New DA namelist alpha_vertloc_opt to choose how to get the alpha_vertloc info

[jamiebresch]

TYPE: enhancement

KEYWORDS: WRFDA, alpha_vertloc, alpha_vertloc_opt

SOURCE: Jamie Bresch (NCAR/MMM)

DESCRIPTION OF CHANGES:

PR #850 discussed about the issues in current var/gen_be/gen_be_vertloc.f90.
Instead of modifying the stand-alone var/gen_be/gen_be_vertloc.f90 utility that generates be.vertloc.dat, this PR proposes a simpler and better solution inside WRFDA.

1. A new namelist alpha_vertloc_opt is added to replace alpha_vertloc to choose how to handle
   vertical localization for EnVar applications.
   alpha_vertloc_opt=1, the behavior is the same as before, except that the new code now gives proper error message when be.vertloc.dat does not exist.
   alpha_vertloc_opt=2 (default, recommended), let WRFDA calculate logP-based vertical localization. be.vertloc.dat will be written out.
   alpha_vertloc_opt = 0, no vertical localization.
   alpha_vertloc_opt is only used when ensdim_alpha>0, so the alpha_vertloc_opt setting does not matter when ensdim_alpha=0.
2. frame/module_configure.F is modified to notify users about the obsolete alpha_vertloc option.
3. var/README.namelist is updated.

LIST OF MODIFIED FILES:
M Registry/registry.var
M frame/module_configure.F
M var/README.namelist
M var/build/depend.txt
A var/da/da_setup_structures/da_get_alpha_vertloc.inc
M var/da/da_setup_structures/da_setup_be_nmm_regional.inc
M var/da/da_setup_structures/da_setup_be_regional.inc
M var/da/da_setup_structures/da_setup_structures.f90

TESTS CONDUCTED:
A case to test the new code works as expected.

RELEASE NOTE: For EnVar DA applications, logical alpha_vertloc namelist switch is replaced by new integer option alpha_vertloc_opt with default=2. See var/README.namelist.

[jjguerrette]

I am thinking that only alpha_vertloc_opt is needed and not alpha_vertloc. @jamiebresch, do you think the logical on/off will help users very much?

[jamiebresch]

I did not touch alpha_vertloc in order to keep the change to a minimum.
The only benefit is that if a non-EnVar user has alpha_vertloc in the namelist, the new code still works.
alpha_vertloc can certainly be removed. I have no preference.

[jjguerrette]

I think alpha_vertloc can be removed. If alpha_vertloc_opt is set to a non-zero value for a non-EnVar application, WRFDA should quit with an informative error message.

[jjguerrette]

@jamiebresch, sorry for the delay on this one. The previous default was to have vertical localization turned off. I can see why that was not ideal. Should the release note state that the new default is to turn on the localization? Other than that, this looks ready to me.

[jjguerrette]

@liujake, note that the following REGTEST namelist entries need to be removed or changed to alpha_vertloc_opt=2:

namelist.input.4denvar_large_conus: alpha_vertloc = .true.,
namelist.input.dual_res_hybrid: alpha_vertloc = .true.,
namelist.input.realtime_hybrid: alpha_vertloc=.true.

The reference output will change as well. Or they can use alpha_vertloc_opt=1 and no change to references will be needed.