A new parameter of geomagnetic storms for the severity of space weather

Using the continuous Dst data available since 1957 and H component data for the Carrington space weather event of 1859, the paper shows that the mean value of Dst during the main phase of geomagnetic storms, called mean Dst(MP), is a unique parameter that can indicate the severity of space weather. All storms having high mean Dst(MP) (<=-250 nT), which corresponds to high amount of energy input in the magnetosphere-ionosphere system in short duration, are found associated with severe space weather events that caused all known electric power outages and telegraph system failures.