I have recently used the WRF-CMAQ model to simulate the regional AOD in China.My purpose was to validate the results of the WRF-CMAQ simulation based on the Himawari-8 hourly AOD data. I browsed the official userguide website and found that the AOD data of Himawari-8 was obtained at 500 nm (JAXA Himawari Monitor | User's Guide). However, the AOD results with WRF-CMAQ simulation was obtained at 295,303,310,316,333,380 and 574nm. I would like to ask you a question. According to the WRF-CMAQ simulation results, which nm AOD needs to be compared with the AOD of himawai-8 at 500nm?
Could you please clarify which version of WRF-CMAQ you are running, whether you are running the two-way coupled or offline version, and which output file you are obtaining the AOD data from? This doesn’t change the general answer below, but does change the specific variable names used in the example.
To obtain WRF-CMAQ AOD output at 500 nm, you can use Angstrom interpolation between AOD values for the two adjacent wavelengths present in your output, i.e. 380 nm and 574 nm. To do so, first you would compute the Angstrom coefficient:
ANGSTROM380_578 = -1*(log(AOD_380/AOD_574)/log(380./574.))
Next, you would use that coefficient to do the actual interpolation to 500 nm:
AOD_500 = AOD_380*((500./380.)^(-ANGSTROM380_578))
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Thank you very much for your answer, it was very useful for me. The version of WRF-CMAQ I am running is 5.0 with two-way coupled. I got the AOD results in RJ_1_2019-07-01.nc.
If you are running WRF-CMAQ5.0 two-way coupled, you should also have AOD output in the wrfout files, and the wavelengths for which they are available are a bit closer to your target of 500 nm than the photolysis-wavelength-based values in the RJ_1 files that stem from the CMAQ photolysis calculations.
Specifically, the variables SW_TTAUXAR_## in the wrfout files contain AOD as calculated by the two-way radiation code, with the following wavelength assignments:
SW_TTAUXAR_01 = 388 nm
SW_TTAUXAR_02 = 533 nm
SW_TTAUXAR_03 = 702 nm
SW_TTAUXAR_04 = 1010 nm
SW_TTAUXAR_05 = 1271 nm
So, in this case you could do the following:
ANGSTROM388_533 = -1*(log(SW_TTAUXAR_01/SW_TTAUXAR_02)/log(388./533.))
AOD_500 = SW_TTAUXAR_01*((500./388.)^(-ANGSTROM388_533))
Note that the calculations in the two-way coupled radiation code and the CMAQ photolysis code are not identical, so the estimated 500 nm AOD will be different depending on which set of variables you work with.
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Thank you very much for your answer. According to your description, I didn’t find the SW_TTAUXAR_### variable in the wrfout files. There might be something wrong with my previous answer. I actually use the WRF-CMAQ Adjoint Forward model. The version of WRF-CMAQ Adjoint Forward model I am running is 5.0 with two-way coupled. The question I would like to ask is whether the results obtained by WRF-CMAQ Adjoint Forward model are consistent with the results of the WRF-CMAQ model? Is my failure to find the variables you mentioned because of the WRF-CMAQ Adjoint Forward model I used?
Unfortunately, I have no familiarity with the WRF-CMAQ v5.0 Adjoint model and how it relates to the WRF-CMAQ5.0 two-way coupled model. If you don’t have these SW_TTAUXAR_## variables in your wrfout files, you’ll need to fall back to the variables from the RJ_1 files.
Special thanks for your answer.