We have downloaded grib2 files for GFS model from NOAA and extracted irradiance (Downwards shortwave radiation flux) data. Following is a sample output for cordinates at [52.0,4.0]:
| Timestamp | Value | | 2017-01-01T03:00:00 | 00 | | 2017-01-01T06:00:00 | 00 | | 2017-01-01T09:00:00 | 00 | | 2017-01-01T12:00:00 | 40 | | 2017-01-01T15:00:00 | 50 | | 2017-01-01T18:00:00 | 20 | | 2017-01-01T21:00:00 | 00 |
We know that the values are averaged. We doubt that the averaging is performed over a window of 3 hours such as the values between $hour$ and $(hour-3)$ are averaged and assigned to the timestamp at $hour$.
We haven't found any documentation explaining this fact. Can you please explain the principle behind averaging and timestamping? A reference will be very helpful.