnetization at its Neel temperature of 120 degrees C. This remanence, extremely stable, is due to the presence of unbalanced spins in the antiferromagnetic structure; the spins may result from grain size, imperfections, or impurities.

Summary Palaeomagnetic examination of Middle and Upper Pennsylvanian, Permian and Triassic redbeds from the western and eastern slopes of the Colorado Front Range suggests that a late Pennsylvanian‐Permian reversed interval equivalent to the Kiaman magnetic interval has been located on the North American continent. Collections made from a stratigraphic interval of 2000 ft on the eastern slope and 4000 ft on the western slope showed reversed directions only. Available stratigraphic data indicate that the zone extends from the beginning of Late Pennsylvanian to Late Permian or into Early Triassic. This time span is in good agreement with the age assignment, based on radioisotope dating and stratigraphic position, of the Australian igneous rocks on which the magnetic interval was defined. Thus it appears that the redbeds of this study acquired their magnetic direction at the time of deposition or very soon thereafter. Palaeomagnetic poles calculated on the basis of these data are: Middle Pennsylvanian, 39°N, 105°E; Upper Pennsylvanian and Permian, 33°N, 126°E, for the western slope and 48°N, 119°E, for the eastern slope; Lower Triassic, 56°N, 100°E.