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Space weather effects on midlatitude HF propagation paths: Observations and a data-driven D region model Eccles J. V., R. D. Hunsucker, D. Rice, J. J. Sojka (2005), Space weather effects on midlatitude HF propagation paths: Observations and a data-driven D region model, Space Weather, 3, S01002, doi:10.1029/2004SW000094. 2005-01-06 Abstract: A two-pronged study is under way to improve understanding of the D region response to space weather and its effects on HF propagation. One part, the HF Investigation of D region Ionospheric Variation Experiment (HIDIVE), is designed to obtain simultaneous, quantitative propagation and absorption data from an HF signal monitoring network along with solar X-ray flux from the NOAA GOES satellites. Observations have been made continuously since late December 2002 and include the severe disturbances of October–November 2003. GOES satellite X-ray observations and geophysical indices are assimilated into the Data-Driven D Region (DDDR) electron density model developed as the second part of this project. ACE satellite proton observations, the HIDIVE HF observations, and possibly other real-time space weather data will be assimilated into DDDR in the future. Together with the Ionospheric Forecast Model developed by the Space Environment Corporation, DDDR will provide improved specification of HF propagation and absorption characteristics when supplemented by near-real-time propagation observations from HIDIVE. Copyright 2005 by the American Geophysical Union.	[HTML] [PDF]

Determining shock velocities for inputs to Sun-to-Earth models from radio and coronagraph data Smith Z., M. Dryer, C. D. Fry (2005), Determining shock velocities for inputs to Sun-to-Earth models from radio and coronagraph data, Space Weather, 3, S07002, doi:10.1029/2004SW000136. 2005-07-28 Abstract: The speed of a shock that precedes ejecta from a solar energetic eruption is one of the key parameters used for input by many numerical models that predict the arrival of interplanetary shocks at Earth. These shocks are likely to be followed by significant geomagnetic activity. Near-real-time “fearless forecasts” of shock arrival times at the L1 libration point have been made for more than 6 years with several models. Initially, these models used, for input speeds near the Sun, speeds obtained from observations of metric type II radio bursts that are signatures of shocks propagating out through the solar corona. More recently, speeds of halo/partial halo coronal mass ejections (CMEs) were also considered in these models as another measure of shock speeds close to the Sun. During the period of high solar activity in October–November 2003, the data required for input into the models were often available in near real time from a number of observing stations. Therefore the fearless forecasts were issued in some cases with alternative inputs. These forecasts provided a basis on which to compare the success of the predictions (in terms of how close each prediction of the shock arrival time was to the observed time). The results of the analysis of this data set provide guidelines for selecting the input speed for shock propagation models. Both CME and metric type II radio burst measurements are shown to be useful and complementary. In general, the highest speed gave the best predictions. This demonstrates the desirability of having coronagraph data available for operational use. Copyright 2005 by the American Geophysical Union.	[HTML] [PDF]

An overview of the impulsive geomagnetic field disturbances and power grid impacts associated with the violent Sun-Earth connection events of 29–31 October 2003 and a comparative evaluation with other contemporary storms Kappenman J. G. (2005), An overview of the impulsive geomagnetic field disturbances and power grid impacts associated with the violent Sun-Earth connection events of 29–31 October 2003 and a comparative evaluation with other contemporary storms, Space Weather, 3, S08C01, doi:10.1029/2004SW000128. 2005-08-02 Abstract: An overview is provided of the geomagnetic storms and impacts on electric power grids associated with the violent Sun-Earth events of October 2003. During the period from 29 to 31 October 2003, two large geomagnetic storms were observed, as measured by periods of high Kp, Ap, and Dst indices. In fact, these storms had Ap rankings of 6th and 16th all time. This ranking would suggest that the October 2003 storms would be significant with regard to geomagnetically induced currents (GIC) in power grids. However, the resulting geomagnetic storms were much lower in delta B and dB / dt intensity than other historically large geomagnetic storms. A variety of geomagnetic storm processes drove observed GIC. For example, ground observations indicated the presence of large dB / dt pulsations and GIC at North American midlatitude locations on 29 October 2003 that may be due to unusually intense Kelvin-Helmholtz shearing. Sustained disturbance conditions at low-latitude and equatorial latitude locations that are likely linked to ring current intensifications may be the source of sustained GIC at these locations and the cause of large power transformer failures. Comparative evaluations will be provided for the 29–31 October 2003 storms and other important and contemporary storms, such as those observed on 13–14 March 1989, 13–14 July 1982, and 15–16 July 2001. Rather than an index-based evaluation method, the comparative evaluations presented in this paper are based on comparisons of storm morphology. This approach provides a more meaningful comparison of geomagnetic field disturbance dynamics that are important to characterize large GIC threats to power grid infrastructures. Copyright 2005 by the American Geophysical Union.	[HTML] [PDF]

