A.Pulkkinen Establishing the Geomagnetic Disturbance Benchmark Event for Evaluation of the Space Weather Hazard on Power Grids NASA Goddard Space Flight Center S pace W eather R esearch C enter

Background Following the FERC Order No. 779, NERC is coordinating the development of geomagnetic disturbance (GMD) standards.Following the FERC Order No. 779, NERC is coordinating the development of geomagnetic disturbance (GMD) standards. The space physical and geophysical extreme event analyses are the foundation for subsequent engineering analyses.The space physical and geophysical extreme event analyses are the foundation for subsequent engineering analyses. The question about extreme GIC of interest also from the basic science viewpoint. The extreme event studies challenge our understanding of the space weather phenomena.The question about extreme GIC of interest also from the basic science viewpoint. The extreme event studies challenge our understanding of the space weather phenomena.

Requirements for the GMD scenario Science side needs to provide information about a physical parameter that is directly applicable to further engineering analyses. (geoelectric field)Science side needs to provide information about a physical parameter that is directly applicable to further engineering analyses. (geoelectric field) We need to address the following key characteristics of the extreme geoelectric fields:We need to address the following key characteristics of the extreme geoelectric fields: i. Amplitude. Amplitude. ii. Spatial structure including directionality and appropriate spatial scale lengths. Spatial structure including directionality and appropriate spatial scale lengths. iii. Temporal waveform. Temporal waveform. Science analyses also need to characterize the occurrence rates of i-iii.Science analyses also need to characterize the occurrence rates of i-iii. (Element 1) (Element 2) (Element 3)

Key ingredients from the geophysical standpoint The geomagnetic induction process that generates the geoelectric field is dependent on external and internal factors:The geomagnetic induction process that generates the geoelectric field is dependent on external and internal factors:  Many different near space electric currents systems contribute to driving of geomagnetic induction. The effect of the geomagnetic latitude needs to be taken into account. Many different near space electric currents systems contribute to driving of geomagnetic induction. The effect of the geomagnetic latitude needs to be taken into account.  The local ground conductivity dictates the ground response. Local geology needs to be taken into account. The local ground conductivity dictates the ground response. Local geology needs to be taken into account. (Element 4) (Element 5)

Spatial scales Spatial structure of storm-time high-latitude geoelectric fields can be very complex.Spatial structure of storm-time high-latitude geoelectric fields can be very complex. Spatiotemporally localized geoelectric field features are common.Spatiotemporally localized geoelectric field features are common. Snapshot of the March 1989 storm (1-min global data)

Spatial scales Since wide-area effects caused by a severe GMD are of main interest, we need to approach the statistics from a new angle  spatially averaged fields.Since wide-area effects caused by a severe GMD are of main interest, we need to approach the statistics from a new angle  spatially averaged fields. Occurrence of spatially averaged ~500 km scale high-latitude geoelectric field amplitudes (data for used) Visual extrapolation to 1-in- 100 year amplitudes

Proposed approach for the GMD scenario Element 1: amplitude Element 2: spatial structure Element 3: reference temporal waveform Element 4: geomagnetic latitude dependence Element 5: depedence on the local ground conductivityElement 5: depedence on the local ground conductivity Data acknowledgements: USGS, NRCan, FMI Scaling factor for the drop between deg Scaling factors for different physiographic regions

Summary GMD scenarios are necessary for engineering analyses of the GIC impact.GMD scenarios are necessary for engineering analyses of the GIC impact. Inclusion of appropriate spatial scales of the geomagnetic induction phenomenon is important for the hazards assessments.Inclusion of appropriate spatial scales of the geomagnetic induction phenomenon is important for the hazards assessments. NERC GMD Standards Drafting Team has proposed an approach that addresses 5 key elements of the GIC phenomenon – white papers on the topic will be posted soon.NERC GMD Standards Drafting Team has proposed an approach that addresses 5 key elements of the GIC phenomenon – white papers on the topic will be posted soon.