Year | gm∙cm−2 |
1996 | 1.96 |
1997 | 2.01 |
1998 | 2.06 |
1999 | 2.01 |
2000 | 2.00 |
2001 | 2.03 |
2002 | 2.05 |
2003 | 2.05 |
2004 | 2.04 |
2005 | 2.07 |
2006 | 2.05 |
2007 | 2.06 |