TYPE: new feature

KEYWORDS: gwd_opt, projection

SOURCE: internal

DESCRIPTION OF CHANGES:

This PR supersedes PR #208, which was closed.

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^o), notify the user and stop. The original GWD data has information at four directions, each separated by 45^o angles. Therefore anything larger than a 22.5^o 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^o) 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^o 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^o) = 0.38. If the SINALPHA (or SINA) field has values greater than 0.38, the WRF model will gracefully stop. Internal to the code, if the projection angle > 22.5^o, the model stops.
4. A regular lat/lon or a Mercator projection will always work

LIST OF MODIFIED FILES:

M dyn_em/start_em.F
M Registry/Registry.EM_COMMON

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
/