| Months | A, W.m−2 | B, dimensionless | C, dimensionless |
| January 21 | 1230 | 0.142 | 0.058 |
| February 21 | 1215 | 0.144 | 0.060 |
| March 21 | 1185 | 0.156 | 0.071 |
| April 21 | 1135 | 0.180 | 0.097 |
| May 21 | 1103 | 0.196 | 0.121 |
| June 21 | 1088 | 0.205 | 0.134 |
| July 21 | 1085 | 0.207 | 0.136 |
| August 21 | 1107 | 0.201 | 0.122 |
| September 21 | 1151 | 0.177 | 0.092 |
| October 21 | 1192 | 0.160 | 0.073 |
| November 21 | 1220 | 0.149 | 0.063 |
| December 21 | 1233 | 0.142 | 0.057 |