Comparative ionospheric impacts and solar origins of nine strong geomagnetic storms in 2010–2015

Abstract

For nine of the strongest geomagnetic storms in solar cycle 24 we characterize, quantify, and compare the impacts on ionospheric total electron content (TEC) and the U.S. Wide Area Augmentation System (WAAS) with the heliospheric morphology and kinematics of the responsible coronal mass ejections (CMEs) and their solar source regions. Regional TEC responses to the events are similar in many respects, especially in the initial positive phase. For the subsequent negative phase, Dst is a better indicator than ap of the magnitude of the TEC decrease. The five events that arrive between 13:00 UT and 21:00 UT (local daytime in the U.S.) produce large WAAS degradations, and the four events that arrive outside this time of day produce lesser or no WAAS degradation. Our sample of geoeffective events includes CMEs with only modestly fast speeds, ones that only provided glancing impacts on Earth by their shock sheaths and ones not associated with any significant flare. While all of the CMEs traveled faster than the solar wind, they nevertheless have a wide range of velocities and produced a range of Bz values; neither speed nor Bz correlates significantly with ionospheric impact. Comparison with the locations of surface activity leads to estimates of deflection for the CMEs, with the average deflection being 19°. At least a few events may have missed Earth entirely in the absence of coronal deflection.