dtc/develop: final PR before merging to develop or master (fractional landmask changes)

[climbfuji]

Contains the following PR:

• Changing ice fraction definition (Changing ice fraction definition #398)

Also:

• removed unused argument kdt, recently introduced, from MP Thompson

Associated PRs:

NOAA-EMC/NEMS#43
#409
NCAR/fv3atm#31
NCAR/ufs-weather-model#28

For regression testing info, see NCAR/ufs-weather-model#28.

[grantfirl]

This looks fine to me. IMO, it would be super helpful to have good documentation for how the fractional sea/land/ice mask is implemented -- perhaps as part of the CCPP scientific documentation. Something like a flow chart would do wonders for understanding the implementation. If the logic can be replaced by "subcolumn" functionality in the CCPP framework, then such documentation may not be necessary, however. This is not a request for changes, just something to keep in mind as potential future work for somebody with a good understanding of this (or who wants to develop one).

[climbfuji]

This looks fine to me. IMO, it would be super helpful to have good documentation for how the fractional sea/land/ice mask is implemented -- perhaps as part of the CCPP scientific documentation. Something like a flow chart would do wonders for understanding the implementation. If the logic can be replaced by "subcolumn" functionality in the CCPP framework, then such documentation may not be necessary, however. This is not a request for changes, just something to keep in mind as potential future work for somebody with a good understanding of this (or who wants to develop one).

Can't agree more. @shansun6 .