Quantifying the Solar Cycle Modulation of Extreme Space Weather
Abstract
By obtaining the analytic signal of daily sunspot numbers since 1818 we construct a new solar cycle phase clock that maps each of the last 18 solar cycles onto a single normalized 11 year epoch. This clock orders solar coronal activity and extremes of the aa index, 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, ±2π/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.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- Jun 08, 2020
- Source ID
- 10.1029/2020gl087795
Entities
People
- Nicholas W Watkins
- Robert Leamon
- S. W. Mcintosh
- Sandra Chapman
Organizations
- Air Force Office of Scientific Research
- Goddard Space Flight Center
- London School of Economics and Political Science
- National Center for Atmospheric Research
- Science and Technology Facilities Council
- The Open University
- University of Maryland
- University of Warwick