timestamp radiation physics

Radiation physics is not calculated for each time step but at intervals radt. I have set radt to 15 minutes and WRF output interval (history interval) to 5 minutes. Starting the WRF run at 9:00, the radiation physics will be updated at 9:00, 9:15, 9:30 etc.
WRF output is written to file at 9:00, 9:05, 9:10, etc.
In the output file I find that parameters associated to radiation physics, such as COSZEN, SWDDDIR and SWDDIF have the same value for 3 consequtive times, e.g. 9:05, 9:10, 9:15 or 9:20, 9:25 and 9:30.
This is rather puzzling to me.
It seems that output values at 9:05, 9:10 and 9:15 all have been calculated during the radiation physics update at 9:00.
I conclude that parameter output values at 9:15, 9:30, 9:45, etc have been calculated during the radiation physics update 15 minutes earlier.
Can someone confirm this finding, or provide clarification?
Is the 9:00 radiation physics update excuted after WRF parameters for the 9:00 timestamp have been written to file?

Hi,

Your interpretation of the radiation results is correct. Note that radiation is the first physics scheme that is called once WRF starts. wrfout at intiialtial time is written before all the variables are updated. Similarly, all wrfout files are written out at the specified history output time before the variables are updated at this time. The model will then update everything and these updates will show in the next wrfout file.

In your case, radiation scheme is called at 9:00 but the updates will be shown in wrfout files at 9:05, 9:10, and 9:15. At 9:15, the radiation is called again and updates are present in wrfout files at 9:20, 9:25 and 9:30.

Dear Ming Chen
Thanks for the clear answer.
Could you help me on a consequence of the radiation update times.
In the morning - before noon - the solar radiation will increase gradually, whereas in the afternoon the solar radiation will decrease between radiation updates. As the radiation is fixed for a period radt, the influx of solar energy will too low in the morning and too high in the afternoon. Assuming 6 hours between 0 and maximum and again 6 hours to zero again, and radt is 15 minutes, I would expect a systematic difference of 2 - 5 % for each interval of duration radt.
I suppose the energy shortage in the morning and surplus the afternoon will have an impact on the weather forecast.
Questions:
1. which parameters are influenced most?
2. does WRF include code to mitigate this effect?
Regards, Gerard