Year Month SOI 1999 1 15.36 1999 2 8.53 1999 3 9.61 1999 4 18.72 1999 5 0.66 1999 6 0.39 1999 7 4.93 1999 8 2.57 1999 9 -0.11 1999 10 9.06 1999 11 12.59 1999 12 13.20 2000 1 4.54 2000 2 13.20 2000 3 9.39 2000 4 17.25 2000 5 3.97 2000 6 -5.57 2000 7 -4.16 2000 8 5.10 2000 9 10.09 2000 10 10.10 2000 11 22.23 2000 12 8.27 2001 1 8.51 2001 2 12.18 2001 3 6.33 2001 4 1.16 2001 5 -9.86 2001 6 2.47 2001 7 -3.70 2001 8 -8.60 2001 9 1.49 2001 10 -2.18 2001 11 8.11 2001 12 -9.21 2002 1 3.04 2002 2 7.48 2002 3 -5.56 2002 4 -4.40 2002 5 -15.18 2002 6 -6.72 2002 7 -7.46 2002 8 -14.99 2002 9 -7.84 2002 10 -7.23 2002 11 -5.65 2002 12 -10.97 2003 1 -1.74 2003 2 -7.81 2003 3 -6.92 2003 4 -5.67 2003 5 -7.04 2003 6 -13.06 2003 7 2.82 2003 8 -1.45 2003 9 -2.05 2003 10 -2.21 2003 11 -3.12 2003 12 9.78 2004 1 -11.86 2004 2 9.26 2004 3 0.93 2004 4 -15.84 2004 5 12.77 2004 6 -15.30 2004 7 -7.11 2004 8 -7.67 2004 9 -2.99 2004 10 -3.42 2004 11 -8.54 2004 12 -8.24 2005 1 1.97 2005 2 -28.68 2005 3 -0.11 2005 4 -11.39 2005 5 -14.03 2005 6 2.30 2005 7 1.22 2005 8 -7.25 2005 9 3.46 2005 10 10.67 2005 11 -2.59 2005 12 0.07 2006 1 12.92 2006 2 0.13 2006 3 14.12 2006 4 14.50 2006 5 -9.26 2006 6 -6.34 2006 7 -9.69 2006 8 -14.95 2006 9 -5.14 2006 10 -15.62 2006 11 -1.06 2006 12 -3.53 2007 1 -7.79 2007 2 -2.40 2007 3 -1.13 2007 4 -3.54 2007 5 -3.33 2007 6 5.65 2007 7 -4.57 2007 8 2.19 2007 9 1.61 2007 10 5.94 2007 11 9.63 2007 12 14.68 2008 1 13.97 2008 2 21.38 2008 3 12.37 2008 4 4.87 2008 5 -4.50 2008 6 4.90 2008 7 2.06 2008 8 8.66 2008 9 13.51 2008 10 13.23 2008 11 17.15 2008 12 13.26 2009 1 9.11 2009 2 14.92 2009 3 0.14 2009 4 8.77 2009 5 -5.53 2009 6 -2.09 2009 7 1.78 2009 8 -4.45 2009 9 3.45 2009 10 -14.60 2009 11 -6.74 2009 12 -7.22 2010 1 -9.52 2010 2 -15.37 2010 3 -11.08 2010 4 14.44 2010 5 9.98 2010 6 2.43 2010 7 20.08 2010 8 18.22 2010 9 25.52 2010 10 18.20 2010 11 16.42 2010 12 27.03 2011 1 19.97 2011 2 22.56 2011 3 21.29 2011 4 25.73 2011 5 1.72 2011 6 1.58 2011 7 10.37 2011 8 2.03 2011 9 11.42 2011 10 8.37 2011 11 12.99 2011 12 22.98 2012 1 9.88 2012 2 2.37 2012 3 2.92 2012 4 -6.53 2012 5 -2.74 2012 6 -10.73 2012 7 -1.03 2012 8 -5.72 2012 9 2.88 2012 10 2.18 2012 11 3.92 2012 12 -6.13 2013 1 -0.29 2013 2 -3.80 2013 3 11.00 2013 4 0.66 2013 5 7.82 2013 6 13.25 2013 7 7.78 2013 8 -0.53 2013 9 4.66 2013 10 -2.26 2013 11 9.89 2013 12 0.47 2014 1 12.30 2014 2 -1.21 2014 3 -13.13 2014 4 8.09 2014 5 4.26 2014 6 -1.20 2014 7 -3.35 2014 8 -11.51 2014 9 -6.98 2014 10 -7.80 2014 11 -9.54 2014 12 -5.77 2015 1 -7.80 2015 2 0.54 2015 3 -11.28 2015 4 -3.40 2015 5 -14.05 2015 6 -11.85 2015 7 -14.84 2015 8 -20.14 2015 9 -17.14 2015 10 -20.10 2015 11 -4.57 2015 12 -1.85 2016 1 -20.29 2016 2 -19.27 2016 3 -5.10 2016 4 -21.49 2016 5 2.69 2016 6 5.25 2016 7 4.02 2016 8 4.65 2016 9 13.82 2016 10 -4.66 2016 11 0.04 2016 12 2.34 2017 1 1.32 2017 2 -2.00 2017 3 4.98 2017 4 -6.74 2017 5 0.26 2017 6 -10.36 2017 7 7.52 2017 8 3.10 2017 9 6.32 2017 10 9.46 2017 11 11.04 2017 12 -1.49 2018 1 9.35 2018 2 -6.30 2018 3 10.65 2018 4 4.42 2018 5 2.08 2018 6 -6.23 2018 7 1.43 2018 8 -6.70 2018 9 -9.77 2018 10 3.09 2018 11 0.26 2018 12 9.74 2019 1 -1.10 2019 2 -13.37 2019 3 -7.00 2019 4 -2.15