Figure 2.

Cycle average of number of days that has been spent in each space-weather situation during solar cycle 17 to 23. Note: Cycle average was calculated based on daily Ap index, but because the location of auroral oval can be determined by Kp, measurements were interpreted as equal amounts of Kp. Constructed based on the Kp and Ap data from National Oceanic and Atmospheric Association (NOAA) [12] by the kind permission of NOAA.

Sajedi and Abdollahi BMC Neurology 2012 12:100   doi:10.1186/1471-2377-12-100
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