Geomagnetic disturbances can be monitored by ground-based magnetic observatories recording the three magnetic field components. The global Kp index is obtained as the mean value of the disturbance levels in the two horizontal field components, observed at 13 selected, subauroral stations . ... Geomagnetic activity is the occurrence of K variations. ... But K still remains a local index, describing disturbances in the vicinity of each observatory. ...