Add CAMtr_volume_mixing_ratio for SSPs (#1553)

TYPE: enhancement

KEYWORDS: CMIP6, GHG, SSP, climate, radiation

SOURCE: Jesus Fernandez (Instituto de Fisica de Cantabria CSIC-UC, Santander, Spain)

DESCRIPTION OF CHANGES:
Problem:
Missing GHG concentration files for the new Shared Socioeconomic Pathways used in CMIP6 and IPCC AR6 
([Meinshausen et al. 2020](https://doi.org/10.5194/gmd-13-3571-2020)). They are required to nest WRF into 
CMIP6 global models for future regional climate simulation.

Solution:
Add corresponding GHG concentration files using global average data provided via input4MIP (namely, via CSV files 
provided by https://greenhousegases.science.unimelb.edu.au). Note that yearly hemispheric averages are also 
available from this source, and also 15-degree resolution monthly values. These could be used to tailor GHG 
evolution files for a particular WRF domain (see the code used to generate these files in 
https://github.com/SantanderMetGroup/wrf-ghg-files/tree/v0.1.2). The files included in this PR are global averages, 
consistent with previous CAMtr RCP files.

The files are used as the existing RCP CAMtr files, by renaming or linking the appropriate file with the exact name 
CAMtr_volume_mixing_ratio in the WRF running directory. For this to work, WRF needs to be compiled with the macro 
`-DCLWRFGHG` and the long-wave radiation parameterization set to one of: RRTM, CAM, RRTMG (ra_lw_physics = 1, 
3, 4).

A successful reading of the files leads to messages such as the following at the beginning of the WRF standard output log:
```
d01 2033-12-27_00:00:00  CLWRF reading...: istatus:  0 idata: 1 year: 1765 co2:    277.913000000000      n2o:    274.372000000000      ch4:   738.986000000000
d01 2033-12-27_00:00:00  CLWRF reading...: istatus:  0 idata: 2 year: 1766 co2:    277.958000000000      n2o:    274.392000000000      ch4:   739.831000000000
d01 2033-12-27_00:00:00  CLWRF reading...: istatus:  0 idata: 3 year: 1767 co2:    278.017000000000      n2o:    274.426000000000      ch4:   740.729000000000
d01 2033-12-27_00:00:00  CLWRF reading...: istatus:  0 idata: 4 year: 1768 co2:    278.078000000000      n2o:    274.447000000000      ch4:   741.222000000000
```

LIST OF MODIFIED FILES: 

M       run/README.physics_files
A       run/CAMtr_volume_mixing_ratio.SSP119
A       run/CAMtr_volume_mixing_ratio.SSP126
A       run/CAMtr_volume_mixing_ratio.SSP245
A       run/CAMtr_volume_mixing_ratio.SSP370
A       run/CAMtr_volume_mixing_ratio.SSP585

TESTS CONDUCTED: 
1. Model runs with the new files, which are just ASCII files formatted exactly as the existing ones for RCPs used in 
CMIP5.
2. The new files were compared to the existing ones for RCPs to ensure a consistent order of magnitude and 
evolution of the concentration values. No long-term climate simulation has been yet conducted with the new data 
files, but the files are within the order of magnitude of existing RCP files, which were extensively tested. 
![CAMtr file comparison](https://raw.githubusercontent.com/SantanderMetGroup/wrf-ghg-files/v0.1.2/CAMtr_files.png)
  
RELEASE NOTE: Added new CAMtr_volume_mixing_ratio data files for CMIP6 SSPs (https://doi.org/10.5281/zenodo.5507554) containing yearly global average concentrations from input4MIPs (v1.2.0 for historical part and v1.2.1 for scenario evolution).

run/README.physics_files

@@ -93,12 +93,17 @@ Radiation
 RRTM (ra_lw_physics Option 1): 
 	RRTM_DATA
 	RRTM_DATA_DBL
-        (if compiled with -DCLWRFGHG)
+        (if compiled with -DCLWRFGHG, rename/link one of the following to CAMtr_volume_mixing_ratio)
 	        CAMtr_volume_mixing_ratio.A1B
         	CAMtr_volume_mixing_ratio.A2
         	CAMtr_volume_mixing_ratio.RCP4.5
         	CAMtr_volume_mixing_ratio.RCP6
         	CAMtr_volume_mixing_ratio.RCP8.5
+        	CAMtr_volume_mixing_ratio.SSP119
+        	CAMtr_volume_mixing_ratio.SSP126
+        	CAMtr_volume_mixing_ratio.SSP245
+        	CAMtr_volume_mixing_ratio.SSP370
+        	CAMtr_volume_mixing_ratio.SSP585
 
 CAM (Option 3):
         aerosol.formatted
@@ -111,12 +116,17 @@ CAM (Option 3):
         	ozone.formatted
         	ozone_lat.formatted
         	ozone_plev.formatted
-        (if compiled with -DCLWRFGHG)
+        (if compiled with -DCLWRFGHG, rename/link one of the following to CAMtr_volume_mixing_ratio)
         	CAMtr_volume_mixing_ratio.A1B
         	CAMtr_volume_mixing_ratio.A2
         	CAMtr_volume_mixing_ratio.RCP4.5
         	CAMtr_volume_mixing_ratio.RCP6
         	CAMtr_volume_mixing_ratio.RCP8.5
+        	CAMtr_volume_mixing_ratio.SSP119
+        	CAMtr_volume_mixing_ratio.SSP126
+        	CAMtr_volume_mixing_ratio.SSP245
+        	CAMtr_volume_mixing_ratio.SSP370
+        	CAMtr_volume_mixing_ratio.SSP585
 
 RRTMG (Option 4,24,14):
 	RRTMG_LW_DATA
@@ -131,12 +141,17 @@ RRTMG (Option 4,24,14):
         	ozone.formatted
         	ozone_lat.formatted
         	ozone_plev.formatted
-        (if compiled with -DCLWRFGHG)
+        (if compiled with -DCLWRFGHG, rename/link one of the following to CAMtr_volume_mixing_ratio)
         	CAMtr_volume_mixing_ratio.A1B
         	CAMtr_volume_mixing_ratio.A2
         	CAMtr_volume_mixing_ratio.RCP4.5
         	CAMtr_volume_mixing_ratio.RCP6
         	CAMtr_volume_mixing_ratio.RCP8.5
+        	CAMtr_volume_mixing_ratio.SSP119
+        	CAMtr_volume_mixing_ratio.SSP126
+        	CAMtr_volume_mixing_ratio.SSP245
+        	CAMtr_volume_mixing_ratio.SSP370
+        	CAMtr_volume_mixing_ratio.SSP585
 
 Goddard (Option 5):
 	BROADBAND_CLOUD_GODDARD.bin