What happened
A study published in Space Weather says geomagnetic storms can stress power grids in a slower and less visible way than the usual sharp current spikes. The study examined the severe June 2015 storm over New Zealand and found that geomagnetically induced currents rose gradually for about 90 minutes and reached only about 20 amperes, yet remained long enough to pose transformer risks.
The research team used multiple datasets and Transpower New Zealand measurements. The team linked the pattern to a possible mid-latitude ionospheric current wedge, in which part of the ring current was diverted into the ionosphere.
Why the finding matters
The study suggests that current storm-assessment tools may miss hazards when geomagnetic disturbance does not appear as a brief spike. The current pattern did not match conventional indicators such as H', which means grid operators may need broader screening methods for prolonged current exposure.
The risk depends not only on the solar event but also on local ground conductivity and power-line layout. That makes grid protection a problem of both space-weather forecasting and infrastructure design.