Structure of magnetic fields in NOAA active regions 0486 and 0501 and in the associated interplanetary ejecta Yurchyshyn V., Q. Hu, V. Abramenko (2005), Structure of magnetic fields in NOAA active regions 0486 and 0501 and in the associated interplanetary ejecta, Space Weather, 3, S08C02, doi:10.1029/2004SW000124. 2005-08-17 Abstract: Spectacular burst of solar activity in October–November 2003, when large solar spots and intense solar flares dominated the solar surface for many consecutive days, caused intense geomagnetic storms. In this paper we analyze solar and interplanetary magnetic fields associated with the storms in October–November 2003. We used space- and ground-based data in order to compare the orientations of the magnetic fields on the solar surface and at 1 AU as well as to estimate parameters of geomagnetic storms during this violent period of geomagnetic activity. Our study further supports earlier reports on the correlation between the coronal mass ejection speed and the strength of the magnetic field in an interplanetary ejecta. A good correspondence was also found between directions of the helical magnetic fields in interplanetary ejecta and in the source active regions. These findings are quite significant in terms of their potential to predict the severity of geomagnetic activity 1–2 days in advance, immediately after an Earth directed solar eruption. Copyright 2005 by the American Geophysical Union.	[HTML] [PDF]

Geomagnetic storm of 29–31 October 2003: Geomagnetically induced currents and their relation to problems in the Swedish high-voltage power transmission system Pulkkinen A., S. Lindahl, A. Viljanen, R. Pirjola (2005), Geomagnetic storm of 29–31 October 2003: Geomagnetically induced currents and their relation to problems in the Swedish high-voltage power transmission system, Space Weather, 3, S08C03, doi:10.1029/2004SW000123. 2005-08-25 Abstract: On 30 October 2003, an ongoing geomagnetic superstorm knocked down a part of the high-voltage power transmission system in southern Sweden. The blackout lasted for an hour and left about 50,000 customers without electricity. The incident was probably the most severe geomagnetically induced current (GIC) failure observed since the well-known March 1989 Québec blackout. The “three-phase” storm produced exceptionally large geomagnetic activity at the Fennoscandian auroral region. Although the diversity of the GIC drivers is addressed in the study, the problems in operating the Swedish system during the storm are attributed geophysically to substorms, storm sudden commencement, and enhanced ionospheric convection, all of which created large and complex geoelectric fields capable of driving large GIC. On the basis of the basic twofold nature of the failure-related geoelectric field characteristics, a semideterministic approach for forecasting GIC-related geomagnetic activity in which average overall activity is supplemented with statistical estimations of the amplitudes of GIC fluctuations is suggested. The study revealed that the primary mode of GIC-related failures in the Swedish high-voltage power transmission system were via harmonic distortions produced by GIC combined with too sensitive operation of the protective relays. The outage in Malmö on 30 October 2003 was caused by a combination of an abnormal switching state of the system and tripping of a low-set residual overcurrent relay that had a high sensitivity for the third harmonic of the fundamental frequency. Copyright 2005 by the American Geophysical Union.	[HTML] [PDF]