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.

[1] An empirical model of the quiet daily geomagnetic field variation has been constructed based on geomagnetic data obtained from 21 stations along the 210 Magnetic Meridian of the Circum-pan Pacific Magnetometer Network (CPMN) from 1996 to 2007. Using the least squares fitting method for geomagnetically quiet days (Kp ≤ 2+), the quiet daily geomagnetic field variation at each station was described as a function of solar activity SA, day of year DOY, lunar age LA, and local time LT. After interpolation in latitude, the model can describe solar-activity dependence and seasonal dependence of solar quiet daily variations (S) and lunar quiet daily variations (L). We performed a spherical harmonic analysis (SHA) on these S and L variations to examine average characteristics of the equivalent external current systems. We found three particularly noteworthy results. First, the total current intensity of the S current system is largely controlled by solar activity while its focus position is not significantly affected by solar activity. Second, we found that seasonal variations of the S current intensity exhibit northsouth asymmetry; the current intensity of the northern vortex shows a prominent annual variation while the southern vortex shows a clear semi-annual variation as well as annual variation. Thirdly, we found that the total intensity of the L current system changes depending on solar activity and season; seasonal variations of the L current intensity show an enhancement during the December solstice, independent of the level of solar activity.

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.

Presented is an analysis of the occurrence of postsunset Equatorial Plasma Bubbles (EPBs) detected using a Global Positioning System (GPS) receiver at Vanimo. The three year data set shows that the EPB occurrence maximizes (minimizes) during the equinoxes (solstices), in good agreement with previous findings. The Vanimo ionosonde station is used with the GPS receiver in an analysis of the day-to-day EPB occurrence variability during the 2000 equinox period. A superposed epoch analysis (SEA) reveals that the altitude, and the change in altitude, of the F layer height is ∼1 standard deviation (1 ) larger on the days for which EPBs were detected, compared to non-EPB days. These results are then compared to results from the Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM), which show strong similarities with the observations. The TIEGCM is used to calculate the flux-tube integrated Rayleigh-Taylor (R-T) instability linear growth rate. A SEA reveals that the modeled R-T growth rate is 1 higher on average for EPB days compared to non-EPB days, and that the upward plasma drift is the most dominant contributor. It is further demonstrated that the TIEGCM's success in describing the observed daily EPB variability during the scintillation season resides in the variations caused by geomagnetic activity (as parameterized by Kp) rather than solar EUV flux (as parameterized by F 10.7 ). Geomagnetic activity varies the modeled high-latitude plasma convection and the associated Joule heating that affects the low-latitude F region dynamo, and consequently the equatorial upward plasma drift.

[1] The objective of this study is to understand better the propagation of Pi 2 waves in the nighttime region. We examined Pi 2 oscillations that showed high correlation between high-and low-latitude Magnetic Data Acquisition System/Circum Pan-Pacific Magnetometer Network stations (correlation coefficient: jgj ! 0.75). For each horizontal component (H and D) we examined the magnetic local time (MLT) dependence of the delay time of high-latitude Pi 2 oscillations that corresponds to the highest correlation with the low-latitude Pi 2 oscillation. We found the delay time of the high-latitude H showed remarkable MLT dependence, especially in the premidnight sector: we found that in the premidnight sector the high-latitude H oscillation tends to delay from the low-latitude oscillation (<100 s). On the other hand, the delay time of the high-latitude D oscillation was not significant ($±10 s) in the entire nighttime sector. We propose a Pi 2 propagation model to explain the observed delay time of high-correlation highlatitude H. The model quantitatively explains the trend of the event distribution. We also examined the spatial distribution of high-correlation Pi 2 events relative to the center of auroral breakups. It was found that the high-correlation Pi 2 events tend to occur away from the center of auroral breakups by more than 1.5 MLT. The present result suggests that the high-correlation H component Pi 2 oscillations at high latitude are a manifestation of forced Alfvén waves excited by fast magnetosonic waves.