Geomagnetic storms over the last solar cycle: A superposed epoch analysis

• Published in: Journal of Geophysical Research: Space Physics Vol. 116; no. A9
• Main Authors: Hutchinson, J. A., Wright, D. M., Milan, S. E.
• Format: Journal Article
• Language: English
• Published: Washington Blackwell Publishing Ltd 01.09.2011
• Subjects: Astrophysics; Atmospheric sciences; CME/CIR storms; geomagnetic storms; Magnetism; Planetology; ring current; Space; storm occurrence; storm phase durations; Storms; superposed epoch analysis
• ISSN: 0148-0227; 2169-9380; 2156-2202; 2169-9402
• DOI: 10.1029/2011JA016463

Presented here is a discussion of the results of a superposed epoch analysis of geomagnetic storms over the last solar cycle. Storms, identified by means of their characteristic SYM‐H evolution, are separated by size into weak (−150 < SYM‐H ≤ −80) nT, moderate (−300 < SYM‐H ≤ −150) nT, and intense (SYM‐H ≤ −300) nT categories. Where possible, the corresponding solar wind (SW) onset mechanisms were located by means of 1 min ACE OMNI data. Intense storms were observed to be driven solely by coronal mass ejections (CMEs); moderate storms were dominated by CME onset, while only weak storms were driven by both CMEs and corotating interaction regions (CIRs) at a ratio of ∼2:1, respectively. As might be expected, more intense storms resulted from the largest SW enhancements. Individual storm phase durations for different storm sizes were investigated, revealing that the duration of the main phase increases with storm size to a critical point, then decreases for more intense storms, contrary to the findings of a previous study by Yokoyama and Kamide (1997). Various SW‐magnetosphere coupling functions were investigated for this data set in an attempt to estimate storm size from SW conditions. Key Points Presents a new trend seen in storm main phase durations with storm size in SYM‐H Uses a different superposition technique and compares to previous studies Shows superposed statistics in SYM‐H and ACE data, including CME/CIR comparisons