The atmospheric DA applies IAU increments on temperature (among other variables), while the land surface increments are applied once at the start of the DA (cycle?) window. This could lead to the land surface (soil and snow) temperature being out of sync with near surface atmospheric temperature.
Solution
Add a Land IAU module to calculate increments for soil temperature. Later on, this can be extended to include snow temperature, and if necessary, the other soil and snow variables. The module’s functions will be called either from within the noahmpdrv ccpp scheme or right before the noahmpdrv run.
Alternatives
The existing atmospheric IAU module (fv_iau_mod.F90) can be modified with few additions for land, but because fv_iau_mod.F90 is part of the dynamical core there is strong resistance by repo owners. Having a separate land IAU module as part of ccpp’s Land_Model components (also closer to the schemes that use it) is a better option.
Description
The atmospheric DA applies IAU increments on temperature (among other variables), while the land surface increments are applied once at the start of the DA (cycle?) window. This could lead to the land surface (soil and snow) temperature being out of sync with near surface atmospheric temperature.
Solution
Add a Land IAU module to calculate increments for soil temperature. Later on, this can be extended to include snow temperature, and if necessary, the other soil and snow variables. The module’s functions will be called either from within the noahmpdrv ccpp scheme or right before the noahmpdrv run.
Alternatives
The existing atmospheric IAU module (fv_iau_mod.F90) can be modified with few additions for land, but because fv_iau_mod.F90 is part of the dynamical core there is strong resistance by repo owners. Having a separate land IAU module as part of ccpp’s Land_Model components (also closer to the schemes that use it) is a better option.
Dependent PRs: