Geomagnetic variations and their time derivatives during geomagnetic storms at different levels of intensity

The latitudinal distributions of horizontal geomagnetic variations, ΔH, and their time derivatives, ∂H/∂t, were analysed statistically over the three-year period 2003–2005. It appears that the amplitude distributions of horizontal geomagnetic variations and their time derivatives differ systematically between different geomagnetic latitudes and storm intensity levels. We show that the magnetic field variations observed at auroral and polar cap latitudes are under all geomagnetic storm levels comparable in amplitude (in a statistical sense) while they are smaller at subauroral latitudes. In contrast, their time derivatives are clearly the largest at auroral latitudes at all storm levels. These distributions determine in a general sense where and with which probability technological systems and operational procedures may be affected by geomagnetic storms. However, one observes in individual cases that the peak ∂H/∂t (the largest in all horizontal directions) is not necessarily the one which triggers a power system blackout.