On March 9, 1989, a huge cloud of solar material exploded from the sun, twisting toward Earth. When this cloud of magnetized solar material – called a coronal mass ejection, or CME – reached our planet, it set off a chain of events in near-Earth space that ultimately knocked out power to the Canadian province Quebec for about nine hours. Though CMEs hit Earth often, those with the potential to shut down an entire power grid are rare – and scientists want to make sure that next time, we're prepared.
Because space weather can have – at its very worst – such significant consequences, scientists from NASA's Goddard Space Flight Center in Greenbelt, Maryland, are creating models to simulate how space weather can impact our power grid. Scientists developing this next-generation project – called Solar Shield – have recently incorporated six test sites around the country, where they compare computer simulations of forecasted space weather impacts with the actual observations on the ground. Solar Shield, which combines research efforts from several agencies, is supported by the Department of Homeland Security Science and Technology directorate. Simulations – like those used by the Solar Shield project – can ultimately be used to improve operational space weather forecasts, such as those issued by NOAA's Space Weather Prediction Center, the U.S. government's official source for space weather forecasts.
"We really want to create models that accurately show incoming space weather," said Antti Pulkkinen, a research astrophysicist at Goddard, and the lead of the Solar Shield project. "That way, space weather forecasters can provide the grid operators the information they need to know what's happening when they start seeing weird fluctuations in the power grid."
To create better protection for power grids, the Solar Shield project must take into account not just what's happening on Earth, but what's happening on the sun and in the space in between.
When the most intense CMEs and solar wind streams hit Earth's magnetic bubble, the magnetosphere, it can start to rattle violently, changing the strength and direction of the magnetic field in different places on Earth. But such severe geomagnetic storms, as they are called, only happen in certain circumstances.
"One of the problems we need to solve is predicting the direction of the magnetic field embedded in a CME," said Pulkkinen. "They only generate major storms within the magnetosphere if they're pointed opposite Earth's magnetic field when they hit – otherwise, it may give an initial punch and then just kind of fizzle."
If the storm is particularly strong, however, our power grids may need some protection. The quick-changing magnetic fields in the magnetosphere can create electric currents at Earth's surface, called geomagnetically induced currents, or GICs. Because much of our planet is criss-crossed with long metal structures – from oil pipelines beneath the surface to power lines yards above our heads – these electric currents have perfect, wire-like pathways that allow them to flow across long distances. For example, a powerful geomagnetic storm in 1859, known as the Carrington Event, caused GICs so strong that telegraph wires were unable to handle the huge amount of electricity, interrupting communications.
The consequences of GICs in modern power lines are more direct. In order to transmit power effectively, there must be the right combination of voltage and current in power lines. The extra current of GICs can disrupt this balance, possibly resulting in stressed transformers or voltage collapse. The GICs brought on by the March 1989 geomagnetic storm introduced so much extra current to the Quebec power grid that protective relays were tripped and the voltage collapsed.
To better understand what space weather situations cause the most intense GICs, scientists working on Solar Shield use CME measurements, solar wind observations, and other physical parameters to model the timing, location, and strength of the GICs. Using pictures of CMEs from a special type of instrument called a coronagraph – which blocks out the overwhelmingly bright disk of the sun, allowing us to see the comparatively faint atmosphere, known as the corona – they estimate the size, speed and direction of these CMEs, one of the driving forces behind geomagnetic storms. Measurements of fast solar wind streams currently come from NASA's Advanced Composition Explorer, or ACE, which resides between us and the sun at a distance of about a million miles from Earth. Solar wind data from NOAA's Deep Space Climate Observatory, launched in 2015, will replace ACE data later this year.
Scientists input their estimates of the characteristics of these solar events into computer models, which simulate when, where, and at what speed the solar material will strike Earth, as well as the location and strength of the resulting induced currents. The models that Solar Shield scientists use are tested and validated at the Community Coordinated Modeling Center, or CCMC, at Goddard. Once they have GIC simulations from the model, scientists compare them to measurements taken at six power substations around the U.S. By comparing the predicted characteristics with the actual characteristics of the GICs, scientists can improve the Solar Shield simulations.
With accurate advance warning, power engineers have quite a few options to protect the grid. With a day or two of notice, power grid companies can alter maintenance schedules to make sure that as many critical lines are up and running as possible. Even with just 20 minutes of lead time – which is how long it could take for a CME to travel from our advanced warning satellite to Earth, a distance of nearly a million miles – grid operators can take steps to prevent blackouts and damage. One such step is injecting reserve power into the system, helping to stabilize the system voltage.
As projects like Solar Shield help improve our space weather models, the hope is that forecasting will improve just as terrestrial weather forecasts have improved, and – like meteorologists who fine tune their warnings of hurricanes as the storm waxes and wanes – space weather prediction can provide highly accurate details on the force of any incoming solar storm.
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