Warn users when projection is inappropriate for GWD_OPT=1

[davegill]

TYPE: new feature

KEYWORDS: gwd_opt, projection

SOURCE: internal

DESCRIPTION OF CHANGES:

Assume that the user is trying to use gravity wave drag (GWD), gwd_opt=1 in the ARW model. For domain 1, if the projection has a large rotation angle anywhere within the domain ("rotation" is directly from the sina variable in the WRF input and output, and "large" means greater than a default value of 22.5 degrees), notify the user and stop. The original GWD data has information at 45 degree angles. Therefore anything larger than a 22.5 degree projection rotation (usually only violated in parts of the domain) means that the wind components are using the wrong topographic directional information.

For the determined user, the namelist variable max_rot_angle_gwd = 100 (really, anything greater than 90) will always permit GWD to be used, regardless of the projection.

How to estimate that the domain will or will not work within the 22.5 degree restriction:

1. Only be concerned with d01
2. If the pole is in the domain AND this is not a global projection - the domain will not work
3. Look at the SINALPHA field from metgrid (SINA field from wrfinput). SIN(22.5) = 0.38. If the SINALPHA or SINA fields have values greater than 0.38, the WRF model will gracefully stop
4. A regular lat/lon or a Mercator projection will always work

LIST OF MODIFIED FILES:

M dyn_em/start_em.F

TESTS CONDUCTED:

• Reggie 3.07, passed
• Test GSD RAP domain - it does not allow gwd_opt=1

Max projection rotation angle for domain 1 = 90.00
This projection may not be appropriate for using the gravity wave drag option.
In namelist.input make one of the two following changes:
 1) gwd_opt = 0
 2) max_rot_angle_gwd > 90.00
-------------- FATAL CALLED ---------------
FATAL CALLED FROM FILE:  <stdin>  LINE:     196
--- ERROR: gwd_opt does not work with this domain
-------------------------------------------

For a domain above the pole, to use gwd_opt=1 NO MATTER WHAT:

&dynamics
 gwd_opt                             = 1
 max_rot_angle_gwd                   = 100
/

[davegill]

swap the degrees for the sin of the variable that is max allowed

[davegill]

ask Jimy for a reasonable value

[dudhia]

yes, we discussed 22.5 degrees as the data is every 45 degrees of rotation.

…

On Fri, Mar 24, 2017 at 11:20 AM, Dave Gill ***@***.***> wrote: ask Jimy for a reasonable value — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#208 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/ARGf_J18caTDBdMcXwMMZviRxn-zJXR0ks5ro_tDgaJpZM4MnisT> .

[jamiebresch]

max_sa? Do you mean max_rot_angle?

[davegill]

@jamiebresch
My test was serial, so I never saw this compiler oops
Thanks

[davegill]

I ran this branch 4 times through the WTF v3.07. Each time it failed serial PGI for all of ARW. No compiler errors. I merged it to the repo top, and it passed. I am proposing the merged version #213