Forecasting the Impact of Space Weather on the Electrical Power Grid through Coupling of the Operational SWMF Geospace Model and the Joint NOAA/USGS Geoelectric Field Model

One of the well-known impacts of space weather is the induction of current in artificial conductors during strong-to-extreme geomagnetic storms. The physical phenomena causing this effect is the geoelectric field at the surface of the Earth, which drives the induced currents that impact our critical, ground-based infrastructure. Through an extended collaboration between NOAA/SWPC, USGS, NRCan and an extensive program to collect magneto-telluric surveys (i.e. the NSF funded USArray program and the NASA & USGS funded USMTArray program), it is now possible to estimate the geoelectric field over nearly all of the contiguous United States in near real-time using operational magnetic observatories over the U.S. and Canada. To accomplish this we interpolate the magnetometer data to each of the survey site locations, and then convolve the magnetic field time series with the surface impedance (a product of the survey), to calculate the geoelectric field. These geoelectric fields are resampled to a regular grid and are routinely provided to the public in as timely a manner as possible on the NOAA/SWPC web pages.

However, operators of the electric power grid would be able to respond much more effectively to the impact of these storms if they could get reliable warnings of impending activity in advance. Current space weather operational capability has been limited to the provision of advanced warnings of globally averaged activity indicators (e.g. the Kp index or other global indices), but the need for more specific, regional forecasts has motivated the space weather community and the SWPC to invest extensive resources into the development and operationalization of an advanced model for the complex magnetosphere-ionosphere system, namely the geospace model which is part of the University of Michigan’s space weather modeling framework (SWMF). Using upstream solar wind measurements and the F10.7 solar radio flux, the geospace model is able to provide forecasts of the magnetic field perturbations at the surface of the Earth. Therefore it is now possible to couple the geospace model with the geoelectric field model to investigate our ability to predict the geoelectric field and to determine if there is a sufficiently reliable predictive signal in the coupled models to inform user actions in advance of impending activity.

In this presentation, we use this framework to compare the forecasts with the nowcasts of the geoelectric field. While we find that the minute-by-minute variations typically do not have a high correlation level, we are able to device a probabilistic forecast by categorizing the maximum E-field level over a time window of fixed duration into discrete levels (i.e. an E-field index) and by developing contingency tables that indicate the probability distribution of observed activity levels, given a particular forecast activity level. The results allow us to make a probability forecast which an operator can then use to make an informed risk assessment based on objective information about the predictive performance of the end-to-end coupled model output.