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Sydney, Australia

Marshall R.A.,IPS Radio and Space Services | Waters C.L.,University of Newcastle | Sciffer M.D.,University of Newcastle
Space Weather | Year: 2010

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. Copyright 2010 by the American Geophysical Union. Source

Kumar V.V.,La Trobe University | Parkinson M.L.,IPS Radio and Space Services | Dyson P.L.,La Trobe University
Journal of Geophysical Research: Space Physics | Year: 2010

Superposed Epoch Analysis (SEA) is used to examine a 5-year (1999 to 2003) database of Digisonde drift measurements made at Bundoora (145.1°E, 37.7°S geographic, 49°S magnetic), Australia, to determine the temporal evolution of midlatitude F region electric fields associated with the magnetospheric (lifetimes of about an hour) and ionospheric disturbance (lifetimes of a few to several hours) dynamos. The magnetospheric effects are qualified using AE "step-up" and "step-down" temporal filters and the SEA results reveal features fairly consistent with under- and over-shielding conditions described by the Rice Convention Model (RCM). The disturbance dynamo effects are qualified using onset times of AE- and Dst-defined storms. These onset times are further subdivided into three categories: short-, medium- and long-duration storms. We find there are no noticeable changes in ionospheric electric fields near Bundoora during short-duration AE-defined storms. In contrast, the SEA responses for medium-duration AE-defined storms and short- and medium-duration Dst-defined storms are in good agreement with the ionospheric disturbance dynamo predictions. The SEA results associated with long-duration AE or Dst-defined storms indicate that the electric field perturbations agree with the effects of the high-latitude two-cell convection pattern expanding to the latitude of the station (49° magnetic) for up to 20 h after t = 0 h. Overall, the perturbation drifts are predominantly westward with largest amplitudes in the dusk to midnight sector and continued for nearly 50 h in storm time. These enhancements are also consistent with the influence of the sub-auroral polarization stream (SAP) extending to the latitude of the station. Copyright 2010 by the American Geophysical Union. Source

Yamazaki Y.,Kyushu University | Yumoto K.,Kyushu University | Uozumi T.,Kyushu University | Abe S.,Kyushu University | And 5 more authors.
Journal of Geophysical Research: Space Physics | Year: 2010

We reexamined the daily Sq-equatorial electrojet (EEJ) relationship based on these extended magnetometer networks in the east Asian region: (1) the Circum-pan Pacific Magnetometer Network (CPMN), (2) the International Real-time Magnetic Observatory Network (INTERMAGNET), and (3) the World Data Center for Geomagnetism, Kyoto (WDC). Daily variations of the geomagnetic field for geomagnetically quiet days (Kp ≤ 2+) from 1996 to 2005 were analyzed. Noontime eastward Sq current intensities were estimated by latitudinally integrating the north-south component of the S q field. The corresponding EEJ intensities were estimated from the daily geomagnetic field variations observed at Davao station (dip latitude of -0.84°deg). We discovered that these intensities of daily Sq and EEJ are well correlated on a long-term basis (r = 0.80). The dependences on the solar activity (as indicated by F10.7) and season (the day number) of S q and EEJ variations were examined. It was demonstrated that both daily Sq and EEJ intensities are correlated to F10.7 with similar sensitivities. F10.7 is known to show similar variations with solar EUV radiation which causes ionization and heating of the ionosphere. For seasonal dependence, both daily Sq and EEJ intensities show predominant semiannual variations with similar spring-fall asymmetry. The effect of seasonal changes of the EUV flux into the low-latitude ionosphere is considered. Our results indicate that the daily values of Sq and EEJ react, in the same manner, to temporal changes of solar ionization and heating of the ionosphere. Copyright 2010 by the American Geophysical Union. Source

Takla E.M.,Kyushu University | Yumoto K.,Kyushu University | Nikiforov V.M.,Russian Academy of Sciences | Marshall R.,IPS Radio and Space Services
Physics of the Earth and Planetary Interiors | Year: 2011

The Molise region, on 31 October and 1 November 2002, was struck by two earthquakes of moderate magnitudes (Mw = 5.7) at depth between 12 and 24. km. Geomagnetic data from the Circum-pan Pacific Magnetometer Network (CPMN) were analyzed in order to detect any anomalous geomagnetic variations in association with the Molise earthquakes. Our results indicate the presence of long-term anomalous variations in the geomagnetic components at L'Aquila (LAQ) station (near the epicenter), which started about four months before the occurrence of the Molise earthquakes. Moreover, the geomagnetic components recorded at LAQ are found to show no correlation with those at other conjugate stations in the period between June and October 2002. In addition, anomalous ULF signal (Pc 3:10-45. s) started few weeks before the Molise earthquakes and lasted for about one week after the onset of the seismic activity. The observed anomalous variations may be explained as a result of the crustal stress variations and the enhancement of the lithospheric conductivity in the Molise region during the preparation period of the Molise earthquakes. © 2010 Elsevier B.V. Source

Marshall R.A.,IPS Radio and Space Services | Dalzell M.,Transpower | Waters C.L.,University of Newcastle | Goldthorpe P.,University of Newcastle | And 2 more authors.
Space Weather | Year: 2012

Adverse space weather conditions have been shown to be directly responsible for faults within power networks at high latitudes. A number of studies have also shown space weather to impact power networks at lower latitudes, although most of these studies show increases in GIC activity within networks not directly related to hardware faults. This study examines a GIC event that occurred in New Zealand's South Island power network on 6th November 2001. A transformer failure that occurred during this day is shown to be associated with a change in the solar wind dynamic pressure of nearly 20 nPa. Measurements of GICs recorded on the neutral lines of transformers across the Transpower network during this event show good correlation with a GIC-index, a proxy for the geoelectric field that drives GIC. Comparison of this event with GIC activity observed in the Transpower network during large space weather storms such as the "2003 Halloween storm," suggests that solar wind shocks and associated geomagnetic sudden impulse (SI) events may be as hazardous to middle latitude power networks as GIC activity occurring during the main phase of large storms. Further, this study suggests that the latitudinal dependence of the impacts of SI events on power systems differs from that observed during large main phase storms. This study also highlights the importance of operating procedures for large space weather events, even at middle latitude locations. © 2012 by the American Geophysical Union. Source

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