| 年代际 | 春季 | 夏季 | 秋季 | 冬季 | 全年 | |||||
| MEAN | STD | MEAN | STD | MEAN | STD | MEAN | STD | MEAN | STD | |
| 1951~1959 | 23.2 | 4.3 | 28.3 | 1.3 | 24.4 | 3.3 | 16.5 | 3.4 | 23.2 | 5.3 |
| 1960~1969 | 23.2 | 4.1 | 28.4 | 1.3 | 24.6 | 3.1 | 16.3 | 3.7 | 23.1 | 5.5 |
| 1970~1979 | 23.2 | 4.2 | 28.3 | 1.4 | 23.9 | 3.7 | 16.4 | 3.6 | 23.0 | 5.4 |
| 1980~1989 | 23.0 | 4.4 | 28.6 | 1.4 | 24.7 | 3.3 | 16.3 | 3.4 | 23.2 | 5.6 |
| 1990~1999 | 23.4 | 4.2 | 28.9 | 1.4 | 25.1 | 3.1 | 17.1 | 3.5 | 23.6 | 5.3 |
| 2000~2009 | 23.6 | 4.1 | 28.6 | 1.4 | 24.6 | 3.3 | 17.0 | 3.7 | 23.5 | 5.3 |