It is well documented that power networks at high latitudes are vulnerable to the effects of space weather. In recent years the eastern Australia state power networks have been connected across state boundaries in order to improve robustness under increasing load demands and deliver power at competitive prices. However, this interconnectivity is likely to increase susceptibility of the network to space weather. Geomagnetically induced currents (GICs) flow in power transmission lines as the result of “geoelectric” fields and their associated geomagnetic field variations according to Faraday's Law. In this paper previously documented occurrences of GIC activity from regions around the world are investigated and categorized by their effects on nearby power networks. A frequency domain filter that produces an index representing GIC activity is applied to geomagnetic field data recorded at locations near the documented GIC activity to determine risk level “GIC index” thresholds. Geomagnetic field data from the Australian region are processed using the “GIC filter” to provide a preliminary risk assessment of space weather related GIC activity to the Australian power network. The analysis suggests lower limit threshold GICy indices of 50, 100, 250, and 600 corresponding to the risk levels of “low,” “moderate,” “high,” and “extreme,” respectively. Analysis of GICy indices derived from Australian magnetometer data shows that only southern Australian regions reached the “moderate” risk levels defined in this study with mainland southern Australia stations reaching this risk level twice over the previous two solar cycles. Southern Australian regions such as Tasmania reached moderate levels approximately 20 times during the previous solar cycle. Furthermore, elevated risk levels are typically only observed in Australia during solar maximum and its decline phase.

[1] The propagation of ultra low frequency (ULF; 1-100 mHz) waves from the magnetosphere to the ground is examined in the presence of oblique background magnetic fields. The problem is developed analytically for a thin sheet ionosphere, neutral atmosphere, and perfectly conducting ground. The cold plasma, ideal magnetohydrodynamic (MHD) Alfvén wave modes are assumed to propagate in the MHD medium above the ionosphere. A reflection and wave mode conversion coefficient matrix (RCM) is derived which describes mixing and conversion between shear Alfvén and fast mode energy when interacting with the ionosphere/atmosphere/ground system. The RCM is found to depend in a complicated way on the background magnetic field dip angle, the horizontal wave vector, and the conductivity of the ionosphere. For an oblique background magnetic field,B 0 in the XZ plane, the perpendicular wave number, k y , is shown to be a critical parameter that determines reflection and mode conversion characteristics. This study also highlights the need for spatial information of ULF wave energy in order to interpret experimental ULF wave data recorded at ground level in terms of magnetospheric processes.

[1] Coordinated observations from GOES-9, DMSP F-13, and Chokurdakh (CHD) have shown concurrent Pc1-2 band wave activity in the late afternoon sector, close to 16 MLT. The left-hand polarization of the waves in space indicates that these are electromagnetic ion cyclotron (EMIC) waves. In the region of field line conjunction, DMSP also observed 6-30 keV energy ion precipitation. We have examined the propagation of the EMIC waves from the magnetosphere to the ionosphere using both time series analysis and a 2 1 2 -D magnetohydrodynamic model. Our analysis suggests that the EMIC are generated by interactions with cold plasma within a drainage plume, consistent with theory, and that the waves primarily propagate earthward along geomagnetic field lines at the eastward (outer) edge of the plume.

Abstract. A one dimensional, computational model for the propagation of ultra low frequency (ULF; 1-100 mHz) wave fields from the Earth's magnetosphere through the ionosphere, atmosphere and into the ground is presented. The model is formulated to include solutions for high latitudes where the Earth's magnetic field, (B0), is near vertical and for oblique magnetic fields applicable at lower latitudes. The model is used to investigate the wave polarisation azimuth in the magnetosphere compared with the ground wave fields, as a function of the dip angle of B0. We find that for typical ULF wave scale sizes, a 90° rotation of the wave polarisation azimuth from the magnetosphere to the ground occurs at high latitudes. However, this effect does not necessarily occur at lower latitudes in all cases. We show that the degree to which the wave polarisation azimuth rotates critically depends on the properties of the compressional ULF wave mode.

1] Long, steel pipelines used to transport essential resources such as gas and oil are potentially vulnerable to space weather. In order to inhibit corrosion, the pipelines are usually coated in an insulating material and maintained at a negative electric potential with respect to Earth using cathodic protection units. During periods of enhanced geomagnetic activity, potential differences between the pipeline and surrounding soil (referred to as pipe-to-soil potentials (PSPs)) may exhibit large voltage swings which place the pipeline outside the recommended "safe range" and at an increased risk of corrosion. The PSP variations result from the "geoelectric" field at the Earth's surface and associated geomagnetic field variations. Previous research investigating the relationship between the surface geoelectric field and geomagnetic source fields has focused on the high-latitude regions where line currents in the ionosphere E region are often the assumed source of the geomagnetic field variations. For the Australian region Sq currents also contribute to the geomagnetic field variations and provide the major contribution during geomagnetic quiet times. This paper presents the results of a spectral analysis of PSP measurements from four pipeline networks from the Australian region with geomagnetic field variations from nearby magnetometers. The pipeline networks extend from Queensland in the north of Australia to Tasmania in the south and provide PSP variations during both active and quiet geomagnetic conditions. The spectral analyses show both consistent phase and amplitude relationships across all pipelines, even for large separations between magnetometer and PSP sites and for small-amplitude signals. Comparison between the observational relationships and model predictions suggests a method for deriving a geoelectric field proxy suitable for indicating PSP-related space weather conditions. Citation: Marshall, R. A., C. L. Waters, and M. D. Sciffer (2010), Spectral analysis of pipe-to-soil potentials with variations of the Earth's magnetic field in the Australian region, Space Weather, 8, S05002,