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Table 1 Occurrence of solar flares of different classes (C, M, X) as observed by GOES for the periods of data analysis (*low solar activity, **moderate solar activity) together with the average sunspot numbers for each year

From: Solar flare effects on D-region ionosphere using VLF measurements during low- and high-solar activity phases of solar cycle 24

Months Average sunspot no. (R z ) Number of flares
C M X
*December 2006 13.6 53 5 4
*January 2007–December 2007 7.5 72 10 0
*January 2008–December 2008 2.9 13 2 0
*January 2009–December 2009 3.1 5 0 0
*January 2010–December 2010 16.5 54 10 0
**January 2012–December 2012 57.7 680 70 6
**January 2013–December 2013 64.9 671 47 8
Total   1548 144 18