Quantifying the solar cycle modulation of extreme space weather

This clock orders solar coronal activity and extremes of theaaindex, which tracks geomagnetic storms at the Earth's surface over the last 14 solar cycles. We identify geomagnetically quiet intervals that are 40% of the normalized cycle, +/- 2 pi/5 in phase or +/- 2.2 years around solar minimum.

Since 1868 only two severe (aa>300 nT) and one extreme (aa>500 nT) geomagnetic storms occurred in quiet intervals; 1-3% of severe (aa>300 nT) geomagnetic storms and 4-6% of C-, M-, and X-class solar flares occurred in quiet intervals. This provides quantitative support to planning resilience against space weather impacts since only a few percent of all severe storms occur in quiet intervals and their start and end times are quantifiable.