The strength of magnetic storms can be quantified using the so-called K-index. The index can assume values on the scale from 0 to 9. At values from 0 to 3, the index bars are colored in green (the field is calm), at 4 – yellow (attention) – disturbances are observed in the field, at values ≥ 5 – the bars are colored in red – a storm has been registered. Information on the local geomagnetic K-indices according to PGO Panagyurishte for each year can be accessed on the following page .