A recent study looked into why some large solar storms "slip by" human detection, potentially putting power supply and communication networks on Earth at risk.

The Tihany Magnetic Observatory registered a solar storm similar to the largest one on record while other observatories across the globe somehow missed the massive event, the Spanish Foundation for Science and Technology (FECYT) reported. In 1859 the largest and most powerful solar storm ever recorded, known as the Carrington Event, caused power outages and fires at telegraph system facilities across Europe and North America.

One of the most widely used indices for measuring geomagnetic storms is the Dst (Disturbance storm time), which is taken hourly and consists of averaging the data recorded at four observatories: Hermanus (South Africa), Kakioka (Japan), Honolulu (Hawaii, USA) and San Juan (Puerto Rico). A more precise version called SYM-H assesses the horizontal component of the Earth's magnetic field. The method uses data from more observatories and operates every minute. Neither of these widely used systems were able to detect the huge magnetic perturbation that hit the Earth on Oct. 29, 2003, which affected power plants in Sweden and South Africa.

"One of the conclusions is that the indices commonly used by scientists -such as Dst or SYM-H, which are based on an overall perspective of the Earth and obtained by calculating averages,- failed to detect such an important event, and they most likely would have failed to detect the Carrington Event as well," said Consuelo Cid, the lead author.

These solar events could evade scientists' detection because of a phenomenon in which positive and negative magnetic disturbances cancel each other out, leaving them almost invisible. The researchers have developed the Local Disturbance index for Spain (LDiñ), which calculates the geomagnetic perturbation in the region. The data is calculated based on the magnetic field recorded at the San Pablo Observatory in Toledo.

"An index similar to LDiñ could be used in [neighboring] countries, such as Portugal, France and Italy; likewise, indices adjusted to each region could be developed for use in other parts of the world]," Cid concluded.

The findings were published in a recent edition of the Journal of Space Weather and Space Climate.