CHGRES_CUBE and vertical velocity

[GeorgeGayno-NOAA]

Russ had problems running the model when using tiled, warm restart data as input to chgres. He noticed large vertical velocities in the log file. He wrote:

 The C384L127 forecast from the chgres'd C768L127 files failed.   
 I noticed the following in the forecast job log file:

 W max =    3842.734      min =   -2243.542
 Before adi: W max =    3842.734      min =   -2243.542

Because chgres works with both the old spectral model (which output omega) and fv3 (which outputs 'w'), logic was added to the model to convert from omega to 'w' depending on the source of the chgres'd data. The source is identified via a global attribute. The conversion is done in routine routine external_ic.F90. The problem is that the logic does thinks data from warm restart files is 'omega', not 'w'. After discussing with Fanglin and Jun, it was decided to have chgres zero out 'w' for tiled input data instead of updating routine external_ic.F90. According to Fanglin:

Changing resolution from high-res tiles to low_res tiles may produce 
strong w that the low-res model can’t sustain. I think it is better to zero it out. 

[GeorgeGayno-NOAA]

Zero out vertical velocity when using tiled history files and tiled warm restart files as input to chgres_cube. The feature/chgres_cube_w branch was successfully compiled on Jet, Hera, Dell and Cray. The regression tests were also run on those machines. As expected, the "c192_fv3_history" and "c96_fv3_restart" tests failed (the vertical velocity records were different). Will update the baseline regression test data on the four machines. Merging to develop.

[GeorgeGayno-NOAA]

Work complete. Closing.