Auto PR - develop → MAPL-v3 - placeholder for documentation of S2S-3 met forcing (README.MetForcing_and_BCS.md)

doc/README.MetForcing_and_BCS.md

@@ -289,12 +289,12 @@ COMMONLY USED values for `MET_TAG`:
   MET_TAG  : cross_d5294_GEOSIT
   ```
 
-#### Forcing from post-processed output of the GEOS S2S system 
+#### Forcing from post-processed output of the GEOS S2S-2 system 
 
- - Forcing derived through post-processing of daily average output from the GEOS S2S system,
+ - Forcing derived through post-processing of daily average output from the GEOS S2S-2 system,
    including S2S hindcasts/forecasts ("FCST") and the "AODAS" used for S2S initialization. 
 
-   S2S output is from the geosgcm_vis2d and geosgcm_surf Collections for FCST and from the 
+   S2S-2 output is from the geosgcm_vis2d and geosgcm_surf Collections for FCST and from the 
    geosgcm_rad and geosgcm_surf Collections for AODAS (see GMAO Office Note No. 16).
 
    For FCST, post-processing includes a monthly bias correction to the MERRA-2 climatology.
@@ -307,7 +307,7 @@ COMMONLY USED values for `MET_TAG`:
    separated by double underscores.
 
    As of 14 Jun 2021:
-   - Preparation of S2S forcing data ignores the 3-hour offset between S2S daily averages 
+   - Preparation of S2S-2 forcing data ignores the 3-hour offset between S2S daily averages 
    (21z-21z) and the MERRA-2 daily averages (0z-0z) used for the temporal disaggregration.
    - The processing of the S2S output incorrectly partitioned total precipitation into snowfall 
    and convective precipitation.  Therefore, rainfall and snowfall are determined in the 
@@ -319,6 +319,38 @@ COMMONLY USED values for `MET_TAG`:
    MET_TAG  : GEOSs2sAODAS
    ```
 
+#### Forcing from post-processed output of the GEOS S2S-3 system
+
+ - Forcing derived through post-processing of 3-hourly and monthly average output from the 
+   GEOS S2S-3 system, including S2S hindcasts/forecasts ("FCST") and the "AODAS" used for 
+   S2S initialization.
+
+   S2S-3 output is from the sfc_tavg_3hr__glo_L720x361_sfc and rad_tavg_1mo_glo_L720x361_slv 
+   Collections for both FCST and AODAS. For surface pressure and lowest-model-level air
+   temperature and humidity, the forcing reader estimates the values at the synoptic and 
+   off-synoptic times (0z, 3z, ...) by taking the mean of the 3-hourly time average data from 
+   the adjacent 3-hour intervals. This minimizes the phase shift but exacerbates the reduction 
+   in the diurnal amplitude.
+
+   Because S2S-3 does NOT output 3-hourly surface downward shortwave radiation (SWGDN) and 
+   absorbed longwave radiation (LWGAB), these 2 variables are estimated from 3-hourly land surface 
+   net radiation (SWLAND and LWLAND), snow cover fraction (ASNOW), surface skin temperature (TS), 
+   as well as land surface albedo and emissivity.
+
+   A 1-year offline simulation using the same boundary conditions and resolution as in S2S-3 was 
+   carried out to produce the (climatological) 3-hourly surface albedo over snow-free areas. 
+   Albedo over snow-covered areas and emissivity are estimated using the model's parameterizations 
+   to the extent possible (e.g., snow mass impact on albedo is considered but snow density is 
+   assumed to always be that of fresh snow because snow density is not in the S2S-3 output).
+
+   For FCST, MET_TAG must specify S2S ensemble member ('ensX', where X can be either 1 or 2 digits, 
+   e.g., 'ens1','ens2','ens10', 'ens11'), and date of forecast initialization in format of 
+   'YYYYMMDD' (e.g., '20160101'), separated by double underscores.
+
+   ```
+   MET_TAG  : GEOSS2S3FCST__[ensX]__[YYYYMMDD]             # note uppercase 'S2S'
+   MET_TAG  : GEOSS2S3AODAS                                # note uppercase 'S2S'
+   ```
 
 #### SMAP L4_SM