Forecasting the Auroral Electrojets and Ground-Induced Currents

 

 

Plans to create a national electricity grid will interconnect North American electric utilities on a continental scale. Economic competition stimulated by deregulation of the electric power industry will require this complex grid to be operated efficiently with minimal excess capacity. These two trends are causing power system operations to become increasingly susceptible to the disruptive effects of so-called ground-induced currents (GICs). GICs are stray currents that flow in long, electrically conducting transmission lines during periods of enhanced geomagnetic activity accompanying earthward-streaming solar disturbances. With 10-minute advance warning of a probable onset of GICs, operators can implement nonloss-of-service countermeasures to protect their systems from the destructive effects of GICs1-3. The goal of the research proposed here is to develop and validate a forecasting model that can be used by the NOAA Space Environment Center (SEC), in concert with power distribution system operators, to provide accurate advance warning.

 The proximate causes of GICs are fast, intense variations in the auroral electrojets—powerful zonal electric currents that flow in the ionosphere and that induce surface electric fields and ground potential variations at the polar, auroral, and subauroral latitudes spanning Canada and the northern United States. At Dartmouth, we now have a unique capability to calculate the auroral electrojets from a global magnetohydrodynamic (Lyon-Fedder-Mobary) model of the coupled solar wind-magnetosphere-ionosphere system using the real-time ACE data stream posted on the SEC web site. The simulation model can run with 1-minute lag relative to the SEC/ACE data stream, producing a 2-minute resolution output stream of ionospheric currents on a 2° latitude ´ 10° longitude spatial grid at geomagnetic latitudes greater than 45°. Depending on the solar wind speed, the simulation can provide a 15-60 minute forecast of ionospheric currents, corresponding to the time of transit of the solar wind from the ACE satellite L1 orbit to the earth’s subsolar magnetopause.

In the first phase of this research project, the provisional accuracy of the LFM model will be evaluated by calculating the ground-surface magnetic fields induced by the simulated ionospheric currents, initially assuming the earth to be a perfect conductor, i.e., an idealized version of the Maxwell boundary value problem. This validation process will be conducted for selected time intervals and events under the auspices of the “Auroral Electrojet Prediction and Nowcast Challenge,” a research-community initiative with the objectives of collecting and comparing ground-based magnetometer and model simulation data. Should the comparison between actual and simulated ground magnetic measurements reveal significant inadequacies in the existing LFM approach, further model development may be required. The feasibility of using a simplified model for the ionospheric currents, e.g. a three-parameter electrojet model4-5 will also be assessed. The second phase of work will make use of electrical impedance models for the earth’s crust based on existing empirical data to calculate the surface electric fields induced by electrojet currents, taking into account coastal geography, igneous rock formations, etc. Research engineers from the American Electric Power Company of Ohio have expressed interest in participating with us in a benchmark study of GIC model predictions, and prospective GIC data from the Sunburst 2000 project (www.gic2000.com) involving an international consortium of 18 power companies may also be available for validation studies. Algorithms for forecasting the auroral electrojets will be ported to NOAA/SEC.

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1 Geomagnetic Storms Can Threaten Electric Power Grid, J.G. Kappenman, L.J. Zanetti, and W.A. Radasky, Earth in Space, Vol. 9, No. 7, March 1997, pp.9-11, 1997.

2Shielding grids from solar storms, T.S. Molinski, W.E. Feero, and B.L. Damsky, IEEE Spectrum, Vol. 37 No. 11, pp. 55-60, 2000. [426 kB]

3The effects of geomagnetic disturbances on electrical systems at the earth’s surface, D.H. Boteler, R.J. Pirjola, and H. Nevanlinna, Advances in Space Research, Vol. 22, No. 1, pp. 17-27, 1998. [1 MB]

4On calculating the electric and magnetic fields produced in technological systems at the earth’s surface by a “wide” electroject, D.H. Boteler, R.J. Pirjola, and L. Trichtchenko, J. Atmos. Solar-Terrestrial Phys., Vol. 62, pp. 1311-1315, 2000. [126 kB]

5Prediction of geomagnetically induced currents in power transmission systems, R. Pirjola, D.H. Boteler, A. Viljanen, and O. Amm, Advances in Space Research, Vol. 26, No. 1, pp. 5-14, 2000. [650 kB]

 

BIBLIOGRAPHY

Telluric currents: The natural environment and interactions with man-made systems, L.J. Lanzerotti and G.P. Gregori, in The Earth’s Electrical Environment, National Academy Press, Washinton, D.C., pp.232-258, 1986. [57 kB]

Space Weather: Hazard to Earth? F. Jansen, R. Pirjola, and R. Favre, Swiss Re Publishing, Zurich, 2000. [1.7 MB]

Space Weather: Physics and forecasts, J. Luhmann, Physics World, Vol. 13, Issue 7, pp. 31-36, 2000.

 

LINKS

Finnish Metereological Institute                                  

GIC Homepage