| 月份 | 面积指数 | 西伸脊点(E) | 脊线位置(N) | ||||||
| 30年平均 | 1998 | 2017 | 30年平均 | 1998 | 2017 | 30年平均 | 1998 | 2017 | |
| 1 | 34 | 148 | 45 | 145.5 | 90 | 125.0 | 7.9 | 17.4 | 18.3 |
| 2 | 25 | 134 | 52 | 151.4 | 90 | 132.5 | 6.5 | 16.5 | 17.3 |
| 3 | 39 | 144 | 57 | 132.8 | 90 | 120.0 | 10.1 | 17.3 | 16.9 |
| 4 | 53 | 142 | 147 | 119.8 | 90 | 95.0 | 14.1 | 18.4 | 17.1 |
| 5 | 67 | 170 | 198 | 121.3 | 90 | 92.5 | 17 | 19.2 | 18.6 |
| 6 | 115 | 237 | 223 | 123.7 | 97.5 | 110.0 | 21.5 | 20.4 | 20.7 |