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| 年 | 1月 | 2月 | 3月 | 4月 | 5月 | 6月 | 7月 | 8月 | 9月 | 10月 | 11月 | 12月 | 平均 |
| 1995 | 6.1 | 6.2 | 9.8 | 14.6 | 18.9 | 22.1 | 27.5 | 30.3 | 24.2 | 19.9 | 12.1 | 7.2 | 16.6 |
| 1996 | 6.3 | 5.2 | 8.9 | 12.7 | 19.6 | 23.4 | 27.5 | 28.3 | 23.3 | 18.5 | 13.7 | 8.7 | 16.3 |
| 1997 | 6.0 | 5.8 | 10.1 | 15.1 | 19.9 | 23.7 | 26.7 | 28.5 | 24.3 | 18.2 | 14.1 | 8.9 | 16.8 |
| 1998 | 5.9 | 7.8 | 10.6 | 17.7 | 21.6 | 23.3 | 27.8 | 29.4 | 25.6 | 20.8 | 13.7 | 9.8 | 17.8 |
| 1999 | 6.4 | 5.9 | 10.6 | 14.7 | 20.5 | 23.5 | 26.8 | 29.1 | 27.2 | 20.1 | 14.1 | 8.7 | 17.3 |
| 2000 | 7.0 | 4.9 | 8.9 | 14.6 | 20.7 | 23.3 | 28.7 | 29.6 | 25.8 | 19.7 | 14.6 | 8.8 | 17.2 |
| 2001 | 5.2 | 6.6 | 9.7 | 15.5 | 20.6 | 24.0 | 29.2 | 28.8 | 24.4 | 19.5 | 13.2 | 8.3 | 17.1 |
| 2002 | 7.2 | 7.3 | 11.6 | 16.6 | 20.0 | 23.6 | 29.0 | 29.0 | 25.1 | 18.9 | 11.1 | 8.2 | 17.3 |
| 2003 | 5.1 | 6.8 | 8.4 | 15.9 | 20.2 | 23.7 | 25.3 | 28.3 | 25.9 | 18.1 | 15.5 | 9.1 | 16.9 |
| 2004 | 5.8 | 7.9 | 10.2 | 16.4 | 21.1 | 24.8 | 29.5 | 28.4 | 26.2 | 19.0 | 15.2 | 10.2 | 17.9 |
| 2005 | 6.2 | 6.1 | 9.2 | 16.2 | 19.5 | 24.9 | 27.5 | 28.7 | 26.1 | 19.8 | 13.7 | 5.9 | 17.0 |
| 2006 | 5.5 | 6.7 | 8.6 | 13.6 | 19.7 | 24.3 | 27.2 | 29.8 | 24.6 | 20.4 | 14.8 | 9.1 | 17.0 |
| 2007 | 7.5 | 8.7 | 10.1 | 14.6 | 19.8 | 23.6 | 25.9 | 29.9 | - | - | - | - | 15.7 |
| 平均 | 6.2 | 6.6 | 9.7 | 15.2 | 20.2 | 23.7 | 27.6 | 29.0 | 25.2 | 19.4 | 13.8 | 8.6 | 17.0 |
