A comprehensive high‐throughput analysis of substorms observed by IMAGE magnetometer network: Years 1993–2003 examined

The annual and yearly variation of the substorm activity during a complete solar cycle, from year 1993 to year 2003, has been examined. Almost 6000 substorms were identified by an automated search engine. The identification method was found to be robust and applicable to all activity levels. To examine the long‐term (annual, yearly, and solar cycle) variability in the substorm occurrence rate, we formed a measure called the substorm number. The substorm number and peak amplitude were found to only weakly follow the Sun's activity measured by a sunspot number. During the years of sunspot maxima in the solar cycle 23, the Northern Hemisphere auroral region was only moderately active. The largest substorm numbers and peak amplitudes were found during the declining solar cycle phases when the interplanetary high‐speed streams hit the Earth. We found out that the substorms last longer during the least active season (i.e., summer months) and during the least active years (e.g., 1997 and 2001). Furthermore, the substorm number and peak amplitude show much larger values for winter than for summer, which may be partly due to the fact that the maximum southward component of the interplanetary magnetic field ( B south ) occurs in February and the minimum occurs in June.